p16 Overexpression: A Potential Early Indicator of Transformation in Ovarian Carcinoma

Objective: The recently cloned gene p16 (MST 1) has been identified as a putative tumor suppressor gene that binds to CDK4 and CDK6 (cyclin-dependent kinases), preventing their interaction with cyclin D1 and thereby preventing cell cycle progression at the G1 stage. In addition, the p16 gene has been shown to have a high frequency of mutation in some tumor cell lines; however, it has also been shown that a much lower frequency of mutation occurs in primary tumors. This study investigated the mRNA expression level and mutation status of the p16 gene in ovarian tumors. Methods: We performed quantitative polymerase chain reaction and direct cDNA sequencing analysis. To confirm the p16 protein level in ovarian tumors, Western blotting and immunohistochemical staining were performed. Expression levels of mRNA for the p16 gene relative to the β-tubulin gene were examined in 32 ovarian tumors (24 carcinomas, six low malignant potential tumors, and two benign tumors) and six normal ovaries. Results: The mRNA expression level of p16 was significantly elevated in 28 ovarian tumors (22 carcinomas, five low malignant potential tumors, and one benign tumor) compared with that of normal ovaries. Western blotting analysis and immunohistochemical staining confirmed elevated p16 protein levels in ovarian tumor samples. Among 32 ovarian tumors, cDNA sequencing of the p16 gene showed no p16 mutation resulting in a coding error, although one silent mutation and three polymorphisms were found. Conclusions: Although p16 is seldom mutated in ovarian tumors, the overexpression of p16 in most ovarian tumor cases indicates a dysfunction in the regulatory complex for G1 arrest. Therefore, overexpression of p16 may be an important early event in the neoplastic transformation of the ovarian epithelium.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68382/2/10.1177_107155769700400209.pd

Cigarette smoking, von Hippel–Lindau gene mutations and sporadic renal cell carcinoma

We investigated whether smoking is associated with mutations in the Von Hippel–Lindau (VHL) gene in 337 cases of sporadic renal cell carcinoma (RCC) among 120 852 people followed for 11.3 years; the findings suggest that smoking causes RCC independently of VHL gene mutations

Comprehensive analysis of the 9p21 region in neuroblastoma suggests a role for genes mapping to 9p21–23 in the biology of favourable stage 4 tumours

Chromosome 9p21 is frequently deleted in many cancers. Previous reports have indicated that 9p21 LOH is an uncommon finding in neuroblastoma (NB), a tumour of childhood. We have performed an extensive analysis of 9p21 and genes located in this region (cyclin-dependent kinase inhibitor 2A – CDKN2A/p16INK4a, CDKN2A/p14ARF, CDKN2B/p15INK4b, MTAP, interferon α and β cluster). LOH was detected in 16.4% of 177 NB. The SRO was identified between markers D9S1751 and D9S254, at 9p21–23, a region telomeric to the CDKN2A and MTAP genes. A significantly better overall and progression-free survival was detected in stage 4 patients displaying 9p21–23 LOH. Hemizygous deletion of the region harbouring the CDKN2A and CDKN2B loci was identified in two tumours by means of fluorescent in situ hybridisation and MTAP was present by immunostaining in all but one tumour analysed. The transcriptional profile of tumours with 9p21–23 LOH was compared to that of NB displaying normal 9p21–23 status by means of oligonucleotide microarrays. Four of the 363 probe sets downregulated in tumours with 9p21–23 LOH were encoded by genes mapping to 9p22–24. The only well-characterised transcript among them was nuclear factor I-B3. Our results suggest a role for genes located telomeric of 9p21 in good risk NB

Inhibiting tumorigenic potential by restoration of p16 in nasopharyngeal carcinoma

The p16 gene, encodes a key checkpoint protein p16 in the cell cycle, has been reported inactivation in a wide variety of human cancers. We have previously demonstrated high frequency of p16 alterations in primary nasopharyngeal carcinoma (NPC), xenografts and cell lines. The finding implied that inactivation of the p16 gene may play an important role in the NPC development. To investigate the tumour suppressor function of p16 in NPC, we tranfected p16-deficient NPC cell line, NPC/HK-1, with a wild-type p16 expression construct, and evaluated growth and tumorigenic properties of the clones stably expressing exogenous p16. Expression of the exogenous wild-type p16 significantly inhibited cell growth by more than 70% when compared to that of the parental and empty vector-transfected cells. This growth inhibition was attributable to a significant proportion of p16-expressing cells arrested at G1 phase in the cell cycle as revealed by flow cytometric analysis. By anchorage-independent colony forming assay, we found that the ability to form colonies in soft agar was highly reduced in cells expressing p16. NPC/HK1 cells expressing functional p16 also showed suppressed tumorigenicity in athymic nude mice. Taken together, our results provide strong evidence for a tumour suppressor role of p16 in NPC.link_to_subscribed_fulltex