Roles of TGFbeta signaling in epidermal/appendage development

The transforming growth factor beta (TGFbeta) superfamily encompasses a number of structurally related proteins that can be divided into several subfamilies including TGFbetas, activins/inhibins and bone morphogenetic proteins (BMPs). The Smads are major intracellular mediators in transducing the signals of TGFbeta superfamily members, and are abundantly expressed in the developing epidermis and epidermal appendages. Moreover, the phenotypes of transgenic/knockout mice with altered components of the TGFbeta superfamily signaling pathway suggest that TGFbeta superfamily signaling is required for epidermal/appendage development. TGFbeta superfamily members are involved in most events during epidermal/appendage development through the TGFbeta signal transduction pathway and through cross talk with other signaling pathways. Future studies will be instrumental in defining the precise roles for TGFbeta superfamily signaling in epidermal/appendage development.     

Extracellular control of TGFbeta signalling in vascular development and disease

The intracellular mechanism of transforming growth factor-beta (TGFbeta) signalling via kinase receptors and SMAD effectors is firmly established, but recent studies of human cardiovascular syndromes such as Marfan syndrome and pre-eclampsia have refocused attention on the importance of regulating the availability of active extracellular TGFbeta. It seems that elastic extracellular matrix (ECM) components have a crucial role in controlling TGFbeta signalling, while soluble and membrane bound forms of TGFbeta co-receptors add further layers of regulation. Together, these extracellular interactions determine the final bioavailability of TGFbeta to vascular cells, and dysregulation is associated with an increasing number of vascular pathologies.     

Peptide signaling in vascular development

In plants and animals, putative small peptide ligands have been suggested to play crucial roles in development as signal molecules of cell-cell communication. Recent studies of CLAVATA3/ENDOSPERM SURROUNDING REGION (CLE) genes and their products have revealed that distinctive dodeca-CLE peptide ligands function in various developmental processes. In particular, the finding and characterization of TDIF, a dodeca-CLE peptide suppressing tracheary element differentiation, indicates regulation of vascular organization by cell-cell communication through CLE peptides. In addition, other extracellular peptides such as phytosulfokine, proteins such as xylogen, and phytohormones all participate in the ordered formation of vascular tissues.     

TGFbeta signaling at the summit

Ligands belonging to the transforming growth factor (TGF) beta superfamily have emerged as major regulators of a wide variety of developmental events, ranging from the earliest steps in germ layer patterning of the pre-gastrula embryo to tissue healing, regeneration and homeostasis in the adult. Recently, Caroline Hill and Bob Lechleider organized the third in a bi-annual series of FASEB meetings on TGFbeta signaling and development at Snowmass (CO, USA). This meeting highlighted the ongoing interplay between advances in our understanding of the molecular biology of TGFbeta family signaling and in investigations into its roles in specific developmental events.     

Glycoproteome profiling of transforming growth factor-beta (TGFbeta) signaling: nonglycosylated cell death-inducing DFF-like effector A inhibits TGFbeta1-dependent apoptosis

Transforming growth factor-beta (TGFbeta) is a potent regulator of cell growth, differentiation, and apoptosis. TGFbeta binds to specific serine/threonine kinase receptors, which leads to activation of Smad-dependent and Smad-independent signaling pathways. O-Glycosylation is a dynamic PTM which has been observed in many regulatory proteins, but has not been studied in the context of TGFbeta signaling. To explore the effect of TGFbeta1 on protein O-glycosylation in human breast epithelial cells, we performed analyses of proteins which were affinity purified with Helix pomatia agglutinin (HPA). HPA lectin allowed enrichment of proteins containing GalNAc and GlcNAc linked to serine and threonine residues. Using 2-DE and MALDI-TOF-MS, we identified 21 HPA-precipitated proteins, which were affected by treatment of cells with TGFbeta1. Among these proteins, regulators of cell survival, apoptosis, trafficking, and RNA processing were identified. We found that TGFbeta1 inhibited the appearance of cell death-inducing DFF-like effector A (CIDE-A) in 2-D gels with HPA-precipitated proteins. CIDE-A is a cell death activator which promotes DNA fragmentation. We observed that TGFbeta1 did not affect expression of CIDE-A, but inhibited its glycosylation. We found that deglycosylation of CIDE-A correlated with enhanced nuclear export of the protein, and that high level of nonglycosylated CIDE-A inhibited TGFbeta1-dependent cell death. Thus, inhibition of the glycosylation of CIDE-A may be a mechanism to protect cells from apoptosis.     

