Protease inhibitor–induced stabilization of p21^waf1/cip1 and cell‐cycle arrest in chemical carcinogen–exposed mammary and lung cells†

Abstract

In previous studies, we have shown that human breast and lung carcinoma cells and mouse nontransformed type II lung cells fail to undergo cell-cycle arrest in G(1) phase in response to treatment with hydrocarbon carcinogens but rather accumulate in the S phase with damaged DNA. This situation may lead to replication of DNA on a damaged template and enhance frequency of mutations. The mechanism of this G(1) arrest failure was examined. Western immunoblot analyses of MCF7 human mammary cancer cells exposed to actinomycin D (used as a positive control for G(1) cell-cycle arrest) or hydrocarbon carcinogens revealed that while all of these chemicals caused an increase in p53, only trace levels of p21(waf1/cip1) protein were observed in the hydrocarbon carcinogen-treated samples. Similarly, in murine lung E10 type II cells, p53 but not p21(waf1/cip1) protein increased in response to benzo[a]pyrene dihydrodiol epoxide. Treatment of either MCF7 mammary or E10 lung cells with the protease inhibitor calpain I resulted in increased levels of p21(waf1/cip1) protein and enhancement of arrest of the cells in early phases of the cell cycle (G(1) and early S phase). The results suggest that failure of cell-cycle arrest in carcinogen-treated mammary and lung cells is related to increased protease-mediated degradation of p21(waf1/cip1) and/or related regulatory proteins.

Downregulation of Cdc2/CDK1 Kinase Activity Induces the Synthesis of Noninfectious Human Papillomavirus Type 31b Virions in Organotypic Tissues Exposed to Benzo[ a ]pyrene

“…2A). The inability of BaP treatment to affect p21 WAF1 expression was not unexpected, since studies published elsewhere have reported that bypassing p21 WAF1 tumor suppressor functions is a characteristic of the stealth nature of cigarette smoke carcinogens, by which the carcinogens induce DNA damage and propagate mutations without inducing cell cycle arrest (20,35,36). However, in the current study, the observed lack of p21 WAF1 induction with BaP could also be due to the HPV E6 oncoprotein targeting of p53 functions.…”

Distinct Regulatory Functions of Calpain 1 and 2 during Neural Stem Cell Self-Renewal and Differentiation

“…p27 transcription and degradation, in turn, was also shown to be mediated by calpains in other models, including osteoblasts, cortical neurons and preadipocytes [51]–[53]. Further, p21 accumulation induced by calpain inhibition has also been observed in other studies, where in vitro incubation with calpain 1 and 2 resulted in rapid degradation of p21 [54],[55]. It has been demonstrated that calcium oscillations occurring in G1 to S transition are required for cell cycle progression in both neural progenitor and undifferentiated cells, correlating with G1 shortening and increased proliferation [22], [56].…”

Targeted Deletion of Capn4 in Cells of the Chondrocyte Lineage Impairs Chondrocyte Proliferation and Differentiation

“…Cip1 is a calpain substrate in cytomegalovirus-infected and chemical carcinogen-exposed lung and mammary cells (6,20); however, we detected slight, if any, accumulation of p21…”