Erk1/Erk2 MAP kinases are key regulators of cell behaviour and their activation is generally associated with tyrosine kinase signalling. However, TGF-beta stimulation also activates Erk MAP kinases through an undefined mechanism, albeit to a much lower level than receptor tyrosine kinase stimulation. We report that upon TGF-beta stimulation, the activated TGF-beta type I receptor (TbetaRI) recruits and directly phosphorylates ShcA proteins on tyrosine and serine. This dual phosphorylation results from an intrinsic TbetaRI tyrosine kinase activity that complements its well-defined serine-threonine kinase function. TGF-beta-induced ShcA phosphorylation induces ShcA association with Grb2 and Sos, thereby initiating the well-characterised pathway linking receptor tyrosine kinases with Erk MAP kinases. We also found that TbetaRI is tyrosine phosphorylated in response to TGF-beta. Thus, TbetaRI, like the TGF-beta type II receptor, is a dual-specificity kinase. Recruitment of tyrosine kinase signalling pathways may account for aspects of TGF-beta biology that are independent of Smad signalling.

Postnatal alveolar formation is the most important and the least understood phase of lung development. Alveolar pathologies are prominent in neonatal and adult lung diseases. The mechanisms of alveologenesis remain largely unknown. We inactivated Pdgfra postnatally in secondary crest myofibroblasts (SCMF), a subpopulation of lung mesenchymal cells. Lack of Pdgfra arrested alveologenesis akin to bronchopulmonary dysplasia (BPD), a neonatal chronic lung disease. The transcriptome of mutant SCMF revealed 1808 altered genes encoding transcription factors, signaling and extracellular matrix molecules. Elastin mRNA was reduced, and its distribution was abnormal. Absence of Pdgfra disrupted expression of elastogenic genes, including members of the Lox, Fbn and Fbln families. Expression of EGF family members increased when Tgfb1 was repressed in mouse. Similar, but not identical, results were found in human BPD lung samples. In vitro, blocking PDGF signaling decreased elastogenic gene expression associated with increased Egf and decreased Tgfb family mRNAs. The effect was reversible by inhibiting EGF or activating TGFβ signaling. These observations demonstrate the previously unappreciated postnatal role of PDGFA/ PDGFRα in controlling elastogenic gene expression via a secondary tier of signaling networks composed of EGF and TGFβ.

WNT5a is a mainly “non-canonical” WNT ligand whose dysregulation is observed in lung diseases such as idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD) and asthma. Germline deletion of Wnt5a disrupts embryonic lung development. However, the temporal-specific function of WNT5a remains unknown. In this study, we generated a conditional loss-of-function mouse model (Wnt5aCAG) and examined the specific role of Wnt5a during the saccular and alveolar phases of lung development. The lack of Wnt5a in the saccular phase blocked distal airway expansion and attenuated differentiation of endothelial and alveolar epithelial type I (AT1) cells and myofibroblasts. Postnatal Wnt5a inactivation disrupted alveologenesis, producing a phenotype resembling human bronchopulmonary dysplasia (BPD). Mutant lungs showed hypoalveolization, but endothelial and epithelial differentiation was unaffected. The major impact of Wnt5a inactivation on alveologenesis was on myofibroblast differentiation and migration, with reduced expression of key regulatory genes. These findings were validated in vitro using isolated lung fibroblasts. Conditional inactivation of the WNT5a receptors Ror1 and Ror2 in alveolar myofibroblasts recapitulated the Wnt5aCAG phenotype, demonstrating that myofibroblast defects are the major cause of arrested alveologenesis in Wnt5aCAG lungs. Finally, we show that WNT5a is reduced in human BPD lung samples, indicating the clinical relevance and potential role for WNT5a in pathogenesis of BPD.

