The cyclin D1 gene encodes a rate-limiting component of the holoenzyme which phosphorylates and inactivates the retinoblastoma tumor suppressor gene (pRb). The abundance of cyclin D1 is increased in metastatic human tumors including breast and colon cancer. In the prior funding period we identified the molecular mechanisms by which oncogenes/growth factors regulate cyclin D1 expression and demonstrated cyclin D1 coordinated transcriptional activity through binding HDACs and histone acetylases. Using transgenic and knockout mice, we identified a molecular genetic signature regulated by cyclin D1 antisense in vivo and in mammary tumors induced by cyclin D1. These genes regulate cellular migration and mitochondrial function. The proposed studies will determine the mechanisms by which cyclin D1 regulates these two functions, the relationship between these two functions and the role of these cyclin D1-mediated functions in tumorigenesis. We hypothesize cyclin D1 regulates migration and invasion by affecting (1) transcriptional target genes, (2) protein-protein interactions, (3) secreted factors and (4) mitochondrial factors. In the proposed studies we will:
Aim 1. Determine the role of cyclin D1-mediated gene expression in promoting cellular migration. Cyclin D1 is overexpressed in a subset of metastatic cancers. Reproduction of cyclin D1 into cyclin D1-deficient cells promotes cell migration. Cyclin D1 regulates expression of target genes governing migration (ROCKII, c-Jun). These studies will determine the functional significance of these transcriptional targets of cyclin D1 in cyclin D1-mediated migration and the mechanisms involved.
Aim 2. Determine the role of cyclin D1-interacting proteins in cellular migration and invasion. We have identified a role for cyclin D1 protein interaction domains in promoting migration. We have identified cyclin D1-interacting proteins (PACSIN2, cdks, pRb, p27/p21, HDACs). We will determine the role of cyclin D1- interacting proteins in promoting cellular migration and invasion.
Aim 3. Determine the role of cyclin D1-mediated secretory factors and mitochondrial gene activity in cellular migration and collaborative oncogenesis. Cyclin D1 regulates the secretion of migratory factors (TSP1 (Thrombospondin-1), SCF (stem cell factor)). Cyclin D1 inhibits mitochondrial metabolism. Cyclin D1 phosphorylates and inactivates a transcription factor NRF1 that in turn regulates mitochondrial gene expression. Microarray analysis of NRF1-regulated and cyclin D1-regulated genes identified genes regulating cell migration and stem cell expansion. We will determine how cyclin D1 regulates mitochondrial metabolism and the role of this activity in cellular migration and collaborative oncogenesis. Together these three integrated Aims will determine the role of cyclin D1-regulated functions in cellular migration, invasion and tumorigenesis.
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