Publications

Gelatinase A, also denoted matrix metalloproteinase 2, plays multiple critical roles in the neoplastic process, including facilitation of neoangiogenesis and formation of distal metastases. The transcriptional regulation of the gelatinase A gene is under the control of strong, evolutionarily conserved cis-acting enhancer elements, designated the r2 (human) or RE-1 (rat), that harbor contiguous binding motifs for the transcription factors activating protein-2 (AP2), p53, and YB-1. Using recombinant transcription factors, complex patterns of RE-1 binding were observed by electrophoretic mobility shift assay. Increased complex formation was detected with the AP2/YB-1 and AP2/p53 combinations, while YB-1 competed with p53 for binding. The combination of AP2, p53, and YB-1 yielded novel ternary complexes, particularly when binding to single-stranded RE-1 probes. Transient transfection of hepatocellular carcinoma cell lines with a series of gelatinase A luciferase reporter constructs were in accordance with the binding patterns determined by electrophoretic mobility shift assay. Combined AP2 and p53 increased gelatinase A luciferase reporter activity significantly, and the inclusion of YB-1 yielded further increase in both reporter activity and secreted levels of gelatinase A protein. YB-1 and p53 expression are increased following multiple genotoxic stresses, including irradiation, and the synergistic interactions of these induced transcription factors with the widely expressed AP2 protein provide a probable pathophysiologic mechanism for the enhanced tumor cell synthesis of gelatinase A induced by radiation.

Integrins, matrix metalloproteases (MMPs), and the cytokine TGF-beta have each been implicated in homeostatic cell behaviors such as cell growth and matrix remodeling. TGF-beta exists mainly in a latent state, and a major point of homeostatic control is the activation of TGF-beta. Because the latent domain of TGF-beta1 possesses an integrin binding motif (RGD), integrins have the potential to sequester latent TGF-beta (SLC) to the cell surface where TGF-beta activation could be locally controlled. Here, we show that SLC binds to alpha(v)beta8, an integrin expressed by normal epithelial and neuronal cells in vivo. This binding results in the membrane type 1 (MT1)-MMP-dependent release of active TGF-beta, which leads to autocrine and paracrine effects on cell growth and matrix production. These data elucidate a novel mechanism of cellular homeostasis achieved through the coordination of the activities of members of three major gene families involved in cell-matrix interactions.