p 53-Dependent and independent expression of p 21 during cell growth , differentiation , and DNA damage

Expression of p21 has been shown to be up-regulated by the p53 tumor suppressor gene in vitro in response to DNA-damaging agents. However, p21 expression can be regulated independently of p53, and here we show that expression of p21 in various tissues during development and in the adult mouse occurs in the absence of p53 function. However, most tissues tested did require p53 for p21 induction following exposure of the whole animal to ~/irradiation. These results show that normal tissue expression of p21 to high levels is not dependent on p53 and confirm that induction of p21 by DNA-damaging agents does require p53. p21 is expressed upon differentiation of p53-deficient murine erythroleukemia (MEL1 cells, and the kinetics of induction of p21 in this system suggest that it may be involved in the growth arrest that precedes terminal differentiation. The gene is up-regulated in mouse fibroblasts in response to serum restimulation but the kinetics and levels of induction differ between wild-type and mutant cells. Expression of p21 message following serum restimulation is superinducible by cycloheximide in wild-type but not in p53-deficient cells. The increases in p21 mRNA are reflected in changes in p21 protein levels, p21 expression also appears to be regulated at the post-transcriptional level because moderate increases in mRNA expression, during differentiation of MEL cells and upon serum restimulation of fibroblasts, are followed by large increases in protein levels. Regulation of the mouse p21 promoter by p53 depends on two critical p53-binding sites located 1.95 and 2.85 kb upstream from the transcriptional initiation site. The sequences mediating serum responsiveness of the promoter map to a region containing the proximal p53 site. p53 appears to play a critical role in p21 induction following DNA damage. Moreover, p21 can be regulated independently of p53 in several situations including during normal tissue development, following serum stimulation, and during cellular differentiation.

[1]  James M. Roberts,et al.  p 27 Kip 1 , a cyclin-Cdk inhibitor , links transforming growth factor-13 and contact inhibition to cell cycle arrest , 2007 .

[2]  A. Balmain,et al.  The Role of p 53 in Spontaneous and Radiation-induced Apoptosis in the Gastrointestinal Tract of Normal and p 53-deficient Mice 1 , 2006 .

[3]  Y. Honma.  [Induction of differentiation of leukemia cells]. , 1998, [Rinsho ketsueki] The Japanese journal of clinical hematology.

[4]  G. Wahl,et al.  DNA damage triggers a prolonged p53-dependent G1 arrest and long-term induction of Cip1 in normal human fibroblasts. , 1994, Genes & development.

[5]  W. Clark,et al.  Germline p16 mutations in familial melanoma , 1994, Nature Genetics.

[6]  M. Skolnick,et al.  A cell cycle regulator potentially involved in genesis of many tumor types. , 1994, Science.

[7]  R. Weinberg,et al.  Tumor spectrum analysis in p53-mutant mice , 1994, Current Biology.

[8]  D. Beach,et al.  Subunit rearrangement of the cyclin-dependent kinases is associated with cellular transformation. , 1993, Genes & development.

[9]  P. Marks,et al.  Hexamethylenebisacetamide-induced erythroleukemia cell differentiation involves modulation of events required for cell cycle progression through G1. , 1993, Proceedings of the National Academy of Sciences of the United States of America.

[10]  R. Treisman,et al.  The SRF accessory protein Elk-1 contains a growth factor-regulated transcriptional activation domain , 1993, Cell.

[11]  Richard Treisman,et al.  Functional analysis of a growth factor-responsive transcription factor complex , 1993, Cell.

[12]  L. Donehower,et al.  Mice deficient for p53 are developmentally normal but susceptible to spontaneous tumours , 1992, Nature.

[13]  I. Verma,et al.  Transcriptional autoregulation of the proto-oncogene fos , 1988, Nature.

[14]  H. Varmus,et al.  Expression of the proto-oncogene int-1 is restricted to postmeiotic male germ cells and the neural tube of mid-gestational embryos , 1987, Cell.