Molecular and Cellular Biology, May 1999, p. 3816-3828, Vol. 19, No. 5
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Laboratory of Cellular and Molecular Biology,
Received 20 October 1998/Returned for modification 23 November
1998/Accepted 24 February 1999
In the present study, we investigated the potential role of
insulin-like growth factor I (IGF-I) receptor (IGF-IR) in cell proliferation by overexpressing it in 32D myeloid progenitor cells. The
overexpression of IGF-IR caused the transfectants to proliferate in
response to IGF-I in the absence of insulin receptor substrate (IRS)
expression. The activation of overexpressed wild-type IGF-IR, but not
that of an ATP-binding mutant of IGF-IR, resulted in the increased
tyrosine phosphorylation of several intracellular proteins, including
SHC, Src homology 2-containing inositol-5-phosphatase, protein kinase
C-
, and Erk2. Grb2 association with SHC and mitogen-activated protein kinase (MAPK) activity was also enhanced in response to IGF-I
stimulation. Interestingly, the stimulation of the IGF-IR transfectants
with interleukin 4 (IL-4) also resulted in strong mitogenesis
independent of IRS expression. Moreover, IGF-I and/or IL-4 induced
long-term cell growth of the IGF-IR transfectants. IL-4 was able to
synergize with IGF-I for DNA synthesis, even in the parental 32D cells
and a pro-B-cell line, Baf3, indicating the physiological importance of
the two growth factors in hematopoietic cell proliferation. IL-4
stimulation of the IGF-IR transfectants resulted in enhanced tyrosine
phosphorylation of SHC, Erk2, and signal transducer and activator of
transcription 6 (STAT6) proteins. Both IL-4 and IGF-I were able to
induce c-myc early response gene expression, and this
expression was maximal in the presence of both factors. Finally, we
demonstrated that a MAPK kinase inhibitor was able to suppress
mitogenesis of the IGF-IR transfectants in response to IGF-I and/or
IL-4. Together, our results suggest that IL-4 synergizes with IGF-I for
hematopoietic cell proliferation, likely through cross talk between
SHC/Grb2/MAPK and STAT6 pathways and through c-myc gene
up-regulation.
*
Corresponding author. Mailing address: Laboratory of
Cellular and Molecular Biology, National Cancer Institute, Bldg. 37, Room 1E24, 9000 Rockville Pike, Bethesda, MD 20892. Phone: (301) 496-1347. Fax: (301) 496-8479. E-mail:
liwe{at}dc37a.nci.nih.gov.
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