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Molecular and Cellular Biology, February 2000, p. 971-978, Vol. 20, No. 3
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
RIM101-Dependent and -Independent
Pathways Govern pH Responses in Candida albicans
Dana
Davis,
R. Bryce
Wilson, and
Aaron P.
Mitchell*
Department of Microbiology and Institute of
Cancer Research, Columbia University, New York, New York 10032
Received 2 August 1999/Returned for modification 27 September
1999/Accepted 4 November 1999
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ABSTRACT |
Growth and differentiation of Candida albicans over a
broad pH range underlie its ability to infect an array of tissues in susceptible hosts. We identified C. albicans RIM101,
RIM20, and RIM8 based on their homology to
components of the one known fungal pH response pathway. PCR
product-disruption mutations in each gene cause defects in three
responses to alkaline pH: filamentation, induction of PRA1
and PHR1, and repression of PHR2. We find that RIM101 itself is an alkaline-induced gene that also depends
on Rim20p and Rim8p for induction. Two observations indicate that a
novel pH response pathway also exists. First, PHR2 becomes
an alkaline-induced gene in the absence of Rim101p, Rim20p, or Rim8p. Second, we created strains in which Rim101p activity is independent of
Rim20p and Rim8p; in these strains, filamentation remains pH dependent.
Thus, pH governs gene expression and cellular differentiation in
C. albicans through both RIM101-dependent and
RIM101-independent pathways.
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INTRODUCTION |
Candida albicans is the
most common human fungal pathogen. In most individuals, it is a
commensal fungus that can colonize environmentally diverse niches, such
as the oral and vaginal cavities (19). In susceptible hosts,
C. albicans can infect virtually any tissue (9).
Thus, both colonization and infection by C. albicans require
its adaptation to diverse environments.
One environmental variable, extracellular pH, governs C. albicans cellular morphology. At acidic pH, C. albicans
grows in the yeast form; at alkaline pH, it grows primarily in the
filament form (19). Alkaline-induced filamentation
correlates with a number of physiological changes, such as alterations
in cell wall architecture and adhesion properties (4). These
responses to alkaline pH are thought to be dependent on changes in gene expression.
Differential expression screens have led to the identification of two
alkaline-induced genes, PRA1 and PHR1. PRA1
specifies a cell wall protein that has a minor role in alkaline-induced filamentation (22). PHR1 also specifies a cell
wall protein; however, it is required for both growth and filamentation
at alkaline pH (21). Ectopic expression of PHR2,
a PHR1 homolog that is not normally expressed at alkaline
pH, permits both filamentation and growth of the
phr1
/phr1 mutant
(18). Since PHR2 does not promote filamentation
when it is normally expressed, the
phr1/phr1 alkaline-induced
filamentation defect appears to be a result of the growth defect. Thus,
the functions of known alkaline-induced genes do not explain how
alkaline pH induces filamentation.
A number of regulators that control the yeast-to-filament transition
have been identified, including Efg1p, Cph1p, and Tup1p (3, 12,
14), but these factors are not thought to be specific for
alkaline responses. A conserved alkaline response pathway has been
identified in the fungi Aspergillus nidulans,
Saccharomyces cerevisiae, and Yarrowia lipolytica
(6, 10, 11, 15, 20, 25, 26). In this pathway, the zinc
finger transcription factor Rim101p/PacC, from S. cerevisiae
and A. nidulans, respectively, stimulates expression of
alkaline response genes and represses acidic response genes
(26). Rim101p/PacC activity is controlled by proteolytic
processing. In acidic conditions, Rim101p exists primarily in a
full-length "long" form which has no known function (11,
20). In alkaline conditions, a C-terminal portion is cleaved to
yield the active "short" form. Proteolysis is controlled by pH
through the action of a number of gene products, including Rim20p/PalA,
Rim8p/PalF, Rim13p/PalB, and Rim9p/PalI (5, 6, 11, 15). Here
we have used the partial C. albicans genomic database to
identify RIM101 pathway members in C. albicans
and to determine their role in alkaline responses. Our studies
demonstrate that the RIM101 pathway in C. albicans is required for some alkaline responses. Further, our
results also indicate that a second pH response pathway must exist in
C. albicans.
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MATERIALS AND METHODS |
Strains and plasmids.
The C. albicans strains
used in this study are derivatives of CAI4 and are described in Table
1. Creation of the
rim101/rim101 and
rim20/rim20 strains was
described previously (27). They were referred to as
hrm101/hrm101 and
enx3/enx3, respectively. For
complementation and suppression studies (see below for details), the
appropriate strains were subjected to transformation and selection for
histidine prototrophy. Plasmids were maintained and amplified with the
bacterial strain DH5
.
