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Mol. Cell. Biol., 10 1997, 5888-5896, Vol 17, No. 10
S Prabhu, A Ignatova, ST Park and XH Sun
The helix-loop-helix transcription factor E2A plays important roles not
only in promoting cellular differentiation but also in suppressing cell
growth. Id proteins, the inhibitors of E2A, have opposite effects on cell
differentiation and growth. To understand the mechanisms by which E2A
suppresses cell growth, we examined the role of E2A in regulating the
expression of the cyclin-dependent kinase inhibitor p21CIP1/WAF1/SD11,
which prevents cell cycle progression upon overexpression. By using
transient-cotransfection assays of luciferase reporter constructs in HeLa
cells, we have found that overexpression of E2A can transcriptionally
activate the p21 gene. To identify the sequences that mediate this
activation in the promoter of the p21 gene, we carried out mutational
analyses. Out of the eight putative E2A- binding sequences (E1 to E8) in
the promoter, the E1 to E3 sequences located close to the transcription
start site are found to be essential. In addition, loss of the E boxes in
the promoter also reduces p21 expression without cotransfection with E2A in
HIT pancreatic cells, where the endogenous E2A-like activity is high.
Furthermore, we have also shown that overexpression of E2A in 293T cells
activates expression of the endogenous p21 gene at both the levels of mRNA
and protein. In correlation with the finding that E47 overexpression leads
to growth arrest in NIH 3T3 cells, we have shown that Id1 overexpression in
NIH 3T3 cells accelerates cell growth and inhibits p21 expression. Taken
together, these results provide insight into the mechanisms by which E2A
and Id proteins control cell growth.
Copyright © 1997, American Society for Microbiology
Regulation of the expression of cyclin-dependent kinase inhibitor p21 by E2A and Id proteins
Department of Cell Biology, New York University Medical Center, New York 10016, USA.
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