The E3 ubiquitin-protein ligase Triad1 inhibits clonogenic growth of primary myeloid progenitor cells

Abstract

IntroductionGranulocytes and monocytes develop from common myeloid progenitor cells through a complex network of cell growth, differentiation, and apoptosis-regulating factors. Alterations in these processes may cause acute myeloid leukemia, which is characterized by uncontrolled proliferation of immature myeloid cells that fail to differentiate toward mature functional cells. 1,2 In leukemia, mutations occur in genes encoding tyrosine kinases such as Fms-like tyrosine kinase 3 (Flt3), c-kit, neuroblastoma ras (N-ras) and transcription factors such as AML1 (acute myeloid leukemia 1), CBFB (core binding factor ␤), GATA1 (GATA binding protein 1), PU.1, C/EBP␣ (CCAAT/enhancer binding protein ␣), and RAR␣ (retinoic acid receptor ␣). 1,2 Although the transcription factors predominantly play a role in lineage commitment, activation of tyrosine kinases is thought to result in proliferative and/or survival signals. 1,2 Recent studies have shown that several proteins involved in myelopoiesis (including proteins mutated in leukemia) are inactivated through ubiquitin (Ub)-proteasomal degradation pathways. [3][4][5][6][7] This form of targeted protein degradation is accomplished by the covalent conjugation of Ub to substrate proteins, usually in the form of a multi-Ub chain, which marks these proteins for progressive degradation by the 26S proteasome. 8,9 Protein ubiquitination is catalyzed through a cascade of reactions. Ub is first activated by the adenosine triphosphate (ATP)-dependent Ub-activating E1 enzyme and subsequently transferred to one of a set of E2 Ub-conjugating enzymes. The E2 enzymes act in conjunction with accessory E3 Ub protein ligases. In the E2-E3 complex, the E3 component binds to protein substrates, allowing the E2 to form a multi-Ub chain linked to a lysine of the substrate protein. 8,9 Thus, the E3 Ub ligases play a crucial role in this process because these proteins recognize the cellular proteins destined for ubiquitination. 10 To date, several types of E3 Ub ligases have been described. These include HECT (homologous to E6-AP carboxyl terminus), RING (really interesting new gene) finger, U-box, SOCS (suppressor of cytokine signaling)-box, F-box, and cullin ligases. [11][12][13][14][15][16][17][18][19][20] Although the first 3 types of proteins are actively involved in substrate ubiquitination, the last 3 do not ubiquitinate substrate proteins themselves but are part of larger protein complexes that exhibit Ub ligase activity. [15][16][17][18][19] From the Central Hematology Laboratory, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands; the Department of Hematology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands; the Institute of Hematology, Erasmus University Medical Center Rotterdam, The Netherlands. The online version of the article contains a data supplement.Reprints: Bert A. van der Reijden, Central Hematology Laboratory, University Medical Center Nijmegen, PO BOX 9101, 6500 HB Nijmegen, The Netherlands; e-mail: b.vanderreijden@chl.umcn.nl.The publi...

High BRE expression predicts favorable outcome in adult acute myeloid leukemia, in particular among MLL-AF9–positive patients

“…18,20 BRE QPCR and MLL-AF9 fusion gene detection BRE expression was measured by QPCR on cDNA samples using a commercially available primer/probe set (Applied Biosystems; Hs01046283_m1), and data were normalized by PBGD or ␤-ACTIN quantitative PCR (QPCR). 22 MLL-AF9 breakpoint PCR on the cohort of 525 patients was performed as described previously. 23,24 For the validation cohort, conventional chromosome banding and FISH for MLL-AF9 translocations were performed as previously described.…”

HoxA10 Influences Protein Ubiquitination by Activating Transcription of ARIH2, the Gene Encoding Triad1

“…Co-overexpression of Triad1 and UbcH7 increases total protein ubiquitination in myeloid progenitor cells or myeloid cell lines, but genuine Triad1/UbcH7 substrate proteins have not been identified (20). Although Triad1 is ubiquitously expressed, expression increases during myelopoiesis and is greatest in mature neutrophils (19). Other investigators found that engineered overexpression of Triad1 in myeloid progenitor cells results in decreased colony formation (19).…”

“…The E3 ligase attaches ubiquitin to the substrate, thereby tagging the substrate for proteasomemediated degradation. Previous studies determined that Triad1 interacts functionally with several E2 ligases, including Ubch7 and Ubc13 (19,20). Co-overexpression of Triad1 and UbcH7 increases total protein ubiquitination in myeloid progenitor cells or myeloid cell lines, but genuine Triad1/UbcH7 substrate proteins have not been identified (20).…”

“…In the current study, we report that HoxA10 activates ARIH2 transcription. This gene encodes Triad1, an E3 ubiquitin ligase (also referred to as ariadne-like 2) (18,19).…”

Ubiquitylation in normal and malignant hematopoiesis: novel therapeutic targets

“…35 Another member of the TRIAD family of E3 ligases, Triad3, was shown to catalyze the ubiquitylation of the Toll-like receptors TLR4 and 9. This results in the proteasomal degradation of these receptors.…”