Protein profiling: a possible molecular mechanism to mislocalization and down-expression of p27(Kip1) in tumor cells

p27(Kip1) (here after referred to as p27) is a member of a family of cyclin-dependent kinase inhibitors that control cell cycle. There is a considerable evidence that p27 plays a pivotal role in multiple foundational cellular processes, including cell proliferation, cell differentiation, and apoptosis. A large number of studies have characterized p27 as an independent prognostic factor in various human cancers and as a target for cancer therapeutics. The function of p27 is regulated by changes in its intracellular concentration as well as in its sub-cellular localization in the cell. Many tumor cells show p27 down-regulated or no detectable expression, p27 might act as an adverse prognostic marker for various types of cancers. Until recently, displacement of p27 into the cytoplasm has been identified as a mechanism of which cancer cells promote cancerogenesis in human. But much less is known about the molecular mechanisms of its abnormal expression and mislocalization in tumor cell. p27 protein has various interacting molecules. The different formation of p27 complexes maybe cause disregulation of p27 expression and localization in human cancer. We hypothesize here that different interacting protein profile may be a fundamentional step for the abnormal expression and cytoplasmic localization in tumor cells.