The roles of activins in repair processes of the skin and the brain

Production of Mature Recombinant Human Activin A in Transgenic Rice Cell Suspension Culture

Activin A belongs to the transforming growth factor (TGF) family member, which exhibits a wide range of biological activities, including the regulation of cellular proliferation and differentiation and the promotion of neuronal survival. The isolation of AA from natural sources can only produce limited quantities of this bioactive protein. In this study, the whole gene of the precursor form of recombinant human activin A (rhAA) contains a signal peptide, and a pro-region and a mature region were cloned into an expression vector under the control of the rice α-amylase 3D (RAmy3D) promoter. To obtain the mature (active) form of rhAA, an enterokinase cleavage site was inserted between the pro-region and mature region of rhAA. The rice seed (Oryza sativa L. cv. Dongjin) was transformed with recombinant vectors by the Agrobacterium-mediated method, and the integration of the target gene into the plant genome was confirmed by genomic PCR. The transcript expression of rhAA in transgenic rice calli was confirmed by a Northern blot analysis of mRNA. The production of rhAA was verified by Western blot analysis and ELISA. The accumulation of secreted rhAA in the culture medium was purified by Ni2+-NTA. The mature form of AA was released from the precursor form of rhAA after proteolytically processing with enterokinase. Western blot shows that the mature AA was split into monomer and homodimer with molecular weights of 14 kDa and 28 kDa under reducing and non-reducing conditions, respectively. These results suggest that the mature form of rhAA could be produced and purified using transgenic rice cell suspension culture.

Genome-wide characterization of the TGF-β gene family and their expression in different tissues during tail regeneration in the Schlegel's Japanese gecko Gekko japonicus

The transforming growth factor-β (TGF-β) gene family is unique to animals and is involved in various important processes including tissue regeneration. Here, we identified 52 TGF-β family genes based on genome sequences of the gecko (Gekko japonicus), compared TGF-β genes between G. japonicus and other four reptilian species, and evaluated the expression of 14 randomly selected genes in muscle, kidney, liver, heart, and brain during tail regeneration to investigate whether their expression was tissue-dependent. We detected 23 conserved domains, 13 in the TGF-β ligand subfamily, and 10 in the receptor subfamily. The pattern of higher genetic variation in the ligand subfamily than in the receptor subfamily in vertebrates might result from the precise localization of agonists and antagonists in the cell surface and intracellular compartment. TGF-β genes were unevenly distributed across 15 chromosomes in G. japonicus, presumably resulting from gene losses and gains during evolution. Genes in the TGF-β receptor subfamily (ACVR2A, ACVR2B, ACVR1, BMPR1A, ACVRL1, BMPR2 and TGFBR1) played a vital role in the TGF-β signal pathway. The expression of all 14 randomly selected TGF-β genes was tissue-specific. Our study supports the speculation that some TGF-β family genes are involved in the early stages of tail regeneration.

Antagonistic effects of activin A and TNF-α on the activation of L929 fibroblast cells via Smad3-independent signaling

Fibroblasts play an important role in inflammation and tissue fibrosis. Both activin A and TNF-α can activate immune cells, however, the roles and relationship of them in activating fibroblasts in inflammation remain unclear. Here, this study revealed that TNF-α promoted the release of NO and IL-6 by L929 fibroblast cells, but co-treatment with activin A attenuated these effects. In contrast, activin A induced cell migration and increased the production of tissue fibrosis-related TGF-β1 and fibronectin, while TNF-α inhibited these function changes of L929 cells induced by activin A. Moreover, this study revealed that activin A and TNF-α regulated the activities of L929 cells via ERK1/2/MAPK pathway, rather than Smad3-dependent signaling pathway. Taken together, these data indicate that activin A and TNF-α exert mutually antagonistic effects on regulating fibroblasts activities, and the balance between their action may determine the process and outcome of fibroblasts-mediated inflammation.

