Increased expression of Rab5a correlates directly with accelerated maturation of Listeria monocytogenes phagosomes

Previous studies have shown that Listeria monocytogenes (LM) modulates phag ocytic membrane traffic. Here we explore whether Rab5a, a GTPase associated with phagosome-endosome fusion, is related to phagosome maturation and to the intracellular survival of LM. Stable transfection of Rab5a cDNA into ma crophages accelerates intracellular degradation of LM. Morphological studie s confirmed that phagosome maturation and phagosome-lysosome fusion is enha nced by overexpression of Rab5a. Down-regulation experiments using antisense oligonucleotides targeted to th e Rab5a mRNA efficiently reduced RabBa synthesis, reduced phagosome-endosom e traffic, blocked phagosome-lysosome fusion, and extended intraphagosomal survival of LM. Down-regulation of Rab5a had no effect on LM internalizatio n. Down-regulation of Rab5c had no effect on phagosome maturation and phago some-lysosome fusion. The results indicate that RabBa controls early phagos ome-endosome interactions and governs the maturation of the early phagosome leading to phagosome-lysosome fusion.