The
rim8/rim8 mutant (DAY61) was
generated as follows. Strain BWP17 was subjected to consecutive rounds
of transformation
with
rim8::ARG4 and
rim8::URA3 using primers RIM8-5DR-2 and RIM8-3DR-2
as described previously (
27). This deletes sequences from
77
to +1620, removing residues 1 to 398 of the predicted protein.
Correct integration was demonstrated by PCR with the primers rim8-3-2
and rim8-5-2, which flank the site of integration (Fig.
1).
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FIG. 1.
Confirmation of the
rim8/rim8 mutant. The figure
shows a gel following PCR with flanking detection primers of genomic
DNA of wild type (sample 1), rim8::ARG4
transformants (samples 2 to 5), and rim8::URA3
transformants (samples 6 and 7). Note integration at both
RIM8 copies in one case (sample 5) following tranformation
with rim8::ARG4.
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Plasmid pDDB61 was constructed as follows. Full-length
RIM101 was PCR amplified with primers seq4c and gc3cloneSalI
(Table
2) and cloned into pGEM-T
(Promega) to generate plasmid pDDB52.
pDDB52 was digested with
SalI, and the
RIM101-containing fragment
was
cloned into the
SalI site of pGEM-HIS1 (
27),
generating
pDDB61.
Plasmid pDDB71, which contains the
RIM101-405 allele, was
generated as follows. pDDB61 was digested with
EcoRI, filled
in
with Klenow polymerase, and religated to create pDDB71. This
generates
a
RIM101 gene with a stop codon following amino
acid N405. pDDB61
and pDDB71 were digested with
PpuMI for
transformations to target
integration to the
RIM101 or
rim101 locus.
Plasmid pRIM8-URA3 was constructed as follows. A fragment of
C. albicans RIM8 was amplified by PCR with primers carim8-5 and
carim8-3 and cloned into pGEM-T, generating plasmid pBW113. pBW113
was
digested with
SacII and
SpeI, and the
RIM8-containing fragment
was cloned into
SacII/
SpeI-digested pRSARG4
SpeI
(
27), generating
plasmid pRIM8-ARG4. Plasmid pGEMT-URA3
(
27) was digested with
SalI and
SphI,
and the
URA3-containing fragment was cloned into
SalI/
SphI-digested pBR322, generating plasmid
pBRURA3. pBRURA3
was digested with
ClaI/
SpeI, and
the
URA3-containing fragment
was cloned into
ClaI/
SpeI-digested pRIM8-ARG4, generating plasmid
pRIM8-URA3.
Plasmid pRS424ARG4-URA3-BH1 was constructed as follows. Plasmid
pGEMT-URA3 was digested with
SacII and
SpeI, and
the
URA3-containing
fragment was cloned into the
SacII/
SpeI site of pRSARG4
SpeI,
generating
plasmid pRS314ARG4-URA3. An
Asp718-
BamHI linker
was
inserted into the
KpnI site of pRS314ARG4-URA3,
generating plasmid
pRS314ARG4-URA3-BH1. pRS314ARG4-URA3-BH1 was
digested with
BamHI
and
SacII, and the
ARG4-URA3-containing fragment was cloned into
BamHI/
SacII-digested pRS424, generating plasmid
pRS424ARG4-URA3-BH1.
Media and growth conditions.
C. albicans was routinely
grown in YPD plus uridine (2% Bacto Peptone, 1% yeast extract, 2%
dextrose, and 80 µg of uridine per ml). Selection following
transformation was done on synthetic medium (6.7% yeast nitrogen base
plus ammonium sulfate and without amino acids, 2% dextrose, 80 µg of
uridine per ml except when selecting for URA3, and
supplemented with the necessary auxotrophic requirements of the cells)
(1). TC199 medium (Gibco BRL) was buffered at either pH 4.0 or pH 8.0 with 150 mM HEPES and supplemented with 80 µg of uridine
per ml. Cell densities were determined by light scattering at 600 nm.
For filamentation and Northern blot analyses, strains were grown
overnight in YPD plus uridine at 30°C. The following day,
cells were
pelleted, washed with ddH
2O, and diluted 40 to 100×
into
buffered TC199 or serum (germ tube medium; Remel) prewarmed
to 38°C.
Retrieval of RIM101, RIM20, and
RIM8.
C. albicans RIM101 was cloned by plasmid
insertion-retrieval. pRS424-ARG4-URA3-BH1 was digested with
BglII and integrated into rim101::ARG4
of DAY2. Genomic DNA was purified, digested with NcoI,
ligated at 16°C for 5 days, and recovered in Escherichia coli by electroporation. Appropriate plasmids were purified on a
Qiagen column and sequenced.
The 5' end of
RIM20 was cloned by integration of
PpuMI-digested pRS424-ARG4-URA3-BH1 into DAY18. Genomic DNA
was purified,
digested with
BamHI and
BglII, and
religated, and the vector with
5' flanking DNA was recovered in DH5
.
