Protein kinase C α regulates nuclear pri-microRNA 15a release as part of endothelin signaling

Endothelin-1 induced signaling is characterized by an early induction of a nuclear factor-kappa B p65/mitogen-activated phosphokinase p38 transcription complex via its A-receptor versus a late induction via diacylglycerol, and protein kinase C. A possible interaction between these two pathways and a potential function for protein kinase C in this context has not previously been elucidated. Here we report that in Caki-1 tumor cells, protein kinase C α is a part of the transcription complex. With importin α4 and α5 as chaperones, the transcription complex transmigrates into the nucleus. Protein kinase C α blocks the nuclear release of pri-microRNA 15a by direct binding shown by electrophoretic mobility shift assay and Duolink immune histology. The expression levels of miRNA 15a can be further manipulated by transfection of si-protein kinase C α, or an expression vector containing protein kinase C α or miRNA 15. The miRNA 15a regulation by protein kinase C α is detectable in different malignant human tumor cell lines (renal cell carcinoma, breast carcinoma, and melanoma). Furthermore, all three cell lines harbor both endothelin receptors (ETAR/ETBR). Specific blockage of each receptor leads to major reduction of miRNA 15a expression due to increased nuclear protein kinase C α translocation. We conclude that the nuclear binding of pri-microRNA 15a is a novel function of protein kinase C α, which plays an important role in endothelin-1 mediated signaling. Since several endothelin-sensitive, malignant tumor cell lines harbor this regulation, it could indicate a more general role in tumor biology.