Chua, B. H. | bioRxiv Science

bioRxiv2025

The TARZN complex binds de novo enhancer mutations and promotes oncogenic expression in T-ALL

TAL1 is overexpressed in 40-60% of T-cell acute lymphoblastic leukemia (T-ALL) cases and forms an oncogenic core regulatory circuit (CRC) with other transcription factors such as LMO1, LMO2 and GATA3. In 5% of T-ALL cases an insertion of a consensus GT dinucleotide (MuTE) is observed upstream of the TAL1 gene, driving TAL1 overexpression. Using an in vitro reconstitution DNA pull-down assay combined with quantitative mass spectrometry, we identified proteins that preferentially bound to the MuTE sequence and demonstrated that among the candidates the RNA methyltransferase TARBP1 and the zinc finger proteins ZBTB2, ZBTB25 and ZNF639 form a complex that we term TARZN. Interestingly, the TARZN complex also bound to de novo super enhancer sites upstream of the LMO1 and LMO2 genes in T-ALL cells, indicating a putative common mechanism between these different non-coding driver mutations. Furthermore, knock-down of all TARZN members resulted in lower TAL1 protein expression in MuTE-positive but not in MuTE-negative T-ALL cells. Given TARZNs methyltransferase activity and the lack of concomitant TAL1 mRNA level changes, we investigated reduced TAL1 translation and identified reduced neo-synthesised TAL1 protein levels upon TARBP1 knockdown. Overall, these data suggest that the TARZN complex promotes oncogenic expression in T-ALL via co-transcriptional RNA methylation.

cell biology↗

bioRxiv2023

E4F1 and ZNF148 are transcriptional activators of the A57C and wildtype TERT promoter

Point mutations within the TERT promoter are the most recurrent somatic non-coding mutations identified across different cancer types, including glioblastoma, melanoma, hepatocellular carcinoma, and bladder cancer. They are most abundant at C146T and C124T and rarer at A57C, with the latter originally described as a familial case but subsequently shown also to occur somatically. All three mutations create de novo ETS (E-twenty-six specific) binding sites and result in the reactivation of the TERT gene, allowing cancer cells to achieve replicative immortality. Here, we employed a systematic proteomics screen to identify transcription factors preferentially binding to the C146T, C124T and A57C mutations. While we confirmed binding of multiple ETS factors to the mutant C146T and C124T sequences, we identified E4F1 as an A57C-specific binder and ZNF148 as a TERT WT binder that is excluded from the TERT promoter by the C124T allele. Both proteins are activating transcription factors that bind specifically to the A57C and wildtype (at position 124) TERT promoter sequence in corresponding cell lines and upregulate TERT transcription and telomerase activity. Our work describes new regulators of TERT gene expression with possible roles in cancer.

cancer biology↗