CLK1 and cancer: SRSF1 regulates MAPK signaling pathway to promote PAAD progression; SRSF5 promotes the proliferation of PAAD cancer cells under CLK1 phosphorylation; miR-193a-5p targets SRSF6 to promote PAAD progression; SRSF3 regulates lncRNA ANRIL and m6A modification to improve drug resistance in cancer cells