Activin B signaling may promote the conversion of normal fibroblasts to scar fibroblasts

This study is to explore the molecular mechanism of benign bile duct hypertrophic scar formation.Differential proteins between the normal fibroblast (NFB) and scar fibroblast (SCFB) were screened by protein chip assay, and analyzed by pathway-enrichment analysis and function-enrichment analysis. The differential proteins were further tested by ELISA. SiRNA-Act B was transfected to SCFB to down-regulate the expression of Act B. NFB was incubated with rh-Act B. The cell apoptosis and cell cycle were determined by flow cytometry. The expression of Act B, Smad2/3, transforming growth factor-β1 (TGF-β1), endothelin-1 (ET-1), thrombospondin-1 (Tsp-1), and Oncostatin M (OSM) were detected by Western blot.A total of 37 differential proteins were identified in SCFBs by microarray (P < .05), including 27 up-regulated proteins and 10 down-regulated proteins (P < .05). Their function were associated with Activin signaling, synthesis and degradation of extracellular matrix, formation and activation of cytokine, inflammatory reaction, immunoreaction, tissue damage reaction, cell cycle, migration, apoptosis, and secretion, etc. ELISA results showed that the expression of Act B, TGF-β1, ET-1 were higher in SCFBs, while the expression of Tsp-1 and OSM were lower in SCFBs (P < .05). After interfered by siRNA-Act B, the expression of Act B mRNA decreased (P < .05). The percentage of early apoptosis increased (P < .05). The expression of Act B, Smad2/3, TGF-β1 were decreased and Tsp-1, OSM were increased (P < .05). After treatment with rh-Act B, the percentage of G0/G1 phase of NFBs was decreased and that of S phase was increased without significance (P > .05). The expression of Act B, Smad2/3, TGF-β1 were increased (P < .05) and Tsp-1, OSM were decreased (P < .01).There are differentially expressed proteins between SCFBs and NFBs. Activin B signal plays an important role in the process of NFB transforming to SCFB, and TGF-β1, Smad2/3, Tsp-1, and OSM are important participants.

The role of microRNAs in the healing of diabetic ulcers

MicroRNAs (miRNAs) are small protected molecules with a length of 18 to 25 nucleotides. Many studies have recently been conducted on miRNAs, illustrating their role in regulating many biological, physiological, and pathological activities, such as maintaining cellular signalling and regulating cellular pathways. The main role of miRNAs is to regulate the expression of genes after translation, which can lead to the destruction or suppression of translation by binding to mRNAs. As any change in the regulation of miRNAs is associated with several physiological abnormalities, such as type 2 diabetes and its complications, these molecules can be used for therapeutic purposes or as biomarkers for the diagnosis of diseases such as diabetes and its complications. In this review article, we will discuss important findings about the miRNAs and the role of these molecules in different phases of the wound-healing process of chronic wounds, especially diabetic ulcer.

Neuroprotective Effects of Anthraquinones from Rhubarb in Central Nervous System Diseases

Rhubarb is a well-known traditional Chinese medicine; it has been used in China for thousands of years. Rhubarb anthraquinones are the major medicinal ingredients derived from rhubarb including emodin, aloe-emodin, chrysophanol, rhein, physcion, and danthron. These different anthraquinone derivatives alone or in combination play a therapeutic role in central nervous system diseases (CNSD), such as cerebral ischemic stroke, intracerebral hemorrhage, traumatic brain injury, brain tumor, Alzheimer's disease, depression, and others. We review the experimental studies on these six anthraquinones in the treatment of CNSD by consulting literature published in the last 20 years in PubMed and then give a future perspective on it. In the end of this paper some deficiencies related to these studies also have been pointed out.

Activin B Regulates Adhesion, Invasiveness, and Migratory Activities in Oral Cancer: a Potential Biomarker for Metastasis

Activin B, a homodimer of inhibin beta b (INHBB), is a multifunctional cytokine belonging to the transforming growth factor-β (TGF-β) family. However, the molecular functions and clinical relevance of activin B have not been determined in oral cancer. We investigated the critical roles of activin B in oral squamous cell carcinoma (OSCC). We performed quantitative reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemistry to study INHBB expression in OSCC-derived cell lines and OSCC clinical samples. The INHBB expression levels were significantly (P < 0.05) overexpressed in OSCCs compared to normal counterparts in vitro and in vivo. Activin B-positivity in OSCC cases was significantly (P < 0.05) correlated with regional lymph node metastasis. The INHBB knockdown (shINHBB) cells promoted cellular adhesion and suppression of cellular invasiveness and migration. After treatment of shINHBB cells with activin B, those activities were restored similar to the shMock cells. In the processes of invasiveness and metastasis, the cells cause epithelial-mesenchymal transition (EMT). TGF-β and its family members are promoters of the EMT process. To investigate whether activin B is related to EMT, we examined the expressions of EMT-related genes and found that INHBB was related closely to EMT. Our results suggested for the first time that activin B indicates tumoral metastasis in OSCCs and might be a useful biomarker for OSCC metastasis.