Notch signaling in ocular vasculature development and diseases

Ocular angiogenesis, characterized by the formation of new blood vessels in the avascular area in eyes, is a highly coordinated process involved in retinal vasculature formation and several ocular diseases such as age-related macular degeneration, proliferative diabetic retinopathy and retinopathy of prematurity. This process is orchestrated by complicated cellular interactions and vascular growth factors, during which endothelial cells acquire heterogeneous phenotypes and distinct cellular destinations. To date, while the vascular endothelial growth factor has been identified as the most critical angiogenic agent with a remarkable therapeutic value, the Notch signaling pathway appears to be a similarly important regulator in several angiogenic steps. Recent progress has highlighted the involvement, mechanisms and therapeutic potential of Notch signaling in retinal vasculature development and pathological angiogenesis-related eye disorders, which may cause irreversible blindness.     

Retinoic acid signaling in vascular development

Formation of the vasculature is an essential developmental process, delivering oxygen and nutrients to support cellular processes needed for tissue growth and maturation. Retinoic acid (RA) and its downstream signaling pathway is vital for normal pre‐ and post‐natal development, playing key roles in the specification and formation of many organs and tissues. Here, we review the role of RA in blood and lymph vascular development, beginning with embryonic yolk sac vasculogenesis and remodeling and discussing RA's organ‐specific roles in angiogenesis and vessel maturation. In particular, we highlight the multi‐faceted role of RA signaling in CNS vascular development and acquisition of blood–brain barrier properties.     

Intracellular dynamics of Smad-mediated TGFbeta signaling

The transforming growth factor-beta (TGFbeta) family represents a class of signaling molecules that plays a central role in morphogenesis, growth, and cell differentiation during normal embryonic development. Members of this growth factor family are particularly vital to development of the mammalian secondary palate where they regulate palate mesenchymal cell proliferation and extracellular matrix synthesis. Such regulation is particularly critical since perturbation of either cellular process results in a cleft of the palate. While the cellular and phenotypic effects of TGFbeta on embryonic craniofacial tissue have been extensively catalogued, the specific genes that function as downstream mediators of TGFbeta action in the embryo during palatal ontogenesis are poorly defined. Embryonic palatal tissue in vivo and murine embryonic palate mesenchymal (MEPM) cells in vitro secrete and respond to TGFbeta. In the current study, elements of the Smad component of the TGFbeta intracellular signaling system were identified and characterized in cells of the embryonic palate and functional activation of the Smad pathway by TGFbeta1, TGFbeta2, and TGFbeta3 was demonstrated. TGFbeta-initiated Smad signaling in cells of the embryonic palate was found to result in: (1) phosphorylation of Smad 2; (2) nuclear translocation of the Smads 2, 3, and 4 protein complex; (3) binding of Smads 3 and 4 to a consensus Smad binding element (SBE) oligonucleotide; (4) transactivation of transfected reporter constructs, containing TGFbeta-inducible Smad response elements; and (4) increased expression of gelatinases A and B (endogenous genes containing Smad response elements) whose expression is critical to matrix remodeling during palatal ontogenesis. Collectively, these data point to the presence of a functional Smad-mediated TGFbeta signaling system in cells of the developing murine palate.     

