A tissue microarray containing 86 specimens from esophageal cancer and 40 specimens from adjacent non-cancer tissue was constructed to survey the expression of p53, p16 and COX-2 by immunohistochemistry.
The dual hits (concomitant loss) of pRb and p16INK4a expression suggest that these two components are not mutually exclusive, and can both be altered in a significant proportion of primary ESCCs serving as putative diagnostic markers for esophageal cancer.
Western blot analysis showed that stromal cells of lung tumours were characterised by a statistically significantly lower expression level of the p16 protein as compared with that in normal lung stromal cells.
Moreover, and consistent with p14ARF being a determinant of CHK2 phosphorylation in lung carcinogenesis, a strong correlation between p14ARF and phospho-CHK2 (Thr68) protein expression is observed in human lung tumors (P < 0.00006).
H1299 lung cancer cells, lacking Fhit, Wwox, p16(INK4a) and Rassf1a expression due to epigenetic modifications, were used to assess efficacy of epigenetically targeted protocols in suppressing growth of lung tumors, by injection of 5-aza-2-deoxycytidine (AZA) and trichostatin A (TSA) in nude mice with established H1299 tumors.
Moreover, 36.7% (22/60) of the non-small cell lung tumours without p16 expression showed p16 promoter methylation, detecting a significant correlation between p16 methylation and the histological subtype of squamous cell carcinomas (SCC) (P=0.04).
The lack of complete concordance between p15 and p16 expression implies that the genes are not functionally redundant and that loss of either gene may be important in the pathogenesis of MM.
The results show that inactivation of p16INK4a is not as frequent in primary melanoma as has been reported in cell lines, and warrant further search for another tumour suppressor on 9p21-22.
This paper reviews the current literature on p16 expression in melanoma and pancreatic cancer, explores factors that place patients with these cancers in categories of high risk for metastases or recurrence, and addresses whether aberrant gene expressions should influence awareness of and current recommendations for the management of these aggressive cancers.
Interestingly, all the aggressive cases did not express p16(INK4a), thus suggesting that loss of senescence control could be related to clinical aggressiveness of LCH, as in melanoma.
We identified melanoma patients that were heterozygous for non-coding germline variants in the 5'-UTR of CDKN2A (c.-21C > T; c.-25C > T&c.-180G > A; c.-56G > T; c.-67G > C) and examined their impact on the p16(INK4a) 5'-UTR activity using two luciferase-based reporter vectors that differ in basal transcription level and that were transfected into the melanoma-derived WM266-4 and in the breast cancer-derived MCF7 cells.
The evolutionary approach towards tumorigenesis and tumor progression used in this study thus confirms the role of p16ink4 inactivation for melanoma progression but not for melanoma initiation; it suggests the existence of additional putative tumor suppressor genes located on 9p as well as on the long arm of chromosome 14 and shows that microsatellite instability may represent an alternative pathway of tumor cell evolution in malignant melanoma.
Inactivation of p16INK4a and/or activation of cyclin-dependent kinase-4 (CDK4) are strongly associated with both susceptibility and progression in melanoma.
The p16 protein was weakly expressed in one of the metastatic melanoma cell lines (FM55M1) and negative in the other metastasis (FM55M2) as compared to their matched primary melanoma cells (FM55P).
Screening of an autologous melanoma cDNA library with clone T1D1 T cells in a cell line expressing the mutated HLA-A11 gene product resulted in the isolation of a p14ARF transcript containing a 2-bp deletion in exon 2.
Our data pinpoint: i) a frequent impairment of p14ARF and p16INK4A gene expression by epigenetic modifications in melanoma; ii) histone hypoacetylation as the dominant mechanism of p14ARF silencing; and iii) 5' CpG promoter methylation as the major mechanism of p16INK4A gene inactivation.