The expression and secretion of different isoforms of transforming growth factor-β
(TGFβ) were examined in cultured transformed and nontransformed human retinal pigment
epithelial (RPE) cells. Transformed RPE cells were found to express high levels of
TGFβ1 mRNA, low levels of TGFβ3 mRNA but no detectable TGFβ2 mRNA. If the cells were
grown under serum-free conditions the expression of TGFβ increased. The mRNA expression
was accompanied by secretion of TGFβ1 (but not TGFβ2) protein into the culture media.
By comparison, nontransformed RPE cells were found to secrete similar amounts of TGFβ
as transformed cells but predominantly secreted TGFβ2. The secretion of TGFβ from
both transformed and nontransformed RPE cells increased if the cells were grown without
serum. In conclusion, the results show that TGFβ is expressed and secreted by transformed
and nontransformed human RPE cells and that this expression and secretion are regulated
by the presence or absence of exogenous factors.