Differential activation of Smads in HeLa and SiHa cells that differ in their response to transforming growth factor-β

We assessed the responsiveness of six human cervical cancer cell lines to transforming growth factor (TGF)-beta with p3TP-lux reporter assay and found that HeLa and SiHa cells were highly responsive to TGF-beta. However, when pSBE4-BV/Luc reporter with four Smad binding elements was used, only the SiHa, not the HeLa, cells showed Smad activation. Smad DNA binding activity was relatively more in SiHa than in HeLa cells upon TGF-beta treatment, and the active complex contained Smad 2 and Smad 4. In 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays, HeLa cells treated with 5 ng/ml of TGF-beta for 24 h showed proliferation, whereas SiHa cells showed growth inhibition under the same conditions. TGF-beta treatment resulted in G(0)/G(1) arrest with a reduction in S-phase only in SiHa cells. A chemical inhibitor of Smad activation (SB203580) blocked the growth inhibitory effect of TGF-beta in SiHa, whereas the proliferative response in HeLa was unaffected. TGF-beta-induced translocation of phospho-Smad 2 was relatively less in HeLa than in SiHa cells. MAPK activation occurred within 5 min and persisted up to 15 min upon TGF-beta treatment in HeLa but was negligible in SiHa cells. TGF-beta activated JNK in HeLa, but SiHa cells showed a down-regulation of its activity. When an inhibitor of MAPK (U0126) was used, the TGF-beta-mediated proliferative response in HeLa cells was completely abolished. SB203580 did not affect MAPK activation induced by TGF-beta in HeLa cells. We report for the first time an activation, presumably independent of Smad activation, of TGF-beta-dependent MAPK within 5 min of treatment that resulted in cell cycle progression in a cervical adenocarcinoma cell line.