Tautomycetin inhibits growth of colorectal cancer cells through p21^cip/^WAF1 induction via the extracellular signal-regulated kinase pathway

Tautomycetin is an antifungal antibiotic retaining potent immunosuppressive function. We have identified the roles of tautomycetin on cellular proliferation and transformation of colorectal cancer cells. The proliferation and anchorage-independent growth of HCT-15, HT-29, and DLD-1 colorectal cancer cells were efficiently inhibited without induction of apoptosis by 150 nmol tautomycetin. These growth inhibitory effects were dependent on p21^Cip/WAF induction via the extracellular signal - regulated kinase pathway, and the tautomycetin effects were abolished in HCT-116 colon cells and eight other types of cells that did not induce P21^Cip/WAF by 150 nmol tautomycetin. The crucial role of p21^Cip/WAF1 in the extracellular signal - regulated kinase pathway-dependent antiproliferative responses by tautomycetin was confirmed by using p21^Cip/WAF1 gene-deleted HCT-116 cells. The growth inhibitory effect of tautomycetin was acquired by regulation of Raf-1 activity through inhibition of protein phosphatase type 1 and protein phosphatase type 2A with high preference toward protein phosphatase type 1. Tautomycetin could be a potential drug for colorectal cancer.