Mouse keratinocytes immortalized with large T antigen acquire alpha 3 beta1 integrin-dependent secretion of MMP-9/gelatinase B

Remodeling of the extracellular matrix during tissue development, wound rep air and tumor cell invasion depends on the coordinated regulation of cell a dhesion receptors, matrix proteins and enzymes that proteolyse the extracel lular matrix. Integrin alpha 3 beta 1 is a major receptor on epidermal kera tinocytes for laminin-5 in the cutaneous basement membrane and is required for normal basement membrane organization during skin development. alpha 3 beta 1 is also expressed at high levels in the majority of adherent transfo rmed cells and in most tumors, and it could have similar roles in extracell ular matrix remodeling during tumorigenesis and cell invasion. In the prese nt study, we show that alpha 3 beta 1 expression is required in immortalize d mouse keratinocytes (MK) for the production of the matrix metallproteinas e MMP-9/gelatinase B, an MMP that is coexpressed with alpha 3 beta 1 in epi thelial cell carcinomas and during wound healing, and contributes to the in vasive potential of some tumor cells, MMP-9 was expressed in MK cells deriv ed from wild-type mice, but not in MK cells derived from alpha 3-null mice. Reconstitution of alpha 3 beta 1 expression in a3-null MK cells through tr ansfection with the alpha 3 subunit restored MMP-9 secretion, indicating an alpha 3 beta 1-dependent pathway for MMP-9 production. alpha 3 beta 1-depe ndent expression of MMP-9 was associated with the immortalized phenotype, s ince nonimmortalized, primary keratinocytes required soluble growth factors , but not alpha 3 beta 1, for efficient expression of MMP-9. Our results su ggest that an alpha 3 beta 1-independent pathway(s) for MMP-9 production is suppressed in keratinocytes immortalized with large T antigen, and that an alpha 3 beta 1-dependent pathway is required for sustained production of M MP-9 in the absence of other pathways.