Increased proteasome-dependent degradation of the cyclin-dependent kinase inhibitor p27 in aggressive colorectal carcinomas.
The cell-cycle inhibitor p27 is a potential tumor suppressor, but its gene has never been found inactivated in human tumors. Because cell-cycle regulation of p27 cellular abundance occurs at the post-transcriptional level, we analyzed p27 protein expression and degradation in human colorectal carcinomas. Proteasome-mediated degradation activity of p27 was compared with its protein levels in a subset of tumor samples. We found that carcinomas with low or absent p27 protein displayed enhanced proteolytic activity specific for p27, suggesting that low p27 expression can result from increased proteasome-mediated degradation rather than altered gene expression. Patients whose tumors expressed p27 had a median survival of 151 months, whereas patients who lacked p27 (10%) had a median survival of 69 months. By multivariate analysis, p27 was found to be an independent prognostic marker. Lack of p27 was associated with poor prognosis (2.9 risk ratio for death; P = 0.003). The absence of p27 protein expression is thus a powerful negative prognostic marker in colorectal carcinomas, particularly in stage II tumors, and thereby may help in the selection of patients who will benefit from adjuvant therapy. These data suggest that aggressive tumors may result from the selection of a clone or clones that lack p27 due to increased proteasome-mediated degradation.
Loda
M
M
Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA.
Cukor
B
B
Tam
S W
SW
Lavin
P
P
Fiorentino
M
M
Draetta
G F
GF
Jessup
J M
JM
Pagano
M
M
D000230:Adenocarcinoma / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D000368:Aged; D014408:Biomarkers, Tumor; D018797:Cell Cycle Proteins; D015179:Colorectal Neoplasms / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D005260:Female; D016147:Genes, Tumor Suppressor; D018816:Genes, cdc; D006801:Humans; D008297:Male; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009367:Neoplasm Staging; D011379:Prognosis; D046988:Proteasome Endopeptidase Complex; D025521:Tumor Suppressor Proteins
D014408:Biomarkers, Tumor; D018797:Cell Cycle Proteins; D008869:Microtubule-Associated Proteins; D009097:Multienzyme Complexes; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex