ATPase-defective mammalian VPS4 localizes to aberrant endosomes and impairs cholesterol trafficking

The yeast vacuolar sorting protein Vps4p is an ATPase required for endosomal trafficking that couples membrane association to its ATPase cycle. To investigate the function of mammalian VPS4 in endosomal trafficking, we have transiently expressed wild-type or ATPase-defective human VPS4 (hVPS4) in cultured cells. Wild-type hVPS4 was cytosolic, whereas a substantial fraction of hVPS4 that was unable to either bind or hydrolyze ATP was localized to membranes, including those of specifically induced vacuoles. Vacuoles were exclusively endocytic in origin, and subsets of enlarged vacuoles stained with markers for each stage of the endocytic pathway. Sorting of receptors from the early endosome to the recycling compartment or to the trans-Golgi network was not significantly affected, and no mutant hVPS4 associated with these compartments. However, many hVPS4-induced vacuoles were substantially enriched in cholesterol relative to the endosomal compartments of untransfected cells, indicating that expression of mutant hVPS4 gives rise to a kinetic block in postendosomal cholesterol sorting. The phenotype described here is largely consistent with the defects in vacuolar sorting associated with class E vps mutants in yeast, and a role for mammalian VPS4 is discussed in this context

Eosinophils: Biological properties and role in health and disease

Eosinophils are pleiotropic multifunctional leukocytes involved in initiation and propagation of diverse inflammatory responses, as well as modulators of innate and adaptive immunity. In this review, the biology of eosinophils is summarized, focusing on transcriptional regulation of eosinophil differentiation, characterization of the growing properties of eosinophil granule proteins, surface proteins and pleiotropic mediators, and molecular mechanisms of eosinophil degranulation. New views on the role of eosinophils in homeostatic function are examined, including developmental biology and innate and adaptive immunity (as well as their interaction with mast cells and T cells) and their proposed role in disease processes including infections, asthma, and gastrointestinal disorders. Finally, strategies for targeted therapeutic intervention in eosinophil-mediated mucosal diseases are conceptualized