Primers for sequencing
were generated to sequences from contig 3-3609 which contains
preliminary sequence data including
RIM20.
The 3' end of
RIM20 was sequenced following PCR
amplification with primers rim20dn5
and
rim20dn3.
The 5' end of the
RIM8 sequence was obtained through
searches of the
C. albicans genomic database with
S. cerevisiae RIM8 sequence (W. Xu and A. P. Mitchell,
unpublished data). Ambiguous
regions were sequenced following PCR
amplification of
RIM8 with
primers RIM8-500 clone and seq3c.
The 3' end of
C. albicans RIM8 was cloned and sequenced by
plasmid retrieval similar to that
for
RIM101, except that
pRIM8-URA3 was digested with
BglII to
target integration and
genomic DNA was digested with
SacI prior
to ligation and
introduction into DH5
.
Northern blot analyses.
Following 4 h of incubation at
38°C in TC199 medium, cells were harvested by vacuum filtration. RNA
was purified either directly or from frozen cell pellets
(1). Fifteen micrograms of total RNA was dried, resuspended
in sample buffer, and separated by 1.2% formaldehyde gel
electrophoresis. RNA was transferred to nylon membranes by capillary
action and cross-linked. PCR-amplified PHR2,
PHR1, PRA1, RIM101, and
TEF1 from C. albicans genomic DNA were used to
make probes (see Table 2 for primers used). Probes were made by using
the High Prime kit (Boehringer Mannheim) and purified by using the
QiaQuick PCR purification kit. Blots were analyzed with a
phosphorimager and quantitated with IQMac v1.2.
Filamentation.
Following 4 h of incubation at 38°C in
TC199 medium plus uridine or 2 h in serum plus uridine at 38°C,
cells were fixed with 2 volumes of 100% ethanol. Cells were pelleted
and resuspended in phosphate-buffered saline prior to microscopic
analysis. At least 200 cells were counted for each sample.
Nucleotide sequence accession numbers.
The GenBank accession
numbers for RIM101, RIM20, and RIM8
are AF173841, AF173843, and AF173842, respectively.
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RESULTS |
Cloning and sequencing of RIM101, RIM8, and
RIM20.
To identify potential pH response regulators in
C. albicans, we searched the partial Candida
genomic database and identified short sequences with homology to
S. cerevisiae RIM101, RIM20, and RIM8.
To test the role of these sequences in the pH response, we generated
insertion-deletion mutants with a PCR-product-directed gene disruption
technique (27). Promising results from these studies,
described below, prompted us to clone the remainder of these genes by
plasmid integration and retrieval (see Materials and Methods).
C. albicans RIM101 specifies a protein of 604 amino acids.
The Rim101p/PacC family has limited sequence identity over the
entire
protein sequence;
C. albicans and
S. cerevisiae
Rim101p
are approximately 20% identical. However, they do share three
structural features (Fig.
2A). First, the
zinc finger domain of
the Rim101p/PacC family is highly conserved;
C. albicans Rim101p
has 57% identity and 87% similarity to
the other homologs. Second,
all members of this family have a 50- to 90-residue D/E-rich C-terminal
domain;
C. albicans
Rim101p has an 84-amino-acid C-terminal region
that is 32% D/E
residues. Third, these proteins are similar in
size, ranging from 585 to 667 amino acids, with the zinc fingers
positioned approximately 50 to 150 amino acids from the N terminus.
C. albicans Rim101p
also has several Q-rich regions, a feature
shared with Rim101p from
Y. lipolytica (
10). This level of structural
homology indicates that the sequence we identified specifies a
Rim101
homolog.
C. albicans RIM20 specifies a protein of 785 amino acids
that is approximately 30% identical and 50% similar to Rim20p/PalA
from
S. cerevisiae and
A. nidulans (Fig.
2B).
Unlike the Rim101p/PacC
family, the Rim20p/PalA family has homology
over the entire molecule.
C. albicans Rim20p has homology
with a number of signal transduction
proteins from higher eukaryotes,
including Xp95 from
Xenopus laevis,
Alix/AIP1 from mice, and
a putative
Caenorhabditis elegans protein.
The level of
homology between Rim20p/PalA and
C. albicans Rim20p
suggests
that the sequence we identified specifies a Rim20p
homolog.
C. albicans RIM8 specifies a protein of 602 amino acids that
is approximately 28% identical and 40% similar to Rim8p/PalF
from
S. cerevisiae and
A. nidulans (Fig.
2C). The
Rim8p/PalF family
also has homology over the entire molecule.
Therefore, the
C. albicans RIM8 gene specifies a Rim8p
homolog.
RIM101 is required for alkaline-induced
filamentation.
We considered the hypothesis that C. albicans
RIM101 is required for alkaline responses. To test this
possibility, alkaline-induced filamentation was analyzed in
RIM101/RIM101 (BWP17),
RIM101/rim101 (DAY2), and
rim101/rim101 (DAY5) cells.
