Human cervical tumor cell (SiHa) surface α_vβ₃ integrin receptor has associated matrix metalloproteinase (MMP-2) activity

Abstract.

Purpose: Integrins are transmembrane heterodimeric molecules that mediate cellular adhesion and are involved in different biological processes, such as tumor development and invasion of tumor cells. Matrixmetalloproteases (MMP) are a family of secreted or membrane proteins capable of digesting extracellular matrix. It has been shown that MMP-2 binds to α_vβ₃ integrin. Recent evidence suggests that a complex of membrane-type MMP (MT1-MMP) and tissue inhibitor of metalloptroteinase-2 (TIMP-2) participate in the activation of α_vβ₃-associated MMP-2. We investigated whether α_vβ₃ and MMP-2 are associated on the membranes of a human cell line, SiHa, and the possible involvement of MT1-MMP and TIMP-2 in the modulation of MMP-2 activity. Methods: Immunoprecipitation of SiHa membrane extracts with monoclonal antibodies against α_v or MMP-2, and western blots of immunoprecipitates and serum-free conditioned media were performed. TIMP-2 in conditioned medium and MT1-MMP in the membrane fraction was assayed by western blot. Zymography of anti-α_v antibody immunoprecipitates and conditioned media were used to show gelatinolytic activity. Results: The coprecipitation of MMP-2 with α_vβ₃ by anti-α_v antibody is a strong indication that SiHa cell surface α_vβ₃ integrin is a receptor for MMP-2. Immunoblot assays show the expression of MT1-MMP on SiHa cell membranes and secreted TIMP-2 and pro-MMP-2 in the medium. Conclusions. SiHa cells express all the molecules which are reported to form a complex to activate pro-MMP-2. Active MMP-2 associated with α_vβ₃ may regulate matrix degradation and thereby modulate directed motility of SiHa cells.