Classical and novel protein kinase C (PKC) isoforms are down-regulated as a result of chronic activation by certain tumour promoters and physiological stimuli; however, the mechanisms leading to down-regulation are not fully understood. In the present study, we have studied the PMA ('TPA')-induced degradation of PKCΔ in NIH 3T3 cells under culture conditions where PKCΔ displays cell-cycle-dependent down-regulation. In contrast with previous studies, a hyperphosphorylated form of this PKC isoform, promoted by calyculin A, was rapidly degraded in PMA-treated cells. Similarly, the presence of calyculin A enhanced the down-regulation of PKCΔ observed on G1/S-phase progression through the cell cycle. Analysis of phosphorylation-site mutants indicated that the T-loop Thr505 phosphorylation site was critical for induced degradation.
Phosphorylation is required for PMA- and cell-cycle-induced degradation of protein kinase Cδ
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Jyoti SRIVASTAVA, Katarzyna J. PROCYK, Xavier ITURRIOZ, Peter J. PARKER; Phosphorylation is required for PMA- and cell-cycle-induced degradation of protein kinase Cδ. Biochem J 15 November 2002; 368 (1): 349–355. doi: https://doi.org/10.1042/bj20020737
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