Oncogenic Serine-Threonine Kinase Receptor-Associated Protein Modulates the Function of Ewing Sarcoma Protein through a Novel Mechanism

Abstract

Although much is known about the oncogenic functions of chimeric Ewing sarcoma (EWS) fusion proteins that result from chromosomal translocations, the cellular role of the normal EWS protein is not well characterized. We have previously identified a WD domain-containing protein, serine-threonine kinase receptor-associated protein (STRAP), which inhibits transforming growth factor B (TGF-B) signaling through interaction with receptors and Smad7 and promotes growth and enhances tumorigenicity. Here, we report the interaction between STRAP and EWS using matrix-assisted laser desorption/ionization, time-of-flight and tandem mass spectrometry. Although STRAP is localized in both cytoplasm and nucleus, nuclear STRAP colocalizes and associates specifically with EWS in the nucleus through its NH 2 and COOH termini. We have found that normal EWS protein is upregulated in human cancers, which correlates with the upregulation of STRAP in 71% of colorectal cancers and 54% of lung cancers, suggesting a cooperative role of these two proteins in human cancers. TGF-B has no effect on STRAP and EWS interaction. However, EWS, like STRAP, attenuates TGF-B-dependent transcription. STRAP inhibits EWS-dependent p300-mediated transactivation of EWS target genes, such as ApoCIII and c-fos, in a TGF-B-independent manner. Interestingly, we have shown that STRAP blocks the interaction between EWS and p300, whereas the complex formation between STRAP and EWS is not affected by p300. These results suggest that STRAP inhibits the transactivation function of EWS by displacing p300 from the functional transcriptional complex. Thus, this study provides a novel TGF-B-independent function of STRAP and describes a mechanism by which STRAP regulates the function of oncogenic EWS protein.

NM23-H1 Tumor Suppressor and Its Interacting Partner STRAP Activate p53 Function

“…Moreover, our studies provide evidence as to how the NM23-H1 tumor suppressor cooperates with the p53 tumor suppressor to mediate its suppressive effect on tumor progression. We also demonstrate that, in addition to its proposed oncogenic function (27), STRAP can exert a tumor suppressor effect by activating the function of p53.…”

“…Recent studies also suggest that STRAP might be involved in tumorigenesis and development (26,27). We have recently reported that STRAP-induced inhibition of TGF-␤ signaling was enhanced by direct interaction with the NM23-H1 tumor suppressor, suggesting a possible link between TGF-␤-and NM23-H1-mediated signaling pathways (28).…”

Domain Architecture and Biochemical Characterization of Vertebrate Mcm10

“…Proteolytic fragments from MBP-xMcm10-His 6 were excised from the SDS-PAGE gel and subjected to in-gel digestion with Trypsin Gold (Promega) using standard procedures (32). The resulting peptides were analyzed by matrix-assisted laser desorption/ionization, time-of-flight mass spectrometry (MALDI-TOF MS) and TOF/TOF tandem MS using a Voyager 4700 (Applied Biosciences, Framingham MA).…”

Regulating the stability of TGFβ receptors and Smads

“…Finally, in addition to these Ub ligases, adaptor proteins like STRAP, the stabilizer of Smad7-TGFb receptor complexes, can also be misexpressed in human colon and lung cancers [97]. The oncogenic role of STRAP though, in addition to acting as a TGFb receptor inhibitor, can be due to its ability to interact with nuclear oncogenes like the Ewing sarcoma (EWS) oncoprotein [98].…”