These strains all grew in the yeast form at acidic pH (Fig.
3A and C and Table
3). RIM101/RIM101 and
RIM101/rim101 cells grew primarily in the
filament form at alkaline pH (Fig. 3B and Table 3): approximately 65 to
80% of the RIM101/RIM101 and
RIM101/rim101 cells produced filaments after
4 h at alkaline pH. However,
rim101/rim101 cells did not
produce filaments at alkaline pH after 4 h (Fig. 3D and Table 3)
or 36 h (data not shown). Thus, RIM101 is required for
alkaline-induced filamentation.
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FIG. 3.
Morphology of strains grown at acidic and alkaline pH.
The figure shows wild-type cells (A and B) and
rim101/rim101 (C and D),
rim20/rim20 (E),
rim8/rim8 (F),
rim101/rim101, pRIM101 (G),
rim101/rim101, pRIM101-405 (H),
rim20/rim20 pRIM101-405 (I), and
rim8/rim8 pRIM101-405 (J) cells
grown at acidic (A and C) or alkaline (B and D to J) pH.
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To determine if the
rim101/rim101 filamentation
defect is due to a growth defect, the growth rates of
RIM101/RIM101 and
rim101/rim101 cells were
measured. These strains grew at comparable rates at
both acidic and
alkaline pH (Table
4). These results were
confirmed
by growth tests on plates (data not shown). Therefore, the
alkaline-induced
filamentation defect of the
rim101/rim101 mutant is not due
to an inability to grow at alkaline pH.
RIM101 is distinct
from other genes important for alkaline responses
as it is essential
for the response but dispensable for growth
(
21).
Filamentation can be induced by a number of conditions including
incubation in serum (
16). To determine if
RIM101
is required
for filamentation under all conditions, the ability of
rim101/rim101 cells to filament
in serum was determined. Both
RIM101/RIM101 and homozygous
rim101/rim101 cells produce
filaments at comparable levels in serum (Table
3). Thus,
RIM101 is not essential for filamentation under all
conditions.
Because
C. albicans lacks a sexual cycle, complementation or
suppression tests are required to demonstrate that a defined
mutation
confers a particular phenotype. Using the remaining
his1 marker in our strains, we were able to introduce full-length
RIM101 without having to recycle markers. Integration of
plasmid pRIM101
into the
rim101/rim101 mutant (DAY44)
restored alkaline-induced filamentation ability
(Fig.
3G and Table
3).
Therefore, the alkaline-induced filamentation
defect of the
rim101/rim101 strain is due to
loss of Rim101p
function.
RIM101 is required for alkaline response gene
expression.
C. albicans responds to alkaline pH through
changes in morphology and gene expression. Therefore, the expression of
two alkaline-induced genes, PHR1 and PRA1, was
analyzed in RIM101/RIM101,
RIM101/rim101, and
rim101/rim101 cells. These
strains all had no appreciable expression of either PHR1 or
PRA1 at acidic pH (Fig. 4,
samples 1 to 3). RIM101/RIM101 and
RIM101/rim101 cells expressed both
PHR1 and PRA1 at alkaline pH (Fig. 4, samples 7 and 8). However, rim101/rim101
cells did not express either PHR1 or PRA1 at
alkaline pH (Fig. 4, sample 9). When these Northern blots were
quantitated and normalized for TEF1 mRNA, we found that
RIM101/RIM101 and RIM101/rim101
cells express >10-fold-more PHR1 and PRA1 mRNA
than the rim101/rim101 cells
(Fig. 5, samples 7 to 9). Complementation
of the rim101/rim101 mutant
restored substantial expression of both PHR1 and
PRA1 at alkaline pH (Fig. 4 and 5, sample 10). These results
demonstrate that RIM101 is required for the expression of
these two alkaline-induced genes.
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FIG. 4.
Northern blot analyses of strains grown at acidic and
alkaline pH. RNA was prepared from RIM101/RIM101 (samples 1 and 7), RIM101/rim101 (samples 2 and 8),
rim101/rim101 (samples 3 and 9),
rim101/rim101 pRIM101 (samples 4 and 10), rim20/rim20 (samples 5 and 11), and rim8/rim8 (samples
6 and 12) cells grown at acidic (samples 1 to 6) or alkaline (samples 7 to 12) pH. Northern blots were visualized with a phosphorimager.
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FIG. 5.
Quantitation of Northern blots from Fig. 4. Samples were
normalized for loading with the TEF1 signal. Note that the
scale of PHR2 has been expanded to permit comparison of
maximal wild-type and mutant levels.
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PHR1 is required for growth at alkaline pH (
21).
We observed that
rim101/rim101
cells do not express
PHR1 but are able to grow at alkaline
pH.
