====== CDKN1B ======

[[Cyclin dependent kinase inhibitor]] 1B (p27Kip1) is an enzyme inhibitor that in humans is encoded by the CDKN1B gene.

It encodes a protein which belongs to the Cip/Kip family of cyclin dependent kinase (Cdk) inhibitor proteins. The encoded protein binds to and prevents the activation of cyclin E-CDK2 or cyclin D-CDK4 complexes, and thus controls the cell cycle progression at G1. It is often referred to as a cell cycle inhibitor protein because its major function is to stop or slow down the cell division cycle.

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A study was conducted to evaluate the levels of [[Cdk2]], [[cyclin E]], p21 and p27 in growth hormone adenomas (GHPAs) and analyze their association with clinicopathologic features in 46 patients with GHPAs. Accordingly, we found that the levels of cyclin E and Cdk2 were much higher in invasive GHPA specimens than those in non-invasive specimens (p<0.05). Lower p21 and p27 levels were detected through tissue micro-assay (TMA). Significant differences were found between cyclin E expression and tumor size (p=0.039), cyclin E expression and invasion (p=0.003), and p21 expression and tumor size (p=0.039). Furthermore, tumors were more likely to require whole resection in patients with low cyclin E levels (12/23 vs 19/23, p=0.028). The average progression free survival (PFS) time in the high p27 group was longer than that in the low p27 group (p=0.006). RT-PCR and western-blot analysis revealed a similar trend for Cdk2, cyclin E, p21 and p27 protein levels in GH specimens (p<0.01 for all). An average of 33 CpG sites per sample were analyzed using MALDI-TOF mass array, and in 7 out of the 33 CpG sites, methylation levels of p27 were more than 50%. There were significant differences in 4 CpG sites between invasive and non-invasive specimens (p<0.01). Considering the well-documented role of Cdk2, cyclin E and p27 in cell cycle regulation, overexpression of cyclin E/Cdk2 and loss of p27 appears to be associated with poor prognosis and may play a role in treatment of GHPAs in the future
((Dong W, Zhu H, Gao H, Shi W, Zhang Y, Wang H, Li C, Song G, Zhang Y.
Expression of cyclin E/Cdk2/p27(Kip1) in growth hormone adenomas. World
Neurosurg. 2018 Sep 6. pii: S1878-8750(18)31995-8. doi:
10.1016/j.wneu.2018.08.209. [Epub ahead of print] PubMed PMID: 30196178.
)).