Connie Chao

Modification-specific antibodies were used to characterize the phosphorylation and acetylation of human p53 in response to genotoxic (UV, IR, and adriamycin) and non-genotoxic (PALA, taxol, nocodazole) stress in cultured human cells at 14 known modification sites. In A549 cells, phosphorylation or acetylation was induced at most sites by the three DNA damage-inducing agents, but significant differences between agents were observed. IR-induced phosphorylation reached a maximum 2 h after treatment and returned to near pretreatment levels by 72 h; UV light and adriamycin induced a less rapid but more robust and prolonged p53 phosphorylation, which reached a maximum between 8 and 24 h, but persisted (UV) even 96 h after treatment. Ser33, Ser37, Ser46, and Ser392 were more efficiently phosphorylated after exposure to UV light than after IR. The non-genotoxic agents PALA, taxol and nocodazole induced p53 accumulation and phosphorylation at Ser6, Ser33, Ser46, and Ser392. Some phosphorylation at Ser15 also was observed. Modifications occurred similarly in the HCT116 human colon carcinoma cell line. Analysis of single site mutant p53s indicated clear interdependences between N-terminal phosphorylation sites, which could be classified in four clusters: Ser6 and Ser9; Ser9, Ser15, Thr18 and Ser20; Ser33 and Ser37; and Ser46. We suggest that p53 phosphorylation is regulated through a double cascade involving both the activation of secondary, effector protein kinases as well as intermolecular phosphorylation site interdependencies that check inappropriate p53 inactivation while allowing for signal amplification and the integration of signals from multiple stress pathways. Modification-specific antibodies were used to characterize the phosphorylation and acetylation of human p53 in response to genotoxic (UV, IR, and adriamycin) and non-genotoxic (PALA, taxol, nocodazole) stress in cultured human cells at 14 known modification sites. In A549 cells, phosphorylation or acetylation was induced at most sites by the three DNA damage-inducing agents, but significant differences between agents were observed. IR-induced phosphorylation reached a maximum 2 h after treatment and returned to near pretreatment levels by 72 h; UV light and adriamycin induced a less rapid but more robust and prolonged p53 phosphorylation, which reached a maximum between 8 and 24 h, but persisted (UV) even 96 h after treatment. Ser33, Ser37, Ser46, and Ser392 were more efficiently phosphorylated after exposure to UV light than after IR. The non-genotoxic agents PALA, taxol and nocodazole induced p53 accumulation and phosphorylation at Ser6, Ser33, Ser46, and Ser392. Some phosphorylation at Ser15 also was observed. Modifications occurred similarly in the HCT116 human colon carcinoma cell line. Analysis of single site mutant p53s indicated clear interdependences between N-terminal phosphorylation sites, which could be classified in four clusters: Ser6 and Ser9; Ser9, Ser15, Thr18 and Ser20; Ser33 and Ser37; and Ser46. We suggest that p53 phosphorylation is regulated through a double cascade involving both the activation of secondary, effector protein kinases as well as intermolecular phosphorylation site interdependencies that check inappropriate p53 inactivation while allowing for signal amplification and the integration of signals from multiple stress pathways. When normal mammalian cells are exposed to genotoxic agents, including ionizing radiation (IR) 1The abbreviations used are: IR, ionizing radiation; ADR, adriamycin; ATM, ataxia telangiectasia-mutated; ATR, ATM and Rad3-related; ALLN, N-acetyl-Leu-Leu-Nle-CHO; Chk, checkpoint kinase; CK, casein kinase; ELISA, enzyme-linked immunoadsorbent assay; GST, glutathione S-transferase; Gy, gray; Hprt, hypoxanthine phosphoribosyl transferase; MEF, mouse embryo fibroblasts; PALA, N-phosphonacetyl-l-aspartate; PCAF, p300/CBP-associated factor; Plk3, Polo-like kinase 3; SUMO, small ubiquitin-related modifier; TSA, trichostatin A; UV, ultraviolet.1The abbreviations used are: IR, ionizing radiation; ADR, adriamycin; ATM, ataxia telangiectasia-mutated; ATR, ATM and Rad3-related; ALLN, N-acetyl-Leu-Leu-Nle-CHO; Chk, checkpoint kinase; CK, casein