Thus, we hypothesized that
PHR2, a
PHR1
homolog, may be expressed
in
rim101/rim101 cells.
RIM101/RIM101 cells did not express
PHR2 at
alkaline pH
(Fig.
4, sample 7). However, we found that
rim101/rim101 cells
overexpressed
PHR2 to levels three- to fourfold higher
than
maximal wild-type levels (Fig.
4 and
5, samples 1 and 9).
Complementation of the
rim101/rim101 mutant did reduce
PHR2 expression, although not to wild-type
levels (Fig.
5,
samples 7, 9, and 10). Thus,
PHR2 becomes an alkaline
response gene in the absence of Rim101p. This result argues that
a
RIM101-independent pathway promotes elevated
PHR2
expression
at alkaline
pH.
RIM20 and RIM8 are required for alkaline pH
responses.
Two other homologs of the RIM101 pathway,
RIM20 and RIM8, have been identified in C. albicans. We assayed the requirement of these genes for pH
responses by testing the ability of
rim20/rim20 (DAY23) and
rim8/rim8 (DAY61) cells to form
filaments at alkaline pH. Like
rim101/rim101 cells,
rim20/rim20 and
rim8/rim8 cells grew in the
yeast form at both acidic pH and alkaline pH (Fig. 3E and F and Table
3). RIM20 and RIM8 are not general regulators of
filamentation, as rim20/rim20
and rim8/rim8 cells were able to
form filaments in serum (Table 3). Thus, RIM20 and
RIM8 are required for alkaline-induced filamentation.
We also expected that
RIM20 and
RIM8 would be
required for alkaline response gene expression. We found that
rim20/rim20 and
rim8/rim8 cells did not express
PHR1 or
PRA1 at either acidic or alkaline
pH
(Fig.
4, samples 11 and 12), thus suggesting that Rim101p,
Rim20p, and
Rim8p act in the same pathway. We also found that
PHR2
became an alkaline response gene in
rim20/rim20 and
rim8/rim8 cells (Fig.
4 and
5,
samples 1, 11, and 12). Thus, the pathway
responsible for
PHR2 alkaline induction must be independent of
Rim20p and
Rim8p.
RIM101 is an alkaline-induced gene.
Expression of
many transcription factors is regulated by the condition to which they
respond (23, 24). Therefore, we determined whether
RIM101 expression is regulated in response to alkaline pH.
RIM101/RIM101 cells expressed RIM101 at both
acidic and alkaline pH (Fig. 4, samples 1 and 7). However,
RIM101 expression was elevated fivefold at alkaline pH over
acidic pH levels (Fig. 4 and 5, samples 1 and 7). Although complemented
rim101/rim101 pRIM101 cells
showed the same fivefold increase in expression at alkaline pH as did
the wild type (Fig. 5, samples 4 and 10), we observed that these cells
expressed a longer RIM101 mRNA than did the wild type (Fig.
4, samples 1, 4, 7, and 10). We infer that this longer message includes
neighboring vector sequences following the stop codon. These results
demonstrate that RIM101 is an alkaline-induced gene.
Since
RIM101 is an alkaline response gene, its expression
may also depend on the
RIM101 pathway. To address this
possibility,
rim20/rim20 and
rim8/rim8 cells were analyzed
for expression of
RIM101.
rim20/rim20 and
rim8/rim8 cells expressed
RIM101 at both acidic and alkaline pH (Fig.
4).
However,
both mutants failed to increase
RIM101 expression at
alkaline pH (Fig.
5, samples 5, 6, 11, and 12). Thus,
RIM101
is
an alkaline-induced gene that requires
RIM20 and
RIM8 for increased
expression at alkaline
pH.
Suppression by truncated Rim101p.
S. cerevisiae Rim101p
is activated by proteolytic removal of the D/E-rich C-terminal tail
following shift to alkaline pH (11, 20). If the C terminus
of C. albicans Rim101p is removed in response to alkaline
pH, then a RIM101 allele that lacks the C-terminal D/E-rich
domain should be functional. To test this possibility, we created the
RIM101-405 allele, which has a stop codon following residue
405, introduced it into
rim101/rim101 cells, and assayed
for alkaline-induced filamentation. Although rim101/rim101 cells grew in the
yeast form at alkaline pH (Fig. 3D),
rim101/RIM101-405 cells grew in the filament
form at alkaline pH (Fig. 3H and Table 3). These results demonstrate
that RIM101-405 can complement the alkaline-induced
filamentation defect of
rim101/rim101 cells.
If Rim20p and Rim8p act to stimulate processing of Rim101p, then the
RIM101-405 allele should suppress the filamentation defects
of the
rim20/rim20 and
rim8/rim8 mutants. Therefore,
the pRIM101-405 plasmid was introduced into
rim20/rim20 and
rim8/rim8 cells. Unlike
rim20/rim20 and
rim8/rim8 cells,
rim20/rim20 pRIM101-405 and
rim8/rim8 pRIM101-405 cells grew
in the filament form at alkaline pH (Fig.
