PHENOTYPIC ALTERATIONS IN FIBROBLASTS AND FIBROSARCOMA CELLS THAT OVEREXPRESS LATENT TRANSFORMING GROWTH FACTOR-B-BETA

Mouse embryo-derived AKR-2B fibroblasts and murine fibrosarcoma cells (the 1591 cell line) were transfected with a murine transforming growth factor-beta-1 (TGF-beta-1) cDNA under the transcriptional control of either the simian virus-40 early promoter or the cytomegalovirus promoter/enhancer. Selected clones secreted 2- to 4-fold more TGF-beta-competing activity into their media than the parental cell line or neomycin-transfected controls. The TGF-beta-1 released into the cell-conditioned medium was latent. Despite the latency of the overexpressed TGF-beta-1, the TGF-beta-1-transfected cells exhibited phenotypic features of TGF-beta-1-treated cells. When confluent, the TGF-beta-1-transfected cells had the morphological characteristics of the parental cells that have been treated with active TGF-beta-1. AKR-2B cells that expressed higher levels of TGF-beta-1 also expressed high levels of c-sis and c-myc mRNAs and decreased TGF-beta-2 and TGF-beta-3 mRNAs in the same manner as parental AKR-2B cells that had been treated with active TGF-beta-1. The transfected 1591 cells that overexpressed TGF-beta-1 bound less [I-125]TGF-beta-1 than did parental 1591 cells, but after a mild acid wash demonstrated an increase in [I-125]TGF-beta-1 binding. Our results suggest that these TGF-beta-1-transfected fibroblast and fibrosarcoma cells have the capacity to activate TGF-beta; however, as very little activated TGF-beta is detected in the medium, it is hypothesized that these cells activate latent TGF-beta-1 and bind the activated TGF-beta-1, thus acquiring a phenotype consistent with TGF-beta-1 -treated cells.