Transforming Growth Factor <i>β</i>1 Increases Expression of Contractile Genes in Human Pulmonary Arterial Smooth Muscle Cells by Potentiating Sphingosine-1-Phosphate Signaling

Pulmonary arterial hypertension (PAH) is characterized by elevated pulmonary pressure and carries a very poor prognosis. Understanding of PAH pathogenesis needed to support the development new therapeutic strategies. Transforming growth factor β (TGF-β) drives vascular remodeling increases resistance regulating differentiation proliferation smooth muscle cells (SMCs). Also, sphingosine-1-phosphate (S1P) has been implicated in PAH, but relation between these two signaling mechanisms not well understood. Here, we characterize networks downstream TGF-β human (HPASMCs), which involves mothers against decapentaplegic homolog (SMAD) as Rho GTPases. Activation GTPases regulates myocardin-related transcription (MRTF) serum response (SRF) activity results upregulation contractile gene expression. Our genetic pharmacologic data show that HPASMCs α actin (αSMA) calponin dependent on both SMAD Rho/MRTF-A/SRF transcriptional mechanisms. The kinetics TGF-β–induced myosin light chain (MLC) 2 phosphorylation, measure RhoA activation, are slow, regulation Rho/MRTF/SRF-induced αSMA These suggest TGF-β1 activates Rho/phosphorylated MLC2 through an indirect mechanism, was confirmed sensitivity cycloheximide treatment. As potential mechanism for this action, upregulates mRNA sphingosine kinase (SphK1), enzyme produces S1P, upstream activator, levels S1P receptor (S1PR) 3. SphK1 inhibitor S1PR3 inhibitors (PF543 TY52156/VPC23019) reduce TGF-β1–induced upregulation. Overall, propose model potentiating autocrine/paracrine S1PR3. SIGNIFICANCE STATEMENT In cells, transforming depends bridge interaction Rho/myocardin-related Rho/MRTF pathway node regulatory network target treatment hypertension.