Cancer-associated SF3B1-K700E mutation controls immune responses by regulating Treg function via aberrant Anapc13 splicing

Recurrent somatic mutations in spliceosome factor 3b subunit 1 (SF3B1) are identified in hematopoietic cell-derived malignancies, with SF3B1-K700E being the most common one. Here we show that Treg specific expression of SF3B1-K700E (Sf3b1K700Efl/+/Foxp3YFP-Cre) results in spontaneous autoimmune phenotypes including enlarged spleen and tissue infiltration with IFN-γ-producing CD4+ T cells. CD4+ T cells from Sf3b1K700Efl/+/Foxp3YFP-Cre mice display defective Treg differentiation and inhibitory function, which is demonstrated by failed prevention of adoptive transfer colitis by Sf3b1K700Efl/+/Foxp3YFP-Cre Tregs. Mechanically, SF3B1-K700E induces an aberrant splicing event that results in reduced expression of a cell proliferation regulator Anapc13 due to insertion a 231 bp DNA fragment to the 5’ untranslated region (UTR). Forced expression of Anapc13 gene restores the differentiation and ability of Sf3b1K700Efl/+/Foxp3YFP-Cre Tregs to prevent adoptive transfer colitis. Our results thus highlight the impact of a hematological malignancy-associated SF3B1 mutation on immune responses and indicate a potential relationship between splicing factor mutation-dysregulated immune responses and cancer development. To investigate the influnce of Cancer-associated SF3B1-K700E mutation in the Treg cell differentiation,we sort Naive CD4+ T cells from Sf3b1K700E/fl or Sf3b1K700E/fl /Cd4Cre mice were differentiated into Tregs in 48-well plates in the presence of TGFβ (5 ng/ml), hamster anti-CD3 , hamster anti-CD28,anti–IL-4, and anti-IFNγ for 36 hours. CD4+ cells after 36 hours of Treg differentiation were collected and subjected to RNA extraction with the RNeasy Mini Kit (QIAGEN). Comparative gene expression and splicing events profiling analysis using data obtian from RNA-Seq data.