Mitomycin C and decarbamoyl mitomycin C induce p53-independent p21WAF1/CIP1 activation

Mitomycin C (MC), a commonly used anticancer drug, induces DNA damage via DNA alkylation. Decarbamoyl mitomycin C (DMC), another mitomycin lacking the carbamate at C10, generates similar lesions as MC. Interstrand cross-links (ICLs) are believed to be the lesions primarily responsible for the cytotoxicity of MC and DMC. The major ICL generated by MC (alpha-ICL) has a trans stereochemistry at the guanine-drug linkage whereas the major ICL from DMC (beta-ICL) has the opposite, cis, stereochemistry. In addition, DMC can provoke strong p53-independent cell death. Our hypothesis is that the stereochemistry of the major unique beta-ICL generated by DMC is responsible for this p53-independent cell death signaling. p53 gene is inactively mutated in more than half of human cancers. p21(WAF1/CIP1) known as a major effector of p53 is involved in p53-dependent and-independent control of cell proliferation and death. This study revealed the role of p21(WAF1/CIP1) on MC and DMC triggered cell damage. MCF-7 (p53-proficient) and K562 (p53-deficient) cells were used. Cell cycle distributions were shifted to the G1/S phase in MCF-7 treated with MC and DMC, but were shifted to the S phase in K562. p21(WAF1/CIP1) activation was observed in both cells treated with MC and DMC, and DMC triggered more significant activation. Knocking down p53 in MCF-7 did not attenuate MC and DMC induced p21(WAF1/CIP1) activation. The a-ICL itself was enough to cause p21(WAF1/CIP1) activation.