L-428 nodular sclerosing Hodgkin's cell secretes a unique transforming growth factor-beta active at physiologic pH

Nodular sclerosing Hodgkin's disease is characterized by dense collagen fibrosis. Although transforming growth factor-beta (TGF-beta) is an important bifunctional growth factor for fibroblasts and is stored and released by many cells, it requires acidification to pH 2.0-3.0 before it becomes a biologically active growth factor. We show here that the L-428 Hodgkin's cell releases a high molecular weight TGF that competes for the TGF-beta cell membrane receptor but not the TGF-alpha receptor. This growth factor is most active at physiologic pH and is 97% inactivated by acidification. Hodgkin's TGF is also inactivated by proteases and can be preserved by protease inhibitors. The Hodgkin's TGF can be separated from an autocrine growth factor using either column chromatography or electroelution from gels and is shown to have a molecular weight of approximately 350,000. Incubation of the Hodgkin's TGF in SDS releases a 25,000-D protein with reduced biological activity but which cross-reacts with anti-TGF-beta IgG. We propose that L-428 nodular sclerosing Hodgkin's disease fibrosis is mediated by a potent high molecular weight TGF-beta which, unlike TGF-beta characterized to date, is secreted in a form most active at physiologic pH.