Homozygous Deletion of p16INK4 and p15INK4B Genes in Human Advanced Ovarian Carcinoma

Lee, Chul Min; Kang, Soon Beom

Abstract

OBJECTIVE
p16INK4 and p15INK4B genes are known to be tumor suppressor genes which reside in p21 region of chromosome 9 and are related to cell cycle control as an inhibitor of cyclin-dependent-kinase. We designed this study to search for deletion and decreased expression of p16INK4 and p15INK4B genes in advanced ovarian carcinomas. METHODS: Polymerase chain reaction (PCR)-based analysis was performed to search for deletion of p16INK4 and p15INK4B using DNA extracted from frozen tissue in liquid nitrogen of thirty-one advanced ovarian carcinoma patients. The intensities of PCR bands were analyzed using an imaging densitometer to determine gene dosage in tumor samples and the relative gene dosage was calculated by comparing band intesity of p16INK4 or p15INK4B with that of beta-globin gene. Homozygous deletions were assigned to tumors in which the ratio was reduced to less than 25% in any one of exons of p16INK4 and p15INK4B. Immunohistochemical techniques were used to study the expression of p16INK4. p16-negative cells were characterized by the absence of nuclear staining, whereas cytoplasmic staining was variable. Clinico-pathologic features, complete remission rates and survivals were analyzed according to the status of p16INK4 and p15INK4B genes. RESULTS: Homozygous deletion of p16INK4 was detected in 12.9% of advanced ovarian carcinoma patients and that of p15INK4B in 35.5%. Clinico-pathologic features such as FIGO stage, histological grade, serum CA-125 levels were not different from groups with homozygously deleted p16INK4 and p15INK4B to those with normal genes. The survival of patients (13 [6-20] months) with homozygously deleted p16INK4 was significantly shorter than that (30 [8-52] months) of patients with normal p16INK4 (p=0.046; Log-rank test).
CONCLUSION
These observations indicate that deletions of p16INK4 and p15INK4B gene might be involved in tumorigenesis of ovarian carcinoma and could be useful as a prognostic factor. A prospective, controlled study with more patients will be mandatory in the future.