No abstract

Pulmonary fibrosis is a well-known toxic response to bleomycin treatment. Here we demonstrate the direct effects of bleomycin on lung fibroblasts that resulted in a marked increase of collagen synthesis as compared with total noncollagen protein synthesis. Bleomycin treatment of rat lung fibroblast cultures resulted in an increase of total cellular transforming growth factor-beta (TGF-beta) mRNA and increased secretion of TGF-beta protein into the conditioned media. beta 2-Microglobulin was measured as an mRNA that did not increase with bleomycin treatment. The bleomycin-induced increase of TGF-beta mRNA was decreased by cells cultured in the presence of either cycloheximide, an inhibitor of protein synthesis, or 2-mercapto-1-(beta-4-pyridethyl) benzimidazole, an inhibitor of RNA synthesis. To assess the mechanism underlying increased steady-state mRNA levels, the nuclear fraction was isolated from bleomycin-treated cells and the TGF-beta transcripts were determined. Transcription of TGF-beta mRNA was increased 12 h after bleomycin treatment, whereas the transcription of type I procollagen, type III procollagen, and beta-actin mRNAs were increased after 48 h of bleomycin treatment. beta 2-Microglobulin mRNA synthesis was not increased within this time frame. These results suggest bleomycin regulation of TGF-beta at both the mRNA and protein levels. Rats lung fibroblasts were separated by cell sorting into two subpopulations. One population of fibroblasts demonstrated increased procollagen type I mRNAs, whereas fibroblasts in the other population had increased procollagen type III mRNA. Following bleomycin treatment, TGF-beta mRNA was shown to be located more prominently in those fibroblasts that contain primarily collagen type I mRNAs.

Transforming growth factor-beta (TGF-beta) is a ubiquitous growth-regulating protein that is capable of influencing the growth and function of heart cells in vitro. To better understand the role TGF-beta might play as a paracrine mediator of cardiac hypertrophy, the expression, secretion, and growth effects of TGF-beta were examined. Neonatal cardiac fibroblasts in vitro secreted latent TGF-beta 1 and TGF-beta 2 as high as 15 ng/10(6) cells. Angiotensin II (ANG II) and norepinephrine (NE) each augmented up to threefold the expression and secretion of latent TGF-beta 1 and TGF-beta 2 and also induced a shift in isoform predominance from beta 1 to beta 2. Each agent individually produced hypertrophic growth of neonatal cardiocytes and hyperplastic growth of cardiac fibroblasts. Paradoxically, the combination of NE and ANG II at intermediate and high concentrations resulted in less TGF-beta secretion (compared with either agent alone) and in hypertrophic growth of fibroblasts. These results suggest that the growth-promoting effects of ANG II and NE may in part be mediated via a paracrine stimulation of TGF-beta secretion.

We report here that the antiestrogen tamoxifen (TAM) induces cell death in human breast cancer cell line MCF-7. We assessed the type of cell death induced by TAM in this breast cancer cell line on the basis of morphological and biochemical characteristics. Dying cells showed morphological characteristics of apoptosis, such as chromatin condensation and nuclear disintegration. DNA isolated from these cells revealed a pattern of distinctive DNA bands on agarose gel. The DNA fragmentation in MCF-7 cells induced by TAM could also be detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin end labeling. Northern blot hybridization revealed a substantial increase in the amounts of TRPM-2 and TGF-beta 1 mRNAs in MCF-7 cells after treatment with TAM. In contrast, the mRNA level of the estrogen-induced pS2 gene was strongly suppressed. The biological activity of TGF-beta was increased at least fourfold in the media from MCF-7 cells treated with TAM. The results presented in this study suggest that TAM induces apoptosis of MCF-7 cells and it may be mediated by the secretion of active TGF-beta.