3I and J and Table
3). The
rim20/rim20 and
rim8/rim8 alkaline-induced
filamentation defects were not suppressed by
introduction of the
wild-type pRIM101 allele (Table
3). These
results indicate that Rim20p
and Rim8p promote the pH response
by processing
Rim101p.
In
rim20/rim20 pRIM101-405
and
rim8/rim8 pRIM101-405
strains, Rim101p activity is independent of Rim20p and Rim8p. However,
these strains filament weakly at acidic pH compared to alkaline
pH
(Table
3). Therefore, alkaline pH still induces filamentation
independent of upstream
RIM101 pathway components, provided
that
Rim101p is expressed in an active
form.
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DISCUSSION |
The ability of C. albicans to adapt to diverse
environments is central to its pathogenesis. Here we have used a
streamlined genetic approach to dissect the mechanisms that govern the
response of C. albicans to external pH. We identified
possible homologs of fungal pH regulatory genes in the
Candida genomic database and assessed their functional
significance through PCR product-directed gene disruption. The
homozygous mutants displayed pH response defects, thus prompting us to
retrieve and characterize each entire gene. Finally, because we used a
triply marked strain, we carried out complementation and suppression
analyses without having to recycle markers. Our findings support two
main conclusions (Fig. 6). First, the
RIM101 pathway is conserved in C. albicans and governs several alkaline responses. Second, both disruption and bypass
mutants of the RIM101 pathway demonstrate the existence of
an additional alkaline response pathway.
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FIG. 6.
Model for RIM101-dependent and
RIM101-independent control of alkaline responses. Alkaline
pH stimulates Rim101p activity through increased expression and
proteolytic activation, both of which require Rim8p and Rim20p.
Full-length Rim101p-long does not have a known activity. Processed
Rim101p-short is required for the alkaline response, which includes
activation of alkaline-induced genes, repression of alkaline-repressed
genes, and filamentation. Since RIM101 is an
alkaline-induced gene, its expression may depend on autoregulation by
Rim101p-short. Alkaline pH also stimulates a
RIM101-independent pathway. (We have diagrammed one
RIM101-independent pathway for simplicity, but there may be
several.) This pathway activates PHR2 expression (in the
absence of a functional RIM101 pathway) and stimulates
filamentation in conjunction with Rim101p.
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The RIM101 pathway plays a distinct role in each of three
alkaline responses (Fig. 6). First, Rim101p, Rim8p, and Rim20p are positive regulators of the alkaline-induced genes PRA1,
PHR1, and RIM101 itself, because loss of
RIM101 pathway function blocks induction of these genes at
alkaline pH. Second, these proteins are negative regulators of the
alkaline-repressed gene PHR2, because loss of
RIM101 pathway function permits expression of
PHR2 at alkaline pH. Third, these proteins are positive
regulators of alkaline-induced filamentation, because loss of
RIM101 pathway function prevents filamentation at alkaline
pH. The finding that truncated Rim101-405p suppresses the
rim8/rim8 and
rim20/rim20 alkaline-induced
filamentation defects suggests that Rim101p is processed by and acts
downstream of Rim8p and Rim20p. These results are expected based on
findings from Saccharomyces, Aspergillus, and
Yarrowia (10, 11, 20, 25, 26).
However, unlike Aspergillus and Yarrowia,
C. albicans remains pH responsive in the absence of the
RIM101 pathway. For example, the dominant
RIM101-405 allele, which complements the filamentation defect of the rim101/rim101
mutant, promotes filamentation very weakly at acidic pH. Thus, the
uncoupling of Rim101p processing from the upstream regulators does not
completely bypass the control of filamentation by external pH. In
addition, PHR2 becomes an alkaline-induced gene in cells that lack RIM101 pathway function. Thus, both morphological
and gene expression responses point to the existence of a
RIM101-independent pH response pathway. This pathway has two
roles: to stimulate PHR2 expression at alkaline pH, and to
act in conjunction with Rim101p to activate filamentation. We have
depicted this pathway as a positively acting pathway (Fig. 6), but
other explanations are also possible.
Often a particular organism has a unique balance between the
contributions of partially redundant pathways. For example, filamentous growth is activated by both the Ste12p/Cph1p and Phd1p/Efg1p pathways in Saccharomyces and C. albicans, and yet
Ste12p/Cph1p is the major pathway in Saccharomyces and
Phd1p/Efg1p is the major pathway in C. albicans (8,
12-14). Similarly, Rim101p seems to be the major activator of
sporulation in Yarrowia but has roles overlapping with those
of Mck1p and Ime4p in Saccharomyces (10, 25).
Thus, it seems reasonable that an additional pH response pathway exists in these other fungi and that its unique balance with the
RIM101 pathway in C. albicans has simplified its detection.
