Vertebrate Lonesome Kinase Regulated Extracellular Matrix Protein Phosphorylation, Cell Shape, and Adhesion in Trabecular Meshwork Cells

J Cell Physiol. 2017 Sep;232(9):2447-2460. doi: 10.1002/jcp.25582. Epub 2017 Mar 27.


Glaucoma, a leading cause of irreversible blindness, is commonly associated with elevated intraocular pressure (IOP) due to impaired aqueous humor (AH) drainage through the trabecular meshwork (TM). Although dysregulated production and organization of extracellular matrix (ECM) is presumed to increase resistance to AH outflow and elevate IOP by altering TM cell contractile and adhesive properties, it is not known whether regulation of ECM protein phosphorylation via the secretory vertebrate lonesome kinase (VLK) influences TM cellular characteristics. Here, we tested this possibility. Experiments carried out in this study reveal that the 32 kDa protein is a prominent VLK isoform detectable in lysates and conditioned media (CM) of human TM cells. Increased levels of VLK were observed in CM of TM cells subjected to cyclic mechanical stretch, or treated with dexamethasone, TGF-β2, and TM cells expressing constitutively active RhoA GTPase. Downregulation of VLK expression in TM cells using siRNA decreased tyrosine phosphorylation (TyrP) of ECM proteins and focal adhesions, and induced changes in cell shape in association with reduced levels of actin stress fibers and phospho-paxillin. VLK was also demonstrated to regulate TGF-β2-induced TyrP of ECM proteins. Taken together, these results suggest that VLK secretion can be regulated by external cues, intracellular signal proteins, and mechanical stretch, and VLK can in turn regulate TyrP of ECM proteins secreted by TM cells and control cell shape, actin stress fibers, and focal adhesions. These observations indicate a potential role for VLK in homeostasis of AH outflow and IOP, and in the pathobiology of glaucoma. J. Cell. Physiol. 232: 2447-2460, 2017. © 2016 Wiley Periodicals, Inc.

MeSH terms

  • Adult
  • Aged
  • Aqueous Humor / metabolism
  • Cell Adhesion* / drug effects
  • Cell Shape* / drug effects
  • Cells, Cultured
  • Culture Media, Conditioned / metabolism
  • Dexamethasone / pharmacology
  • Extracellular Matrix Proteins / metabolism*
  • Focal Adhesions / enzymology
  • Glaucoma / enzymology
  • Glaucoma / pathology
  • Glaucoma / physiopathology
  • Humans
  • Intraocular Pressure
  • Mechanotransduction, Cellular
  • Middle Aged
  • Mutation
  • Paxillin / metabolism
  • Phosphorylation
  • Protein-Tyrosine Kinases / genetics
  • Protein-Tyrosine Kinases / metabolism*
  • RNA Interference
  • Stress Fibers / enzymology
  • Time Factors
  • Trabecular Meshwork / drug effects
  • Trabecular Meshwork / enzymology*
  • Transfection
  • Transforming Growth Factor beta2 / pharmacology
  • Tyrosine
  • Young Adult
  • rhoA GTP-Binding Protein / genetics
  • rhoA GTP-Binding Protein / metabolism


  • Culture Media, Conditioned
  • Extracellular Matrix Proteins
  • PXN protein, human
  • Paxillin
  • Transforming Growth Factor beta2
  • Tyrosine
  • Dexamethasone
  • Protein-Tyrosine Kinases
  • VLK protein, human
  • rhoA GTP-Binding Protein