Volume 272, Number 19, Issue of May 9, 1997 pp. 12529-12535
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

Post-translational Modifications of ₅₁ Integrin by Glycosaminoglycan Chains
THE ₅₁ INTEGRIN IS A FACULTATIVE PROTEOGLYCAN

(Received for publication, October 2, 1996, and in revised form, December 23, 1996)

Silvio S. Veiga ^§ , Maria Carolina Q. B. Elias , Waldemiro Gremski ^§ , Marimelia A. Porcionatto , Roseli da Silva , Helena B. Nader and Ricardo R. Brentani

From the  Ludwig Institute for Cancer Research, R. Prof. Antonio Prudente, 109, 4 A, 01509-010, São Paulo, SP, Brazil, the ^§ Department of Cell Biology, Federal University of Parana, Curitiba, Centro Politécnico, Seter de Ciências Biológicas, Jardim des Americas, 81531-990, Curitiba, PR, and the  Department of Biochemistry, Federal University of São Paulo, Universidade Federal de São Paulo, Escola Paulista de Medicina, rea 3 de maio, 100 4 andar, 04044-020, São Paulo, SP, Brazil

Cell-fibronectin interactions, mediated through several different receptors, have been implicated in a wide variety of cellular properties. Among the cell surface receptors for fibronectin, integrins are the best characterized, particularly the prototype ₅₁ integrin. Using [¹²⁵I]iodine cell surface labeling or metabolic radiolabeling with sodium [³⁵S]sulfate, we identified ₅₁ integrin as the only sulfated integrin among ₁ integrin heterodimers expressed by the human melanoma cell line Mel-85. This facultative sulfation was confirmed not only by immunoprecipitation reactions using specific monoclonal antibodies but also by fibronectin affinity chromatography, two-dimensional electrophoresis, and chemical reduction. The covalent nature of ₅₁ integrin sulfation was evidenced by its resistance to treatments with high ionic, chaotrophic, and denaturing agents such as 4 M NaCl, 4 M MgCl₂, 8 M urea, and 6 M guanidine HCl. Based on deglycosylation procedures as chemical -elimination, proteinase K digestion, and susceptibility to glycosaminoglycan lyases (chondroitinase ABC and heparitinases I and II), it was demonstrated that the ₅₁ heterodimer and ₅ and ₁ integrin subunits were proteoglycans. The importance of ₅₁ sulfation was strengthened by the finding that this molecule is also sulfated in MG-63 (human osteosarcoma) and HCT-8 (human colon adenocarcinoma) cells.

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