Activin/follistatin system in grass carp pituitary cells: - Regulation by local release of growth hormone and luteinizing hormone and its functional role in growth hormone synthesis and secretion

Gonadotrophin regulation by activin/follistatin system is well-documented, but the corresponding effect on growth hormone (GH) has not been fully characterized and with little information available in lower vertebrates, especially in fish models. In grass carp, local interactions of GH and luteinizing hormone (LH) can induce GH release and gene expression at pituitary level via autocrine/paracrine mechanisms. To shed light on the role of activin/follistatin system in GH regulation by local actions of GH and LH, grass carp activin βA and βB were cloned, shown to be single-copy genes expressed in the pituitary, and confirmed to encode activin proteins capable of transactivating promoter with activin-responsive elements. In grass carp pituitary cells, activin A and B were effective in reducing GH secretion and GH cell content with concurrent drop in GH mRNA level whereas the opposite was true for follistatin, the activin-binding protein known to neutralize the effects of endogenous activin. Treatment with activin A and B not only could suppress basal but also inhibit GH mRNA expression induced by GH and human chorionic gonadotropin (hCG), a functional analogue of LH in fish model. Apparently, down-regulation of GH mRNA by activin was mediated by reducing GH transcript stability with concurrent inhibition on GH promoter activity via the SMAD pathway. In reciprocal experiments, GH treatment was found to up-regulate activin βA, activin βB and follistatin mRNA levels in carp pituitary cells but the opposite was noted by removing endogenous GH with GH antiserum. Interestingly, parallel treatment with hCG could also inhibit basal as well as GH-induced activin βA, activin βB and follistatin gene expression. These results, as a whole, indicate that the pituitary activin/follistatin system can serve as a regulatory target for local interactions of GH and LH and contribute to GH regulation by autocrine/paracrine mechanisms in the carp pituitary.

Esophageal squamous cell carcinoma invasion is inhibited by Activin A in ACVRIB-positive cells

Background

Esophageal squamous cell carcinoma (ESCC) is a global public health issue, as it is the eighth most common cancer worldwide. The mechanisms behind ESCC invasion and progression are still poorly understood, and warrant further investigation into these processes and their drivers. In recent years, the ligand Activin A has been implicated as a player in the progression of a number of cancers. The objective of this study was to investigate the role of Activin A signaling in ESCC.

Methods

To investigate the role Activin A plays in ESCC biology, tissue microarrays containing 200 cores from 120 ESCC patients were analyzed upon immunofluorescence staining. We utilized three-dimensional organotypic reconstruct cultures of dysplastic and esophageal squamous tumor cells lines, in the context of fibroblast-secreted Activin A, to identify the effects of Activin A on cell invasion and determine protein expression and localization in epithelial and stromal compartments by immunofluorescence. To identify the functional consequences of stromal-derived Activin A on angiogenesis, we performed endothelial tube formation assays.

Results

Analysis of ESCC patient samples indicated that patients with high stromal Activin A expression had low epithelial ACVRIB, the Activin type I receptor. We found that overexpression of stromal-derived Activin A inhibited invasion of esophageal dysplastic squamous cells, ECdnT, and TE-2 ESCC cells, both positive for ACVRIB. This inhibition was accompanied by a decrease in expression of the extracellular matrix (ECM) protein fibronectin and podoplanin, which is often expressed at the leading edge during invasion. Endothelial tube formation was disrupted in the presence of conditioned media from fibroblasts overexpressing Activin A. Interestingly, ACVRIB-negative TE-11 cells did not show the prior observed effects in the context of Activin A overexpression, indicating a dependence on the presence of ACVRIB.

Conclusions

We describe the first observation of an inhibitory role for Activin A in ESCC progression that is dependent on the expression of ACVRIB.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2920-y) contains supplementary material, which is available to authorized users.

