ETS1 Associated Protein II (EAPII, also called TTRAP, TDP2) was originally identified by two-hybrid screening as a novel protein that interacts with both ETS1 and the cytoplasmic domain of CD40 receptor. EAPII may represent a novel component in signal transduction processes that regulates eukaryotic gene expression in response to extracellular signals. In support of this hypothesis, we have demonstrated that EAPII negatively modulates ETS1 transcriptional activity and attenuates synergistic transactivation by ETS1 and NFκB. However, the mechanism by which EAPII transduces signals is elusive. In this report, we provide the evidence of EAPII protein sumoylation in vivo. Sumoylation is an important posttranslational modification that involves conjugation of the small ubiquitin-like modifier (SUMO) to lysine residues of the targeting proteins. EAPII is sumoylated by both SUMO-1 and SUMO-2/3. Sumoylation analysis of cell fractions revealed that sumoylation by SUMO-2/3 mainly occurs in the nucleus while that by SUMO-1 in cytoplasm. Since EAPII protein possesses no SUMO consensus motif (≥KxE), we constructed a series of EAPII truncated mutations to determine the potential sumoylation site(s). Our data indicated that the noconsensus sumoylation site(s) may reside between amino acid residues 68 and 279. Interestingly, C-terminal deletion (Del 279-362) significantly increases the sumoylation, suggesting that the C-terminus might contain an inhibitory domain for EAPII sumoylation. It has been hypothesized that sumoylation may mediate extracellular signals in response to stresses, hypoxia and cytokines. Whether EAPII sumoylation interferes with its repressive activity on ETS1 transcription remains to be elucidated, and determination of the signaling pathways that may modulate EAPII sumoylation will provide a better understanding of the modulation of ETS1 functions in specific pathphysiological microenvironments.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2207. doi:1538-7445.AM2012-2207