Regulated binding of importin-? to protein kinase C? in response to apoptotic signals facilitates nuclear import.

ABSTRACT: PKC? translocates into the nucleus in response to apoptotic agents and functions as a potent cell death signal. Cytoplasmic retention of PKC? and its transport into the nucleus are essential for cell homeostasis, but how these processes are regulated is poorly understood. We show that PKC? resides in the cytoplasm in a conformation that precludes binding of importin-?. A structural model of PKC? in the inactive state suggests that the nuclear localization sequence (NLS) is prevented from binding to importin-? through intramolecular contacts between the C2 and catalytic domains. We have previously shown that PKC? is phosphorylated on specific tyrosine residues in response to apoptotic agents. Here, we show that phosphorylation of PKC? at Tyr-64 and Tyr-155 results in a conformational change that allows exposure of the NLS and binding of importin-?. In addition, Hsp90 binds to PKC? with similar kinetics as importin-? and is required for the interaction of importin-? with the NLS. Finally, we elucidate a role for a conserved PPxxP motif, which overlaps the NLS, in nuclear exclusion of PKC?. Mutagenesis of the conserved prolines to alanines enhanced importin-? binding to PKC? and induced its nuclear import in resting cells. Thus, the PPxxP motif is important for maintaining a conformation that facilitates cytosplasmic retention of PKC?. Taken together, this study establishes a novel mechanism that retains PKC? in the cytoplasm of resting cells and regulates its nuclear import in response to apoptotic stimuli.

SUBMITTER: Adwan TS 

PROVIDER: S-EPMC3195609 | biostudies-literature | 2011 Oct

REPOSITORIES: biostudies-literature