AKAP13, a RhoA GTPase-specific guanine exchange factor, is a novel regulator of TLR2 signaling.
Members of the guanine exchange factor (GEF) family of scaffold proteins are involved in the integration of signal flow downstream of many receptors in adaptive immunity. However, the full complement of GEFs that function downstream of Toll-like receptors (TLRs) requires further identification and functional understanding. By systematically integrating expression profiles from immune and epithelial cells with functional studies, we demonstrate that protein kinase A anchoring protein 13 (AKAP13), a scaffold protein with GEF activity, is an activator of NF-kappaB downstream of TLR2 signaling. Stimulation of the human macrophage cell line THP-1 and epithelial cells with a TLR2 ligand caused a significant up-regulation in AKAP13 mRNA, corresponding to an increase in protein expression. Analysis of TLR2 reporter cell lines deficient in AKAP13 expression revealed significantly reduced NF-kappaB activation and reduced secretion of interleukin-8 and MCP-1 in response to specific ligand stimulation. Furthermore, NF-kappaB activation was partially inhibited by a GEF-deficient AKAP13 mutant. AKAP13 was also involved in phosphorylation of JNK but not of extracellular signal-regulated kinase ERK1 and -2 following ligand stimulation. Together, our results suggest that AKAP13 plays a role in TLR2-mediated NF-kappaB activation and suggest that GEF-containing scaffold proteins may confer specificity to innate immune responses downstream of TLRs.
Shibolet
Oren
O
Gastroenterology Unit, Center for Study of Inflammatory Bowel Disease, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
Giallourakis
Cosmas
C
Rosenberg
Ian
I
Mueller
Tobias
T
Xavier
Ramnik J
RJ
Podolsky
Daniel K
DK
D054758:A Kinase Anchor Proteins / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D005786:Gene Expression Regulation; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D015778:Minor Histocompatibility Antigens; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008954:Models, Biological; D016328:NF-kappa B / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000737:chemistry* / Q000378:metabolism; D015398:Signal Transduction; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
D054758:A Kinase Anchor Proteins; C085467:AKAP13 protein, human; C526201:Akap13 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D015778:Minor Histocompatibility Antigens; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; C495342:TLR2 protein, human; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D020742:rhoA GTP-Binding Protein