Rim101p may activate filamentation through a functional interaction
with the negative regulator Tup1p or the positive regulators Cph1p and
Efg1p. It is intriguing that Rim101p and Tup1p together regulate
transcription from the Saccharomyces IME1 and
DIT1/DIT2 promoters (2, 7, 17). In fact,
regulation of these target genes in Saccharomyces is
parallel to the regulation of filamentation in C. albicans:
they are positively regulated by Rim101p and negatively regulated by
Tup1p. Thus, Rim101p and Tup1p may converge on a common set of
filamentation-specific promoters in C. albicans.
| |
ACKNOWLEDGMENTS |
We thank Teresa Lamb and Brian Enloe for critical reading of the
manuscript and all members of the Mitchell lab for numerous helpful
discussions. We gratefully acknowledge Stew Scherer for maintaining an
accessible and updated Candida genomic database. Dana Davis
wishes to thank Debra McWilliam for continued support throughout the
course of this work.
This work was supported by a Mycology Scholar Award from the Burroughs
Wellcome Fund (to A.P.M.) and by grants T32 AI07161-21 and PO1 AI377194
from the National Institutes of Health.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Department of
Microbiology, Columbia University, 701 W. 168th St., New York, NY
10032. Phone: (212) 305-8251. Fax: (212) 305-1741. E-mail:
apm4{at}columbia.edu.
| |
REFERENCES |
| 1.
|
Adams, A.,
D. E. Gotschling,
C. A. Kaiser, and T. Stearns.
1997.
Methods in yeast genetics.
Cold Spring Harbor Laboratory Press, Plainview, N.Y.
|
| 2.
|
Bogengruber, E.,
T. Eichberger,
P. Briza,
I. W. Dawes,
M. Breitenbach, and R. Schricker.
1998.
Sporulation-specific expression of the yeast DIT1/DIT2 promoter is controlled by a newly identified repressor element and the short form of Rim101p.
Eur. J. Biochem.
258:430-436[Medline].
|
| 3.
|
Braun, B. R., and A. D. Johnson.
1997.
Control of filament formation in Candida albicans by the transcriptional repressor TUP1.
Science
277:105-109[Abstract/Free Full Text].
|
| 4.
|
Chaffin, W. L.,
J. L. Lopez-Ribot,
M. Casanova,
D. Gozalbo, and J. P. Martinez.
1998.
Cell wall and secreted proteins of Candida albicans: identification, function, and expression.
Microbiol. Mol. Biol. Rev.
62:130-180[Abstract/Free Full Text].
|
| 5.
|
Denison, S. H.,
S. Negret-Urtasun,
J. M. Mingot,
J. Tilburn,
W. A. Mayer,
A. Goel,
E. A. Espeso,
M. A. Penalva, and H. N. Arnst.
1998.
Putative membrane components of signal transduction pathways for ambient pH regulation in Aspergillus and meiosis in Saccharomyces are homologous.
Mol. Microbiol.
30:259-264[CrossRef][Medline].
|
| 6.
|
Denison, S. H.,
M. Orejas, and H. N. Arnst.
1995.
Signaling of ambient pH in Aspergillus involves a cysteine protease.
J. Biol. Chem.
270:28519-28522[Abstract/Free Full Text].
|
| 7.
|
Friesen, H.,
S. Hepworth, and J. Segall.
1997.
An Ssn6-Tup1-dependent negative regulatory element controls sporulation-specific expression of DIT1 and DIT2 in Saccharomyces cerevisiae.
Mol. Cell. Biol.
17:123-134[Abstract].
|
| 8.
|
Gimeno, C. J., and G. R. Fink.
1994.
Induction of pseudohyphal growth by overexpression of PHD1, a Saccharomyces cerevisiae gene related to transcriptional regulators of fungal development.
Mol. Cell. Biol.
14:2100-2112[Abstract/Free Full Text].
|
| 9.
|
Kwon-Chung, K. J., and J. E. Bennett.
1992.
Medical mycology, 1st ed.
Lea & Febiger, Philadelphia, Pa.
|
| 10.
|
Lambert, M.,
S. Blanchin-Roland,
F. L. Louedec,
A. Lepingle, and C. Gaillardin.
1997.
Genetic analysis of regulatory mutants affecting synthesis of extracellular proteinases in the yeast Yarrowia lipolytica: identification of a RIM101/pacC homolog.
Mol. Cell. Biol.
17:3966-3976[Abstract].
|
| 11.
|
Li, W., and A. P. Mitchell.
1997.
Proteolytic activation of Rim1p, a positive regulator of yeast sporulation and invasive growth.
Genetics
145:63-73[Abstract].
|
| 12.
|
Liu, H.,
J. Kohler, and G. R. Fink.
1994.
Suppression of hyphal formation in Candida albicans by mutation of a STE12 homolog.
