CONSTITUTIVELY ACTIVE RECEPTORS AS A DISEASE-CAUSING MECHANISM

Membrane receptors have appeared early in evolution as the means for t he unicellular organism to sense its environment. With the emergence o f social cellular life in multicellular organisms, membrane receptors have acquired the additional functions of sensing the presence of simi lar cells (as in the aggregation phenomenon of Dictyostelium discoideu m) (Klein et al., 1988) or the presenceof the mate (in Saccharomyces c erevisiae) (Cross et al., 1988), and to detectendocrine signals emmitt ed by cells in distant tissues. As the latter function is central to h omeostasis and regulation of cell growth, the downstream regulatory ca scades under receptor control are the subject of intense research with implications in virtually all fields of biomedical science. The impac t of the analysis of tyrosine kinase-activated cascades on our underst anding of carcinogenesis is but one example of such an advance.