kinase; ELISA, enzyme-linked immunoadsorbent assay; GST, glutathione S-transferase; Gy, gray; Hprt, hypoxanthine phosphoribosyl transferase; MEF, mouse embryo fibroblasts; PALA, N-phosphonacetyl-l-aspartate; PCAF, p300/CBP-associated factor; Plk3, Polo-like kinase 3; SUMO, small ubiquitin-related modifier; TSA, trichostatin A; UV, ultraviolet. or ultraviolet (UV) light, they exhibit a number of responses including a transient inhibition of DNA and RNA synthesis, activation of several kinase-mediated signaling pathways, and the transcriptional induction or repression of several hundred genes, which result in the arrest of cell cycle progression in late G1, in S, or in G2 or in the induction of apoptosis. These responses are mediated, in part, by the p53 tumor suppressor gene, a transcription factor that integrates a variety of stress response signals (reviewed in Refs. 1Anderson C.W. Appella E. Bradshaw R.A. Dennis E. Handbook of Cell Signaling. Vol. 3. Academic Press, New, York2003: 237-247Google Scholar, 2Appella E. Anderson C.W. Eur. J. Biochem. 2001; 268: 2764-2772Crossref PubMed Scopus (912) Google Scholar, 3Vousden K.H. Lu X. Nat. Rev. Cancer. 2002; 2: 594-604Crossref PubMed Scopus (2715) Google Scholar, 4Wahl G.M. Carr A.M. Nat. Cell Biol. 2001; 3: E277-E286Crossref PubMed Scopus (325) Google Scholar)). Exposing cells to genotoxic agents and some non-genotoxic stresses inhibits the degradation of p53 protein through the ubiquitin-mediated pathway and also activates p53 as a DNA-binding, site-specific transcription factor. However, several studies point to important differences in the cellular responses to agents that produce primarily DNA strand breaks (e.g. IR) compared with those that primarily cause base damage such as UV light (reviewed in Refs. 5Schwartz D. Rotter V. Semin. Cancer Biol. 1998; 8: 325-336Crossref PubMed Scopus (178) Google Scholar and 6Gottlieb T.M. Oren M. Semin. Cancer Biol. 1998; 8: 359-368Crossref PubMed Scopus (221) Google while p53 protein in cells exposed to or UV light, the p53 transcriptional with than IR. In and cells, UV light is a more of than D. Rotter V. Semin. Cancer Biol. 1998; 8: 325-336Crossref PubMed Scopus (178) Google Scholar, 6Gottlieb T.M. Oren M. Semin. Cancer Biol. 1998; 8: 359-368Crossref PubMed Scopus (221) Google Scholar, PubMed Scopus Google p53 accumulation and activation also in response to several that are with DNA including exposure to and by activation 1Anderson C.W. Appella E. Bradshaw R.A. Dennis E. Handbook of Cell Signaling. Vol. 3. Academic Press, New, York2003: 237-247Google p53 accumulation and activation are to be regulated through protein and (reviewed in Refs. 1Anderson C.W. Appella E. Bradshaw R.A. Dennis E. Handbook of Cell Signaling. Vol. 3. Academic Press, New, York2003: 237-247Google Scholar and 2Appella E. Anderson C.W. Eur. J. Biochem. 2001; 268: 2764-2772Crossref PubMed Scopus (912) Google sites in the human p53 primarily in the N-terminal or in the or to the are in response to the activation of stress signaling C.W. Appella E. Bradshaw R.A. Dennis E. Handbook of Cell Signaling. Vol. 3. Academic Press, New, York2003: 237-247Google Scholar, 2Appella E. Anderson C.W. Eur. J. Biochem. 2001; 268: 2764-2772Crossref PubMed Scopus (912) Google at the of human phosphorylation of Ser15, and Ser37, after or UV light, was to p53 PubMed Scopus Google Scholar, M. PubMed Scopus Google at the phosphorylation of and Ser392 was in the of p53 Anderson C.W. Appella E. D. PubMed Scopus Google and to DNA in a M. A.M. M. J. Biol. PubMed Scopus Google Scholar, PubMed Scopus Google of p53 at N-terminal also with the transcriptional and J. PubMed Scopus Google Scholar, J. Biol. 1998; PubMed Scopus Google Scholar, Cell Biol. PubMed Scopus Google Scholar, M. Anderson C.W. Appella E. 1998; PubMed Scopus Google Scholar, Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google while acetylation of was to DNA and to M. Anderson C.W. Appella E. 1998; PubMed Scopus Google Scholar, M. J. J. Biol. 2002; PubMed Scopus Google However, the of p53 in response to genotoxic and non-genotoxic stresses is characterize the of in p53 antibodies that 14 of the known p53 modification sites they M. Anderson