Regulation of endosome fusion

Homotypic fusion between early endosomes can be reconstituted in vitro. By using wortmannin and LY294002, inhibitors of phosphatidylinositol (PI) 3-ki nase, a requirement for this activity has been established in order for fus ion to proceed efficiently. It has been shown that PI 3-kinase activity is required downstream of rab5 activation, although a large excess of activate d rab5 can overcome wortmannin inhibition. A series of experiments have als o been performed which indicate a role for early endosomal autoantigen 1 (E EA1) in determining fusion efficiency, EEA1 dissociates from membranes foll owing wortmannin treatment. It is proposed that the requirement of endosome fusion for PI 3-kinase activity is to promote the association of EEA1 with endosomes.