BackgroundEpithelial-mesenchymal cross talk is centerpiece in the development of many branched organs, including the lungs. The embryonic lung mesoderm provides instructional information not only for lung architectural development, but also for patterning, commitment and differentiation of its many highly specialized cell types. The mesoderm also serves as a reservoir of progenitors for generation of differentiated mesenchymal cell types that include αSMA-expressing fibroblasts, lipofibroblasts, endothelial cells and others. Transforming Growth Factor β (TGFβ) is a key signaling pathway in epithelial-mesenchymal cross talk. Using a cre-loxP approach we have elucidated the role of the TGFβ type I receptor tyrosine kinase, ALK5, in epithelial-mesenchymal cross talk during lung morphogenesis.ResultsTargeted early inactivation of Alk5 in mesodermal progenitors caused abnormal development and maturation of the lung that included reduced physical size of the sub-mesothelial mesoderm, an established source of specific mesodermal progenitors. Abrogation of mesodermal ALK5-mediated signaling also inhibited differentiation of cell populations in the epithelial and endothelial lineages. Importantly, Alk5 mutant lungs contained a reduced number of αSMApos cells and correspondingly increased lipofibroblasts. Elucidation of the underlying mechanisms revealed that through direct and indirect modulation of target signaling pathways and transcription factors, including PDGFRα, PPARγ, PRRX1, and ZFP423, ALK5-mediated TGFβ controls a process that regulates the commitment and differentiation of αSMApos versus lipofibroblast cell populations during lung development.ConclusionALK5-mediated TGFβ signaling controls an early pathway that regulates the commitment and differentiation of αSMApos versus LIF cell lineages during lung development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-016-0242-9) contains supplementary material, which is available to authorized users.

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Recent molecular genetic and embryonic organ culture studies have implicated several novel regulatory processes in the coordination of lung development. Failure of pulmonary initiation results from interruptions of the sonic hedgehog/patched/Gli and Nkx 2.1 signaling pathways. Sonic hedgehog null mutants and Gli2/Gli3 compound null mutants each exhibited failed tracheoesophageal septation. However, proximodistal epithelial differentiation is disrupted by compound Gli mutation, but is preserved in sonic hedgehog mutants. Null mutation of Nkx 2.1 also abrogates tracheoesophageal septation in association with thyroid and pituitary agenesis. Primary tracheal branching is regulated by fibroblast growth factor-10 signaling; in the murine fibroblast growth factor-10 null phenotype, the lung fails to separate from the foregut and morphogenesis is arrested distal to the trachea. Several genes in the fibroblast growth factor-10 pathway have homologous roles in fruit fly tracheal organogenesis, and corresponding Drosophila mutations yield strikingly similar phenotypes. Recent data also indicate that airway branching can be regulated by vascular endothelial growth factor, suggesting mutual regulation of airway and vascular development. The bases of pulmonary left-right asymmetry and laterality have also been investigated. The transforming growth factor-beta superfamily members Lefty-1, Lefty-2, and nodal comprise a regulatory pathway whose function is required for the development of left-right asymmetry, whereas left-right laterality is dependent on regulation of dynein expression by the transcription factor hepatocyte nuclear factor-4. Terminal lung differentiation is modulated by yet another set of signals. Hoxa5 null mutants exhibit tracheal occlusion and surfactant protein deficiency, whereas fibroblast growth factor receptor-2 and -4 compound null phenotypes include abrogated neonatal alveolization, perturbed alveolar myofibroblast differentiation, and persistent neonatal elastin deposition. These new contributions represent substantial advances toward a comprehensive molecular model of pulmonary development.

Introduction The breast cancer susceptibility gene BRCA1 is involved in the repair of double-strand breaks induced by ionizing radiation and chemotherapy drugs. BRCA1 interacts with coactivators such as p300 and CREB-binding protein (CBP) to activate target gene transcription. Estrogen and retinoic acid receptors (ER and RAR) also require coactivator proteins for their ligand-dependent functions. Few studies have suggested a role for nuclear hormone receptors in DNA repair.

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