The CCND1 gene, which is frequently overexpressed in
cancers, encodes the regulatory subunit of a
holoenzyme that phosphorylates the
retinoblastoma protein. Although it is known that
cyclin D1 regulates
estrogen receptor (ER)α transactivation using heterologous reporter systems, the in vivo biological significance of
cyclin D1 to
estrogen-dependent signaling, and the molecular mechanisms by which
cyclin D1 is involved, are yet to be elucidated. Herein, genome-wide expression profiling conducted of 17β-estradiol-treated castrated virgin mice deleted of the Ccnd1 gene demonstrated that
cyclin D1 determines
estrogen-dependent gene expression for 88% of
estrogen-responsive genes in vivo. In addition, expression profiling of 17β-estradiol-stimulated
cyclin D1 small interfering RNA treated MCF7 cells shows
cyclin D1 is required for
estrogen-mediated gene expression in vitro. Genome-wide
chromatin immunoprecipitation-Seq analysis revealed a
cyclin D1-DNA bound form associated with genes that were regulated by
estrogen in a
cyclin D1-dependent manner. The
cyclin D1-dependent
estrogen signaling pathways identified in vivo were highly enriched for extracellular membrane-associated
growth factor receptors (
epidermal growth factor receptor, ErbB3, and EphB3) and their
ligands (
amphiregulin, encoded by AREG gene), and
matrix metalloproteinase. The AREG
protein, a pivotal
ligand for
epidermal growth factor receptors to promote cellular proliferation, was induced by
cyclin D1 via the AREG promoter.
Chromatin immunoprecipitation analysis demonstrated the recruitment of
cyclin D1 to the
breast cancer 1 (Brca1)/ERα binding site of the Areg gene.
Cyclin D1 genetic deletion demonstrated the in vivo requirement for
cyclin D1 in assembling the
estrogen-dependent amplified in
breast cancer 1-associated multiprotein complex. The current studies define a requirement for
cyclin D1 in
estrogen-dependent signaling modules governing
growth factor receptor and
ligand expression in vivo and reveal a noncanonical function of
cyclin D1 at ERα target gene promoters.
Cyclin D1 mediates the convergence of ERα and
growth factor signaling at a common cis-
element of
growth factor genes.