The current research in my lab is directed at understanding the molecular and cellular mechanisms for the signaling pathways of G protein-coupled receptors (GPCR) and transcription factor NF-kB. Parallel comparative studies are performed using primary cell and organ cultures as well as animal colitis models. For my previous research interests, please refer to my contributions.

• Inflammatory regulation of smooth muscle contraction/relaxation in the gut.  

Smooth muscle cells are the major components of hollow organs and contribute to many common diseases such as inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), hypertension, atherosclerosis, asthma, and interstitial cystitis. They are capable of synthesizing and secreting a variety of pro- and anti-inflammatory mediators, including cytokines, chemokines, growth factors, and cell-adhesion molecules that contribute to the maintenance and resolution of the inflammatory response. Recent studies have shown that inflammatory stimuli elicit distinct patterns of inflammatory mediators that either decrease or increase smooth muscle cell contractility.  A pattern involving time-dependent release of IL-1b, TNF-a, IL-6, and IL-8 is accompanied by decrease in the response of smooth muscle to excitatory neurotransmitters (hypocontractility), whereas the pattern observed with helminth infection involves transient activation of IL-4 and IL-13 followed by sustained expression of TGF-b1, COX-2, and PAR-1 receptors resulting in hypercontractility.  The specific steps in the signaling pathways mediating contraction or relaxation that are affected by these cytokine patterns have not been identified. We hypothesize that the major pro-inflammatory cytokine IL-1b, acting via transcriptional and post-transcriptional mechanisms, inhibits smooth muscle contractility by inducing or suppressing the expression of critical signaling targets mediating contraction and relaxation.  Initial contraction of intestinal smooth muscle involves sequential activation of G proteins and PLC-b, resulting in IP₃-dependent Ca²⁺ release and myosin light chain (MLC) kinase-stimulated phosphorylation of MLC20.  Sustained Ca²⁺-independent contraction is mediated by Rho kinase-stimulated phosphorylation of the regulatory subunit of MLC phosphatase (MYPT1) and/or PKC-stimulated phosphorylation of CPI-17, an endogenous inhibitor of MLC phosphatase. Relaxation of smooth muscle involves activation of adenylyl and guanylyl cyclases that generate cAMP and cGMP and activate PKA and PKG, respectively. We have identified four major targets, RGS proteins (RGS4 and RGS12), SERCA2 and CPI-17 and two regulatory enymes NOX1 and NOX4 in the signaling cascades that mediate initial and sustained contraction, and two targets, soluble guanylyl cyclase (sGC), and cAMP-specific PDE4D5 in the signaling cascades that mediate relaxation. These studies will provide a comprehensive analysis of the effects of a prototypic inflammatory cytokine on the major signaling targets mediating intestinal smooth muscle contraction and relaxation, and the mechanisms by which it inhibits both functions.

• Signaling pathways of NF-kB activation in the gut.

Nuclear Factor kB (NF-kB) is a transcriptional factor that can be stimulated by many signals outside the cells through various cell signal pathways.  It regulates an array of genes important in a number of biological processes and pathological conditions. High basal activity of NF-kB is reported in many types of human tumors. Sustained activation of NF-kB induced by inflammatory mediators is critical for inflammation-related cancer. However, the origins and mechanisms of NF-kB activation are not well understood. In most cases, NF-kB is held in the cytoplasm via Inhibitor of NF-kB (IkB). After phosphorylation by IkB kinase (IKK), IkB is degraded, leading to NF-kB activation. How the IKK complex is activated remains a focus of considerable research interest. We have recently discovered a novel protein NIBP (for NF-kB-inducing kinase and IKK2-Binding Protein) that increases IKK2-mediated NF-kB activation and is required for growth and differentiation of neuronal cell line PC12. However, it is not known whether NIBP is essential for neuronal differentiation and survival in primary neurons from central, peripheral and enteric nervous system. In addition, much more functions of NIBP and their mechanisms remain to be elucidated. Our preliminary studies suggested that NIBP-like immunoreactivity is present in myenteric and submucosal neurons as well as mucosal epithelium. Unigene assay showed that NIBP is widely expressed in gastrointestinal tract. Therefore, we are interested in investigating the role of NIBP in mediating the development and differentiation of the enteric nervous system.  Since NIBP is widely expressed in various human tumors and cancer cell lines, we are also interested in characterizing the function and mechanisms of NIBP in the proliferation, survival and tumor-formation of cancer cells.