Résumé : Four inositol phosphate kinases catalyse the phosphorylation of the second messenger inositol 1,4,5-trisphosphate (Ins(1,4,5)P3 ) to inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4 ): the three isoenzymes of inositol 1,4,5-trisphosphate 3-kinase (Itpk) referred to as Itpka, Itpkb and Itpkc and the inositol polyphosphate multikinase (IPMK). The four enzymes that act on Ins(1,4,5)P3 are all expressed in rat pheochromocytoma PC12 cells, a model used to study nerve growth factor (NGF)-induced neurite outgrowth. We have compared the effect of the overexpression of the four kinases GFP tagged on NGF-induced neurite outgrowth. Our data establish that overexpression of Itpka and Itpkb isoforms inhibit NGF-induced neurite outgrowth, but overexpression of Itpkc and IPMK does not. Surprisingly, the overexpression of N-terminal F-actin binding domain of Itpka, which lacks catalytic activity, was as effective at inhibiting neurite outgrowth as was the full-length enzyme. Neurite length was also significantly decreased in cells overexpressing Itpka and Itpkb but not Itpkc or IPMK. This conclusion was not depending on the overexpression level of any of the kinases upon transfection. PC12 overexpressing kinase dead mutants of GFP-Itpka/b have shorter neurites than the GFP control cells. The decrease in neurite length was never as pronounced as what we see with the wild type GFP-Itpka/b. Finally, the percentage of neurite bearing cells was increased in cells overexpressing the membranous type I Ins(1,4,5)P3 5-phosphatase. We concluded that Itpka and Itpkb inhibit neurite outgrowth through both F-actin binding and localised Ins(1,4,5)P3 3-kinase activity. Itpkc and IPMK do not influence neurite outgrowth or neurite length in this model. This article is protected by copyright. All rights reserved.