title: Role of SM22 in the differential regulation of phasic vs. tonic smooth muscle.
abstract: Preliminary proteomics studies between tonic vs. phasic smooth muscles identified three distinct protein spots identified to be those of transgelin (SM22). The latter was found to be distinctly downregulated in the internal anal sphincter (IAS) vs. rectal smooth muscle (RSM) SMC. The major focus of the present studies was to examine the differential molecular control mechanisms by SM22 in the functionality of truly tonic smooth muscle of the IAS vs. the adjoining phasic smooth muscle of the RSM. We monitored SMC lengths before and after incubation with pFLAG-SM22 (for SM22 overexpression), and SM22 small-interfering RNA. pFLAG-SM22 caused concentration-dependent and significantly greater relaxation in the IAS vs. the RSM SMCs. Conversely, temporary silencing of SM22 caused contraction in both types of the SMCs. Further studies revealed a significant reverse relationship between the levels of SM22 phosphorylation and the amount of SM22-actin binding in the IAS and RSM SMC. Data showed higher phospho-SM22 levels and decreased SM22-actin binding in the IAS, and reverse to be the case in the RSM SMCs. Experiments determining the mechanism for SM22 phosphorylation in these smooth muscles revealed that Y-27632 (Rho kinase inhibitor) but not Gö-6850 (protein kinase C inhibitor) caused concentration-dependent decreased phosphorylation of SM22. We speculate that SM22 plays an important role in the regulation of basal tone via Rho kinase-induced phosphorylation of SM22.
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania; and satish.rattan@jefferson.edu.
authors.forename: Satish
authors.initials: S
authors.lastname: Rattan
authors.affiliation: The Research Institute at Nationwide Children's Hospital, Columbus, Ohio.
authors.forename: Mehboob
authors.initials: M
authors.lastname: Ali
mesh_terms: D000199:Actins / Q000378:metabolism; D001003:Anal Canal / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D055785:Gene Knockdown Techniques; D008297:Male; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D009119:Muscle Contraction / Q000187:drug effects; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D040901:Proteomics / Q000379:methods; D034622:RNA Interference; D017207:Rats, Sprague-Dawley; D012007:Rectum / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000199:Actins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D047428:Protein Kinase Inhibitors; C051615:transgelin; D054460:rho-Associated Kinases
keywords: actin-myosin binding; proteomics; transgelin-actin binding