Protein kinase C delta is phosphorylated on five novel Ser/Thr sites following inducible overexpression in human colorectal cancer cells.

Phosphorylation plays an important role in regulation of protein kinase C delta (PKCdelta). To date, three Ser/Thr residues (Thr 505, Ser 643, and Ser 662) and nine tyrosine residues (Tyr 52, Tyr 64, Tyr 155, Tyr 187, Tyr 311, Tyr 332, Tyr 512, Tyr 523, and Tyr 565) have been defined as regulatory phosphorylation sites for this protein (rat PKCdelta numbering). We combined doxycycline-regulated inducible gene expression technology with a hypothesis-driven mass spectrometry approach to study PKCdelta phosphorylation pattern in colorectal cancer cells. We report identification of five novel Ser/Thr phosphorylation sites: Thr 50, Thr 141, Ser 304, Thr 451, and Ser 506 (human PKCdelta numbering) following overexpression of PKCdelta in HCT116 human colon carcinoma cells grown in standard tissue culture conditions. Identification of potential novel phosphorylation sites will affect further functional studies of this protein, and may introduce additional complexity to PKCdelta signaling.