SHP-2 tyrosine phosphatase inhibits p73-dependent apoptosis and expression of a subset of p53 target genes induced by EGCG

Abstract

Green tea polyphenol, epigallocatechin-3-gallate (EGCG) differentially regulates the cellular growth of cancer cells in a p53-dependent manner through apoptosis and/or cell cycle arrest. In an effort to further elucidate the mechanism of differential growth regulation by EGCG, we have investigated the role of the tyrosine phosphatase, SHP-2. Comparing the responses of mouse embryonic fibroblasts (MEFs), expressing either WT or functionally inactive/truncated SHP-2, we find that inactivation of SHP-2 remarkably sensitizes cells to EGCG-mediated killing. MEFs lacking functional SHP-2 undergo massive apoptosis upon treatment with EGCG. By comparing gene expression profiles, we have identified a set of transcriptional targets of p53 that are differentially modulated in cells undergoing apoptosis. Western blot and real-time PCR analyses of a select group of genes further confirm that the expression is SHP-2-dependent. Similar observations were made in MEFs lacking p53, confirming that the expression of these ''p53 target genes'' is p53-independent. In addition, EGCG treatment induced the expression of p73 mRNA and protein in both cell types, but not p63. Inactivation of p73 in cells expressing nonfunctional SHP-2 markedly inhibited apoptosis and p53 target gene expression. Although phosphorylation of JNK is differentially regulated by SHP2, it was found to be dispensable for EGCG-induced apoptosis and p53 target gene expression. Our results have identified SHP-2 as a negative regulator of EGCG-inducedapoptosis and have identified a subset of p53 target genes whose expression is paradoxically not mediated by p53 but by one of its family members, p73.green tea ͉ MAPK pathway ͉ mouse embryonic fibroblasts ͉ transcriptional activation

Cancer Preventive Mechanismsof the Green Tea Polyphenol (-)-Epigallocatechin-3-gallate

“…Amin et al [46] have identified SHP-2 (a kind of tyrosine phosphatase) as a protective factor of cells lacking functional p53 from EGCG-induced apoptosis. Moreover, they revealed a number of targets for EGCG-induced apoptosis which were expressed in the absence of functional p53.…”

Small-molecule RETRA suppresses mutant p53-bearing cancer cells through a p73-dependent salvage pathway

“…Still, a number of p53 mutant proteins can associate with p63 and p73, blocking their transcriptional activity and thus contributing to the malignant phenotype of cancer cells (9)(10)(11). Activation of p73 in human cancer can produce substantial cytotoxic effect even in the cells lacking p53 (12)(13)(14)(15)(16), which allows considering p73 as a separate anticancer drug target. We decided to search for small molecules that release suppressor activities of the p53 family members blocked by mutant p53.…”

(-)-Epigallocatechin-3-gallate induces apoptosis in gastric cancer cell lines by down-regulating survivin expression

“…6E, p73 activation kinetics was different, but rather reciprocal, from that of p53, suggesting that distinct mechanisms may underlie EGCG-induced p53 and p73 activation. Two reports show that p73 is activated by EGCG (9,40). One of these studies showed that reactive oxygen species produced by EGCG is the factor that activates p73 (9).…”

“…Two reports show that p73 is activated by EGCG (9,40). One of these studies showed that reactive oxygen species produced by EGCG is the factor that activates p73 (9). Elucidation of this mechanism is one of our future goals.…”

“…EGCG administration inhibits formation of spontaneous intestinal tumors in APC min/+ mice (5). Reportedly, EGCG suppresses growth of cancer cells by inhibiting the nuclear factor-κB (NF-κB) (6) and Akt pathways (7), and by activating the p53 (8) and p73 pathways (9). The fascinating advantage of EGCG as a chemopreventive agent lies in its ability to eliminate transformed or neoplastic cells selectively, while sparing, or in some cases, protecting normal cells.…”