Abstract. A single enzyme found in both Drosophilaand mammalian cells is able to selectively bind and degrade transforming growth factor (TGF)-alpha and insulin, but not EGF, at physiological concentrations. These growth factors are also able to inhibit binding and degradation of one another by the enzyme. Although there are significant immunological differences between the mammalian and Drosophila enzymes, the substrate specificity has been highly conserved. These results demonstrate the existence of a selective TGFalpha-degrading enzyme in both Drosophila and mammalian cells. The evolutionary conservation of the ability to degrade both insulin and TGF-alpha suggests that this property is important for the physiological role of the enzyme and its potential for regulating growth factor levels.

Abstract. The identification of a novel protein from Drosophila melanogaster that binds both mammalian epidermal growth factor (EGF) and insulin has been reported (Thompson, K. L., S. J. Decker, and M. R. Rosner, 1985, Proc. Natl. Acad. Sci. USA., 82:8443-8447). This 100-kD protein (designated dpl00) is also recognized by an antiserum against the human EGF receptor. To further characterize the properties of this protein, we have determined the binding spectrum, glycosylation state, and cellular distribution of dpl00. Our results indicate that dpl00 binds to other insulin-like and EGF-like growth factors with dissociation constants ranging from 10 -6 to 10 -9 M, and these ligands compete with each other for binding to dpl00.All other ligands tested, including platelet-derived growth factor, transforming growth factor-beta, nerve growth factor, and glucagon, either did not bind or bound with a Kd >10 -6 M. Unlike the Drosophila insulin receptor, dpl00 does not bind to wheat germ agglutinin and is present in a cytoplasmic as well as a membrane-bound form that cannot be differentiated by two-dimensional PAGE. Further, dpl00 is the sole transforming growth factor-alpha-binding protein detected by affinity labeling in Drosophila Kc cells.These results indicate that dpl00 shares properties in common with, but distinct from, the Drosophila homologues of the insulin and EGF receptors.

Neuroblastoma tumors are derived from the neural crest and exhibit substantial phenotypic heterogeneity and various degrees of differentiation and maturation. The identification of new cell surface markers in neuroblastoma has relevance to disease classification and therapy. As a means to categorize neuroblastomas based on cell surface protein expression, we have obtained a comprehensive profile of the cell surface proteome of the MYCN nonamplified SH-SY5Y neuroblastoma cell line. Biotinylated cell surface proteins were captured using an avidin affinity column, fractionated by reversed-phase chromatography and subjected to in-depth analysis by LC-MS/MS. An extensive list of proteins was established and a subset of surface membrane proteins was assessed by immunohistochemistry in a set of neuroblastoma tissue microarrays. Among identified proteins tested, NCAM and CD147 exhibited increased expression in poorly differentiated tumors (p < 0.01 and <0.03, respectively). CD147 expression was previously associated with aggressive carcinomas but has not been described in neuroblastoma. This comprehensive neuroblastoma cell surface profile has identified novel potential markers for neuroblastoma classification and novel potential targets for therapy.