Matrix metalloproteinases (MMPs) 2 are a family of zinc enzymes responsible for degradation of extracellular matrix components including basement membrane collagen, interstitial collagens, fibronectin (FN), and various proteoglycans during normal remodeling and repair processes (1, 2). The potent proteolytic activities of MMPs are mainly regulated by the concomitant expression of specific tissue inhibitors of matrix metalloproteinases (3). Excessive or inappropriate expression of MMPs may contribute to the pathogenesis of tissue destructive processes in a wide variety of diseases including lung disorders like bronchial asthma, chronic obstructive pulmonary disease, acute lung injury, pulmonary hypertension, and interstitial lung diseases (2, 4). In addition, MMPs have been implicated in the progression and metastases of different tumors including lung cancer (see later in text).One member of the MMP family is the 92-kDa type IV collagenase MMP-9. The MMP-9 gene is encoded on chromosome 20 and its expression is under the control of a 2.2-kb upstream regulatory sequence harboring binding sites for AP-1, NF-B, Sp1, and others (5). MMP-9 expression is increased in malignant cancers when compared with benign tumors and non-invasive ones, and there is compelling in vitro and in vivo evidence for a role of MMP-9 in tumor invasion and angiogenesis (6, 7). Its dramatic overexpression in cancer and various inflammatory conditions suggest that this protease is a potential target for the development of novel therapeutic interventions (8).Because of its perceived importance, our research focuses on the factors that increase MMP-9 expression in the lung. Our search led us to FN, a matrix glycoprotein highly expressed in tobacco-related lung disease that has been shown to stimulate lung carcinoma cell growth through several mechanisms (9 -11). Cell adhesion to FN results in MMP secretion in normal and tumor cell systems (12)(13)(14). These studies suggest that tumor cell interactions with FN might lead to MMP-9 expression thereby promoting cancer cell migration, invasion, and related processes. However, the mechanisms by which FN stim-* This work was supported by American Lung Association Bioresearch Grant RG-10215N (to S. W. H.) and by a Merit Review Grant from the Department of Veterans Affairs (to J. R.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C.