A non-enzymatic p21 protein inhibitor of stress-activated protein kinases

Abstract

The stress-activated protein kinases (SAPKs), which are identical to the c-Jun amino-terminal kinases (JNKs), are activated in response to a variety of cellular stresses, including DNA damage, heat shock or tumour-necrosis factor-alpha. SAPK, a subfamily of the mitogen-activated protein (MAP) kinases, is a major protein kinase that phosphorylates c-Jun and other transcription factors. SAPK phosphorylation of transcription factors is important in stress-activated signalling cascades. Here we report that the protein p21 WAF1/CIP1/Sd:1, a DNA-damage-inducible cell-cycle inhibitor, acts as an inhibitor of the SAPK group of mammalian MAP kinases. This highlights a new biochemical activity of p21, which may provide the first evidence for a non-enzymatic inhibitory protein for SAPK. We suggest that p21, by inhibiting SAPK, may participate in regulating signalling cascades that are activated by cellular stresses such as DNA damage.

p21WAF1 induces permanent growth arrest and enhances differentiation, but does not alter apoptosis in PC12 cells

“…Speci®cally, this hypothesis has been supported by experiments with undi erentiated and NGF-di erentiated PC12 cells showing that trophic factor withdrawal induced apoptosis could be blocked by dominant-negative ras (Ferrari and Greene, 1994) or various chemical agents capable of inhibiting proliferation (Ferrari et al, 1995;Farinelli and Greene, 1996;Park et al, 1996). In the current study, p21 was clearly able to completely inhibit proliferation of PC12 cells.…”

“…It should also be noted that p21 has been reported to inhibit the activity of stress-activated protein kinases (SAPKs) JNK1 and p38 (Shim et al, 1996), though inhibition of speci®c processes regulated by SAPKs has not yet been reported. JNK is thought to play a role in death following numerous stimuli, including u.v.…”

“…More recently, it has been shown that inducing p21 can decrease apoptosis in di erentiating muscle cell lines (Wang and Walsh, 1996) and prostaglandin treated colon carcinoma cell lines (Gorospe et al, 1996), while decreasing expression during di erentiation of a neuronal line increases apoptosis (Poluha et al, 1996). p21 has also been demonstrated to inhibit two members of the stress activated protein kinase family (SAPK), JNK and p38 (Shim et al, 1996), proteins thought to be involved in the signalling pathways leading to cell death in response to stress (Davis, 1994;.…”

“…Additionally, there are numerous apoptotic paradigms that have been established for PC12 cells, including those involving removal of trophic support (Greene, 1978;Batistatou and Greene, 1991;Pittman et al, 1993). Given that some studies have implicated aberrant or inappropriate cell cycle in the death of trophic factor deprived PC12 cells and sympathetic neurons (Batistatao and Greene, 1993;Rubin et al, 1993;Farinelli and Greene, 1996;Park et al, 1996), this system provides a means for testing the hypothesis that p21 expression would block death resulting from trophic factor removal.…”

The carboxy terminus of p53 mimics the polylysine effect of protein kinase CK2-catalyzed MDM2 phosphorylation

“…The I 0.5 , ie. the concentration of p21 WAF1/CIP1 required for 50% inhibition of CK2 activity was determined to be 3610 76 M. Shim et al (1996) had found that p21 WAF1/CIP1 acts as a non-enzymatic inhibitor of stress kinases. The observation that p21 WAF1/CIP1 also can act as an inhibitor of CK2 suggests it has several biochemical activities beside the ones originally described (El-Deiry et al, 1993;Harper et al, 1994).…”