Expression and autoregulation of transforming growth factor beta receptor mRNA in small-cell lung cancer cell Lines

In small-cell lung cancer cell lines resistance to, (TGF)-beta(1), was previously shown to correlate with lack of TGF-beta receptor I (RT) and II (RII) proteins. To further investigate the role of these receptors, the expression of mRNA for RI, RII and beta-glycan (RIII) was examined. The results showed that loss of RII mRNA, correlated with TGF-beta(1) resistance. In contrast, RI- and beta-glycan mRNA was expressed by all cell lines, including those lacking expression of these proteins. According to Southern blot analysis, the loss of type II mRNA was not due to gross structural changes in the gene. The effect of TGF-beta(1) on expression of TGF-beta receptor mRNA (receptor autoregulation) was examined by quantitative Northern blotting in four cell lines with different expression of TGF-beta receptor proteins. In two cell lines expressing all three TGF-beta receptor proteins beta-glycan mRNA was rapidly down regulated and this effect was sustained throughout the 24 h observation period. RI and RII mRNAs were slightly increased 24 h after treatment. In one cell line sensitive to growth inhibition by TGF-beta(1), but lacking beta-glycan expression, and one cell line expressing only beta-glycan and thus TGF-beta(1)-resistant, no autoregulation of mRNA of either TGF-beta receptor was demonstrated. The results suggest that TGF-beta(1) regulates the expression of its receptors, in particular beta-glycan, and that tills effect is dependent on co-expression of beta-glycan, RI and RII.