Our current hypothesis is that specific responses to Wnt signals are determined by both plakoglobin and beta-catenin in a manner dependent on their other protein associations and modifications. Preliminary results show that (1) transgenic expression of plakoglobin inhibits hair growth; (2) transgenic expression of beta-catenin produces tumors in mammary gland; (3) plakoglobin is glycosylated in the putative CSK-3beta phosphorylation site.
Our aims address the following questions: (1b) does plakoglobin act antagonistically, synergistically or interchangably with beta-catenin to regulate cell growth in normal cells? K14-deltaN89beta-catenin mice will be created and their hair phenotype compared to the existing K14-deltaN80-plakoglobin mice. The spontaneous tumor incidence of existing MMTV-deltaN89beta-catenin and MMTV-deltaN80-plakoglobin mice will be compared. Antagonism or synergy will be tested in vivo by crossing of these pairs of mice and in vitro by examining cultured transgenic keratinocytes for the effects of expressing one transgene on the localization, stability and interaction of the produce of the other transgene. (1b) does up-regulated plakoglobin activate FGFR? K14-deltaN80-plakoglobin mice will be bred to FGF5-/- angora mice to look for counteraction of the long hair phenotype as evidence of intersection of the pathways. K14-deltaN80-plakoglobin trangenic keratinocytes will be examined for up-regulation of cadherins and for up-regulation of FGFs as potential FGFR ligands. (2) Does plakoglobin and beta-catenin up-regulation predispose epidermis to tumorigenesis? A panel of chemically induced skin tumors will be screened for up-regulation and relocation and mutations of plakoglobin and beta-catenin. K14 transgenic mice will be tested for enhanced or suppressed susceptibility to tumor induction by (a) breeding to mice expressing v-rasHa: (b0 transforming transgenic keratinocytes with v-rasHa and grafting to athymic mice; (c) standard chemical carcinogenesis protocols. (3) does glycosylation of plakoglobin play a role in protein stability, junction formation and Wnt-signaling? subcellular fractions of keratinocytes+/- junction formation and PC12 cells +/- wnt expression will be examined for presence and extent of plakoglobin glycosylaiton.
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