SUPT5H mutations associated with elevation of Hb A2 level: Identification of two novel variants and literature review

β-thalassemia is one of the most common monogenic disorders in areas of the tropics and subtropics, which represents a major familial and social burden to local people. The elevated Hb A2 level, generally specified as greater than 3.5 %, is commonly used as a high efficiency index for screening of β-thalassemia carriers. However, mutations in other genes such as GATA1 and KLF1, could also result in increased Hb A2 level. In this study, we identified two novel variants in the SUPT5H gene: a frameshift mutation (SUPT5H: c.3032_3033delTG, p.M1011Mfs*9) and a nonsense mutation (SUPT5H: c.397C > T, p.Arg133*) in two Chinese individuals. Utilizing a combination of phenotype analysis, bioinformatics analysis, and functional analysis, we deduced that these two variants modified the SUPT5H protein's structure, thereby impacting its function and consequently leading to the heightened Hb A2 level phenotype found in the carriers. Furthermore, through a comprehensive literature review, a mutation spectrum was consolidated for SUPT5H, an investigation into the genotype-phenotype correlation was conducted, and factors known to influence Hb A2 levels were identified. Based on this in-depth understanding, clinicians are better equipped to carry out large scale screenings in regions with high prevalence of β-thalassemia.

β-Thalassemia Trait Caused by SUPT5H Defects: Another Case Report

We identified a novel mutation in the SUPT5H gene in a Chinese female who presented with a β-thalassemia trait. The substitution of c.193C > T (p.Arg65*) leads to a premature stop codon on residue 65 and could be associated with haploinsufficiency. This variant was inherited from the mother who also had the asymptomatic phenotype of β-thalassemia trait. Our case further supports the role of SUPT5H as a potential β-globin chain production-modulating gene.

RNA polymerase II pausing temporally coordinates cell cycle progression and erythroid differentiation

Controlled release of promoter-proximal paused RNA polymerase II (RNA Pol II) is crucial for gene regulation. However, studying RNA Pol II pausing is challenging, as pause-release factors are almost all essential. In this study, we identified heterozygous loss-of-function mutations in SUPT5H, which encodes SPT5, in individuals with β-thalassemia. During erythropoiesis in healthy human cells, cell cycle genes were highly paused as cells transition from progenitors to precursors. When the pathogenic mutations were recapitulated by SUPT5H editing, RNA Pol II pause release was globally disrupted, and as cells began transitioning from progenitors to precursors, differentiation was delayed, accompanied by a transient lag in erythroid-specific gene expression and cell cycle kinetics. Despite this delay, cells terminally differentiate, and cell cycle phase distributions normalize. Therefore, hindering pause release perturbs proliferation and differentiation dynamics at a key transition during erythropoiesis, identifying a role for RNA Pol II pausing in temporally coordinating the cell cycle and erythroid differentiation.

A stepwise haematological screening and whole-exome sequencing reveal multiple mutations from SUPT5H causing an elevation of Hb A2 from a cohort of 47336 individuals

INTRODUCTION

Though an increase in Hb A₂ is one of the most key markers of β-thal carriers, a few independent cases are reported to show elevated Hb A₂ levels caused by mutations in other genes beyond β-globin gene.

METHODS

We reviewed the haematological indices of 47336 individuals to analyse the phenotype-genotype correlation and identified 1439 individuals (3.04%) positive in the elevation of Hb A₂ . Globin and KLF1 genes analysis was performed, and further whole-exome sequencing was carried to dissect the genetic causes of those positive samples without β-thalassemic or KLF1 mutations.

RESULTS

Of these 1439 individuals with elevated Hb A₂ , 1381 had a molecular defect in globin genes, and most were β-thalassemic mutation; 10 had a molecular defect in KLF1 gene. Finally, among the 38 individuals without β-thalassemic or KLF1 mutations, 7 were identified to carried a loss-of-function mutation in SUPT5H.

CONCLUSION

This study has provided a mutation spectrum of SUPT5H in a cohort screening leading to the elevation of Hb A₂ . According to the previous observations that individuals with a combination of β-thal mutation and a SUPT5H variant might present moderate β-thaelassemia, these findings emphasized the importance of comprehensive molecular diagnosis to prevent birth defects of β-thaelassemia caused by rare mutations from modifier genes.

MYC Recruits SPT5 to RNA Polymerase II to Promote Processive Transcription Elongation

The MYC oncoprotein binds to promoter-proximal regions of virtually all transcribed genes and enhances RNA polymerase II (Pol II) function, but its precise mode of action is poorly understood. Using mass spectrometry of both MYC and Pol II complexes, we show here that MYC controls the assembly of Pol II with a small set of transcription elongation factors that includes SPT5, a subunit of the elongation factor DSIF. MYC directly binds SPT5, recruits SPT5 to promoters, and enables the CDK7-dependent transfer of SPT5 onto Pol II. Consistent with known functions of SPT5, MYC is required for fast and processive transcription elongation. Intriguingly, the high levels of MYC that are expressed in tumors sequester SPT5 into non-functional complexes, thereby decreasing the expression of growth-suppressive genes. Altogether, these results argue that MYC controls the productive assembly of processive Pol II elongation complexes and provide insight into how oncogenic levels of MYC permit uncontrolled cellular growth.

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MYC enhances productive transcription by defining the protein composition of Pol II

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MYC directly binds SPT5 and hands it over to Pol II in a CDK7-dependent manner

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Transfer of SPT5 increases speed and processivity of Pol II

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MYC’s effects on Pol II function shape its tumor-specific gene expression profile

Suppressor of Ty homolog-5, a novel tumor-specific human telomerase reverse transcriptase promoter-binding protein and activator in colon cancer cells

The human telomerase reverse transcriptase (hTERT) promoter promotes differential hTERT gene expression in tumor cells and normal cells. However, information on the mechanisms underlying the differential hTERT transcription and induction of telomerase activity in tumor cells is limited. In the present study, suppressor of Ty homolog-5 (SPT5), a protein encoded by the SUPT5H gene, was identified as a novel tumor-specific hTERT promoter-binding protein and activator in colon cancer cells. We verified the tumor-specific binding activity of SPT5 to the hTERT promoter in vitro and in vivo and detected high expression levels of SUPT5H in colorectal cancer cell lines and primary human colorectal cancer tissues. SUPT5H was more highly expressed in colorectal cancer cases with distant metastasis than in cases without distant metastasis. Inhibition of endogenous SUPT5H expression by SUPT5H gene-specific short hairpin RNAs effectively attenuated hTERT promoter-driven green fluorescent protein (GFP) expression, whereas no detectable effects on CMV promoter-driven GFP expression in the same cells were observed. In addition, inhibition of SUPT5H expression not only effectively repressed telomerase activity, accelerated telomere shortening, and promoted cell senescence in colon cancer cells, but also suppressed cancer cell growth and migration. Our results demonstrated that SPT5 contributes to the up-regulation of hTERT expression and tumor development, and SUPT5H may potentially be used as a novel tumor biomarker and/or cancer therapeutic target.