Interaction of PDK1 with Phosphoinositides Is Essential for Neuronal Differentiation but Dispensable for Neuronal Survival

Abstract

3-Phosphoinositide-dependent protein kinase 1 (PDK1) operates in cells in response to phosphoinositide 3-kinase activation and phosphatidylinositol-3,4,5-trisphosphate [PtdIns(3,4,5)P₃] production by activating a number of AGC kinases, including protein kinase B (PKB)/Akt. Both PDK1 and PKB contain pleckstrin homology (PH) domains that interact with the PtdIns(3,4,5)P₃ second messenger. Disrupting the interaction of the PDK1 PH domain with phosphoinositides by expressing the PDK1 K465E knock-in mutation resulted in mice with reduced PKB activation. We explored the physiological consequences of this biochemical lesion in the central nervous system. The PDK1 knock-in mice displayed a reduced brain size due to a reduction in neuronal cell size rather than cell number. Reduced BDNF-induced phosphorylation of PKB at Thr308, the PDK1 site, was observed in the mutant neurons, which was not rate limiting for the phosphorylation of those PKB substrates governing neuronal survival and apoptosis, such as FOXO1 or glycogen synthase kinase 3 (GSK3). Accordingly, the integrity of the PDK1 PH domain was not essential to support the survival of different embryonic neuronal populations analyzed. In contrast, PKB-mediated phosphorylation of PRAS40 and TSC2, allowing optimal mTORC1 activation and brain-specific kinase (BRSK) protein synthesis, was markedly reduced in the mutant mice, leading to impaired neuronal growth and differentiation.

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Correction for Zurashvili et al., Interaction of PDK1 with Phosphoinositides Is Essential for Neuronal Differentiation but Dispensable for Neuronal Survival

ACKNOWLEDGMENTS

We thank Dario Alessi (MRC Protein Phosphorylation Unit, Dundee, Scotland) for the mice and the antibodies. We thank Cristina Gutierrez, Mar Castillo, and Núria Barba from the Institut de Neurociencies Cell Culture, Histology, and Microscopy Facilities for technical assistance and Roser Pané, Jessica Pairada, and Nuria Riera from the SCC Estabulari de Rosegadors of the Universitat de Lleida for animal care. We also thank Arnaldo Parra and Carles Saura for their expert advice with the immunohistochemical analysis.

A Ramon y Cajal contract from the Spanish Ministerio de Educación y Ciencia supported J.R.B. T.Z. was supported by a UAB predoctoral fellowship, and X.Z. was supported by a Chinese Scholarship Council predoctoral fellowship. This work was supported by the Ministerio de Sanidad y Consumo (grant FIS-PI070101) and the Ministerio de Ciencia y Innovación (grant AES-PI10/00333).