Purification and characterization of butyrate-induced protein phosphatase involved in apoptosis of Ehrlich ascites tumor cells

Short chain fatty acids including butyrate exhibit wide variety of biological effects towards cell growth, morphology and gene expression. In this report, we study the mechanism by which butyrate (BuA) modulates the expression of protein phosphatase when treated to the cells. As a model system, we used Ehrlich Ascites Tumor (EAT) cells in which BuA-treatment induces expression of a protein phosphatase enzyme. Subsequently, BuA-induced protein phosphatase has been biochemically purified and characterized. Further, pretreatment of caspase-3 inhibitor abolished the activity of BuA-induced protein phosphatase indicating the involvement of caspase-3 in the activation of BuA-induced protein phosphatase. In addition, the relationship between BuA-induced protein phosphatase and apoptosis has been verified. Activation of endonuclease-II has been shown in BuA-treated EAT cells and that activity was completely inhibited by sodium orthovanadate, a tyrosine phosphatase inhibitor suggesting that endonuclease-II may serve as a possible down-stream target for BuA-induced protein phosphatase. Together, the data suggest that activation of protein phosphatase may be an early and essential step in BuA-mediated apoptotic signaling pathway in EAT cells.