Inpp5e increases the Rab5 association and phosphatidylinositol 3-phosphate accumulation at the phagosome through an interaction with Rab20

Phosphoinositide 5-phosphatases have been implicated in the regulation of phagocytosis. However, their precise roles in the phagocytic process are poorly understood. We prepared RAW264.7 macrophages deficient in Inpp5e (shInpp5e) to clarify the role of this lipid phosphatase. In shInpp5e cells, the uptake of solid particles was increased, and the rate of phagosome acidification was accelerated. As expected, levels of PtdIns(3,4,5)P3 and PtdIns(3,4)P2 were increased and decreased, respectively, on the forming phagocytic cups of these cells. Unexpectedly, the most prominent consequence of the Inpp5e deficiency was the decreased accumulation of PtdIns(3)P and Rab5 on the phagosome. The expression of a constitutively active form of Rab5b in shInpp5e cells rescued the PtdIns(3)P accumulation. Rab20 has been reported to regulate the activity of Rabex5, a guanine nucleotide exchange factor for Rab5. The association of Rab20 with the phagosome was remarkably abrogated in shInpp5e cells. Overexpression of Rab20 increased phagosomal PtdIns(3)P accumulation and delayed its elimination. These results suggest that Inpp5e, through functional interactions with Rab20 on the phagosome, activates Rab5, which, in turn, increases PtdIns(3)P and delays phagosome acidification.

Source: BJ Cell - October 1, 2014 Category: Biochemistry Authors: T Segawa, K Hazeki, K Nigorikawa, S Morioka, Y Guo, S Takasuga, K Asanuma, O Hazeki Tags: BJ Cell Source Type: research