Background Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary arterioles, characterized by increased pulmonary arterial pressure and right ventricular failure. The etiology of PAH is complex, but aberrant proliferation of the pulmonary artery endothelial cells (PAECs) and pulmonary artery smooth muscle cells (PASMCs) is thought to play an important role in its pathogenesis. Understanding the mechanisms of transcriptional gene regulation involved in pulmonary vascular homeostasis can provide key insights into potential therapeutic strategies. Methods and Results We demonstrate that the activity of the transcription factor myocyte enhancer factor 2 (MEF2) is significantly impaired in the PAECs derived from subjects with PAH. We identified MEF2 as the key cis-acting factor that regulates expression of a number of transcriptional targets involved in pulmonary vascular homeostasis, including microRNAs 424 and 503, connexins 37, connexin 40, Krűppel Like Factor 2 (KLF2) and KLF4, which were found to be significantly decreased in PAH PAECs. The impaired MEF2 activity in PAH PAECs was mediated by excess nuclear accumulation of two class IIa histone deacetylases (HDACs) that inhibit its function, namely HDAC4 and HDAC5. Selective, pharmacologic inhibition of class IIa HDACs led to restoration of MEF2 activity in PAECs, as demonstrated by increased expression of its transcriptional targets, decreased cell migration and proliferation, and rescue of experimental pulmonary hypertension (PH) models. Conclusions Our results demonstrate that strategies to augment MEF2 activity holds potential therapeutic value in PAH. Moreover, we identify selective HDAC IIa inhibition as a viable alternative approach to avoid the potential adverse effects of broad spectrum HDAC inhibition in PAH.

Syntenin, a tandem PDZ domain containing scaffold protein, functions as a positive regulator of cancer cell progression in several human cancers. We report here that syntenin positively regulates transforming growth factor (TGF)-β1-mediated Smad activation and the epithelial-to-mesenchymal transition (EMT) by preventing caveolin-1-mediated internalization of TGF-β type I receptor (TβRI). Knockdown of syntenin suppressed TGF-β1-mediated cell migration, transcriptional responses and Smad2/3 activation in various types of cells; however, overexpression of syntenin facilitated TGF-β1-mediated responses. In particular, syntenin knockdown abolished both the basal and TGF-β1-mediated repression of E-cadherin expression, as well as induction of vimentin expression along with Snail and Slug upregulation; thus, blocking the TGF-β1-induced EMT in A549 cells. In contrast, overexpression of syntenin exhibited the opposite effect. Knockdown of syntenin-induced ubiquitination and degradation of TβRI, but not TGF-β type II receptor, leading to decreased TβRI expression at the plasma membrane. Syntenin associated with TβRI at its C-terminal domain and a syntenin mutant lacking C-terminal domain failed to increase TGF-β1-induced responses. Biochemical analyzes revealed that syntenin inhibited the interaction between caveolin-1 and TβRI and knockdown of syntenin induced a massive internalization of TβRI and caveolin-1 from lipid rafts, indicating that syntenin may increase TGF-β signaling by inhibiting caveolin-1-dependent internalization of TβRI. Moreover, a positive correlation between syntenin expression and phospho-Smad2 levels is observed in human lung tumors. Taken together, these findings demonstrate that syntenin may act as an important positive regulator of TGF-β signaling by regulating caveolin-1-mediated internalization of TβRI; thus, providing a novel function for syntenin that is linked to cancer progression.

Aberrant adhesion signaling pathways in cancer cells underlie their deadly invasive capabilities. The adhesion-related PDZ adapter protein mda-9/syntenin is a positive regulator of cancer cell progression in breast cancer, melanoma, and other human cancers. In this study, we report that mda-9/syntenin mediates adhesion-mediated activation of protein kinase Cα (PKCα) and focal adhesion kinase (FAK) by fibronectin (FN) in human breast cancer and melanoma cells. FN rapidly stimulated the expression of mda-9/syntenin and the activation of PKCα prior to activation of FAK. Inhibiting PKCα suppressed basal or FN-induced expression of mda-9/syntenin, as well as cell migration and invasion toward FN stimulated by mda-9/syntenin. Several lines of evidence suggested that activation of PKCα and expression of mda-9/syntenin were interdependent. First, mda-9/syntenin inhibition suppressed basal or FN-induced phosphorylation of PKCα at Thr

Treatment of type 2 diabetes mellitus continues to pose an important clinical challenge, with most existing therapies lacking demonstrable ability to improve cardiovascular outcomes. The atheroprotective peptide apelin (APLN) enhances glucose utilization and improves insulin sensitivity. However, the mechanism of these effects remains poorly defined. We demonstrate that the expression of APLNR (APJ/AGTRL1), the only known receptor for apelin, is predominantly restricted to the endothelial cells (ECs) of multiple adult metabolic organs, including skeletal muscle and adipose tissue. Conditional endothelial-specific deletion of Aplnr (AplnrECKO) resulted in markedly impaired glucose utilization and abrogation of apelin-induced glucose lowering. Furthermore, we identified in-activation of Forkhead box protein O1 (FOXO1) and inhibition of endothelial expression of fatty acid (FA) binding protein 4 (FABP4) as key downstream signaling targets of apelin/APLNR signaling. Both the Apln−/− and AplnrECKO mice demonstrated increased endothelial FABP4 expression and excess tissue FA accumulation, whereas concurrent endothelial Foxo1 deletion or pharmacologic FABP4 inhibition rescued the excess FA accumulation phenotype of the Apln−/− mice. The impaired glucose utilization in the AplnrECKO mice was associated with excess FA accumulation in the skeletal muscle. Treatment of these mice with an FABP4 inhibitor abrogated these metabolic phenotypes. These findings provide mechanistic insights that could greatly expand the therapeutic repertoire for type 2 diabetes and related metabolic disorders.