Loss of expression of thep16INK4/CDKN2 gene in cutaneous malignant melanoma correlates with tumor cell proliferation and invasive stage

Abstract

The G 1 /S checkpoint of the cell cycle is regulated by p16, p53 and RB tumor suppressor genes. Loss of expression of the p16 INK4 tumor suppressor protein, the product of the CDKN2 gene, has been associated with a wide variety of human malignancies. Mutations, loss of heterozygosity and deletions of the CDKN2 locus have been reported in sporadic and familial cutaneous malignant melanomas (CMM). To investigate the role of the alterations of p16 expression in melanoma, we evaluated by immunohistochemistry the p16 expression and cell proliferation in 79 primary CMM and 10 benign melanocytic nevi (BMN). Forty-six melanomas (58%) and all BMN were found to be p16 positive; 33 melanomas (42%) were considered p16 negative. The extent of invasion according to Clark was significantly higher in p16-negative tumors than in p16-positive tumors. Cell proliferation as expressed by the proportion of positive cells in Ki-67 immunostaining was found to be significantly higher in p16-negative tumors than in p16-positive tumors, although there was no significant difference in the mitotic index between p16-positive and p16-negative tumors. In p16-positive tumors, the number of Ki-67-positive cells correlated with the mitotic index; in p16-negative tumors, there was no correlation between these parameters. Our data suggest that loss of p16 expression is more common in advanced melanomas, and that G 1 /S checkpoint regulation is disrupted in p16-negative melanomas. Our results show that loss of p16 expression is a common event in primary melanomas, which further substantiates the role of p16 as a major tumor suppressor. Int. J. Cancer 74:255-259, 1997.r 1997 Wiley-Liss, Inc.The progression of mammalian cells from the G 1 phase of the cell cycle to the S phase is regulated by a cascade of protein-protein interactions and protein phosphorylations. During G 1 , the D-type cyclins (cyclin D1, D2 and D3) accumulate and form complexes with CDK4 and CDK6. Cyclin D-CDK4/6 complexes phosphorylate the retinoblastoma protein (pRB), which is found in its hypophosphorylated form during G 1 . The phosphorylation of pRB releases a group of transcription factors essential for progression to S phase and onset of DNA replication. p16 INK4 , the protein product of the CDKN2 gene, is thought to be induced by some of these transcription factors to dissemble and inactivate the cyclin D-CDK4/6 complexes. p16 might also be induced earlier in G 1 by various anti-proliferative signals, arresting the cell in G 1 and thus acting as a powerful G 1 /S checkpoint regulator (reviewed by Grana and Reddy, 1995;Sherr and Roberts, 1995).The growth-inhibitory function of p16 makes it a candidate tumor suppressor. Loss of heterozygosity (LOH), homozygous deletion or mutations of the p16 gene have been found in cell lines established from malignant melanoma; mesothelioma; leukemia; glioma; carcinomas of lung, colon, liver, kidneys, esophagus, pancreas, breast, bladder, ovaries and prostate; and various sarcomas (Liu, Q. et al., 1995;Okamoto et al., 1994). Although it has ...

Cellular senescence in naevi and immortalisation in melanoma: a role for p16?

“…Scale bar, 100 mm. p16 expression in melanocytic lesions has been studied previously, with results largely consistent with ours (Talve et al, 1997;KellerMelchior et al, 1998). However, the authors did not relate p16 expression to senescence, nor examine other cell-senescence effectors.…”

“…We proposed a genetic model, in which benign and dysplastic naevi represent p16 and p53-dependent senescence, while melanomas arise by immortalisation of melanocytes (Bennett, 2003;Sviderskaya et al, 2003;Bennett, 2006). Published biological and molecular data (Talve et al, 1997;Keller-Melchior et al, 1998;Glaessl et al, 1999;Rudolph et al, 2000;Hussein and Wood, 2002;Bennett, 2003;Sviderskaya et al, 2003) were consistent with this model, but not conclusive, although a convincing report of cell senescence in melanocytic naevi has appeared recently (Michaloglou et al, 2005). We have now identified the genetic requirements for immortalisation of human melanocytes, and systematically studied molecular markers and mediators of cell senescence in clinical pigmented lesions of increasing malignancy.…”

Adenoviral vector containing wild-type p16 suppresses prostate cancer growth and prolongs survival by inducing cell senescence

“…Loss of heterozygosity, homozygous deletions, mutations, and promoter hypermethylation have been found in a wide variety of malignancies, including malignant melanoma; 50 mesothelioma; 32 leukemia; 51 glioma; carcinomas of the lung, colon, liver, kidney, 50 esophagus, pancreas, breast, ovary, biliary tract, and prostate; and sarcomas. 37,50,[52][53][54] In some of the major cancers, p16 loss is quite common, with a frequency as high as 85% for pancreatic cancer, 55 49% for breast cancer, 56 -58 52% for esophageal cancer, 55 51% for anaplastic astrocytomas and glioblastomas, 27,55 26% for bladder cancer, 25,37 and up to 46% for prostate cancer (Greenberger MD, et al, submitted for publication). 37,40,41 The emerging body of evidence has also shown that p16 loss correlates with prostate tumor progression.…”

BRAFE600 in benign and malignant human tumours

“…INK4a expression and increased proliferation in human melanoma (Talve et al, 1997;Straume et al, 2000).…”