Cytoplasmic ubiquitin ligase KPC regulates proteolysis of p27Kip1 at G1 phase

Abstract

The cyclin-dependent kinase inhibitor p27(Kip1) is degraded at the G0-G1 transition of the cell cycle by the ubiquitin-proteasome pathway. Although the nuclear ubiquitin ligase (E3) SCF(Skp2) is implicated in p27(Kip1) degradation, proteolysis of p27(Kip1) at the G0-G1 transition proceeds normally in Skp2(-/-) cells. Moreover, p27(Kip1) is exported from the nucleus to the cytoplasm at G0-G1 (refs 9-11). These data suggest the existence of a Skp2-independent pathway for the degradation of p27(Kip1) at G1 phase. We now describe a previously unidentified E3 complex: KPC (Kip1 ubiquitination-promoting complex), consisting of KPC1 and KPC2. KPC1 contains a RING-finger domain, and KPC2 contains a ubiquitin-like domain and two ubiquitin-associated domains. KPC interacts with and ubiquitinates p27(Kip1) and is localized to the cytoplasm. Overexpression of KPC promoted the degradation of p27(Kip1), whereas a dominant-negative mutant of KPC1 delayed p27(Kip1) degradation. The nuclear export of p27(Kip1) by CRM1 seems to be necessary for KPC-mediated proteolysis. Depletion of KPC1 by RNA interference also inhibited p27(Kip1) degradation. KPC thus probably controls degradation of p27(Kip1) in G1 phase after export of the latter from the nucleus.

Mutant B-RAF signaling and cyclin D1 regulate Cks1/S-phase kinase-associated protein 2-mediated degradation of p27Kip1 in human melanoma cells

“…This requirement appears to be distinct from reported results in ocular melanomas, such as those derived from the choroids, in which p27 Kip1 degradation may be mediated by calpain (Delmas et al, 2003). While our studies were in progress, Nakayama co-workers provided evidence that an alternative ubiquitin ligase complex, KPC (Kip1 ubiquitylation-promoting complex) regulates p27 Kip1 degradation in the G1 phase of the cell cycle (Kamura et al, 2004). Whether this E3 ligase, in addition to Skp2, regulates p27 Kip1 in melanoma is unknown, at present.…”

Involvement of CUL4 Ubiquitin E3 Ligases in Regulating CDK Inhibitors Dacapo/p27Kip1 and Cyclin E Degradation

“…To determine whether the decreased levels of CUL4A or DDB1 affect the ability of SCF SKP2 to target the phospho-threonine 187 dependent degradation of p27 in p27 degradation extracts, 3 we prepared cell extracts from control, DDB1, and CUL4A silenced H1299 cells. The SCF-dependent degradation activity of these extracts was assayed with 35 S-methionine labeled p27 in the presence or absence of recombinant cyclin E/CDK2. Our studies suggest that even though DDB1 and CUL4A proteins are markedly reduced by their specific siRNAs, the control and DDB1 or CUL4A deficient extracts retained their ability to proteolyze p27 in the presence of cyclin E/CDK2 (Fig.…”

Autophagy regulates T lymphocyte proliferation through selective degradation of the cell-cycle inhibitor CDKN1B/p27Kip1

“…27 A SKP2-independent pathway, which is mediated by the ubiquitin ligase KIP1 ubiquitination-promoting complex (KPC), also regulates the degradation of CDKN1B during the G 1 phase. 33 Besides regulating cell cycle, CDKN1B also plays roles in mediating other functions of T cells. For example, CDKN1B negatively regulates the CD4 memory response by promoting the apoptosis and inhibiting proliferation in both effector and memory CD4 + T cells.…”