Inhibition of protein kinase C-alpha isoform enhances the P-glycoprotein expression and the survival of LoVo human colon adenocarcinoma cells to doxorubicin exposure.

The aim of the present paper was to analyse the effect of long-term inhibitory treatment, for at least 7 days, of individual protein kinase C (PKC) isoforms on the survival of LoVo human colon adenocarcinoma cells to doxorubicin exposure. The treatment for 2 h, after plating the cells, and after 3 days with 1 microM Gö6976, a specific inhibitor of protein kinase C (PKC)-alpha and -betal isoforms, induced on day 7 in LoVo cell lines (WT) a significant increased survival when these cells were exposed to increasing doxorubicin concentrations. In contrast, resistant LoVo cells (DX) did not show significant changes in the survival to doxorubicin exposure when incubated with the inhibitor of the same specific PKC isoforms. In addition, Gö6976 reduced the PKC-alpha activity (the main calcium-dependent PKC isoforms expressed) in both cell lines with contemporary increased expression. Under such conditions, an increased nuclear activity and an increased P-glycoprotein expression occurred only in WT-treated cells with respect to untreated cells. Taken together, our data indicate a specific relationship between PKC-alpha inhibition, the increased nuclear PKC-alpha activity as well as the increased expression of P-glycoprotein, possibly causing the acquisition of a resistant phenotype in WT LoVo cells.