LAPTM5 protein is a positive regulator of proinflammatory signaling pathways in macrophages.
LAPTM5 (lysosomal-associated protein transmembrane 5) is a protein that is preferentially expressed in immune cells, and it interacts with the Nedd4 family of ubiquitin ligases. Recent studies in T and B cells identified LAPTM5 as a negative regulator of T and B cell receptor levels at the plasma membrane. Here we investigated the function of LAPTM5 in macrophages. We demonstrate that expression of LAPTM5 is required for the secretion of proinflammatory cytokines in response to Toll-like receptor ligands. We also show that RAW264.7 cells knocked down for LAPTM5 or macrophages from LAPTM5(-/-) mice exhibit reduced activation of NF-κB and MAPK signaling pathways mediated by the TNF receptor, as well as multiple pattern recognition receptors in various cellular compartments. TNF stimulation of LAPTM5-deficient macrophages leads to reduced ubiquitination of RIP1 (receptor-interacting protein 1), suggesting a role for LAPTM5 at the receptor-proximate level. Interestingly, we find that macrophages from LAPTM5(-/-) mice display up-regulated levels of A20, a ubiquitin-editing enzyme responsible for deubiquitination of RIP1 and subsequent termination of NF-κB activation. Our studies thus indicate that, in contrast to its negative role in T and B cell activation, LAPTM5 acts as a positive modulator of inflammatory signaling pathways and hence cytokine secretion in macrophages. They also highlight a role for the endosomal/lysosomal system in regulating signaling via cytokine and pattern recognition receptors.
Program in Cell Biology, the Hospital for Sick Children, and Biochemistry Department, University of Toronto, Toronto, Ontario M5G 1L7, Canada.
Wioletta K
WK
Glowacka
Philipp
P
Alberts
Rika
R
Ouchida
Ji-Yang
JY
Wang
Daniela
D
Rotin
D000818:Animals; D003546:Cysteine Endopeptidases; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D011992:Endosomes / Q000235:genetics / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D007249:Inflammation / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008247:Lysosomes / Q000235:genetics / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008264:Macrophages / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination / Q000502:physiology
D016207:Cytokines; D004268:DNA-Binding Proteins; D020690:GTPase-Activating Proteins; D017874:Immediate-Early Proteins; D047908:Intracellular Signaling Peptides and Proteins; C484408:Laptm5 protein, mouse; D008565:Membrane Proteins; D016328:NF-kappa B; C490620:Ralbp1 protein, mouse; D044767:Ubiquitin-Protein Ligases; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3; D003546:Cysteine Endopeptidases; C513261:Tnfaip3 protein, mouse