Chromosome 17 allelic loss and NF1-GRD mutations do not play a significant role as molecular mechanisms leading to melanoma tumorigenesis

NF1 and Neurofibromin: Emerging Players in the Genetic Landscape of Desmoplastic Melanoma

Neurofibromatosis type I (NF1), a monogenic disorder with an autosomal dominant mode of inheritance, is caused by alterations in the NF1 gene which codes for the protein neurofibromin. Functionally, NF1 is a tumor suppressor as it is GTPase-activating protein that negatively regulates the MAPK pathway. More recently, much attention has focused on the role of NF1 and neurofibromin in melanoma as mutations in NF1 have been found to constitute 1 of the 4 distinct genomic categories of melanoma, with the other 3 comprising BRAF, NRAS, and "triple-wild-type" subtypes. In this review, we parse the literature on NF1 and neurofibromin with a view to clarifying and gaining a better understanding of their precise role/s in melanomagenesis. We begin with a historic overview, followed by details regarding structure and function and characterization of neural crest development as a model for genetic reversion in neoplasia. Melanogenesis in NF1 sets the stage for the discussion on the roles of NF1 and neurofibromin in neural crest-derived neoplasms including melanoma with particular emphasis on NF1 and neurofibromin as markers of melanocyte dedifferentiation in desmoplastic melanoma.

Immunohistologic Evaluation of Putatively Mutant p53 Protein in Cutaneous Melanocytic Neoplasms

Mutations in the p53 tumor suppressor gene, located at chromosomal locus 17pI3, are the most commonly seen genetic alterations found in human malignancies. Their role in the pathogenesis of malignant melanoma is thought to be limited, although variable results have been reported in reference to immunoreactivity for putatively mutant p53 protein (mp53) in melanocytic lesions in general. In that light, the authors undertook an immunohistologic evaluation of 256 well-characterized tumors in that category, including common nevi (CN; n=73); Spitz nevi (SN; n=40); nodular melanomas (NMMs; n=32), superficial spreading melanomas (SMMs; n=65); lentigo maligna melanomas (LMMs; n=23); and melanomas arising in preexisting nevi (MANs; n=23). One hundred cells were counted manually in randomly selected high-power microscopic fields, in regard to nuclear labeling for mp53. Results were recorded semiquantitatively, as negative, positive (1-4% of tumor cells); and positive (>5% of tumor cells). No examples of CN or SN demonstrated any immunoreactivity whatever for mp53, whereas 105 of 143 melanomas (73%) did so. However, an mp53 index of >50% was seen in only 29% of the latter lesions. NMMs were most often mp53-positive and showed the highest numerical level of nuclear labeling, followed in respective order by SMMs, and LMMs/MANs. These results suggest that negative mp53-immunostaining cannot be equated with the diagnostic interpretation of a benign melanocytic neoplasm, because 27% of melanomas also failed to label for that determinant. However, the presence of mp53-immunolabeling in a melanocytic proliferation-even if at low levels-should conversely prompt careful consideration of melanoma as the favored diagnosis in the confined setting of morphologically difficult cases, inasmuch as no example of CN or SN in this series had that characteristic.

Human relevance of NRAS/BRAF mouse melanoma models

Melanoma is a major problem for many individuals worldwide. Although no effective treatment is available, promising new strategies are being developed. A better understanding of the inner workings of the disease would undoubtedly lead to improved treatments. Mouse melanoma models have been used to elucidate many key regulatory pathways involved in melanoma initiation and progression, and models with mutations in the oncogenes RAF and RAS have been particularly informative. Here, we summarize and evaluate the human relevance of various RAF and RAS mouse melanoma models and their contribution to our understanding of melanoma.

Neurofibromin physically interacts with the N-terminal domain of focal adhesion kinase

The NF1 gene that is altered in patients with type 1 neurofibromatosis (NF1) encodes a neurofibromin protein that functions as a tumor suppressor. In this report, we show for the first time physical interaction between neurofibromin and focal adhesion kinase (FAK), the protein that localizes at focal adhesions. We show that neurofibromin associates with the N-terminal domain of FAK, and that the C-terminal domain of neurofibromin directly interacts with FAK. Confocal microscopy demonstrates colocalization of NF1 and FAK in the cytoplasm, perinuclear and nuclear regions inside the cells. Nf1+/+ MEF cells expressed less cell growth during serum deprivation conditions, and adhered less on collagen and fibronectin-treated plates than Nf1(-/-) MEF cells, associated with changes in actin and FAK staining. In addition, Nf1+/+ MEF cells detached more significantly than Nf1(-/-) MEF cells by disruption of FAK signaling with the dominant-negative inhibitor of FAK, C-terminal domain of FAK (FAK-CD). Thus, the results demonstrate the novel interaction of neurofibromin and FAK and suggest their involvement in cell adhesion, cell growth, and other cellular events and pathways.

Molecular cloning and characterization of FBXO47, a novel gene containing an F-box domain, located in the 17q12 band deleted in papillary renal cell carcinoma

Genetic alterations of chromosome arm 17q occur in numerous tumor types, including breast and ovarian tumors, suggesting the presence of a tumor-suppressor gene on the long arm of chromosome 17 that is critical for carcinogenesis. Previous studies have shown an allelic imbalance (70% gain or loss) of 17q in papillary renal cell carcinoma (pRCC). In this study, we analyzed 15 cases of pRCC for loss of heterozygosity with the use of 7 microsatellite markers between 17q11 and 17q23. We identified a minimal deleted region in which the D17S250 marker (17q12) was deleted in 50% (7 of 14) of informative cases. We isolated the cDNA of a novel gene named FBXO47, which is near D17S250. Human FBXO47 is composed of 11 exons and spans approximately 30 kb of genomic DNA. FBXO47 cDNA consists of 2,269 bp with a 1,359-bp open-reading frame. Of note is that FBXO47 is preferentially expressed in normal tissue relative to the corresponding tumor tissue, particularly in the kidney, liver, and pancreas and to a lesser extent in the thyroid gland, stomach, and small intestine. The putative protein encoded by this gene is made up of 453 amino acids and belongs to the F-box family, most of whose members, such as SKP2 and FBW7, have been implicated in carcinogenesis. Together, these results indicate that FBX047 has a potential role as a tumor-suppressor gene.

Pigment cell-related manifestations in neurofibromatosis type 1: an overview

Neurofibromatosis type 1 (NF1) is an autosomal dominant neurocutaneous disorder, affecting approximately 1 in 3500 individuals. The most commonly seen tumors in NF1 patients are the (sub)cutaneous neurofibromas. However, individuals with NF1 typically present in childhood with well-defined pigmentary defects, including cafe-au-lait macules (CALMs), intertriginous freckling and iris Lisch nodules. NF1 is considered a neurocristopathy, primarily affecting tissues derived from the neural crest. Since the pigment producing melanocyte originates in the neural crest, the presence of (hyper)pigmentary lesions in the NF1 phenotype because of changes in melanocyte cell growth and differentiation is to be expected. We want to discuss the pigmentary cutaneous manifestations of NF1 represented by CALMs and intertriginous freckles and the pigmentary non-cutaneous manifestations represented by iris Lisch nodules. Several hypotheses have been suggested in explaining the poorly understood etiopathogenesis of CALMs. Whether other pigmentary manifestations might share similar etiopathogenic mechanisms remains obscure. Additional attention will be drawn to a readily seen phenomenon in NF1: hyperpigmentation overlying (plexiform) neurofibromas, which could suggest common etiopathogenetic-environmental cues or mechanisms underlying CALMs and neurofibromas. Finally, we want to address the relationship between malignant melanoma and NF1.