Activin A programs the differentiation of human TFH cells

Follicular helper T (T_FH) cells are CD4⁺ T cells specialized in helping B cells and are associated both with protective antibody responses and autoimmune diseases. The promise of targeting T_FH cells therapeutically has been limited by fragmentary understanding of extrinsic signals regulating human T_FH cell differentiation. A screen of a human protein library identified activin A as new regulator of T_FH cell differentiation. Activin A orchestrated expression of multiple T_FH-associated genes, independently or in concert with additional signals. T_FH programming by activin A was antagonized by the cytokine IL-2. Activin A’s capacity to drive T_FH cell differentiation in vitro was conserved for non-human primates but not mice. Finally, activin A-induced T_FH programming was dependent on SMAD2 and SMAD3 signaling and blocked by pharmacological inhibitors.

Topical 5-azacytidine accelerates skin wound healing in rats

The development of new methods to improve skin wound healing may affect the outcomes of a number of medical conditions. Here, we evaluate the molecular and clinical effects of topical 5-azacytidine on wound healing in rats. 5-Azacytidine decreases the expression of follistatin-1, which negatively regulates activins. Activins, in turn, promote cell growth in different tissues, including the skin. Eight-week-old male Wistar rats were submitted to 8.0-mm punch-wounding in the dorsal region. After 3 days, rats were randomly assigned to receive either a control treatment or the topical application of a solution containing 5-azacytidine (10 mM) once per day. Photo documentation and sample collection were performed on days 5, 9, and 15. Overall, 5-azacytidine promoted a significant acceleration of complete wound healing (99.7% ± 0.7.0 vs. 71.2% ± 2.8 on day 15; n = 10; p < 0.01), accompanied by up to threefold reduction in follistatin expression. Histological examination of the skin revealed efficient reepithelization and cell proliferation, as evaluated by the BrdU incorporation method. 5-Azacytidine treatment also resulted in increased gene expression of transforming growth factor-beta and the keratinocyte markers involucrin and cytokeratin, as well as decreased expression of cytokines such as tumor necrosis factor-alpha and interleukin-10. Lastly, when recombinant follistatin was applied to the skin in parallel with topical 5-azacytidine, most of the beneficial effects of the drug were lost. Thus, 5-azacytidine acts, at least in part through the follistatin/activin pathway, to improve skin wound healing in rodents.

Intertwining of Activin A and TGFβ Signaling: Dual Roles in Cancer Progression and Cancer Cell Invasion

In recent years, a significant amount of research has examined the controversial role of activin A in cancer. Activin A, a member of the transforming growth factor β (TGFβ) superfamily, is best characterized for its function during embryogenesis in mesoderm cell fate differentiation and reproduction. During embryogenesis, TGFβ superfamily ligands, TGFβ, bone morphogenic proteins (BMPs) and activins, act as potent morphogens. Similar to TGFβs and BMPs, activin A is a protein that is highly systemically expressed during early embryogenesis; however, post-natal expression is overall reduced and remains under strict spatiotemporal regulation. Of importance, normal post-natal expression of activin A has been implicated in the migration and invasive properties of various immune cell types, as well as endometrial cells. Aberrant activin A signaling during development results in significant morphological defects and premature mortality. Interestingly, activin A has been found to have both oncogenic and tumor suppressor roles in cancer. Investigations into the role of activin A in prostate and breast cancer has demonstrated tumor suppressive effects, while in lung and head and neck squamous cell carcinoma, it has been consistently shown that activin A expression is correlated with increased proliferation, invasion and poor patient prognosis. Activin A signaling is highly context-dependent, which is demonstrated in studies of epithelial cell tumors and the microenvironment. This review discusses normal activin A signaling in comparison to TGFβ and highlights how its dysregulation contributes to cancer progression and cell invasion.

The Role of MicroRNAs in Diabetic Complications-Special Emphasis on Wound Healing

Overweight and obesity are major problems in today’s society, driving the prevalence of diabetes and its related complications. It is important to understand the molecular mechanisms underlying the chronic complications in diabetes in order to develop better therapeutic approaches for these conditions. Some of the most important complications include macrovascular abnormalities, e.g., heart disease and atherosclerosis, and microvascular abnormalities, e.g., retinopathy, nephropathy and neuropathy, in particular diabetic foot ulceration. The highly conserved endogenous small non-coding RNA molecules, the micro RNAs (miRNAs) have in recent years been found to be involved in a number of biological processes, including the pathogenesis of disease. Their main function is to regulate post-transcriptional gene expression by binding to their target messenger RNAs (mRNAs), leading to mRNA degradation, suppression of translation or even gene activation. These molecules are promising therapeutic targets and demonstrate great potential as diagnostic biomarkers for disease. This review aims to describe the most recent findings regarding the important roles of miRNAs in diabetes and its complications, with special attention given to the different phases of diabetic wound healing.

