Enables cyclin-dependent protein serine/threonine kinase regulator activity; protein kinase activity; and protein kinase binding activity. Involved in negative regulation of epithelial cell differentiation and negative regulation of transcription by RNA polymerase II. Acts upstream of or within several processes, including endoplasmic reticulum unfolded protein response; gland development; and positive regulation of mammary gland epithelial cell proliferation. Located in bicellular tight junction; cytoplasm; and nucleus. Part of cyclin-dependent protein kinase holoenzyme complex. Is expressed in several structures, including alimentary system; central nervous system; genitourinary system; integumental system; and sensory organ. Human ortholog(s) of this gene implicated in several diseases, including carcinoma (multiple); colorectal cancer; hematologic cancer (multiple); invasive lobular carcinoma; and von Hippel-Lindau disease. Orthologous to human CCND1 (cyclin D1). [provided by Alliance of Genome Resources, Apr 2022]