Golgi-associated GSK3β regulates the sorting process of post-Golgi membrane trafficking

Glycogen synthase kinase beta (GSK3 beta) phosphorylates many substrates in mammalian cells, and functions in many physiological processes. We observed that GSK3 beta knockdown by siRNA perturbed both Golgi morphology in HeLa cells and the anterograde transport of cation-independent mannose 6-phosphate receptor (CI-M6PR) from the trans-Golgi network (TGN) to prelysosomal compartments (PLC), diverting it to the exocytic pathway. Moreover, we demonstrate that a portion of GSK3 beta was localized to the TGN through the Golgi peripheral protein p230 and that this localization regulated CLASP2 phosphorylation. Our results also show that GSK3 beta knockdown resulted in accumulation of CLASP2 at microtubule plus ends at the cell periphery. Our findings support the hypothesis that GSK3 beta at the TGN acts as a guide, activates exocytic transport, and redirects CI-M6PR from transport to the PLC into the exocytic pathway by regulating the affinity of CLASPs for microtubules.