Reduced expression and altered subcellular localization of the cyclin-dependent kinase inhibitor p27Kip1 in human colon cancer

Abstract

The p27(Kip1) protein is a negative regulator of the cell cycle and a potential tumor suppressor gene. Reduced expression of the p27(Kip1) protein has been reported in several human tumors and has been associated with higher tumor grade and increased mortality in breast, lung, colon, prostate, bladder, and gastric cancers. On the other hand, increased expression of the p27(Kip1) protein, in the absence of gene mutation, has been observed in primary colon and breast cancers. It was recently suggested that sequestration in the cytoplasm might be an alternative way to inactivate p27(Kip1)-associated inhibitory activity. This study was undertaken to further evaluate p27(Kip1) expression in primary colon tumors and to verify whether differences exist between normal and cancer tissues in terms of subcellular localization of this protein. Both normal and neoplastic tissues expressed variable amounts of the p27(Kip1) protein, as assessed by western blot analyses. Although the mean values were not different between tumor and normal mucosa samples, the expression of total p27(Kip1) was reduced in a subset of tumors. Decreased levels of total p27(Kip1) were associated with high tumor grade (P=0.03) and stage (P=0.04). Moreover, while there was no significant difference in nuclear p27(Kip1), the amount of p27(Kip1) in the cytoplasmic fraction was significantly higher in the tumor samples than in the normal mucosa samples (P=0.0001). These results suggest that p27(Kip1) expression is lost in a subset of colorectal tumors and that alterations in the subcellular localization of this protein might play a role in colon carcinogenesis.

Abnormal integrin-mediated regulation of chronic myelogenous leukemia CD34 + cell proliferation: BCR/ABL up-regulates the cyclin-dependent kinase inhibitor, p27 Kip , which is relocated to the cell cytoplasm and incapable of regulating cdk2 activity

“…An alternative explanation for the inability of p27 Kip to bind to cdk2 would be that p27 Kip and cdk2 are not present in the same cell compartment (37)(38)(39). We extracted proteins from the cell cytoplasm and nucleus separately, and measured p27 Kip , cdk2,and cyclin-H levels by Western blot.…”

Pulmonary Epithelial-Myoepithelial Tumor of Unproven Malignant Potential: Report of a Case and Review of the Literature

“…In normal lung, p63 is restricted to basal cells of the respiratory epithelium and to peripheral, flattened cells of bronchial mucous glands resembling myoepithelial cells. Likewise, in breast tissue, it is exclusively confined to myoepi- early dysplastic lesions and well differentiated carcinomas, rather than in invasive and poorly differentiated tumors (21,22). This suggests that an aberrant subcellular localization of p27/Kip-1 in the neoplastic myoepithelial cells could abrogate its growth-inhibiting function and contribute to tumorigenesis via the unrestricted proliferation of the myoepithelial component.…”

Increased expression of dystroglycan inhibits the growth and tumorigenicity of human mammary epithelial cells

“…Exponentially growing cultures of each cell lines were collected by cell scraping and cell pellets were added to 3-5 volumes of sonication buffer containing proteases and phosphatase inhibitors (20 mM Tris-HCl pH 7.4, 2 mM EGTA, 6 mM β-mercaptoethanol, 1% NP40, 0.1% SDS, 50 mM NaF, 15 µg/ml benzamidine, 10 µg/ml aprotinin, 10 µg/ml leupeptin and 1 mM phenylmethylsulfonyl fluoride) and sonicated at 4˚C, as previously described. 11,19,21 Homogenates were incubated in ice for 30 minutes and then centrifuged at 14000 rpm for 15 min at 4˚C. The supernatants were assayed for protein content and 50 µg of protein from each sample were separated by SDS-PAGE and transferred to immobilon-P membranes (Millipore, Bedford, MA) at 100 volts for 1 hour at 4˚C.…”