Ovarian carcinomas, particularly recurrent forms, are frequently resistant to transforming growth factor-β (TGF-β)-mediated growth inhibition. However, mutations in the TGF-β receptor I and receptor II (TβR-I and TβR-II) genes have only been reported in a minority of ovarian carcinomas, suggesting that alterations in TGF-β-signaling components may play an important role in the loss of TGF-β responsiveness. Using laser-capture microdissection and nested reverse-transcription-PCR, we found that km23, which interacts with the TGF-β receptor complex, is altered at a high frequency in human ovarian cancer patients. A novel form of km23, missing exon 3 (Δexon3-km23), was found in 2 of 19 tumor tissues from patients with ovarian cancer. In addition to this alteration, a stop codon mutation (TAA → CAC) was detected in two patients. This alteration results in an elongated protein, encoding 107-amino-acid residues (Δl07km23), instead of the wild-type 96-amino-acid form of km23. Furthermore, five missense mutations (T38I, S55G, T56S, I89V, and V90A) were detected in four patients, providing a total alteration rate of 42.1% (8 of 19 cases) in ovarian cancer. No km23 alterations were detected in 15 normal tissues. Such a high alteration rate in ovarian cancer suggests that km23 may play an important role in either TGF-β resistance or tumor progression in this disease. In keeping with these findings, the functional studies described herein indicate that both the Δexon3-km23 and S55G/I89V-km23 mutants displayed a disruption in binding to the dynein intermediate chain in vivo, suggesting a defect in cargo recruitment to the dynein motor complex. In addition, the Δexon3-km23 resulted in an inhibition of TGF-β-dependent transcriptional activation of both the p3TP-lux and activin responsive element reporters. Collectively, our results suggest that km23 alterations found in ovarian cancer patients result in altered dynein motor complex formation and/or aberrant transcriptional regulation by TGF-β.
All Science Journal Classification (ASJC) codes
- Cancer Research