Cyclin D3 Expression in Melanoma Cells Is Regulated by Adhesion-dependent Phosphatidylinositol 3-Kinase Signaling and Contributes to G1-S Progression

D-type cyclins regulate G1 cell cycle progression by enhancing the activities of cyclin-dependent kinases (CDKs), and their expression is frequently altered in malignant cells. We and others have previously shown that cyclin D1 is up-regulated in melanoma cells through adhesion-independent MEK-ERK1/2 signaling initiated by mutant B-RAF. Here, we describe the regulation and role of cyclin D3 in human melanoma cells. Cyclin D3 expression was enhanced in a cell panel of human melanoma cell lines compared with melanocytes and was regulated by fibronectin-mediated phosphatidylinositol 3-kinase/Akt signaling but not MEK activity. RNA interference experiments demonstrated that cyclin D3 contributed to G1-S cell cycle progression and proliferation in melanoma cells. Overexpression of cyclin D1 did not recover the effects of cyclin D3 knockdown. Finally, immunoprecipitation studies showed that CDK6 is a major binding partner for cyclin D3, whereas CDK4 preferentially associated with cyclin D1. Together, these findings demonstrate that cyclin D3 is an important regulator of melanoma G1-S cell cycle progression and that D-type cyclins are differentially regulated in melanoma cells.