Expression of the Tumor Suppressor Gene Product p16INK4 in Benign and Malignant Melanocytic Lesions

Abstract

The gene MTS1 encodes p16INK4, an inhibitor of cyclin-dependent kinase 4, and is frequently deleted, mutated, or silenced by promoter methylation in melanoma cells and in the germline of familial melanoma patients. Although MTS1 may thus be the candidate melanoma suppressor gene that maps to chromosome 9p21, it is not clear how dysfunction at that locus temporally relates to melanoma progression. To further test its role in sporadic melanoma, the expression of p16INK4-protein and -mRNA was characterized in melanomas and melanocytic nevi by immunocytochemistry and in situ reverse transcriptase-polymerase chain reaction. Histologic tissue sections were immunolabeled with anti-p16INK4 antibody for 108 melanocytic lesions, including common and atypical nevi, in situ melanomas, primary invasive melanomas, and metastatic tumors. A subset of the lesions was analyzed for expression of p16INK4-mRNA, employing forward and reverse intron-bridging primers for reverse transcriptase-polymerase chain reaction amplification of the transcript corresponding to exons 1 and 2 of MTS1. Strong immunolabeling was detected in the melanocytes of common nevi and of nevi with architectural disorder and cytologic atypia. By digital image analysis, in contrast, labeling intensity decreased significantly and progressively in the melanocytes of in situ, invasive, and metastatic melanomas. Results from the in situ reverse transcriptase-polymerase chain reaction analysis were confirmatory, showing a strong signal in the melanocytic nevi but progressive signal attenuation with increasing stage of melanoma. These data indicate correlation between gradual loss of expression of the MTS1 locus and progression of melanoma, further supporting an emerging role for the gene in the malignant transformation of melanocytes. The failure to demonstrate reduced expression in nevi suggests either that these lesions are not an early stage in melanoma development, in contrast to prevailing assumptions, or that loss of p16INK4 function is not an initiating event in melanocyte transformation.

p15 Expression Differentiates Nevus from Melanoma

“…The increased staining for p16 in nevi compared with melanoma was consistent with findings from the literature, although in the current study the difference was not significant (P Z 0.055). 23 After conditioning on p15 H score in a multivariate logistic model, the p16 H score provided no additional discernible information.…”

“…These findings are consistent with those from a prior study that correlated higher p16 mRNA levels with stronger p16 IHC staining in nevi compared with melanomas. 23 The p15 IHC and RT-qPCR data indicate that mechanisms regulating p15 transcript or mRNA stability may play a role in melanoma formation.…”

Immunohistochemical Expression of p16, p21, p27 and Cyclin D1 in Oral Nevi and Melanoma

“…On the other hand, loss of p16 expression has also been demonstrated in almost 50% of primary cutaneous and oral melanomas, similarly to many other cancers, including pancreatic, esophageal, lung, head and neck, breast, bladder, brain and ovarian [1,5,13,14]. Although there is general consensus regarding the loss of p16 expression in cutaneous melanomas, it is suggested that this occurs in later stages of the disease, as it is not altered in melanoma in situ [16]. However, these findings may not be applied to oral melanomas, because we found reduced p16 expression also in oral in situ melanomas, suggesting that this alteration may be relevant in the initial phases of oral melanoma development.…”

A Novel Human Gene Similar to the Protein Kinase (PK) Coding Domain of the Large Subunit of Herpes Simplex Virus Type 2 Ribonucleotide Reductase (ICP10) Codes for a Serine-Threonine PK and Is Expressed in Melanoma Cells

“…Significant progress has been made in the identification of genes involved in melanoma progression/metastasis most of which function as tumor suppressors (52). With the possible exception of basic fibroblast growth factor and its cognate receptors (53), identification of oncogenes involved in melanocyte transformation has been relatively slow.…”