A Transforming Growth Factor-β Receptor–Interacting Protein Frequently Mutated in Human Ovarian Cancer

Abstract

Ovarian carcinomas, particularly recurrent forms, are frequently resistant to transforming growth factor-B (TGF-B)-mediated growth inhibition. However, mutations in the TGF-B receptor I and receptor II (TbR-I and TbR-II) genes have only been reported in a minority of ovarian carcinomas, suggesting that alterations in TGF-B-signaling components may play an important role in the loss of TGF-B responsiveness. Using laser-capture microdissection and nested reverse-transcription-PCR, we found that km23, which interacts with the TGF-B receptor complex, is altered at a high frequency in human ovarian cancer patients. A novel form of km23, missing exon 3 (#exon3-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 (#107km23), 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-B resistance or tumor progression in this disease. In keeping with these findings, the functional studies described herein indicate that both the #exon3-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 #exon3-km23 resulted in an inhibition of TGF-B-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-B. (Cancer Res 2005; 65(15): 6526-33)

Identification of Tctex2β, a Novel Dynein Light Chain Family Member That Interacts with Different Transforming Growth Factor-β Receptors

“…However, because Tctex2␤ is a DLC, and DLCs are generally involved in signaling by mediating the transport of receptor signaling complexes in a retrograde fashion along the microtubules toward the nucleus, it is conceivable that Tctex2␤ operates downstream of endoglin. Our results seem to be contradictory to the up-regulation of TGF-␤ signaling by mLC7-1; however, the (CAGA) 12 -luciferase reporter becomes activated by the Smad3/Smad4 pathway, whereas p3TP-Lux reporter induction depends on an intact MAPK (mitogen-activated protein kinase) pathway (49). Thus, it is possible that the functions of Tctex2␤ in Smad and non-Smad signaling pathways are different.…”

“…Furthermore, TGF-␤ induces the recruitment of mLC7-1 to the dynein intermediate chain. In addition, it has been demonstrated that mLC7-1 is required for TGF-␤-induced activation of the p3TP-Lux promoter reporter (49).…”

Genetic and Epigenetic Analysis of the Putative Tumor Suppressor km23 in Primary Ovarian, Breast, and Colorectal Cancers

“…Km23 has not previously been investigated for somatic mutations in breast or colorectal cancers, but the absence of somatic genetic (or epigenetic mutations) in any of 104 ovarian cancers contradicts the frequency of 42.1% (8 of 19 cases) reported by Ding et al (1). This difference is extremely statistically significant (Fisher's exact test, P V 0.0001), and it seems unlikely that this could be due to chance sampling errors, particularly, as we had a good representation of the major histologic subtypes of ovarian cancer (49 serous, 18 mucinous, 29 endometrioid/clear cell, and 8 undifferentiated).…”

“…Furthermore, with the exception of TP53, the frequency of mutation is low and/or restricted to specific histologic subtypes of ovarian cancer. Recently, however, Ding et al (1) reported a very high frequency of somatic mutations in the transforming growth factor-h signaling component km23 (also known as DNLC2A) in ovarian cancer (42%). Functional studies showed that some of these mutations disrupt km23 function, which presumably results in aberrant transforming growth factor-h signaling and enhanced tumorigenicity.…”

Dysregulated TGFB Signaling in Ovarian Cancer

“…In an independent study, TGFRIII was notably decreased or absent in ovarian cancers at the RNA and protein levels (Hempel et al, 2007). Mutational analysis of TGFRI and TGFRII uncovered mutations in a minority of ovarian cancers (Ding et al, 2005). Specifically, a frameshift mutation has been identified in Exon 5 of TGFRI in 31% of ovarian tumors (Wang et al, 2000b), in exons 2, 3, 4, and 6 of TGFRI (catalytic domain of the kinase) in 33% primary ovarian cancers (Chen et al, 2001), and deletions in exon 1 of TGFRI in <30% of ovarian tumors (Antony et al, 2010).…”