Loss of p16 contributes to p27 sequestration by cyclin D(1)-cyclin-dependent kinase 4 complexes and poor prognosis in hepatocellular carcinoma.
OBJECTIVE
p27(Kip1) (p27) might act as an adverse prognostic marker for various types of cancers. However, its clinical usefulness remains uncertain, because it is sometimes overexpressed in aggressive types.


METHODS
To precisely evaluate the practical significance of p27 in hepatocellular carcinoma (HCC), we immunohistochemically compared the level of p27 expression with Ki-67 labeling in 74 HCCs and focused on tumors in which cell proliferation increased despite a high level of p27 expression. We then analyzed the status of p27 and related cell-cycle regulators using kinase and immunoprecipitation assays, Western blotting, and methylation-specific PCR to understand the rationale for the functional inactivation of p27 in HCC. We also evaluated relationships between the key biological characteristics of HCC and survival.


RESULTS
Immunohistochemical studies showed that 40 (54%) of 74 HCCs expressed high levels of p27 (>50% of the tumor cells). Of these, the Ki-67 labeling index was low (<20%) in 26 (65%) and high (>20%) in 14 (35%). Increased proliferative activities were closely correlated with elevated kinase activities, sequestration of p27 protein, and p16 gene methylation. The association between a loss of p16 and poor prognosis was significant when p27 expression was high (P < 0.01).


CONCLUSIONS
The loss of p16 appears to be closely related to the functional inactivation of p27, and assessment of p16 status may be useful for a precise prognostic prediction of individuals with HCC expressing high levels of p27.
Matsuda
Yasunobu
Y
Department of Regenerative and Transplant Medicine, Niigata University Graduate School of Medicine and Dental Science, Asahimachi-dori 1-757, Niigata City 951-8510, Japan.
Ichida
Takafumi
T
Genda
Takuya
T
Yamagiwa
Satoshi
S
Aoyagi
Yutaka
Y
Asakura
Hitoshi
H
D000328:Adult; D000368:Aged; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002455:Cell Division; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics*; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D019175:DNA Methylation; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000096:biosynthesis; D008113:Liver Neoplasms / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D011233:Precipitin Tests; D011379:Prognosis; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins; D013997:Time Factors; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D019394:Ki-67 Antigen; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases