CELL-SPECIFIC EXPRESSION OF THE ALPHA-1(I) COLLAGEN PROMOTER CAT TRANSGENE IN SKIN AND LUNG - A RESPONSE TO TGF-BETA SUBCUTANEOUS INJECTIONAND BLEOMYCIN ENDOTRACHEAL INSTILLATION

Transgenic mice containing a rat collagen alpha 1(l) promoter (3.6 kil obases) fused to the reporter gene chloramphenicol acetyl transferase (CAT) express the reporter gene parallel to endogenous gene in most co nnective tissues other than vascular tissue [Pavlin et al. (1992): J C ell Biol 116:227-236; Bedalov et al. (1994): J Biol Chem 269:4903-4909 ]. We have challenged transgenic mice with subcutaneous injections of transforming growth factor-beta (TGF-beta) or intratracheal instillati on of bleomycin. In situ hybridization studies of skin revealed increa sed CAT expression in the papillary dermis of TGF-beta treated animals . In contrast, alpha 1(l) collagen mRNA was expressed throughout the d ermis including granulation tissue and reticular dermis. Therefore, th e transgenic promoter responds to TGF-beta in a subset of dermal fibro blasts. Endotracheal instillation of bleomycin induces lung fibrosis w hich is thought to be mediated in part by TGF-beta. CAT gene expressio n in lungs was increased 6-8-fold at 2 weeks post bleomycin treatment. In situ hybridization studies revealed focal areas of cells expressin g both CAT and collagen genes in the interstitium. However, most regio ns, especially around airways, contained a subset of cells expressing the endogenous gene with little or no CAT expression as judged by in s itu hybridization. These cells could be myofibroblasts that require ad ditional cis-acting elements to activate alpha 1(l) collagen gene expr ession similar to smooth muscle cells. (C) 1996 Wiley-Liss, Inc.