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I. M. Herman, J. T. Durham, H. K. Surks; Retinal Pericyte Contractile Phenotype: Regulation by Myosin Phosphatase-RhoA Interacting Protein (MRIP) and the β-Actin Specific Capping Protein, βcap73. Invest. Ophthalmol. Vis. Sci. 2010;51(13):66.
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Pericyte-endothelial interactions are likely to modulate microvascular morphogenesis during diabetes and aging. Indeed, regulation of endothelial cell growth and capillary tonus have been linked to pericyte contractile phenotype (Kutcher and Herman, 2009). Through opposing functions of myosin light chain phosphatase (MLCP) and myosin light chain kinase (MLCK), pericytes sustain a relaxed or contractile state. While it has been postulated that the RhoA/Rho kinase (ROCK) pathway may regulate retinal pericyte contractile phenotype, the mechanisms by which the key signaling components orchestrate these events remain largely equivocal. Similarly, pericyte RhoA-GTP status has recently been shown to modulate retinal endothelial growth in co-culture studies.
Yeast-two hybrid analyses followed by co-immunoprecipitation and co-immunolocalization studies were employed to characterize protein-protein interactions. Additionally, real-time and immunofluorescence-based assays were performed in MRIP-silenced vs. control-treated pericytes so that cell shape, spreading and cytoskeletal dynamics could be assessed.
Here, we report that a novel interaction exists between MRIP and βcap73 as well as βcap73 and ROCK. Interestingly, upon MRIP silencing, we observe that βcap73 is displaced from the cell periphery without perturbing β-actin localization. Further, MRIP-silenced pericytes exhibit a 2-fold increase in cellular spreading rates.
Pericyte MRIP regulates MLCP- and RhoA-ROCK interactions by binding βcap73, therein creating a molecular scaffold through which cell shape and spreading are likely to be controlled. Further, βcap73 binding to MRIP may coordinate RhoA, ROCK and MLCP function by targeting these components to actomyosin containing stress fibers. In turn, perturbing MRIP-βcap73 association could disrupt pericyte-endothelial interactions and contribute to the pathologic angiogenesis and vascular complications, which accompany diabetic retinopathy or wet age-related macular degeneration.
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