BMP4 and pulmonary arterial hypertension: In as much as it is well established that signaling initiated at the plasma membrane by several cytokines and growth factors, including transforming growth factor β (TGF-β), BMP2, and IL-6, transits the cytoplasm along membrane-associated endocytic pathways to generate a transcriptional response [17,18,19], we investigated the possibility that the IFN-inducible membrane-bioactive MxA might affect BMP4 and BMP9 signaling, and thus participate in IFN-mediated alterations in PAH pathogenesis.