C.W. Appella E. 1998; PubMed Scopus Google Scholar, Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google Scholar, Appella E. Anderson C.W. J. Biol. PubMed Scopus Google Scholar, Anderson C.W. Appella E. J. Biol. PubMed Scopus Google the phosphorylation of p53 at sites in response to of DNA agents, UV light and IR, in A549 cells, a used with p53 that was from a human We also phosphorylation of sites after treatment with four non-genotoxic agents, ALLN, of ubiquitin-mediated degradation by the taxol and which 2001; PubMed Scopus Google Scholar, M. M. 2001; 3: PubMed Scopus Google and which of DNA damage G.M. PubMed Scopus Google p53 in the HCT116 colon carcinoma cell which also was phosphorylated in in response to p53 acetylation was at sites, and We the site of p53 phosphorylation in transient by of mutant p53 that to at most of the phosphorylation sites. the of signaling that the modification of the human p53 in cells exposed to and p53 antibodies for human p53 phosphorylated at Ser6, Ser9, Ser15, Ser33, Ser37, Ser46, or Ser392 or at or M. Anderson C.W. Appella E. 1998; PubMed Scopus Google Scholar, Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google Scholar, Appella E. Anderson C.W. J. Biol. PubMed Scopus Google Scholar, Anderson C.W. Appella E. J. Biol. PubMed Scopus Google antibodies for mouse p53 phosphorylated at and also M. Anderson C.W. Appella E. M. J. 2002; PubMed Scopus Google Scholar, J. Anderson C.W. Appella E. Cell Biol. 2002; PubMed Scopus Google site-specific antibodies were from the by of phosphorylated with The antibodies were through a with the to antibodies that with The of was by enzyme-linked and p53 and by p53 in Cell a human carcinoma cell which was from the as was a human carcinoma cell that is for both p53 a human colon carcinoma cell that was by A549 and cells were in and HCT116 cells were in both with and in a with and mouse were from p53 and were from mutant cells the J. Anderson C.W. Appella E. Cell Biol. 2002; PubMed Scopus Google were cultured in with and in a with In the of was of Cell and were in 24 h to treatment and were at the of treatment. were exposed to UV light a UV or to ionizing radiation at a of a as Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google The was to cells at a of taxol, nocodazole and from Cancer were to and in the they were of agents were after the cell to the The trichostatin was at a of h were at the indicated after treatment and for and as Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google p53 p53 and p53 were as human p53 protein was from of cell by genotoxic and non-genotoxic were the were the in a and and Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google The to cells were in the the cells were with of the indicated or mutant p53 the were exposed to 8 ionizing radiation or UV h after 2 h or 8 h after exposure to or UV light, and to and of p53 in A549 in to DNA characterize the to p53 induced by DNA agents, antibodies for sites that p53 at that The of was by with p53 or by human p53 protein in E. with of the antibodies with the protein and We used antibodies to the phosphorylation of sites in response to treatment with three DNA damage-inducing agents, IR, UV light, or adriamycin Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google We also acetylation at sites in the and as M. Anderson C.W. Appella E. 1998; PubMed Scopus Google were treatment and at after treatment and p53 was by and by We the response of phosphorylation and acetylation to treatment with the three DNA damage-inducing the phosphorylation response after for between 2 and Gy, and after UV for between and at Ser6, Ser15, Ser37, Ser46, and is the induction of p53 with a sites phosphorylation was induced by 2 h after exposure to as as 2 phosphorylation was 8 were for UV light at 8 phosphorylation was at Ser6 with as as maximum induction of phosphorylation studies that 2 h after and 8 h after UV were for phosphorylation responses p53 protein accumulation was after exposure to 8 or result in significant of to was for We the of at of p53 sites between and 96 h after exposure to 8 IR, UV light, or treatment induced p53 with the of also was with ALLN, which induced p53 accumulation to M. Anderson C.W. Appella E. 1998; PubMed Scopus Google or IR, significant accumulation was by h after for UV or ADR, significant p53 accumulation was by was after IR, UV, and ADR, and p53 levels even after treatment with or p53 levels between 8 and 24 h after treatment. 