MCF-7 human breast cancer cells express functional estrogen receptor and grow in response to estrogen stimulation. G (1)-synchronized MCF-7 cells, made quiescent by exposure to the HMG-CoA reductase inhibitor Simvastatin in estrogen-free medium, readily resume cell cycle progression upon stimulation with 17beta-estradiol (E (2)), even under conditions where polypeptide growth factor-triggered signal transduction pathways are inhibited by the continuous presence of Simvastatin in the culture medium. Under these conditions, cyclin D (1) gene transcription is transiently induced within the first 1-9 h of stimulation, as shown by the accumulation of cyclin D (1) mRNA and protein (p36 (D (1))) in the cell and by enhanced expression of stably transfected D (1) promoter-luciferase hybrid genes. Estrogen-induced p36 (D (1)) associates readily with p32 (cdk2) and p34 (cdk4), but not with p31 (cdk5), which is however abundantly expressed in these cells. Only p36 (D (1))-p34 (cdk4) complexes are activated by E (2), as detected in cell extracts by immunoprecipitation with anti-D (1) antibodies followed by assessment of phosphotransferase activity toward the retinoblastoma (Rb) gene product and by analysis of p105 (Rb) phosphorylation in vivo. An estrogen-responsive regulatory region has been mapped within the first 944 bp upstream of the transcriptional startsite of the human D (1) gene. Sequence analysis of this DNA region reveals that the cis-acting elements responsive to estrogen are likely to be different in this case from the canonical EREs.