Collaboration of G1 cyclins in the functional inactivation of the retinoblastoma protein.
The retinoblastoma gene product (pRB) constrains cell proliferation by preventing cell-cycle progression from the G1 to S phase. Its growth-inhibitory effects appear to be reversed by hyperphosphorylation occurring during G1. This process is thought to involve G1 cyclins and cyclin-dependent kinases (cdks). Here we report that the cell cycle-dependent phosphorylation of mammalian pRB is faithfully reproduced when it is expressed in Saccharomyces cerevisiae. As is the case in mammalian cells, this phosphorylation requires an intact oncoprotein-binding domain and is inhibited by a negative growth factor, in this case a mating pheromone. Expression of pRB in cln (-) mutants indicates that specific combinations of endogenous G1 cyclins, Cln3 and either Cln1 or Cln2 are required for pRB hyperphosphorylation in yeast. Moreover, expression of mammalian G1 cyclins in cln (-) yeast cells indicates that the functions of Cln2 and Cln3 in pRB hyperphosphorylation can be complemented by human cyclin E and cyclin D1, respectively. These observations suggest a functional heterogeneity among G1 cyclin-cdk complexes and indicate a need for the involvement of multiple G1 cyclins in promoting pRB hyperphosphorylation and resulting cell-cycle progression.
Whitehead Institute for Biomedical Research, Cambridge, Massachusetts.
M
M
Hatakeyama
J A
JA
Brill
G R
GR
Fink
R A
RA
Weinberg
D017489:CDC28 Protein Kinase, S cerevisiae / Q000502:physiology; D016213:Cyclins / Q000502:physiology*; D016193:G1 Phase / Q000502:physiology*; D005816:Genetic Complementation Test; D006801:Humans; D000072235:Mating Factor; D009154:Mutation; D010455:Peptides / Q000502:physiology; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D000091346:Tripeptidyl-Peptidase 1
D016213:Cyclins; D010455:Peptides; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein; D000091346:Tripeptidyl-Peptidase 1; D000072235:Mating Factor; D017489:CDC28 Protein Kinase, S cerevisiae