PKD in intestinal epithelial cells: rapid activation by phorbol esters, LPA, and angiotensin through PKC

Protein kinase C (PKC) is implicated in the regulation of multiple importan t functions in intestinal epithelial cells, but the downstream signaling ta rgets of PKCs in these cells remain poorly characterized. Here we report th at treatment of normal rat intestinal cell lines IEC-6 and IEC-18 with phor bol 12,13-dibutyrate (PDBu) led to a rapid and striking PKC-dependent activ ation of protein kinase D (PKD; also known as PKC mu). Unlike conventional and novel PKCs, PKD did not undergo downregulation in response to prolonged (24 h) exposure of IEC-6 or IEC-18 cells to PDBu. PKD was also rapidly act ivated in these cells by lysophosphatidic acid (LPA) or angiotensin in a co ncentration-dependent fashion via a PKC-dependent pathway. EC50 values were 0.1 muM and 2 nM for LPA and angiotensin II, respectively. LPA-induced PKD activation was prevented selectively by treatment with pertussis toxin. PK D activation was tightly associated with an increase in PKD autophosphoryla tion at serine 916. Our results identify PKD as a novel early point of conv ergence and integration of G(i) and G(q) signaling in intestinal epithelial cells.