SF3B1 promotes glycolysis and tumor malignancy through splicing-independent activation of HIF1α [ChIP-Seq]

Splicing factor 3b subunit 1 (SF3B1) is one of the most frequently mutated spliceosomal components in cancer. Recent studies additionally imply an involvement of the wildtype protein in tumor progression, but the underlaying mechanism remains elusive. Here we report that SF3B1 acts as a coactivator for hypoxia-inducible factor (HIF) 1α. SF3B1 directly interacts with HIF1a, augments HIF1a-HIF1b heterodimer binding to hypoxia response elements in vivo and enhances transactivation of HIF target genes. In human patients, primary patient cells and in a mouse model of pancreatic ductal adenocarcinoma (PDAC), efficient HIF1a-signalling relies on SF3B1. Monoallelic deletion of Sf3b1 in this mouse tumor model severely delays tumor initiation and development and diminishes HIF target gene transcription, glucose uptake and proliferation in corresponding tumor organoids in hypoxia, while splicing remains functional. Here, we define a subset of aggressive chromophobe renal cell carcinomas (chRCCs) able to transcriptionally compensate monoallelic SF3B1 loss, a feature that correlates with poor prognosis and lymph node spread and we show that the oncogenic hotspot mutation SF3B1K700E has reduced co-activation efficiency. Also, we report increased sensitivity of cells with low levels of SF3B1 to the HIF-inhibitor PX-478. These findings reveal a splicing-independent, tumor promoting function of SF3B1, important in the pathogenesis of PDAC and other cancers. Panc1 cells were treated either with control siRNA (siCtrl) or siRNA targeting SF3B1 (siSF3B1). siCtrl cells were exposed to 1% O2 for 8 hours. ChIP was performed on these samples with a HIF1a antibody, the retrieved ChIP DNA was sequenced with NGS after spike-in of drosophila DNA