Fig. 7.

SRPKs and PP1α have opposite effects on MKNK2 alternative splicing and tumor growth in mice model. SW480 cells transduced with shSRPK1/2, or overexpressing SRPK1&2, or overexpressing PP1α-T320A were subcutaneously injected into six-week male Balb/c nude mice. The mice condition was monitored from the date of observing macroscopical xenograft. The body weight (a) or food consumption (b) of mice in each group showed no statistical difference. c Xenograft growth curves were plotted as described in the Method section. The mice were scarified after monitoring for 20 days, then the xenografts were isolated, weighted (d), and photographed (e). f Levels of MKNK2a and MKNK2b splicing variants were tested via RT-qPCR from isolated xenografts. g Representative H&E staining and Ki-67 immunostaining results of isolated xenografts. Scale bar: 100 μm. h The proliferation index was determined using the percentage of Ki-67 positive cells in isolated xenografts. i A schematic model shows the effects of SRPK1/2 and PP1α on regulating MKNK2a/MKNK2b switch. MKNK2 pre-mRNA can be alternatively spliced into two MKNK2 mRNA isoforms and further translated into two protein isoforms, namely Mnk2a and Mnk2b. Mnk2a perhaps play an anti-tumor role while Mnk2b exerts remarkable oncogenic effects according to our data. In nontumorous cells, Mnk2a is the predominantly protein isoform compared to Mnk2b. In colon adenocarcinoma cells, SRPK1 and SRPK2 are upregulated while PP1α is inactivated, resulting into a hyperphosphorylation status of SRSF1. Phosphorylation of SRSF1 promotes its nucleus transportation in a TNPO3-dependent manner. The nucleus SRSF1 can directly bind to MKNK2 pre-mRNA and significantly generate more MKNK2b isoform, while the MKNK2a proportion is decreased