The nuclear localization of glycogen synthase kinase 3β is required its putative PY-nuclear localization sequences

Glycogen synthase kinase-3 beta(GSK-3 beta), which is a member of the serine/threonine kinase family, has been shown to be crucial for cellular survival, differentiation, and metabolism. Here, we present evidence that GSK-3 beta is associated with the karyopherin beta 2 (Kap beta 2) (102-kDa), which functions as a substrate for transportation into the nucleus. A potential PY-NLS motif ((IVRLRYFFY117)-I-109) was observed, which is similar with the consensus PY NLS motif (R/K/H)X 2-5PY in the GSK-3 beta catalytic domain. Using a pull down approach, we observed that GSK-3 beta physically interacts with Kap beta 2 both in vivo and in vitro. Secondly, GSK-3 beta and Kap beta 2 were shown to be co-localized by confocal microscopy. The localization of GSK-3 beta to the nuclear region was disrupted by putative Kap beta 2 binding site mutation. Furthermore, in transient transfection assays, the Kap beta 2 binding site mutant induced a substantial reduction in the in vivo serine/threonine phosphorylation of GSK-3 beta, where- as the GSK-3 beta wild type did not. Thus, our observations indicated that Kap beta 2 imports GSK-3 beta through its putative PY NLS motif from the cytoplasm to the nucleus and increases its kinase activity.