Regulation of B1 Integrin Glycosylation by RAS

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DESCRIPTION: (provided by applicant) Integrin adhesion receptors regulate many important cellular processes including cell proliferation, cell migration/invasion, cell differentiation and anchorage-dependent growth. Altered integrin function in any of these areas can promote tumorigenesis and/or metastasis, and hence, intense investigation has centered on understanding the regulation of these receptors. Preliminary studies presented in this proposal describe a novel mechanism for integrin regulation. It is shown that expression of oncogenic ras cause Bl integrins to acquire a 5-6-fold greater abundance of a2-6 linked sialic acid residues. The enzyme that directs this linkage, ST6Ga1 I, is upregulated in tumor tissues, and increased ST6Ga1 I is associated with cell invasiveness. Accordingly, increases in ST6Ga1 I activity have long been implicated in cancer progression. Despite these findings, the specific molecular species targeted by this enzyme have not been identified. A central hypothesis is proposed that oncogenic ras increases the expression and/or function of the ST6Ga1 I sialyltransferase, and that this enzyme then acts on the, B1 integrin to increase the number of a2-6 sialic acid residues. In turn, increased a2-6 sialylation of the 31 integrin induces a conformational change that leads to altered function. The broad, long term goals of the proposed research are to demonstrate that variant glycosylation represents an important mechanism for B1 integrin regulation and further, that oncogenic ras-induced expression of a variant glycoform contributes to tumorigenesis and/or metastasis. These goals will be accomplished by: 1) Defining the ras-mediated changes in B1 integrin carbohydrate structure and in ST6Ga1 I activity (Aim 1) To elucidate the mechanism by which ras alters integrin glycosylation, the carbohydrate structures and sites of N-linked glycosylation will be identified, and the activity/expression of ST6Ga1 I will be evaluated. 2) Establishing that altered glycosylation plays a causal role in modifying integrin function (Aim 2) Levels of integrin a2-6 sialylation will be directly altered and integrin function will be examined. In addition, cells with an inducible ras construct will be used to determine whether expression of an altered glycoform is temporally correlated with altered function. 3) Determining whether altered 131 integrin glycosylation contributes to cancer progression (Aim 3) Cells that overexpress ST6Ga1 I will be examined for anchorage-independent growth, migration/invasion, and tumor formation in nude mice. In addition, pancreatic tumor specimens will be assayed for expression of a variant B1 glycoform.