Posttranslational modification of TEL and TEL/AML1 by SUMO-1 and cell-cycle-dependent assembly into nuclear bodies

Abstract

The E-26 transforming specific (ETS)-related gene, TEL, also known as ETV6, encodes a strong transcription repressor that is rearranged in several recurring chromosomal rearrangements associated with leukemia and congenital fibrosarcoma. TEL is a nuclear phosphoprotein that is widely expressed in all normal tissues. TEL contains a DNA-binding domain at the C terminus and a helixloop-helix domain (also called a pointed domain) at the N terminus. The pointed domain is necessary for homotypic dimerization and for interaction with the ubiquitin-conjugating enzyme UBC9. Here we show that the interaction with UBC9 leads to modification of TEL by conjugating it to SUMO-1. The SUMO-1-modified TEL localizes to cell-cycle-specific nuclear speckles that we named TEL bodies. We also show that the leukemia-associated fusion protein TEL͞AML1 is modified by SUMO-1 and found in the TEL bodies, in a pattern quite different from what we observe and report for AML1. Therefore, SUMO-1 modification of TEL could be a critical signal necessary for normal functioning of the protein. In addition, the modification by SUMO-1 of TEL͞AML1 could lead to abnormal localization of the fusion protein, which could have consequences that include contribution to neoplastic transformation. P osttranslational modifications of proteins are important signaling mechanisms during cell cycle, cell development, and cell differentiation. The ubiquitin system is one of the major protein-modification systems required for the highly selective turnover of specific proteins in eukaryotic cells (1). Ubiquitin conjugation involves a protein complex that includes the E1, E2, and E3 enzymes, and it results in formation of an isopeptidic bond between the C terminus of ubiquitin and the -amino group of a lysine in the target protein, leading to degradation of the protein through the 26S proteosome pathway. Eukaryotic cells also express a group of ubiquitin-like proteins, such as SUMO-1 (also known as PIC-1 or UBL1) and RUB-1 (2, 3), that are conjugated to the target protein by an isopeptidic bond similar to that of the ubiquitin system. In contrast to ubiquitination, however, the covalent attachment of ubiquitin-like proteins does not lead to protein degradation. Recently, it was shown that UBC9, a homologue of the E2 enzyme, conjugates SUMO-1 to the target protein (4). Only a few SUMO-1 target proteins have been identified, including PML and SP100, which when modified by SUMO-1 are found in the PML bodies, RanGAP1, IkB␣, HIPK2, and p53 (5-8). The exact function of SUMO-1 modification is not known. In some cases (IkB␣ and p53), it was shown that conjugation of SUMO-1 could lead to protein stabilization and protection from degradation, but in other cases (PML, SP100, RanGAP1, and HIPK2), SUMO-1 conjugation could lead to different subcellular localization of the modified protein (5-8).The TEL gene is also known as ETV6. TEL was originally cloned as one of the two genes rearranged in a t(5;12) chromosomal translocation associated with chronic myelomonocytic leukemia. Thi...

Regulation of the Ets-1 transcription factor by sumoylation and ubiquitinylation

“…SUMO modification appears to play a role in a variety of cellular processes including protein-protein interaction, subcellular localization, protein stabilization and transcriptional regulation (Dohmen, 2004). A large number of SUMO target proteins have been identified, including several members of the Ets transcription factors family (Chakrabarti et al, 2000;Yang et al, 2003;Degerny et al, 2005;Leight et al, 2005;van den Akker et al, 2005;Wasylyk et al, 2005). Recently, we reported that the ERM Ets protein is sumoylated and that sumoylation of ERM represses its transcriptional activity (Degerny et al, 2005).…”

SUMO modification is required for in vivo Hox gene regulation by the Caenorhabditis elegans Polycomb group protein SOP-2

“…The SAM domain of PcG proteins mediates the interaction with UBC-9, leading to sumoylation, and directs the formation of subnuclear bodies whose characteristics are correlated with physiological function. Sumoylation itself has a variety of effects on its targets in cultured cells, including regulating the subnuclear localization of PML, HIPK2 and TEL [14][15][16] and modulating the transactivational activity of Sp3 and LEF1 (refs. 6,17).…”

“…Thus, intrinsic properties of the SAM domain may regulate the characteristics of nuclear body formation. The preferential sumoylation site in TEL, Lys99, is located within the SAM domain 14 , whereas the SAM domains of SOP-2 and PcG proteins lack the corresponding lysine residue and the sumoylated sites in SOP-2 seem to be outside the SAM domain (data not shown). To determine whether the distinct nuclear bodies formed in SOP-2(TEL SAM)::GFP were due to this sumoylation site, we mutated the TEL Lys99 to arginine within the chimeric construct.…”

“…Phylogenetic analysis indicates that the SAM domain of SOP-2 belongs to a new nematode-specific SAM domain subfamily, which also includes the SAM domain of K04C1.2 and is more closely related to the SAM/PNT than to the SPM subfamiliy 3 . Nonetheless, the crystal structure shows that the SAM domains of PH and TEL form identical head-to-tail, left-handed helical polymers 12,13 , and the SAM domain of TEL is also required for its binding to UBC-9 and localization to nuclear bodies 14 . To correlate the functional properties of these SAM domains with their effects on nuclear localization, we undertook a series of domain-swapping experiments.…”

Nicotine coregulates multiple pathways involved in protein modification/degradation in rat brain

“…SUMO-1 modulates the interaction of the target protein with other cellular proteins and often results in changing the protein's location [9,27,43]. For example, a SUMO-attached protein may be transported to the nucleus [27,39].…”