Relationship between expression and methylation status of p16INK4a and the proliferative activity of different areas’ tumour cells in human colorectal cancer

Abstract

The p16(INK4a) gene is a cell cycle inhibitor and a major tumour suppressor protein, but the regulation and effects on tumour cells' invasion process of p16(INK4a) is poorly known. A role for p16(INK4a) in basal cell carcinoma is suggested by the observation that p16(INK4a) was upregulated at the invasive front of the majority of basal cell carcinomas with infiltrative growth patterns, accompanied by cessation of proliferation. In this paper, we explore whether there is a difference of tumour cells' proliferative activity between the centre and the invasion front tissues of human colorectal cancer and its relationship with the expression and methylation status of p16(INK4a) gene. We obtained the centre and the invasion front tissues of colorectal cancer respectively by the technology of laser mircodissection. The expressions of the proliferating cell nuclear antigen ki67 and p16(INK4a) were assessed by immunohistochemistry, methylation-specific polymerase chain reaction (MS-PCR) and reverse-transcription polymerase chain reaction (RT-PCR) in the different areas. There was a significant difference in the expressions of ki67 between the centre and the invasion front tissues (p < 0.05). The difference did not correlate with age, sex, Dukes stage but did correlate with expression of p16(INK4a) gene (chi(2) = 25.37, p < 0.01). Furthermore, hypermethylation of the promoter was the major mechanism of inactivation of p16(INK4a) in the centre areas. Demethylation of the p16(INK4a) promoter, the elevated expression of p16(INK4a) protein and mRNA level was proved in the invasion front. Our finding suggested that enhanced invasion in tumours was accompanied by ceased proliferation in the invasion fronts of human colorectal cancer. This interesting phenomenon may be due to not only the microenvironment, but also the molecular changes such as p16(INK4a) status.

Expression of cell cycle regulatory proteins in endometrial adenocarcinoma: variations in conventional tumor areas and in microcystic, elongated and fragmented glands

“…The upregulation of p16 expression in association with cyclin D1 has also been described at the invasive front of colorectal carcinoma. 52,53 In summary, this study has shown that the immunoreactivity of cell cycle regulatory proteins in uterine low-grade endometrioid adenocarcinomas varies according to microanatomical distribution. Cyclin D1 and b-catenin are most uniformly expressed toward the peripheral or basal aspect of conventional tumor glands.…”

Correlation between Angiogenesis and p53 Expression in Lung Adenocarcinoma of Young Patients

“…To explain the low PCNA labeling index, the activated p16 -RB pathway may have been involved in suppressing cell growth (Tsuji et al 2006;Kim and Sharpless 2006). Jie et al (2007) reported a study of patients with colon cancer in which the expression of p16 and demethylation of the promoter regions were high in areas infiltrated by tumors and low in central areas. In addition, Milyavsky et al (2007) reported that, in human fibroblasts, the p16 -RB pathway induces myocardin, thereby inducing differentiation via TGF-β .…”

Methylation of CpG islands of p16INK4a and cyclinD1 overexpression associated with progression of intraductal proliferative lesions of the breast

“…The p16 INK4a gene, a widely known tumor suppressor gene, is localized on chromosome 9p21; it can form complexes with CDK4, CDK6, and D-type cyclins to arrest the cell cycle's progression from the G1 to the S phase. According to earlier observations, p16 INK4a is suppressed by aberrant promoter hypermethylation in diverse types of malignant tumors, including breast cancer, and in recent years, its inactivation has been gaining increased attention with the development of molecular pathology [1][2][3][4]. For example, Kimberly et al [5] described a new function of p16 INK4a and demonstrated that the loss of p16 INK4a expression generated supernumerary centrosomes, thus driving genomic instability, which was considered an early event in tumorigenesis.…”