Transcriptional upregulation and unmethylation of the promoter region of p16 in invasive basal cell carcinoma cells and partial co‐localization with the γ2 chain of laminin‐332

Abstract

Basal cell carcinoma cells show low proliferation rates at the invasive front and a concordant upregulation of the cdk-inhibitor p16, limiting proliferative capacity. Little is known about the mechanisms of p16 regulation in normal and malignant cells apart from that many transcription factors such as Ets1, Ets2, SP1, SP3, JunB and the polycomb protein Bmi1 have the potential to induce or repress p16 expression. Therefore, the aim of this study was to determine how p16 is regulated in basal cell carcinoma with special focus on its upregulation in invasive cells. By analysing various microdissected areas of basal cell carcinoma using real-time quantitative PCR we observed upregulation of p16 mRNA in invasive tumour cells compared to centrally localized tumour cells. The methylation status of the p16 promoter, analysed by methylation-specific PCR, also showed diminished methylation in tumour cells at the invasive front, supporting the hypothesis that promoter methylation can affect the transcriptional activation of p16 in vivo. There was only sporadic co-localization of Ets, or ERK1/2 phosphorylation with p16 upregulation at the invasive front, suggesting that these factors were not directly involved in the regulation of p16. Furthermore, the gamma 2 chain of laminin-332 has been reported to be increased at the invasive front compared to the central areas of many tumours. Interestingly, in basal cell carcinoma we observed partial co-localization between p16 and the gamma 2 chain of laminin-332 in tumour cells towards areas of ulceration and in the majority of clearly infiltrative tumour cells but not in p16 positive tumour cells with a more pushing invasive growth pattern. These data suggest that concurrent p16 upregulation and decreased proliferation are more general phenomena in different types of invasive growth patterns in basal cell carcinomas and that these only partially overlap with the gamma 2 chain of laminin-332 associated invasion patterns.

Expression of cytoplasmic p16 and anion exchanger 1 is associated with the invasion and absence of lymph metastasis in gastric carcinoma

“…Cytoplasmic p16 is therefore associated with the depth of invasion of gastric cancer, by virtue of the fact that the distinction between early and advanced gastric cancer is based on the criterion of the depth of invasion of cancer cells. This finding is in agreement with that of another study, in which the authors concluded that the invasion of basal cell carcinoma was induced by p16 upregulation (in both the nucleus and cytoplasm) with the requirement of a functional p16/cyclin D/Rb pathway (25).…”

Aberrant expression of ETS1 and ETS2 proteins in cancer

“…The p16 INK4a cyclin-dependent kinase inhibitor (CDKN2a) has been implicated in replicative senescence, the state of permanent growth arrest driven by cell divisions or constitutive Ras-Raf-MEK signaling (see 131–134 for p16 INK4a reviews; Fig. 2).…”

Co-expression of laminin β3 and γ2 chains and epigenetic inactivation of laminin α3 chain in gastric cancer

“…The results suggest that coexpression of laminin β3 and γ2 chains is involved in the aggressive phenotype of gastric cancer cells, resulting in the progression of disease. Previous immunohistochemical studies have shown significant coexpression of laminin β3 and γ2 chains in the cytoplasm of invading or budding tumor cells in colorectal carcinoma, lingual squamous cell carcinoma, hepatocellular carcinoma, and basal cell carcinoma of the skin (4,9,20,21). We have also reported overexpression of laminin β3 and γ2 chains in biliary cancer (3).…”