Prominent role in the regulation of lung development and homeostasis is played by members of the Bone Morphogenetic Protein (BMP) family [8] . BMPs, like all other members of the TGFb superfamily, signal via specific membrane receptors that have serine-threonine kinase catalytic activity [9] . Functional BMP receptor units are composed of two Type-I and two Type-II receptor polypeptides. Four different Type-I BMP receptors (ALK2, ALK3/BMPRIa, ALK6/BMPRIb and ALK1), and three Type-II receptors (BMPRII, ActRIIA and ActRIIB) have been identified [10] . Upon ligand binding, the constitutively active Type-II receptors phosphorylate and thus activate their Type-I partners, which in turn phosphorylate their intracellular targets, the receptor-regulated Smad proteins 1, 5 and 8. Phosphorylated Smads form complexes with the ''common'' Smad4 and translocate to the nucleus where they regulate expression of their target genes, synergistically with other transcription factors [8, 11] . BMPs can also signal via Smad-independent intracellular pathways that involve mitogen-activated protein (MAP) kinases [12, 13] .