Inhibition of cyclin D1 phosphorylation on threonine-286 prevents its rapid degradation via the ubiquitin-proteasome pathway.

作者：John Alan Diehl, Frédérique Zindy, Charles J. Sherr · 发表于：Genes & Development · 年份：1997 · DOI：10.1101/gad.11.8.957 · 被引用次数：750 · 研究领域：Cancer-related Molecular Pathways、Ubiquitin and proteasome pathways、Microtubule and mitosis dynamics

The expression of D-type G1 cyclins and their assembly with their catalytic partners, the cyclin-dependent kinases 4 and 6 (CDK4 and CDK6), into active holoenzyme complexes are regulated by growth factor-induced signals. In turn, the ability of cyclin D-dependent kinases to trigger phosphorylation of the retinoblastoma (Rb) protein in the mid- to late G1 phase of the cell cycle makes the inactivation of Rb's growth suppressive function a mitogen-dependent step. The ability of D-type cyclins to act as growth factor sensors depends not only on their rapid induction by mitogens but also on their inherent instability, which ensures their precipitous degradation in cells deprived of growth factors. However, the mechanisms governing the turnover of D-type cyclins have not yet been elucidated. We now show that cyclin D1 turnover is governed by ubiquitination and proteasomal degradation, which are positively regulated by cyclin D1 phosphorylation on threonine-286. Although "free" or CDK4-bound cyclin D1 molecules are intrinsically unstable (t1/2 < 30 min), a cyclin D1 mutant (T286A) containing an alanine for threonine-286 substitution fails to undergo efficient polyubiquitination in an in vitro system or in vivo, and it is markedly stabilized (t1/2 approximately 3.5 hr) when inducibly expressed in either quiescent or proliferating mouse fibroblasts. Phosphorylation of cyclin D1 on threonine-286 also occurs in insect Sf9 cells, and although the process is enhanced significantly by the...