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The class II Rab11 family‐interacting proteins, FIP3 and FIP4, also termed Arfophilin‐1 and Arfophilin‐2, respectively, are endosomal proteins that function as dual effector proteins for Rab11 and ADP ribosylation factor (Arf) small GTPases. In the present study, we examined the expression and role of FIP4 in neuronal migration during cerebral layer formation. FIP4mRNA was first weakly detected in post‐mitotic migrating neurons in the upper intermediate zone, and expression was markedly increased in the cortical layer. Exogenously expressed FIP4 protein was localized to subpopulations of EEA1‐ and syntaxin 12‐positive endosomes in migrating neurons, and was partially colocalized with FIP3. Knockdown of FIP4 by in utero electroporation significantly stalled transfected neurons in the lower cortical layer and decreased the speed of neuronal migration in the upper intermediate zone and in the cortical plate compared with control small hairpin RNA (shRNA)‐transfected neurons. Furthermore, co‐transfection of shRNA‐resistant wild‐type FIP4, but not wild type FIP3 or FIP4 mutants lacking the binding region for Rab11 or Arf, significantly improved the disturbed cortical layer formation caused by FIP4 knockdown. Collectively, our findings suggest that FIP4 and FIP3 play overlapping but distinct roles in neuronal migration downstream of Arf and Rab11 during cortical layer formation. Family of Rab11‐interacting protein 4 (FIP4)/Arfophilin‐2 regulates neuronal migration in the upper intermediate zone and cortical plate through Arf‐ and Rab11‐dependent endosomal trafficking during cortical layer formation. [ABSTRACT FROM AUTHOR]

Background: Ca 2+ /calmodulin-dependent protein kinase kinase (CaMKK) is a pivotal activator of CaMKI, CaMKIV and 5'-AMP-activated protein kinase (AMPK), controlling Ca 2+ -dependent intracellular signaling including various neuronal, metabolic and pathophysiological responses. Recently, we demonstrated that CaMKKβ is feedback phosphorylated at Thr144 by the downstream AMPK, resulting in the conversion of CaMKKβ into Ca 2+ /CaM-dependent enzyme. However, the regulatory phosphorylation of CaMKKβ at Thr144 in intact cells and in vivo remains unclear., Methods: Anti-phosphoThr144 antibody was used to characterize the site-specific phosphorylation of CaMKKβ in immunoprecipitated samples from mouse cerebellum and in transfected mammalian cells that were treated with various agonists and protein kinase inhibitors. CaMKK activity assay and LC-MS/MS analysis were used for biochemical characterization of phosphorylated CaMKKβ., Results: Our data suggest that the phosphorylation of Thr144 in CaMKKβ is rapidly induced by cAMP/cAMP-dependent protein kinase (PKA) signaling in CaMKKβ-transfected HeLa cells, that is physiologically relevant in mouse cerebellum. We confirmed that the catalytic subunit of PKA was capable of directly phosphorylating CaMKKβ at Thr144 in vitro and in transfected cells. In addition, the basal phosphorylation of CaMKKβ at Thr144 in transfected HeLa cells was suppressed by AMPK inhibitor (compound C). PKA-catalyzed phosphorylation reduced the autonomous activity of CaMKKβ in vitro without significant effect on the Ca 2+ /CaM-dependent activity, resulting in the conversion of CaMKKβ into Ca 2+ /CaM-dependent enzyme., Conclusion: cAMP/PKA signaling may confer Ca 2+ -dependency to the CaMKKβ-mediated signaling pathway through direct phosphorylation of Thr144 in intact cells., General Significance: Our results suggest a novel cross-talk between cAMP/PKA and Ca 2+ /CaM/CaMKKβ signaling through regulatory phosphorylation., (Copyright © 2019 Elsevier B.V. All rights reserved.)