Cyclin D1 is overexpressed in human tumors, correlating with cellular metastasis, and is induced by activating Rho GTPases. Herein, cyclin D1-deficient mouse embryo fibroblasts (MEFs) exhibited increased adhesion and decreased motility compared with wild-type MEFs. Retroviral transduction of cyclin D1 reversed these phenotypes. Mutational analysis of cyclin D1 demonstrated that its effects on cellular adhesion and migration were independent of the pRb and p160 coactivator binding domains. Genomewide expression arrays identified a subset of genes regulated by cyclin D1, including Rho-activated kinase II (ROCKII) and thrombospondin 1 (TSP-1). cyclin D1 ؊/؊ cells showed increased Rho GTP and ROCKII activity and signaling, with increased phosphorylation of LIM kinase, cofilin (Ser3), and myosin light chain 2 (Thr18/Ser19). Cyclin D1 repressed ROCKII and TSP-1 expression, and the migratory defect of cyclin D1 ؊/؊ cells was reversed by ROCK inhibition or TSP-1 immunoneutralizing antibodies. cyclin E knockin to the cyclin D1 ؊/؊ MEFs rescued the DNA synthesis defect of cyclin D1 ؊/؊ MEFs but did not rescue either the migration defect or the abundance of ROCKII. Cyclin D1 promotes cellular motility through inhibiting ROCK signaling and repressing the metastasis suppressor TSP-1.The human cyclin D1 gene was initially cloned as a breakpoint rearrangement within parathyroid adenoma (42). Homology of the cyclin D1 cDNA to the CLN gene in yeast suggested the PRAD1 gene encoded the regulatory subunit of a serine threonine kinase. In subsequent studies, cyclin D1 was shown to bind the retinoblastoma (pRb) protein and through physical association with the cyclin-dependent kinase 4 or 6 (cdk4 or cdk6) subunit to phosphorylate pRb. Phosphorylation of pRb by the cyclin D/cdk4 holoenzyme then alters the conformation of pRb, correlating with sequential phosphorylation by cyclin E/cdk2 and the induction of DNA synthesis. The cyclin D1 gene is overexpressed in human cancers, including breast, colon, and prostate cancer, and hematopoietic malignancies (23, 39). Targeted overexpression of cyclin D1 to the mammary gland in transgenic mice was sufficient for the induction of mammary adenocarcinoma. Cyclin D1 is overexpressed in metastatic cells (19,30). Analysis of cyclin D1-deficient mice indicates a role for cyclin D1 in both cellular survival and DNA synthesis (3). Furthermore, cyclin D1-deficient mice are resistant to gastrointestinal tumors induced by mutation of the Apc gene (28) or tumor formation induced by either mammary-targeted Ras or ErbB2 (82). Such observations are consistent with previous studies demonstrating cyclin D1 antisense abrogates epithelial growth of ErbB2-induced tumors in vivo (34).Mutational analysis of the human cyclin D1 cDNA has identified several distinct domains involved in binding either pRb, cdk, the p160 coactivator, and histone deacetylases (22,23,59). The cdk-binding domain of cyclin D1 is required for the association with cdk4 and sequential phosphorylation of pRb, which in turn, leads to the release...

Cyclin D1 promotes nuclear DNA synthesis through phosphorylation and inactivation of the pRb tumor suppressor. Herein, cyclin D1 deficiency increased mitochondrial size and activity that was rescued by cyclin D1 in a Cdk-dependent manner. Nuclear respiratory factor 1 (NRF-1), which induces nuclear-encoded mitochondrial genes, was repressed in expression and activity by cyclin D1. Cyclin D1-dependent kinase phosphorylates NRF-1 at S47. Cyclin D1 abundance thus coordinates nuclear DNA synthesis and mitochondrial function.mitochondria ͉ phosphorylation

The cyclin D1 gene encodes a regulatory subunit of the holoenzyme that phosphorylates and inactivates the pRb tumor suppressor to promote nuclear DNA synthesis. cyclin D1 is overexpressed in human breast cancers and is sufficient for the development of murine mammary tumors. Herein, cyclin D1 is shown to perform a novel function, inhibiting mitochondrial function and size. Mitochondrial activity was enhanced by genetic deletion or antisense or small interfering RNA to cyclin D1. Global gene expression profiling and functional analysis of mammary epithelial cell-targeted cyclin D1 antisense transgenics demonstrated that cyclin D1 inhibits mitochondrial activity and aerobic glycolysis in vivo. Reciprocal regulation of these genes was observed in cyclin D1-induced mammary tumors. Cyclin D1 thus integrates nuclear DNA synthesis and mitochondrial function.