Inhibition of TGFbeta signaling in cancer therapy

Recent evidence continues to support a central role for TGFbeta in tumor maintenance and progression. Although this may involve TGFbeta-mediated paracrine effects that modulate the tumor microenvironment and the host immune system, some studies causally implicate autocrine TGFbeta in cancer cell motility and survival. Other recent evidence indicates synergy between oncogene and TGFbeta signaling in epithelial cell transformation. This suggests opportunities for dissecting molecular mechanisms of cross-talk as well as providing insights into possible combinatorial molecular anticancer therapies that will include TGFbeta inhibitors.     

Notch signaling in vascular development and physiology

Notch signaling is an ancient intercellular signaling mechanism that plays myriad roles during vascular development and physiology in vertebrates. These roles include regulation of artery/vein differentiation in endothelial and vascular smooth muscle cells, regulation of blood vessel sprouting and branching during both normal development and tumor angiogenesis, and the differentiation and physiological responses of vascular smooth muscle cells. Defects in Notch signaling also cause inherited vascular and cardiovascular diseases. In this review, I summarize recent findings and discuss the growing relevance of Notch pathway modulation for therapeutic applications in disease.     

BMP signaling in vascular development and disease

Genetic and functional studies indicate that common components of the bone morphogenetic protein (BMP) signaling pathway play critical roles in regulating vascular development in the embryo and in promoting vascular homeostasis and disease in the adult. However, discrepancies between in vitro and in vivo findings and distinct functional properties of the BMP signaling pathway in different vascular beds, have led to controversies in the field that have been difficult to reconcile. This review attempts to clarify some of these issues by providing an up to date overview of the biology and genetics of BMP signaling relevant to the intact vasculature.     

Hydrogen peroxide inhibits insulin signaling in vascular smooth muscle cells

Both insulin resistance and reactive oxygen species (ROS) have been reported to play essential pathophysiological roles in cardiovascular diseases, such as hypertension and atherosclerosis. However, the mechanistic link between ROS, such as H2O2 and insulin resistance in the vasculature, remains undetermined. Akt, a Ser/Thr kinase, mediates various biological responses induced by insulin. In this study, we examined the effects of H2O2 on Akt activation in the insulin-signaling pathway in vascular smooth muscle cells (VSMCs). In VSMCs, insulin stimulates Akt phosphorylation at Ser473. Pretreatment with H2O2 concentration- and time-dependently inhibited insulin-induced Akt phosphorylation with significant inhibition observed at 50 microM for 10 min. A ROS inducer, diamide, also inhibited insulin-induced Akt phosphorylation. In addition, H2O2 inhibited insulin receptor binding partially and inhibited insulin receptor autophosphorylation almost completely. However, pretreatment with a protein kinase C inhibitor, GF109203X (2 microM), for 30 min did not block the inhibitory effects of H2O2 on insulin-induced Akt phosphorylation, suggesting that protein kinase C is not involved in the inhibition by H2O2. We conclude that ROS inhibit a critical insulin signal transduction component required for Akt activation in VSMCs, suggesting potential cellular mechanisms of insulin resistance, which would require verification in vivo.     

TNFalpha inhibits insulin's antiapoptotic signaling in vascular smooth muscle cells

Mutations in TIGR/MYOC (myocilin), a secretory protein of unknown function, have been recently linked to glaucoma. Most known mutations map to the C-terminus, an olfactomedin-like domain. We have previously shown that, in contrast to the wild-type, a truncated form of myocilin lacking the olfactomedin domain is not secreted. In this study, we present evidence that the mutant protein is not correctly processed in the endoplasmic reticulum (ER) and accumulates into insoluble aggregates. In addition, we show that the presence of increasing amounts of mutant protein induces a fraction of the soluble, native myocilin to move to the insoluble fraction. Given the importance of such protein aggregates in the etiology of several aging-related diseases, we propose that olfactomedin-defective mutants might contribute to the pathology of glaucoma through a mechanism involving intracellular accumulation of misfolded proteins.