A splice variant of Skp2 is retained in the cytoplasm and fails to direct cyclin D1 ubiquitination in the uterine cancer cell line SK-UT

Abstract

Cyclin D1 is an important regulator of the transition from G1 into S phase of the cell cycle. The level to which cyclin D1 accumulates is tightly regulated. One mechanism contributing to the control of cyclin D1 levels is the regulation of its ubiquitination. SK-UT-1B cells are de®cient in the degradation of D-type cyclins. We show here that p27, a substrate of the SCF Skp2 ubiquitin ligase complex, is coordinately stabilized in SK-UT-1B cells. Further, we show that expression of Skp2 in SK-UT-1B cells rescues the cyclin D1 and p27 degradation defect observed in this cell line. These results therefore indicate that the SCF Skp2 ubiquitin ligase complex aects the ubiquitination of cyclin D1. In addition, we show that SK-UT-1B cells express a novel splice variant of Skp2 that localizes to the cytoplasm and that cyclin D1 ubiquitination takes place in the nucleus. We propose that the translocation of Skp2 into the nucleus is required for the ubiquitination of cyclin D1 and that the absence of the SCF Skp2 complex in the nucleus of SK-UT-1B cells is the mechanism underlying the ubiquitination defect observed in this cell line. Finally, our data indicates that dierential splicing of F-box proteins may represent an additional level of regulation of the F-box mediated ubiquitination pathway. Oncogene (2001) 20, 3641 ± 3650.

Herpes simplex virus 1-infected cell protein 0 contains two E3 ubiquitin ligase sites specific for different E2 ubiquitin-conjugating enzymes

“…SCF complexes containing the F-box protein Skp2 promote the ubiquitylation and degradation of cyclin D1 (39,40). Thus defects in the Ubmediated proteolysis of cyclin D1 by proteins such as Skp2 lead to the stabilization of cyclin D1 in several cancer cell lines (40,41). Therefore, aspartate 199-dependent stabilization of cyclin D1 mediated by ICP0 (16) may result from the degradation of cdc34.…”

“…Cdc34 is the major E2 that interacts with the Skp1-cdc53-F-box (SCF) E3 complex (14). SCF complexes containing the F-box protein Skp2 promote the ubiquitylation and degradation of cyclin D1 (39,40). Thus defects in the Ubmediated proteolysis of cyclin D1 by proteins such as Skp2 lead to the stabilization of cyclin D1 in several cancer cell lines (40,41).…”

The Emerging Role of the COP9 Signalosome in Cancer

“…[10][11][12]. This function has been proposed to be mediated by the catalytic subunit CSN5 but requires the assembly of the entire CSN holocomplex (10)(11)(12)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). The deneddylation of Cullins is required for Cullin-mediated degradation of E3 substrates.…”

“…[44][45][46][47] as well as several cyclins (cyclin D1, cyclin E, and cyclin B1; refs. 17,20,24,28). Theoretically, inhibition of Cullin activity would promote accumulation of the cyclin-dependent kinase inhibitors, restoring control to cell cycle and inhibiting cell proliferation.…”

Oncogenic aberrations of cullin-dependent ubiquitin ligases

“…Marti et al (1999) reported that the transcription factor E2F1 is able to bind Skp2 and Cul1, and that mutations in the E2F1 N-terminal region that abolish binding to Skp2 decrease E2F1 ubiquitinylation and lead to its stabilization. Moreover, Skp2 seems to play a role in the ubiquitinylation and degradation of Cyclin D1 and Cyclin E. Cyclin D1, which is overexpressed in several human tumors, is ubiquitinylated and degraded by the proteasome, and some lines of evidence indicate that Skp2 might be implicated, at least in part, in this process (Yu et al, 1998b;Ganiatsas et al, 2001). Finally, Nakayama et al (2000) found that Skp2 can bind to the CDK-unbound, inactive form of Cyclin E and mediate its ubiquitinylation.…”