Protein kinase C-alpha antagonizes apoptosis induction by histone deacetylase inhibitors in multidrug resistant leukaemia cells.

Previous studies have documented that while several drug-resistant cells enter apoptosis upon treatment with histone deacetylase inhibitors (iHDACs), their drug-sensitive counterparts do not. In the present study, we have investigated at the molecular level why parental drug-sensitive tumor cells do not respond to Trichostatin A and suberoylanilide hydroxamic acid, two iHDACs that promote apoptosis in drug-resistant leukaemia cells. Taking murine leukaemia L1210 cells as a model, we have determined that: (i) PKC-alpha expression is more elevated in parental L1210 than in drug-resistant L1210/R cells, (ii) activation of PKC neutralizes iHDACs-mediated apoptosis in L1210/R cells, (iii) depletion of PKC in parental L1210 cells results in a positive response to iHDACs-mediated apoptosis, and (iv) transfection of a mutant constitutively active PKC-alpha form in L1210/R cells makes the cells refractory to apoptosis induction by iHDACs. These results allow us to conclude that activation/high expression of PKC-alpha protects parental drug-sensitive L1210 cells from iHDACs-mediated apoptosis. Thus, determination of PKC-alpha levels/activity in leukaemia seems to be relevant when choosing efficient chemotherapy protocols based on the use of apoptosis-inducing anticancer drugs.