Genetic deletion and human papillomavirus infection in cervical cancer: Loss of heterozygosity sites at 3p and 5p are important genetic events

Abstract

''High-risk'' human papillomavirus (HPV) types 16/18 are recognized as being associated with cervical cancer. We have already reported frequent loss of heterozygosity (LOH) at 3p, 3q, 4q, 5p and 5q in primary cervical cancer, the frequency at these sites ranging from 31.0 to 56.3%. The present analysis deals with these frequent-deletion sites in relation to HPV infection. HPV Cancer of the uterine cervix is associated with human papillomavirus (HPV) infection. E6/E7 oncoprotein encoded by ''high-risk'' HPV types has been shown to interact with the tumour-suppressor gene p53/pRB, causing abnormal cell-cycle regulation. Thus, HPV infection appears to play an important role in cervical carcinogenesis, though HPV infection alone might not be capable of developing cervical cancer. Further, even the cases which show such development generally need a long latent period between the initial infection and the subsequent development of invasive cervical cancer. The precise mechanism of the role played by HPV remains controversial (zur Hausen, 1994). Genomic deletions are now considered to be an important factor in tumorigenesis. Cytogenetic studies, although limited, have revealed non-random chromosomal changes such as i (5p), deletion at 3p, 6q and 17p (Mitra et al., 1994b;Atkin, 1997), also a correlation between the common fragile sites and integration of HPV DNA (Cannizzaro et al., 1988;Popescu et al., 1990). Mutations or deletions of a tumoursuppressor gene (TSG) have been shown to be frequently accompanied by loss of the remaining allele, leading to homozygous inactivation of the gene (Marshall, 1991). Several molecular genetic studies (Mitra et al., 1994a;Mullokandov et al., 1996;Kersemaekers et al., 1998) have identified a few frequent loss of heterozygosity (LOH) sites, suggesting possible involvement of TSGs in the development of cervical cancer.The current study was undertaken to see (i) how far HPV infection in general is associated with genomic deletion in cervical cancer and (ii) whether any of the frequent LOH sites identified can be correlated with infection by ''high-risk'' HPV type 16/18. We have reported 11 LOH sites (Mitra et al., 1994a). Here, we present the results of detailed analysis of the more frequently observed LOH sites, namely, at 3p, 3q, 4q, 5p and 5q, in relation to HPV status. The study revealed strong evidence of HPV infection in cervical carcinomas. Deletion at 3p appeared dependent on HPV 16/18 infection, while deletion at 5p, the most frequent deletion site, was independent of ''high-risk'' HPV infection. MATERIAL AND METHODS SamplesA total of 53 tumour biopsies and their corresponding blood samples were collected at the cancer clinic, Lok Nayak hospital, Delhi, India. Tumours were histologically diagnosed as being invasive cervical carcinoma. DNA isolation and Southern-blot analysisStandard DNA extraction procedure was followed using the proteinase-K-phenol-alcohol method (Mitra et al., 1994a); 5 to 7 µg of each sample of DNA was digested with appropriate restriction enzymes, and the ...

Intratumor chromosomal heterogeneity in advanced carcinomas of the uterine cervix

“…Gain of 5p has previously been suggested to be involved in the early development of the disease, 26 consistent with our results. Moreover, gain of 3q has been shown to participate in the transition from a preinvasive to an invasive stage.…”

“…First, integration of HPV DNA leads to impaired cell cycle control 25 and may possibly induce genetic aberrations by other mechanisms as well. 26,27 Our observation that the 2 HPV negative tumors were chromosomally homogeneous and had a lower number of aberrations than most of the other tumors is consistent with the hypothesis that HPV infection leads to increased genomic instability. Second, aggregation of chromosomal aberrations may lead to a continuing increase in genomic instability during progression.…”