Protein Kinase C Alpha (PKCα) overexpression leads to a better response to retinoid acid therapy through Retinoic Acid Receptor Beta (RARβ) activation in mammary cancer cells

Purpose Retinoids have proved to be effective for hematologic malignancies treatment but till nowadays, their use as single agent for the solid tumor's management is still controversial. All-trans retinoic acid (ATRA), the main active metabolite of vitamin A, exerts non-genomic interactions with different members of the protein kinase C (PKC) family, recognized modulators of different tumor progression pathways. To determine whether a group of patients could become benefited employing a retinoid therapy, in this study we have evaluated whether PKC alpha expression (a poor prognosis marker in breast cancer) could sensitizes mammary cells to ATRA treatment. Methods PKC alpha overexpression was achieved by stable transfection and confirmed by western blot. Transfected PKC functionality was determined by nuclear translocation-induction and confocal microscopy. In vitro proliferation was evaluated by cell counting and cell cycle distribution was analyzed by flow cytometry. In vivo studies were performed to evaluate orthotopic tumor growth and experimental lung colonization. Retinoic acid response elements (RARE) and AP1 sites-dependent activity was studied by gene reporter assays and retinoic acid receptors (RARs) were measured by RT-qPCR. Results Our findings suggest that high PKC alpha levels improve the differentiation response to ATRA in a RAR signaling-dependent manner. Moreover, RAR beta expression appears to be critical to induce ATRA sensitization, throughout AP1 trans-repression. Conclusion Here we propose that retinoids could lead a highly personalized anticancer treatment, bringing benefits to patients with aggressive breast tumors resulting from high PKC alpha expression but, an adequate expression of the RAR beta receptor is required to ensure the effect on this process.