2 exposure to 8 induced a clear in phosphorylation at Ser6 and Ser15 by h after treatment Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google Scholar, Appella E. Anderson C.W. J. Biol. PubMed Scopus Google and by 2 h maximum phosphorylation was at sites and Ser392. three sites, in phosphorylation was in response to at We and phosphorylation at Ser6 and Ser15 in response to as as after treatment M. Anderson C.W. Appella E. 1998; PubMed Scopus Google Scholar, Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google Scholar, Appella E. Anderson C.W. J. Biol. PubMed Scopus Google In IR-induced phosphorylation at most sites 24 to h after treatment and returned to near pretreatment levels by 72 h In UV light induced a less rapid but more prolonged and robust in p53 at most sites between 2 and h after UV treatment and reached a maximum between 8 and 24 h; at 96 h, significant phosphorylation was in response to the by exposure to UV in and that in the the cells were phosphorylation was at most sites in response to of the three DNA damage-inducing clear differences were at most sites was more induced by UV light and than by IR, at Ser33, Ser37, Ser46, and Ser392. three agents also acetylation of while acetylation of was induced most after UV The of acetylation was to phosphorylation but occurred with a for phosphorylation in p53 acetylation J. Biol. 1998; PubMed Scopus Google Scholar, M. Anderson C.W. Appella E. 1998; PubMed Scopus Google Scholar, Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google sites, Ser6, Ser33, and Ser392 to be phosphorylated at a in the of DNA damage sites, phosphorylation after in with the in p53 but the levels those after treatment with DNA damage-inducing phosphorylation was by that the antibodies with a of protein in E. of p53 in A549 and HCT116 in to and HCT116 human colon carcinoma cells and normal human cell to the modification in A549 cells were in cells after exposure to IR, UV, and We also the of three non-genotoxic agents known to of the of the protein that is for and taxol and nocodazole were with or three agents at three the for the inhibition of by for or also were with for were and to treatment induced significant p53 by the for ALLN, p53 protein accumulation was by 24 h after the of treatment the of Ser9, and the of in HCT116 cells in response to Gy, UV and were to that for A549 cells that the signaling in response to DNA damage are to most cell phosphorylation was at Thr18 in HCT116 cells, and the signals for and were than for A549 We at of the p53 sites after exposure for 24 h to the three non-genotoxic agents PALA, taxol, and at three induced p53 accumulation to levels to those after UV or a of the sites was induced at Ser6, Ser33, Ser46, and Ser392 in both cell by taxol and nocodazole to levels or to those with UV light or In phosphorylation at Ser9, Ser15 and A549 was than with UV light or ADR, some phosphorylation was at phosphorylation was at was acetylation at in response to or but acetylation at site was than after UV to those in also were with normal human and normal human in both of cell the modification signals were than after treatment of A549 or HCT116 N-terminal p53 by interdependencies in p53 phosphorylation through the of p53s to sites. are the of phosphorylation at Ser33 after UV radiation Anderson C.W. Appella E. J. PubMed Scopus Google and the of phosphorylation at Thr18 after Ser15 Anderson C.W. Appella E. J. Biol. PubMed Scopus Google These the of that signaling to the phosphorylation of the p53 protein after DNA a of for p53 in which of the and in the N-terminal of p53 were to Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google We carcinoma cells, which are for both p53 with exposed the cells to or and from for with a of site-specific antibodies Analysis with a indicated that and mutant p53 were at Some phosphorylation in the of treatment was the a response in human cells Anderson C.W. Appella E. J. Biol. PubMed Scopus