The role of the calponin homology domain of smoothelin-like 1 (SMTNL1) in myosin phosphatase inhibition and smooth muscle contraction
- 131 Downloads
In this study, we provide further insight into the contribution of the smoothelin-like 1 (SMTNL1) calponin homology (CH)-domain on myosin light chain phosphatase (SMPP-1M) activity and smooth muscle contraction. SMTNL1 protein was shown to have inhibitory effects on SMPP-1M activity but not on myosin light chain kinase (MLCK) activity. Treatment of β-escin permeabilized rabbit, ileal smooth muscle with SMTNL1 had no effect on the time required to reach half-maximal force (t1/2) during stimulation with pCa6.3 solution. The addition of recombinant SMTNL1 protein to permeabilized, smooth muscle strips caused a significant decrease in contractile force. While the calponin homology (CH)-domain was essential for maximal SMTNL1-associated relaxation, it alone did not cause significant changes in force. SMTNL1 was poorly dephosphorylated by PP-1C in the presence of the myosin targeting subunit (MYPT1), suggesting that phosphorylated SMTNL1 does not possess “substrate trapping” properties. Moreover, while full-length SMTNL1 could suppress SMPP-1M activity toward LC20 in vitro, truncated SMTNL1 lacking the CH-domain was ineffective. In summary, our findings suggest an important role for the CH-domain in mediating the effects of SMTNL1 on smooth muscle contraction.
KeywordsCH-domain Smoothelin-like 1 CHASM Smooth muscle Calcium desensitization Myosin light chain phosphatase MYPT1
This work was supported by research grants from the Heart and Stroke Foundation of Canada (HSFC) to J.A.M. and National Institutes of Health (DK065954-02) to T.A.J.H. M.A.B. was a recipient of Fellowships from the Alberta Heritage Foundation for Medical Research (AHFMR) and HSFC. J.A.M. is recipient of a Canada Research Chair (Tier II) in Smooth Muscle Pathophysiology and a Scholarship from HSFC.
- 2.Wooldridge AA, Fortner CN, Lontay B, Akimoto T, Neppl RL, Facemire C, Datto MB, Kwon A, McCook E, Li P, Wang S, Thresher RJ, Miller SE, Perriard JC, Gavin TP, Hickner RC, Coffman TM, Somlyo AV, Yan Z, Haystead TAJ (2008) Deletion of the protein kinase A/protein kinase G target SMTNL1 promotes an exercise-adapted phenotype in vascular smooth muscle. J Biol Chem 283:11850–11859. doi: 10.1074/jbc.M708628200 PubMedCrossRefGoogle Scholar
- 5.Ishida H, Borman MA, Ostrander J, Vogel HJ, MacDonald JA (2008) Solution structure of the calponin homology (CH) domain from the smoothelin-like 1 protein: a unique apocalmodulin-binding mode and the possible role of the C-terminal type-2 CH-domain in smooth muscle relaxation. J Biol Chem 283:20569–20578. doi: 10.1074/jbc.M800627200 PubMedCrossRefGoogle Scholar
- 16.Wooldridge AA, MacDonald JA, Erdodi F, Ma C, Borman MA, Hartshorne DJ, Haystead TA (2004) Smooth muscle phosphatase is regulated in vivo by exclusion of phosphorylation of threonine 696 of MYPT1 by phosphorylation of Serine 695 in response to cyclic nucleotides. J Biol Chem 279:34496–34504. doi: 10.1074/jbc.M405957200 PubMedCrossRefGoogle Scholar