Purpose: Loss of sensitivity to transforming growth factor beta (TGF-beta) signaling typically occurs in human ovarian cancer cells, but there is paucity of information regarding this in human ovarian tumors. Thus the association of inactivating mutations and/or variations in expression levels of TGF-beta signaling components with human ovarian tumors was evaluated.
Methods: Forty human ovarian tissue samples were analyzed for mutations and/or variations in the expression of transforming growth factor beta signaling components. Mutation studies were done through reverse transcription (RT) PCR, single strand conformation polymorphism analysis and automated DNA sequencing. Expression studies were carried out by semi quantitative RT PCR and western blotting. DNA binding ability of Smad complexes and expression of downstream targets were also analyzed.
Results: The six alanine repeat containing variant of TGF-beta RI was seen in 27% of the tumor cases studied, in addition to the 45 bp nucleotide deletions in exon 1 of the receptor in two ovarian tumor samples. A deletion in the polyadenine tract of exon 3 of TGF-beta RII was seen in 22% of the tumor samples. We also report a loss or decrease in the expression of Smad 4 protein in tumor samples with a concurrent loss or reduced DNA binding ability of the Smad complex and deregulated expression of p21 and c-Myc.
Conclusions: Our results suggest that mutations and/or alterations in expression of TGF-beta receptors and loss of Smad 4 are frequent in human ovarian cancers and may potentially explain the frequent loss of TGF-beta responsiveness that typically occurs in human ovarian cancer.