Title :
MAL2 , a novel raft
protein of the
MAL family, is an essential component of the machinery for transcytosis in hepatoma HepG2 cells
Abstract :
- Transcytosis is used alone (e.g., hepatoma HepG2 cells) or in combination with a direct pathway from the Golgi (e.g., epithelial MDCK cells) as an indirect route for targeting proteins to the apical surface
- The raft-associated MAL protein is an essential element of the machinery for the direct route in MDCK cells
- Herein, we present the functional characterization of MAL2 , a member of the MAL protein family, in polarized HepG2 cells
- MAL2 resided selectively in rafts and is predominantly distributed in a compartment localized beneath the subapical F-actin cytoskeleton
- MAL2 greatly colocalized in subapical endosome structures with transcytosing molecules en route to the apical surface
- Depletion of endogenous MAL2 drastically blocked transcytotic transport of exogenous polymeric immunoglobulin receptor and endogenous glycosylphosphatidylinositol-anchored protein CD59 to the apical membrane
- MAL2 depletion did not affect the internalization of these molecules but produced their accumulation in perinuclear endosome elements that were accessible to transferrin
- Normal transcytosis persisted in cells that expressed exogenous MAL2 designed to resist the depletion treatment
- MAL2 is therefore essential for transcytosis in HepG2 cells