Ligands of the transforming growth factor ␤ (TGF-␤) superfamily control numerous cellular processes, such as proliferation, apoptosis, differentiation, adhesion, and mobility. As a result, they play essential roles in organisms undergoing early development and in adult organisms, in both healthy and diseased states (28). This ligand superfamily can be divided into three major subgroups: the TGF-␤s, the activins and Nodals, and the bone morphogenetic proteins (BMPs)/growth and differentiation factors (40). Signal transduction is mediated by receptor complexes comprising two type II receptors and two type I receptors, both of which are serine/threonine kinases (12). There are five type II receptors in the human genome and seven type I receptors which are named activin receptor-like kinases 1 to 7 (ALK1 to ALK7) (12). It has been very difficult to precisely define which ligands bind which type II-type I receptor complexes, and in fact, recent evidence suggests that multiple combinations can occur. Some type I receptors, such as ALK5, appear to act predominantly with one type II receptor and to bind one class of ligand, in this case, T␤RII and the TGF-␤s, respectively. However, other type I receptors are more promiscuous, for example, ALK2, which acts with a number of different type II receptors and appears to be able to mediate signals from all the subgroups of ligands in different cellular contexts (12).Binding of ligand induces formation of a type II-type I receptor complex in which the constitutively active type II receptor phosphorylates and activates the type I receptor. The signal is then transduced to the nucleus predominantly by members of the Smad family. This is achieved through the phosphorylation of specific receptor-regulated Smads (R-Smads) by an activated type I receptor at two serine residues in an S-M/V-S motif at the extreme C terminus of the R-Smad. There are five different R-Smads: Smad1, Smad2, Smad3, Smad5, and Smad8. Which R-Smads are phosphorylated by which type I receptor is determined by the sequence of the so-called L45 loop in the type I receptor and the L3 loop in the C-terminal Mad homology 2 domain of the R-Smad (5, 12, 33). ALK1, ALK2, ALK3, and ALK6 bind and phosphorylate Smad1, Smad5, and Smad8, whereas ALK4, ALK5, and ALK7 bind and phosphorylate Smad2 and Smad3. This phosphorylation promotes formation of both homomeric Smad complexes and heteromeric complexes with the common mediator Smad, Smad4. These activated Smad complexes accumulate in the nucleus, where they are directly involved in the regulation of target genes (12). Different R-Smad-Smad4 complexes recognize distinct promoter elements (37). Smad3-Smad4 complexes bind repeats of the sequence AGAC or its complement GTCT, which are known as Smad-binding elements. In contrast, the BMP-regulated R-Smads preferentially bind to GC-rich sequences, which are commonly found next to a Smad-binding element, allowing the Smad4 in a Smad1/5-Smad4 complex to also contact DNA. This occurs in conjunction with the transcriptional regulator...

The interplay between sequence-specific DNA-binding transcription factors, histone-modifying enzymes, and chromatin-remodeling enzymes underpins transcriptional regulation. Although it is known how single domains of chromatin "readers" bind specific histone modifications, how combinations of histone marks are recognized and decoded is poorly understood. Moreover, the role of histone binding in regulating the enzymatic activity of chromatin readers is not known. Here we focus on the TGF-β superfamily transcriptional repressor TIF1γ/TRIM33/Ectodermin and demonstrate that its PHD finger-bromodomain constitutes a multivalent histone-binding module that specifically binds histone H3 tails unmethylated at K4 and R2 and acetylated at two key lysines. TIF1γ's ability to ubiquitinate its substrate Smad4 requires its PHD finger-bromodomain, as does its transcriptional repressor activity. Most importantly, TIF1γ's E3 ubiquitin ligase activity is induced by histone binding. We propose a model of TIF1γ activity in which it dictates the residence time of activated Smad complexes at promoters of TGF-β superfamily target genes.

Heterozygous germ-line mutations of BMPR2 are the major contributor to familial clustering of pulmonary arterial hypertension (PAH). To further explore the genetic basis of PAH in isolated cases we undertook a candidate gene analysis to identify potentially deleterious variation.Members of the BMP pathway, namely SMADs 1, 4, 5 and 9, were screened by direct sequencing for gene defects. Four variants were identified in SMADs 1, 4 and 9 amongst a cohort of 324 PAH cases, each not detected in a in a substantial control population. Of three amino-acid substitutions identified, two demonstrated reduced signaling activity in vitro. A putative splice site mutation in SMAD4 resulted in moderate transcript loss due to compromised splicing efficiency. These results emphasize the central role of BMPR2 mutation in the pathogenesis of 2 PAH (MIM# 178600) is a progressive vascular disorder often fatal as a result of right heart failure [Humbert et al., 2010]. Mutations of BMPR2 (MIM# 600799), encoding a bone morphogenetic type II receptor of the TGF-β family, are the major genetic determinant in familial PAH (FPAH). Idiopathic PAH (IPAH), defined as arising spontaneously in the absence of a recorded family history of disease, is indistinguishable from the familial form [Machado et al., 2009]. The detection of germ-line BMPR2 mutation in ~25% of IPAH cases, posing hereditary risk to offspring, has led to the re-classification of mutation carriers as heritable PAH (HPAH) [Deng et al., 2000;Lane et al., 2000;Machado et al., 2009]. Over 70% of HPAH mutations predict premature truncation likely leading to transcript loss via the nonsense-mediated decay (NMD) pathway [Machado et al., 2009]. Deleterious BMPR2 mutation in the IPAH population indicates a genetic basis to disease and suggests the existence of additional genetic and/or environmental factors in PAH pathogenesis yet to be fully annotated. Indeed, rare disease alleles Ethical approval for these studies was obtained by local ethical committees and all patients provided informed consent. A diagnosis of PAH was confirmed as described previously [Machado et al., 2009]. The European IPAH cohort comprised a total of 158 subjects ascertained by specialist UK and European centers and displayed a gender bias favoring females (1.9:1). The PAH panel with associated disease (APAH) (n=136) comprised cases with HIV infection (n=9), portal hypertension (n=11), congenital heart disease (n=15), thromboembolic disease (n=42) and connective tissue disease (n=59). Japanese IPAH subjects (n=30) were ascertained through a single specialist referral centre. All patients had been screened for BMPR2 mutation by direct sequencing and/or DHPLC employing primer sets previously described [Machado et al., 2001].Direct sequencing was performed on ABI377 fragment analyzer. DHPLC was performed using the Transgenomic WAVE Nucleic Acid Fragment Analysis system containing a DNASep column (Transgenomic, Crewe, UK) according to manufacturer's instruction. Due to the inherent limitations of these techni...