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Regulation of transferrin recycling kinetics by PtdIns[4,5]P₂ availability

Sunyun Kim^*, Hyunmyung Kim^*, Belle Chang, Namhui Ahn^*, Suha Hwang^*, Gilbert Di Paolo and Sunghoe Chang^*,1

^* Department of Life Science, Gwangju Institute of Science and Technology, Gwangju, South Korea; and

Department of Pathology, College of Physicians and Surgeons, Columbia University Medical Center, New York, New York, USA

¹Correspondence: Department of Life Science, Gwangju Institute of Science and Technology, 1 Oryong-dong Buk-gu, Gwangju, South Korea. E-mail: sunghoe{at}gist.ac.kr

ABSTRACT

Phosphatidylinositol 4,5-bisphosphate (PtdIns[4,5]P₂) is a phosphoinositide involved in a variety of cellular functions, including signal transduction, organelle trafficking, and actin dynamics. Although the role of PtdIns[4,5]P₂ in endocytosis is well established, the precise trafficking steps relying on normal PtdIns[4,5]P₂ balance in the endosomal pathway have not yet been elucidated. Here we show that decrease in intracellular PtdIns[4,5]P₂ levels achieved by the overexpression of the 5-phosphatase domain of synaptojanin 1 or by siRNA knock-down of PIP5Ks expression lead to severe defects in the internalization of transferrin as well as in the recycling of internalized transferrin back to the cell surface in COS-7 cells. These defects suggest that PtdIns[4,5]P₂ participates in multiple trafficking and/or sorting events during endocytosis. Coexpression of the PtdIns[4,5]P₂ synthesizing enzyme, PIP5KI, was able to rescue these endocytic defects. Furthermore, decreased levels of PtdIns[4,5]P₂ caused delays in rapid and slow membrane recycling pathways as well as a severe backup of endocytosed membrane. Taken together, our results demonstrate that PtdIns[4,5]P₂ availability regulates multiple steps in the endocytic cycle in non-neuronal cells.—Kim, S., Kim, H., Chang, B., Ahn, N., Hwang, S., Di Paolo, G., Chang, S. Regulation of transferrin recycling kinetics by PtdIns[4,5]P₂ availability.

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