p27, also known as p27Kip1, is a cyclin-dependent kinase inhibitor that binds to and inhibits cyclin-dependent kinases, thereby regulating progression from G1 to S phase. p27Kip1 binds to and inhibits cyclinE-Cdk2 complex, cyclinA-CDK2 and cyclinD1-CDK4. p27Kip1 is regulated by phosphorylation on serine 10 (S10) and threonine 187 (T187). Phosphorylation by CDK2 on T187 results in ubiquitination and degradation of p27Kip1, while phosphorylation by hKIS on S10 signals nuclear export to the cytoplasm. The expression level of p27Kip1 is high in normal cells. Decreased expression of p27 is linked to poor prognosis in renal-cell carcinoma, colon carcinoma, small breast carcinomas, non-small-cell lung carcinoma, hepatocellular carcinoma, multiple myeloma, lymph node metastases in papillary carcinoma of the thyroid, and is associated with a more aggressive phenotype of carcinoma in the cervix.