Molecular mechanisms of chemokine receptors activation and regulation

Chemokines are multifunctional mediators responsible for recruitment and activation of the leukocyte at the site of inflammation. They play key roles in many acute and chronic inflammatory diseases including rheumatoid arthritis and asthma, and mediate tumor cell trafficking and metastasis. Chemokine functions are mediated via specific G-protein coupled receptors. Upon activation, these receptors are desensitized and downregulated. Chemokines and chemokine receptors are redundant in their interaction. We have also shown that these receptors are capable of cross-regulating each other’s functions thereby, limiting cellular responsiveness to chemokines. Receptor phosphorylation and modification of downstream effector activities are critical for chemokine receptor cross-regulation. Chemokine receptor functions are also modulated by various adaptor/scaffold proteins. A long-term goal of our laboratory is to delineate the molecular mechanisms by which the Interleukin-8 (IL-8/CXCL8) receptors, CXCR1 and CXCR2, trigger selective inflammatory responses. These receptors bind CXCL8 with similar affinity to mediate leukocyte chemotaxis, but only CXCR1 activates respiratory burst and cross-desensitization. Our hypothesis is that CXCR1 and CXCR2 couple to distinct set of signaling molecules to mediate and regulate cellular responses to CXCL8.  

Current projects in the laboratory include 1) the role of G protein-coupled receptor kinases in CXCR1 and CXCR2-mediated leukocyte activation and regulation, 2) the role of GRK6 and AGS3 interaction in CXCR1 and CXCR2 activation and regulation and, 3) the role of GRK6 and barrestins  in CXCR1 and CXCR2-mediated post-endocytic signaling. These studies employ a multiplicity of approaches including neutrophils, RBL-2H3 cells stably expressing wild type and mutants CXCR1, CXCR2, AGS3 and GRK6, as well as mice deficient in GRK6, barr1, barr2, AGS3, CXCR1 and CXCR2. The understanding of molecular mechanisms of the CXCL8 receptors activation and regulation will aid in understanding the control of inflammation as well as the etiology of many inflammatory disorders. Such information will provide new targets and new assays for the development of therapeutics which modulate inflammation.

Raghuwanshi S. K., Nasser M. W., Malloy K. M., Strieter, R. M. and Richardson, R. M. βarrestin-2 modulates tumor development, invasion and metastasis: Distinct role of CXCR2 and NF-kB (2008) J.Immunol (Accepted)

Beer F., Kuo C., Morohoshi K., Goodliffe, J., Munro, P., Cho C. Aye, Dawson, M., Richardson, M. R., Jones, L.H., Ikeda, Y., Nakamura, T., Toda, M., Tom Flynn, Ohbayashi, K., Miyazaki, D., and S. J. Ono.  Role of β-chemokines in mast cell activation and type I hypersensitivity reactions in the conjunctiva: in vivo and in vitro studies. (2007) Immunological Reviews, 217:96-104.

Nasser M. W., Raghuwanshi S. K., Malloy, K. M., Shim, J., Rajarathnam K., and Richardson, R. M.  CXCR1 and CXCR2 activation and regulation: Role of aspartate 199 of the second extracellular loop of CXCR2 in CXCL8-mediated rapid receptor internalization. (2007)J. Biol. Chem 282: 6906 – 6915.

Brown, S. L., Jala, V. R., Raghuwanshi, S. K., Nasser, M. W., Haribabu, B. and Richardson, R. M. Activation and regulation of platelet-activating factor receptor: role of Gi and Gq in receptor-mediated chemotactic, cytotoxic and cross-regulatory signals (2006)  J. Immunol., 177: 3242 – 3249.

Toda, M., Nakamura, T., Ikeda, Y. Dawson, M. Richardson, R.M., Alan A., Leed B., Miyasaki D. and Ono, S. J. Role of CC chemokines and their receptors in multiple aspects of mast cells Biology: Comparative protein profiling of FceRI- and/or CCR1-engaged mast cells using Protein Chip technology (2005), Novartis Found Symp 271:131-140

Su, Y, Raghuwnshi, S., Y u, Y, Nanney L. B. Richardson R. M and R ichmond A. b -arrestin-2 knockout promotes neovascularization and re-epithelialization in mouse excisional wounds (2005) J. Immunol ., 175 5396-5402.

Nasser, M. W., Marjoram, R. J Raghuwanshi, S. K., Brown, S. and Richardson , R. M. Protein Kinase C-epsilon mediates cross-desensitization among CXCR1, CXCR2 and CCR5. (2005) J. Immunol., 174 6927-6933 .