Faculty Bibliography

Melanomas exhibiting mutated ras genes are frequently invasive and amelanotic. Transfecting melanocytes with ras oncogenes causes transformation and a loss of visible pigmentation. We analyzed murine melanocytes rendered amelanotic by transfection with the v-rasHa oncogene. Consistent with previous reports, tyrosinase and tyrosinase-related protein-1 (TRP-1) were not expressed by transformed cells. In addition, lack of expression of TRP-2 and the product of the silver locus was documented. Levels of melanosomal matrix antigens, the pink-eyed dilution locus protein and lysosome-associated membrane protein-1 were markedly reduced. Residual matrix antigens were localized by immunofluorescence to large vacuoles distributed peri-nuclearly in transfected cells. Electron microscopy demonstrated the absence of typical melanosomes and the presence of large vacuolar structures, also in a peri-nuclear distribution. Although levels of lysosomal hydrolases, such as beta-glucuronidase and cathepsin D, were diminished, marked elevations were observed in the expression of cathepsins B and L, 2 thiol proteases implicated in the acquisition of invasiveness. Our data demonstrate that transfection of melanocytes with v-rasHa is sufficient to disrupt the biogenesis of melanosomes and to up-regulate thiol protease synthesis, providing insights into the amelanotic and invasive nature of melanomas exhibiting mutations in ras genes

CHILD syndrome (congenital hemidysplasia with ichthyosiform nevus and limb defects) occurs, as a rule, exclusively in girls because the underlying X-linked gene exerts a lethal effect on male embryos. In this report the characteristic manifestations of CHILD syndrome are described in a 2-year-old boy with a normal chromosome constitution 46,XY. This exceptional case is best explained by the assumption of an early somatic mutation and thus compatible with the concept of X-linked dominant male-lethal inheritance of this trait

BACKGROUND AND DESIGN: Patients with large congenital melanocytic nevi have been described to have an increased risk for the development of malignant melanoma (MM). Ninety-two patients with large congenital melanocytic nevi were followed up prospectively for the development of MM. Matched individuals from the general population served as control subjects. RESULTS: Ninety-two patients (median age, 3 years) were followed up prospectively for an average of 5.4 years. In three patients (3%), MM developed in extracutaneous sites. The cumulative 5-year life-table risk for the development of MM was calculated to be 4.5% (95% confidence interval, 0% to 9.3%). In individuals in the general US population, matched for age, sex, and length of follow-up to the 92 study patients, 0.013 would be expected to develop MM. The standardized morbidity ratio (adjusted relative risk) was calculated to be 239, which was highly significant (P < .001). CONCLUSIONS: Patients with large congenital melanocytic nevi are at a significantly increased risk for the development of MM and should be kept under continuous surveillance for the development of cutaneous as well as noncutaneous primary MM

Crouzon syndrome, an autosomal dominant condition characterized by craniosynostosis, ocular proptosis and midface hypoplasia, is associated with mutations in fibroblast growth factor receptor 2 (FGFR2) (refs 1-3). For example, we have identified 10 different mutations in the FGFR2 extracellular immunoglobulin III (IgIII) domain in 50% (16/32) of our Crouzon syndrome patients. All mutations described so far for other craniosynostotic syndromes with associated limb anomalies--Jackson-Weiss, Pfeiffer, and Apert--also occur in the extracellular domain of FGFR2, as well as FGFR1 for Pfeiffer syndrome. In contrast, only FGFR3 mutations have been reported in dwarfing conditions--achondroplasia, thanatophoric dysplasia, and hypochondroplasia. For achondroplasia, greater than 99% of mutations occur in the FGFR3 transmembrane domain. We now report the unexpected observation of a FGFR3 transmembrane domain mutation, Ala391Glu, in three unrelated families with Crouzon syndrome and acanthosis nigricans, a specific skin disorder of hyperkeratosis and hyperpigmentation. The association of non-dwarfing and even non-skeletal conditions with FGFR3 mutations reveals the potential for a wide range of FGFR pleiotropic effects as well as locus heterogeneity in Crouzon syndrome. Our study underscores the biologic complexity of the FGFR gene family

Mice homozygous for the platinum (cp) allele at the albino locus manifest severe oculocutaneous albinism despite the presence in vitro of tyrosinase activity at 25% wild-type levels. We demonstrate that the cp allele results from an A-->T substitution, changing a lysine residue at position 489 to a termination codon, with truncation of tyrosinase's cytoplasmic tail. In choroidal melanocytes of neonatal mutant mice, tyrosinase activity could be detected in the trans Golgi network, but was absent from melanosomes. Instead, it was detected in vesicles in the cell periphery and dendrites, and on the extracellular surface. In the retinal pigment epithelium, activity was present on the extracellular apical and basolateral surfaces. Our results demonstrate misrouting of a mutant tyrosinase lacking its cytoplasmic tail, providing an explanation for the severe effect of this mutation on ocular and cutaneous pigmentation

Cutaneous melanomas of Tyr-SV40E transgenic mice (mice whose transgene consists of the tyrosinase promoter fused to the coding regions of simian virus 40 early genes) strikingly resemble human melanomas in their development and progression. Unlike human melanomas, the mouse tumors all arise in genetically identical individuals, thereby better enabling expression of specific genes to be characterized in relation to advancing malignancy. The products of pigment genes are of particular interest because peptides derived from these proteins have been reported to function as autoantigens with immunotherapeutic potential in some melanoma patients. However, the diminished pigmentation characteristic of many advanced melanomas raises the possibility that some of the relevant products may no longer be expressed in the most malignant cells. We have therefore investigated the contributions of several pigment genes in melanotic vs. relatively amelanotic components of primary and metastatic mouse melanomas. The analyses reveal marked differences within and among tumors in levels of mRNAs and proteins encoded by the wild-type alleles at the albino, brown, slaty, and silver loci. Tyrosinase (the protein encoded by the albino locus) was most often either absent or undetectable as melanization declined. The protein encoded by the slaty locus (tyrosinase-related protein 2) was the only one of those tested that was clearly present in all the tumor samples. These results suggest that sole reliance on targeting tyrosinase-based antigens might selectively favor survival of more malignant cells, whereas targeting the ensemble of the antigens tested might contribute toward a more inclusive and effective antimelanoma strategy