Qing Robert Miao, PhD
Professor, Pediatric Surgery and Pediatric Pathology
- Pediatric Surgery and Pediatric Pathology
PhD, Physical Chemistry, Dalian Institute of Chemical Physics, 1995
The Nogo family of proteins is part of a larger superfamily called reticulons (RTN). This nomenclature derives from the observations that they all contain endoplasmic reticulum (ER) retrieval sequences in their carboxyl tails, localize to the ER and contain a 200 amino acid carboxyl terminal reticulon homology domain (RHD). There are four mammalian RTN genes (RTN1, RTN2, RTN 3 and RTN 4) each of which can be alternatively spliced. In general, very little is known about the cellular biology or function of this entire class of proteins. Of the RTN family, the RTN 4 family is the most highly studied. Nogo-A (also called RTN4-A) is the best characterized due to its function as a negative regulator of axon sprouting. Upon injury of myelinated nerves, myelin associated inhibitors, namely Nogo-A and myelin associated glycoprotein (MAG) antagonize nerve regeneration and axon sprouting. Evidence supporting a role for Nogo-A as an inhibitor of nerve regeneration are supported by studies showing that neutralization of Nogo-A with antibodies targeting the N terminus of Nogo-A or peptidomimetic antagonism of Nogo-A from binding its cognate receptor, NgR, improves axonal sprouting and locomotion in rodent models of spinal chord injury. Therefore, there is clear evidence that Nogo-A is a biologically important molecule in the central nervous system (CNS).
There is little information on the actions of Nogo-B (RTN4-B) or Nogo-C (RTN4-C). Nogo-B is a spliced variant of Nogo-A while Nogo-C uses an alternative promoter and unique exon to encode its short amino terminus. Nogo-B is ubiquitously expressed in most cultured cells and tissues whereas Nogo-C is distributed primarily in CNS and in skeletal muscle. Using proteomics as an inductive approach for discovery, Nogo-B has been identified as a protein highly expressed in caveolin-1 enriched microdomains (CEM) and/or lipid rafts (LR) of endothelial cells (EC) and vascular smooth muscle cells (VSMC). Our previous results show that the amino terminus of Nogo-B (AmNogo-B) promotes the adhesion of endothelial and smooth muscle cells, and serves as a chemoattractant for EC while antagonizing PDGF-induced VSMC migration. Using mice deficient in Nogo-A/B, the genetic loss of Nogo-A/B results in an exaggerated neointimal proliferation and abnormal remodeling. Nogo-B has been shown as one of important factors restricting the progression of vascular lesions in animal models and human clinical study. We utilized the expression cloning approach to identify a new cognate receptor for AmNogo-B (NgBR) and characterized its function in regulating AmNogo-B-induced chemotaxis and morphogenesis of endothelial cells. NgBR has a unique cytoplasmic domain, which acts as a scaffold for the binding of farnesylated Ras and thus leading to the activation of PI-3 kinase and Raf-1, which are essential signaling for vasculogenesis, angiogenesis and tumor growth. Recently, we identified several NgBR-interacting proteins by yeast two-hybrid system, which are involved in very important cellular function. These findings suggest that study on NgBR will be a new research avenue.
My laboratory's current research effort focuses on two areas. The first is are to utilize molecular biology and cell biology approach to elucidate the role of Nogo-B receptor (NgBR) in regulating stem cell differentiation to vascular cell lineages, primitive blood vessel formation during embryo development and postnatal blood vessel formation during tumor growth and other vascular diseases. Second, we are establishing in vitro and in vivo models to dissect the molecular mechanisms in regulating the interaction of endothelial cells with microenvironment niche during vasculogenesis and angiogenesis, and developing therapeutic approaches to modulate Nogo-B/NgBR functions in vivo.