Google Scholar, Anderson C.W. Appella E. J. PubMed Scopus Google of the N-terminal and sites in the p53 protein were phosphorylated well after IR, and phosphorylation was after with that the were to p53 and that the p53 protein was in cells in the after as was the p53 protein in the human cell phosphorylation signal was for sites the to Ser33 to also phosphorylation of Ser37; to phosphorylation at Ser33 or at N-terminal sites. was the result of for Ser15 IR-induced phosphorylation at Thr18 Anderson C.W. Appella E. J. Biol. PubMed Scopus Google but also phosphorylation of and while the phosphorylation of Ser6, Ser33, Ser37, and were to phosphorylation of while Thr18 to phosphorylation at but at the N-terminal sites. p53 with phosphorylated Thr18 or and Ser15 to were by or antibodies as well as were the phosphorylated the of to by In to of sites, Ser6 to phosphorylation at and phosphorylation at the N-terminal sites In or to significant the phosphorylation at sites, phosphorylation of the sites, or of the N-terminal phosphorylation sites or at also Ser392 and that Ser15 to in human p53 acetylation at and while Ser6, Ser9, or Thr18 to but or more sites, acetylation at Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google to those in were with the human cell with the p53 and the phosphorylation site also were in cells after exposure to UV light the signaling for p53 phosphorylation after are the of and exposure to UV light are and could be is the of DNA damage signaling the phosphorylation of p53 the activation of such as for the ATM protein kinase cascade Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google Scholar, 2001; PubMed Scopus Google but also the modification of the p53 to p53 as as for human the N-terminal of the of human and through are well and for Ser6, Ser9, Ser15, and Thr18 in We mutant cells and in which the p53 was that cells p53 in which or the of Ser15 or in human were to J. Anderson C.W. Appella E. Cell Biol. 2002; PubMed Scopus Google Scholar, Anderson C.W. Appella E. PubMed Scopus Google phosphorylation of the p53 in p53 phosphorylation in mouse after exposure to adriamycin with antibodies that p53 phosphorylated at or In normal and were well phosphorylated after adriamycin treatment as after exposure to UV light or M. Anderson C.W. Appella E. M. J. 2002; PubMed Scopus Google Scholar, J. Anderson C.W. Appella E. Cell Biol. 2002; PubMed Scopus Google Scholar, Anderson C.W. Appella E. PubMed Scopus Google with the for cells, phosphorylation of the to Thr18 in human was in while phosphorylation of was in Analysis of the phosphorylation of was phosphorylation levels were of the of are with the Ser15 of phosphorylation site interdependencies in human the that p53 is and in response to DNA damage and cellular stresses through to the p53 protein as well as to with which sites in the human p53 protein are in in response to the activation of stress signaling through phosphorylation or acetylation C.W. Appella E. Bradshaw R.A. Dennis E. Handbook of Cell Signaling. Vol. 3. Academic Press, New, York2003: 237-247Google Scholar, 2Appella E. Anderson C.W. Eur. J. Biochem. 2001; 268: 2764-2772Crossref PubMed Scopus (912) Google near the sites be phosphorylated or in Biochem. 2002; PubMed Scopus Google Scholar, Cell Biol. PubMed Scopus Google but the of to sites in while a of the and sites of that p53 to with signal and to for for the a in human cell of the to p53 in response to several genotoxic and non-genotoxic of the responses at multiple sites to agents important in the of the signaling that p53 is to for most modification sites, which the of from that or sites the p53 or The of phosphorylation site-specific antibodies was for the of p53 the of p53 phosphorylation was the of that cause DNA the of such 2 the response of human p53 at 14 sites to three DNA damage-inducing antibodies that with phosphorylated at or which were to be phosphorylated Nat. 1998; PubMed Scopus Google with p53 in A549 cells in A549 cells with UV, IR, or in A549 cells at significant levels or the phosphorylated p53 is and J. Biol. 2001; PubMed Scopus Google We phosphorylation at Nat. 1998; PubMed Scopus Google Scholar, Cell Biol. PubMed Scopus Google X. PubMed Scopus Google D. Cell Biol. 2001; PubMed Scopus Google or D. X. J. 2001; PubMed Scopus (325) Google acetylation at Cell Biol. PubMed Scopus Google at M. V. M. J. PubMed Scopus Google Scholar, J. PubMed Scopus Google is that modification of p53 at most sites is after cells are exposed to the DNA damage-inducing agents 2 and several protein kinases to be in cells exposed to genotoxic the that phosphorylation result from the induced inhibition of p53 as well as from the activation of protein p53 the of both the M. M. J. PubMed Scopus Google and M. M. J. Biochem. 