ABROGATION OF LUNG METASTASIS OF HUMAN FIBROSARCOMA CELLS BY RIBOZYME-MEDIATED SUPPRESSION OF INTEGRIN ALPHA-6 SUBUNIT EXPRESSION

The interaction of tumor cells with the basement membrane plays a cruc ial role in tumor metastasis. VLA-6 (alpha 6 beta 1) integrin is one o f the major surface receptors for the basement membrane, specifically recognizing laminin. To study the role of VLA-6 integrin in tumor inva sion and metastasis, we synthesized a ribozyme that selectively degrad es the integrin alpha 6 subunit mRNA. The catalytic activity of the ri bozyme was verified by in vitro cleavage of cub subunit mRNA. Introduc tion of the anti-alpha 6 ribozyme gene into the human fibrosarcoma cel l line HT 1080 yielded stable transfectants, which expressed a signifi cantly reduced level of integrin alpha 6 mRNA. Flow cytometric analysi s showed that the surface expression of VLA-6, but not other integrins , was reduced by approximately 70% in transfected cells. Ribozyme-tran sfected cells were less adherent to laminin-coated substrata and less invasive into reconstituted basement membrane than mock-transfected ce lls. When injected i.v. into nude mice, ribozyme-transfected cells pro duced no lung metastasis in all except 1 of 35 mice, though mock-trans fected cells produced multiple lung metastases in 22 of 29 mice. Our r esults indicate that VLA-6 integrin plays a critical role in tumor inv asion and metastasis and may serve as a potential target for eradicati on of tumor metastasis in the lung. (C) 1996 Wiley-Liss, Inc.