Science
266:1723-1726[Abstract/Free Full Text].
|
| 13.
|
Liu, H.,
C. A. Styles, and G. R. Fink.
1993.
Elements of the yeast pheromone response pathway required for filamentous growth of diploids.
Science
262:1741-1744[Abstract/Free Full Text].
|
| 14.
|
Lo, H.-J.,
J. R. Kohler,
B. DiDomenico,
D. Loebenberg,
A. Cacciapuoti, and G. R. Fink.
1997.
Nonfilamentous C. albicans mutants are avirulent.
Cell
90:939-949[CrossRef][Medline].
|
| 15.
|
Maccheroni, W.,
G. S. May,
N. M. Martinez-Rossi, and A. Rossi.
1997.
The sequence of palF, an environmental pH response gene in Aspergillus nidulans.
Gene
194:163-167[CrossRef][Medline].
|
| 16.
|
Mitchell, A. P.
1998.
Dimorphism and virulence in Candida albicans.
Curr. Opin. Microbiol.
1:687-692[CrossRef][Medline].
|
| 17.
|
Mizuno, T.,
N. Nakazawa,
P. Remgsamrarn,
T. Kunoh,
Y. Oshima, and S. Harashima.
1998.
The Tup1-Ssn6 general repressor is involved in repression of IME1 encoding a transcriptional activator of meiosis in Saccharomyces cerevisiae.
Curr. Genet.
33:239-247[CrossRef][Medline].
|
| 18.
|
Muhlschlegel, F. A., and W. A. Fonzi.
1997.
PHR2 of Candida albicans encodes a functional homolog of the pH-regulated gene PHR1 with an inverted pattern of pH-dependent expression.
Mol. Cell. Biol.
17:5960-5967[Abstract].
|
| 19.
|
Odds, F. C.
1988.
Candida and candidosis, 2nd ed.
Bailliere Tindall, London, United Kingdom.
|
| 20.
|
Orejas, M.,
E. A. Espeso,
J. Tilburn,
S. Sarkar,
H. N. Arnst, and M. A. Penalva.
1995.
Activation of the Aspergillus PacC transcription factor in response to alkaline pH requires proteolysis of the carboxy-terminal moiety.
Genes Dev.
9:1622-1632[Abstract/Free Full Text].
|
| 21.
|
Saporito-Irwin, S. M.,
C. E. Birse,
P. S. Sypherd, and W. A. Fonzi.
1995.
PHR1, a pH-regulated gene of Candida albicans, is required for morphogenesis.
Mol. Cell. Biol.
15:601-613[Abstract].
|
| 22.
|
Sentandreu, M.,
M. V. Elorza,
R. Sentandreu, and W. A. Fonzi.
1998.
Cloning and characterization of PRA1, a gene encoding a novel pH-regulated antigen of Candida albicans.
J. Bacteriol.
180:282-289[Abstract/Free Full Text].
|
| 23.
|
Smith, H. E.,
S. E. Driscoll,
R. A. L. Sia,
H. E. Yuan, and A. P. Mitchell.
1993.
Genetic evidence for transcriptional activation by the yeast IME1 gene product.
Genetics
133:775-784[Abstract].
|
| 24.
|
Smith, H. E.,
S. Y. Su,
L. Neigeborn,
S. E. Driscoll, and A. P. Mitchell.
1990.
Role of IME1 expression in regulation of meiosis in Saccharomyces cerevisiae.
Mol. Cell. Biol.
10:6103-6113[Abstract/Free Full Text].
|
| 25.
|
Su, S. S. Y., and A. P. Mitchell.
1993.
Molecular characterization of the yeast meiotic regulatory gene RIM1.
Nucleic Acids Res.
21:3789-3797[Abstract/Free Full Text].
|
| 26.
|
Tilburn, J.,
S. Sarkar,
D. A. Widdick,
E. A. Espeso,
M. Orejas,
J. Mungroo,
M. A. Penalva, and H. N. Arnst, Jr.
1995.
The Aspergillus PacC zinc finger transcription factor mediates regulation of both acid- and alkaline-expressed genes by ambient pH.
EMBO J.
14:779-790[Medline].
|
| 27.
|
Wilson, R. B.,
D. Davis, and A. P. Mitchell.
1999.
Rapid hypothesis testing in Candida albicans through gene disruption with short homology regions.
J. Bacteriol.
181:1868-1874[Abstract/Free Full Text].
|
Molecular and Cellular Biology, February 2000, p. 971-978, Vol. 20, No. 3
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-
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-
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[Full Text]
-
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[Full Text]
-
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[Abstract]
[Full Text]
-
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[Abstract]
[Full Text]
-
Lane, S., Birse, C., Zhou, S., Matson, R., Liu, H.
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[Abstract]
[Full Text]
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Abstract
Introduction
