p21^Cip/WAF1 activation is an important factor for the ERK pathway dependent anti-proliferation of colorectal cancer cells

p21^Cip/WAF1, an important regulator of cell proliferation, is induced by both p53- and extracellular signal regulated kinase (ERK) pathways. The induction of p21^Cip/WAF1 occurs by prolonged activation of the ERKs caused by extracellular stimuli, such as zinc. However, not all the cells appeared to respond to ERK pathway dependent p21^Cip/WAF1 induction. Here we investigated the cause of such difference using colorectal cancer cells. p21^Cip/WAF1 induction and concomitant reduction of bromodeoxyuridine (BrdU) incorporation were observed by zinc treatment within HT-29 and DLD-1. However. HCT-116 cells with high endogenous p21^Cip/WAF1 levels did not show any additional increment of p21^Cip/WAF1 levels by zinc treatment and did maintain high BrdU incorporation level. The p21 ^Cip/WAF1 induction by zinc depended upon prolonged activation of extra-cellular signal regulated kinase (ERK) was not observed in HCT-116 cells. The percentage of BrdU positive cells was 50% higher In p21^Cip/WAF1 -/ HCT-116 cells compared to p21^Cip/WAF1 +/+ HCT-116 cells, and no cells induced p21^Cip/WAF1 incorporated BrdU in its nucleus, yet confirming the importance of p21^Cip/WAF1 induction in antiproliferation. These results again support that p21^Cip/WAF1 induction is a determinant in the regulation of colonic proliferation by the ERK pathway.