TRANSFORMING GROWTH-FACTOR-BETA ACTIVATION IN IRRADIATED MARINE MAMMARY-GLAND

The biological activity of TGF-beta, an important modulator of cell pr oliferation and extracellular matrix formation, is governed by dissoci ation of mature TGF-beta from an inactive, latent TGF-beta complex in a process that is critical to its role in vivo. So far, it has not bee n possible to monitor activation in vivo since conventional immunohist ochemical detection does not accurately discriminate latent versus act ive TGF-beta, nor have events associated with activation been defined well enough to serve as in situ markers of this process. We describe h ere a modified immunodetection method using differential antibody stai ning that allows the specific detection of active versus latent TGF-be ta. Under these conditions, we report that an antibody raised to laten cy-associated peptide detects latent TGF-beta, and we demonstrate that LC(1-30) antibodies specifically recognize active TGF-beta 1 in tumor xenografts overproducing active TGF-beta 1, without cross-reactivity in tumors expressing similar levels of latent TGF-beta 1. We previousl y reported that TGF-beta immunoreactivity increases in murine mammary gland after whole-body Co-60-gamma radiation exposure. Using different ial antibody staining we now show that radiation exposure specifically generates active TGF-beta 1. While latent TGF-beta 1 was widely distr ibuted in unirradiated tissue, active TGF-beta 1 distribution was rest ricted. Active TGF-beta 1 increased significantly within 1 h of irradi ation concomitant with decreased latent TGF-beta immunoreactivity. Thi s rapid shift in immunoreactivity provides the first evidence for acti vation of TGF-beta in situ. This reciprocal pattern of expression pers isted for 3 d and was accompanied by decreased recovery of latent TGF- beta 1 from irradiated tissue. Radiation-induced activation of TGF-bet a may have profound implications for understanding tissue effects caus ed by radiation therapy.