2001; PubMed Scopus Google and the was to p53 protein levels and transcriptional X. Cancer 3: PubMed Scopus Google is known the of stress pathway signaling protein 2 also a clear differences between the responses to the three genotoxic agents in more after exposure to than to UV in the response to UV light or ADR, while was less was more robust and was in response to to a of Gy, which breaks in response to UV light to which of a DNA cells to genotoxic agents at that are to p53 phosphorylation at as a of DNA damage that be in also were at sites for the genotoxic In the N-terminal phosphorylation of Thr18 was in response to and than to UV light while phosphorylation at Ser33, Ser37, and was induced more after UV light or than after IR. the phosphorylation was induced at by three agents, while phosphorylation at Ser392 was induced by UV light or ADR, but by M. 1998; PubMed Scopus Google Scholar, M. 1998; PubMed Scopus Google was after exposure of A549 cells to three agents, but more after UV light or ADR, with the more robust induction of phosphorylation at Ser15 and N-terminal sites by agents J. Biol. 1998; PubMed Scopus Google Scholar, Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google was after UV light or ADR, but after IR. some differences between cell (e.g. the to p53 in HCT116 cells induced after exposure of cells to IR, UV, or were to those in A549 cells, and in several cell (e.g. Rotter V. Appella E. PubMed Scopus Google phosphorylation of p53 at Ser15 and a sites also in response to and of which J. Biol. PubMed Scopus Google DNA damage Refs. 1Anderson C.W. Appella E. Bradshaw R.A. Dennis E. Handbook of Cell Signaling. Vol. 3. Academic Press, New, York2003: 237-247Google Scholar and 2Appella E. Anderson C.W. Eur. J. Biochem. 2001; 268: 2764-2772Crossref PubMed Scopus (912) Google Ser15 phosphorylation was in human D. Cell Biol. PubMed Scopus Google but in those Anderson C.W. Appella E. Nat. 2002; PubMed Scopus Google to non-genotoxic agents induced phosphorylation of a of those sites phosphorylated in response to in the of ALLN, phosphorylation at is of degradation by the and p53 accumulation to levels to those induced by DNA damage but transcription M. Anderson C.W. Appella E. 1998; PubMed Scopus Google treatment of cells with phosphorylation, a of phosphorylation at four sites, Ser6, Ser33, and was that in with p53 levels of the used to and and inhibits and to transcription and phosphorylation at several sites. M. M. 2001; 3: PubMed Scopus Google that taxol induced p53 phosphorylation at but Ser15 in HCT116 cells, while 2001; PubMed Scopus Google that both taxol and nocodazole induced a in p53 phosphorylation at multiple sites, including Ser15, in HCT116 and cells, but in normal human In with phosphorylation of Ser15 in A549 or HCT116 cells in response to PALA, taxol, or and significant phosphorylation at However, in response to non-genotoxic agents, also a more robust phosphorylation at Ser6, Ser33, Ser46, and Ser392. phosphorylation was at Ser9, and p53 accumulation occurred in both cell in response to three agents, and were to transcriptional responses 2001; PubMed Scopus Google Scholar, M. M. 2001; 3: PubMed Scopus Google be to more site and cell differences between agents, is clear from that genotoxic stresses in the phosphorylation of a of phosphorylation sites with Ser15 of p53 that be phosphorylated in response to non-genotoxic agents p53 is in response to non-genotoxic that while phosphorylation of Ser15, and to p53 in the of DNA damage D. Oren M. Semin. Cancer Biol. PubMed Scopus Google is by studies of p53 in response to M. M. M. M. J. Biol. 2001; PubMed Scopus