Mnk1/2-mediated regulation of internal translation. (a) HeLa cells stably expressing Cx43-GFP (70 kDa) show an induction of GJA1-20k (20 kDa + 27 kDa GFP = 47 kDa) upon mTOR pathway inhibition with rapamycin (RM). Inhibition of Mnk1/2 with CGP 57380 (CGP) also induces internal translation and the effect is additive upon combining CGP and RM. Inhibition of the upstream EGFR pathway with erlotinib (Eb) modestly induces internal translation in HeLa cells. (b) CGP also induces 20-kDa fragment expression in MDA-MB-231 cells. (c) The Mnk1/2 inhibitor CGP efficiently induces GJA1-20k expression levels in primary human fibroblasts (HFs) and mouse embryonic fibroblasts (MEFs). (d) Mnk1/2 knockout mouse embryonic fibroblasts (MEFs) have constitutively significantly higher levels of the GJA1-20k isoform than wild-type cells. The lack of S209-phosphorylated eIF4E confirms the efficient inhibition of Mnk1/2 with both CGP-treated cells and in Mnk1/2 knockout cells.