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Phosphorylation is required for PMA- and cell-cycle-induced degradation of protein kinase Cdelta
Jyoti Srivastava1, Katarzyna J Procyk, Xavier Iturrioz
1Protein Phosphorylation Laboratory, Cancer Research UK London Institute, Lincoln's Inn Fields Laboratories, 44 Lincoln's Inn Fields, London WC2A 3PX, U.K.
Abstract:
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 PKCdelta in NIH 3T3 cells under culture conditions where PKCdelta 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 PKCdelta observed on G(1)/S-phase progression through the cell cycle. Analysis of phosphorylation-site mutants indicated that the T-loop Thr(505) phosphorylation site was critical for induced degradation.
Insights
Chronic activation of protein kinase C delta (PKCdelta) leads to its degradation. This study reveals that hyperphosphorylation and the Thr505 site are critical for PKCdelta
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- Protein kinase C (PKC) isoforms, including novel ones, undergo down-regulation upon chronic activation by stimuli like tumor promoters.
- The precise molecular mechanisms driving this down-regulation remain incompletely understood.
- PKCdelta exhibits cell-cycle-dependent down-regulation in NIH 3T3 cells under specific culture conditions.
Purpose of the Study:
- To investigate the mechanisms of PMA (phorbol 12-myristate 13-acetate)-induced degradation of PKCdelta.
- To determine the role of protein phosphorylation and specific sites in PKCdelta down-regulation.
- To examine how calyculin A affects PKCdelta degradation during the cell cycle.
Main Methods:
- Utilized NIH 3T3 cells cultured under conditions promoting cell-cycle-dependent PKCdelta down-regulation.
- Applied PMA (TPA) to induce PKCdelta degradation.
- Employed calyculin A to promote hyperphosphorylation of PKCdelta.
- Generated and analyzed phosphorylation-site mutants of PKCdelta, focusing on the T-loop Thr505 site.
Main Results:
- A hyperphosphorylated form of PKCdelta, induced by calyculin A, was rapidly degraded in PMA-treated cells.
- Calyculin A enhanced the cell-cycle-dependent down-regulation of PKCdelta during the G1/S phase transition.
- Mutational analysis identified the T-loop phosphorylation site at Thr505 as essential for PMA-induced PKCdelta degradation.
Conclusions:
- Hyperphosphorylation, particularly at the Thr505 site, is a critical factor in the induced degradation of PKCdelta.
- Calyculin A potentiates PKCdelta down-regulation, highlighting the interplay between phosphorylation status and degradation pathways.
- Understanding these mechanisms provides insight into the regulation of PKC isoforms in cellular processes and disease.