Google and Anderson C.W. Appella E. Nat. 2002; PubMed Scopus Google In J. Biol. PubMed Scopus Google Ser15 phosphorylation, but phosphorylation of after cause DNA p53 protein in and p53 phosphorylation Ser15 was with arrest and activation of the protein be in response to some non-genotoxic (e.g. that DNA result from is the to which phosphorylation at site in the of p53 the of or which are sites of phosphorylation that phosphorylation at Thr18 after the of Ser15 Anderson C.W. Appella E. J. Biol. PubMed Scopus Google and phosphorylation at after exposure to UV Ser33 Anderson C.W. Appella E. J. PubMed Scopus Google the of the interdependencies N-terminal p53 phosphorylation sites was the of interdependencies the of is that in the and activation of p53 in response to genotoxic is the phosphorylation of Ser15 through activation of ATM in response to DNA breaks and in response to the of DNA and transcription 2001; PubMed Scopus Google Scholar, K.H. 2002; PubMed Scopus Google The of Ser15 phosphorylation for p53 was in through transient studies to those in which the phosphorylated was to was used to that phosphorylation of is for p53 PubMed Scopus Google was to the of p53 in mouse cells (e.g. J. Anderson C.W. Appella E. Cell Biol. 2002; PubMed Scopus Google Scholar and Anderson C.W. Appella E. PubMed Scopus Google The that Ser15 also phosphorylation at Ser9, and phosphorylation of but or Ser15, while Thr18 phosphorylation of but or also between Ser6 and Ser9, while phosphorylation of was Ser33 but We suggest that at some of interdependencies that signal amplification and the integration of from signaling by phosphorylation of sites in Ser9, and be phosphorylated Ser15 is and Ser15, and be for p53 cascade to check inappropriate p53 activation or the of the p53 response and kinase activation such as that for the phosphorylation and acetylation of p53 in response to DNA breaks Appella E. Anderson C.W. J. Biol. 2002; PubMed Scopus Google that ATM, which is to Ser15, also is to Ser9, and Ser46, as a result of the activation of effector However, at the several that to phosphorylation site These a in p53 that kinase as well as the of that could the of kinases with We to be at for the is well known that at of kinases (e.g. that phosphorylation for Appella E. Anderson C.W. J. Biol. PubMed Scopus Google Scholar, Anderson C.W. Appella E. J. Biol. PubMed Scopus Google the of p53 is to be in the of a J. J. Biol. 2002; PubMed Scopus Google which that a the of as a of the of for a less in the of and for which p53 phosphorylation in response to genotoxic stress of is that the kinases that N-terminal p53 sites in exhibit phosphorylation for in to a or the of a The are with a in which genotoxic and non-genotoxic agents signaling to p53 and activation through phosphorylation Biochem. 2002; PubMed Scopus Google significant between genotoxic and non-genotoxic stress to be the activation of the ATM and protein kinases that Ser15 of p53 in response to DNA ATM and ATR, in effector kinases that sites in the N-terminal of p53 to signal However, the also suggest that a cascade to that p53 is by effector phosphorylation site also to signals from multiple stress pathways. of both of the protein kinases that p53 in response to We for HCT116 cells, and and for of the We also are to V. and for and

Ser-15 of human p53 (corresponding to Ser-18 of mouse p53) is phosphorylated by ataxia-telangiectasia mutated (ATM) family kinases in response to ionizing radiation (IR) and UV light. To determine the effects of phosphorylation of endogenous murine p53 at Ser-18 on biological responses to DNA damage, we introduced a missense mutation (Ser-18 to Ala) by homologous recombination into both alleles of the endogenous p53 gene in mouse embryonic stem (ES) cells. Our analyses showed that phosphorylation of murine p53 at Ser-18 in response to IR or UV radiation was required for a full p53-mediated response to these DNA damage-inducing agents. In contrast, phosphorylation of p53 at Ser-18 was not required for ATM-dependent cellular resistance after exposure to IR. Additionally, efficient acetylation of the C terminus of p53 in response to DNA damage did not require phosphorylation of murine p53 at Ser-18.