CPSF role on APA regulation

We found that CPSF6, a component of the CFIm, can form liquid-liquid phase separation (LLPS) and the elevated LLPS induces the preferential usage of the distal poly(A) sites. CLK2, a kinase upregulated in cancer cells, destructs LLPS of CPSF6 by phosphorylating its arginine/serine-like domain. Albeit higher expression of CPSF6 in cancer, the reduction of LLPS leads to shortening 3’ UTR of cell cycle related genes and then promotes cell proliferation. These results reveal that LLPS regulation of CPSF6 is a fine tuning way of APA in cancer cells and provide a new mechanism for APA regulation by regulating LLPS of 3’ end processing factors through post-translational modification. We knockdowned CPSF6 and CLK2 in RKO cell with shRNA and Overexpression of CPSF6 and CPSF6 mut in HEK2293T cells, and applied a alternative polyadenylation high sequencing (IVT-SAPAS) method to detect dynamic change of 3‘UTR length.