Aberrant expression of Smad4 results in resistance against the growth-inhibitory effect of transforming growth factor-beta in the SiHa human cervicalcarcinoma cell line

Smad proteins activated by TGF-beta form complexes with Smad4. Upon activat ion, these complexes translocate to the nucleus of the cell, where they ind uce transcription of genes related to inhibition of cell growth, cell diffe rentiation and apoptosis. We investigated the role of Smads in the TGF-beta -mediated signal-transduction cascade in 4 human cervical cancer cell line s: HeLa, Caski, HT-3 and SiHa. Based on our results, SiHa cells show low mR NA expression of mutated Smad4 (Gly(230)Ala, Ala(488)Val) and of Smads 2, 3 , 5 and 6. SiHa cells were likewise defective in TGF-beta signaling, as evi denced by a lack of significant growth inhibition following TGF-beta treatm ent. In addition, TGF-beta did not induce transcription of the PAW gene or change Smad protein levels. Introduction of Smad3 and/or Smad4 into SiHa ce lls restored TGF-beta signaling, as determined by activation of the 3TP-lux reporter gene and by prominent apoptotic cell death with PAI-I induction. Analysis of the downstream targets activated by TGF-beta yielded rapid acti vation of p38 with subsequent phosphorylation of the transcription factor A TF-2 but unchanged SAPK/JNK activation in the 4 cervical cancer cell lines. Our findings demonstrate that (i) decrease of Smad4 mRNA expression is clo sely associated with defective TGF-beta response and lack of growth inhibit ion, (ii) activation of PAW by TGF-beta may be Smad4-dependent and (iii) th e Smad and the p38 cascades are triggered by TGF-beta independently of each other in human cervical cancer. (C) 2001 Wiley-Liss, Inc.