NOTCH1-driven UBR7 stimulates nucleotide biosynthesis to promote T cell acute lymphoblastic leukemia

Abstract

Ubiquitin protein ligase E3 component N-recognin 7 (UBR7) is the most divergent member of UBR box–containing E3 ubiquitin ligases/recognins that mediate the proteasomal degradation of its substrates through the N-end rule. Here, we used a proteomic approach and found phosphoribosyl pyrophosphate synthetases (PRPSs), the essential enzymes for nucleotide biosynthesis, as strong interacting partners of UBR7. UBR7 stabilizes PRPS catalytic subunits by mediating the polyubiquitination-directed degradation of PRPS-associated protein (PRPSAP), the negative regulator of PRPS. Loss of UBR7 leads to nucleotide biosynthesis defects. We define UBR7 as a transcriptional target of NOTCH1 and show that UBR7 is overexpressed in NOTCH1-driven T cell acute lymphoblastic leukemia (T-ALL). Impaired nucleotide biosynthesis caused by UBR7 depletion was concomitant with the attenuated cell proliferation and oncogenic potential of T-ALL. Collectively, these results establish UBR7 as a critical regulator of nucleotide metabolism through the regulation of the PRPS enzyme complex and uncover a metabolic vulnerability in NOTCH1-driven T-ALL.

UBR7 acts as a histone chaperone for post‐nucleosomal histone H3

“…Generation of UBR7KO1 293T clonal cells using UBR7-sgRNA2 (Table EV2) was previously described (Srivastava et al, 2021).…”

“…UBR7-LAP and various truncation mutants were created using gateway cloning into the LAP tag vector (Addgene #67618) containing eGFP and S-tag. UBR7-FLAG and various truncation mutants were previously described (Srivastava et al, 2021). To generate UBR7-3xFLAG (UBR7-FL), UBR7 and 3xFLAG sequences were PCR amplified from UBR7 and 3xFLAG expression constructs using primers UBR7-FL-Fwd1/UBR7-FL-Rev1 (UBR7) and UBR7-FL-Fwd2/UBR7-FL-Rev2 (3xFLAG) (Table EV2).…”

“…Anti-GFP and anti-HA antibodies were used for immunoblotting (Table EV3). Purification of FLAG-tagged full-length and mutant UBR7-FLAG constructs in cells co-transfected with H3.1-HA was performed as described previously (Srivastava et al, 2021). The indicated antibodies were used for immunoblotting (Table EV3).…”

Notch Partners in the Long Journey of T-ALL Pathogenesis

“…The regulation of cellular metabolism by NOTCH has emerged in recent years as an exciting area of research. Although still quite unexplored, strong evidence supports the idea that NOTCH1 signaling promotes T-ALL growth by inducing the activation of anabolic pathways, including glycolysis, glutaminolysis, nucleotide biosynthesis, amino acids metabolism, ribosome biogenesis and protein activation [ 105 , 176 , 177 , 178 ]. On the contrary, NOTCH1 signaling inactivation switches metabolism to catabolic pathways, i.e., increased autophagy, ubiquitination and proteasomal degradation, and reduction in glycolytic and glutaminolytic flux [ 105 ].…”

“…To date, the best-known metabolic routes cooperating with oncogenic NOTCH1 signaling are MYC, PI3K/AKT, and RAS, and they will be discussed below. In addition, very recent studies have uncovered novel players involved in the metabolic reprogramming caused by aberrant NOTCH1 signals, such as the oxidative phosphorylation regulator mitochondrial complex I inhibitor [ 178 ] and the nucleotide biosynthesis regulator ubiquitin protein ligase E3 component N-recognin 7 (UBR7) [ 177 ]. Given that metabolic reprogramming is an essential mechanism of cancer cell outgrowth and dissemination [ 179 ], understanding the multiple levels of interconnections between NOTCH1 and metabolic pathways may help to delineate novel strategies to tackle exacerbated metabolic demand in T-ALL.…”