<P> Immunohistochemical staining of cyclin D1 antibodies is used to diagnose mantle cell lymphoma . </P> <P> Cyclin D1 has been found to be overexpressed in breast carcinoma . Its potential use as a biomarker was suggested . </P> <P> Cyclin D1 is a protein required for progression through the G1 phase of the cell cycle . During the G1 phase, it is synthesized rapidly and accumulates in the nucleus, and is degraded as the cell enters the S phase . Cyclin D1 is a regulatory subunit of cyclin - dependent kinases CDK4 and CDK6 . The protein dimerizes with CDK4 / 6 to regulate the G1 / S phase transition and entry into the S - phase . </P> <P> The cyclin D1 - CDK4 complex promotes passage through the G1 phase by inhibiting the retinoblastoma protein (pRb). Cyclin D1 - CDK4 inhibits pRb through phosphorylation, allowing E2F transcription factors to transcribe genes required for entry into the S phase . Inactive pRb allows cell cycle progression through the G1 / S transition and allows for DNA synthesis . Cyclin D1 - CDK4 also enables the activation of cyclin E-CDK2 complex by sequestering Cip / Kip family CDK inhibitory proteins p21 and p27, allowing entry into the S phase . </P>

Cyclin d1 is a nuclear protein required for cell cycle progression in g1