Endocrine Abstracts

Transforming growth factor-beta (TGF-beta)is present, predominantly in latent forms, in normal and malignant breast tissue. The mechanisms by which TGF-beta is activated physiologically remain largely an enigma. The aim of this study was to assess whether the proteases, cathepsin D and PSA could activate latent TGF-beta 1 and 2 in the MCF-7 hormone responsive and MDA-MB-231 hormone unresponsive human breast cancer cell lines. For the experiments, 1 x 10⁶cells were seeded in 6-well plates and grown in supplemented Dulbecco's modified eagle's medium in 5% CO₂ at 37 degC for 24 hours. The media was then discarded and the cells were treated, in triplicate, with varying concentrations of cathepsin D and PSA in RPMI 1640 (without phenol red) containing 5% charcoal-dextran-stripped foetal bovine serum and 2 mM L-glutamine. Active TGF-beta 1 and 2 were then measured in the media by ELISA after 4, 8, 24 and 72 hours of treatment. TGF-beta 1 and 2 mRNA was measured in the cells by RT-PCR to determine whether any increase in levels of active TGF-beta 1 and 2 was due to increased production. There was a significant increase in only active TGF-beta 2 levels in the MDA-MB-231 cell line with both treatments. Cathepsin D and PSA did not have any effect on TGF-beta 1 and 2 mRNA expression. In conclusion, cathepsin D and PSA were unable to activate latent TGF-beta 1 and 2 in these cell lines. A constant level of TGF-beta 2 mRNA in the control and treated MDA-MB-231 cells suggests that the increase in active TGF-beta 2 levels in the MDA-MB-231 cell line was not due to increased production but was likely to be due to activation independent of cathepsin D and PSA.