Pulmonary surfactant protein A enhances endolysosomal trafficking in alveolar macrophages through regulation of Rab7.
Surfactant protein A (SP-A), the most abundant pulmonary soluble collectin, modulates innate and adaptive immunity of the lung, partially via its direct effects on alveolar macrophages (AM), the most predominant intra-alveolar cells under physiological conditions. Enhanced phagocytosis and endocytosis are key functional consequences of AM/SP-A interaction, suggesting a SP-A-mediated modulation of small Rab (Ras related in brain) GTPases that are pivotal membrane organizers in both processes. In this article, we show that SP-A specifically and transiently enhances the protein expression of endogenous Rab7 and Rab7b, but not Rab5 and Rab11, in primary AM from rats and mice. SP-A-enhanced GTPases are functionally active as determined by increased interaction of Rab7 with its downstream effector Rab7 interacting lysosomal protein (RILP) and enhanced maturation of cathepsin-D, a function of Rab7b. In AM and RAW264.7 macrophages, the SP-A-enhanced lysosomal delivery of GFP-Escherichia coli is abolished by the inhibition of Rab7 and Rab7 small interfering RNA transfection, respectively. The constitutive expression of Rab7 in AM from SP-A(-/-) mice is significantly reduced compared with SP-A(+/+) mice and is restored by SP-A. Rab7 blocking peptides antagonize SP-A-rescued lysosomal delivery of GFP-E. coli in AM from SP-A(-/-) mice. Activation of Rab7, but not Rab7b, by SP-A depends on the PI3K/Akt/protein kinase Cζ (PKCζ) signal transduction pathway in AM and RAW264.7 macrophages. SP-A induces a Rab7/PKCζ interaction in these cells, and the disruption of PKCζ by small interfering RNA knockdown abolishes the effect of SP-A on Rab7. The data demonstrate a novel role for SP-A in modulating endolysosomal trafficking via Rab7 in primary AM and define biochemical pathways involved.
Division of Cellular Pneumology, Department of Experimental Pneumology, Research Center Borstel, Leibniz Center for Medicine and Biosciences, 23845 Borstel, Germany.
Vicky
V
Sender
Christina
C
Moulakakis
Cordula
C
Stamme
D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D011992:Endosomes / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism; D008247:Lysosomes / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism; D016676:Macrophages, Alveolar / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D051058:Oncogene Protein v-akt; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology; D021381:Protein Transport / Q000235:genetics / Q000276:immunology; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology; D037662:Pulmonary Surfactant-Associated Protein A / Q000172:deficiency / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D020691:rab GTP-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D000090802:rab7 GTP-Binding Proteins; D000099221:Protein Kinase C zeta
D051058:Oncogene Protein v-akt; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D051057:Proto-Oncogene Proteins c-akt; D037662:Pulmonary Surfactant-Associated Protein A; D020691:rab GTP-Binding Proteins; D000090802:rab7 GTP-Binding Proteins; D000099221:Protein Kinase C zeta; C000716465:rab7 GTP-binding proteins, mouse; C000716466:rab7 GTP-binding proteins, rat