Activin A prevents neuron-like PC12 cell apoptosis after oxygen-glucose deprivation

In this study, PC12 cells were induced to differentiate into neuron-like cells using nerve growth factor, and were subjected to oxygen-glucose deprivation. Cells were treated with 0, 10, 20, 30, 50, 100 ng/mL exogenous Activin A. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide assay and Hoechst 33324 staining showed that the survival percentage of PC12 cells significantly decreased and the rate of apoptosis significantly increased after oxygen-glucose deprivation. Exogenous Activin A significantly increased the survival percentage of PC12 cells in a dose-dependent manner. Reverse transcription-PCR results revealed a significant increase in Activin receptor IIA, Smad3 and Smad4 mRNA levels, which are key sites in the Activin A/Smads signaling pathway, in neuron-like cells subjected to oxygen-glucose deprivation, while mRNA expression of the apoptosis-regulation gene caspase-3 decreased. Our experimental findings indicate that exogenous Activin A plays an anti-apoptotic role and protects neurons by means of activating the Activin A/Smads signaling pathway.

Emodin prevents hypoxic-ischemic neuronal injury: Involvement of the activin A pathway

Emodin, an extract of dried rhizomes and the root of the Rhizoma Polygoni Cuspidati, can protect neurons from hypoxic-ischemic brain damage. This study aimed to verify the underlying mechanism. After PC12 cells had differentiated into neuron-like cells under the induction of mouse nerve growth factor, cells were subjected to oxygen-glucose deprivation and treated with emodin. Results showed that the viability of neuron-like cells cultured under an ischemia-hypoxia environment decreased, while the expression of activin A and caspase-3 in cells increased. Emodin raised the survival rate of oxygen-glucose deprived neuron-like cells, increased activin A expression, and decreased caspase-3 expression. Experimental findings indicate that emodin can inhibit neuronal apoptosis and alleviate the injury of nerve cells after oxygen-glucose deprivation through the activin A pathway.

Effects of Activin A on the phenotypic properties of human periodontal ligament cells

Periodontal ligament (PDL) tissue plays an important role in tooth preservation by structurally maintaining the connection between the tooth root and the bone. The mechanisms involved in the healing and regeneration of damaged PDL tissue, caused by bacterial infection, caries and trauma, have been explored. Accumulating evidence suggests that Activin A, a member of the transforming growth factor-β (TGF-β) superfamily and a dimer of inhibinβa, contributes to tissue healing through cell proliferation, migration, and differentiation of various target cells. In bone, Activin A has been shown to exert an inhibitory effect on osteoblast maturation and mineralization. However, there have been no reports examining the expression and function of Activin A in human PDL cells (HPDLCs). Thus, we aimed to investigate the biological effects of Activin A on HPDLCs. Activin A was observed to be localized in HPDLCs and rat PDL tissue. When PDL tissue was surgically damaged, Activin A and IL-1β expression increased and the two proteins were shown to be co-localized around the lesion. HPDLCs treated with IL-1β or TNF-α also up-regulated the expression of the gene encoding inhibinβa. Activin A promoted chemotaxis, migration and proliferation of HPDLCs, and caused an increase in fibroblastic differentiation of these cells while down-regulating their osteoblastic differentiation. These osteoblastic inhibitory effects of Activin A, however, were only noted during the early phase of HPDLC osteoblastic differentiation, with later exposures having no effect on differentiation. Collectively, our results suggest that Activin A could be used as a therapeutic agent for healing and regenerating PDL tissue in response to disease, trauma or surgical reconstruction.

Alteration of skin wound healing in keratinocyte-specific mediator complex subunit 1 null mice

MED1 (Mediator complex subunit 1) is a co-activator of various transcription factors that function in multiple transcriptional pathways. We have already established keratinocyte-specific MED1 null mice (Med1^epi−/−) that develop epidermal hyperplasia. Herein, to investigate the function(s) of MED1 in skin wound healing, full-thickness skin wounds were generated in Med1^epi−/− and age-matched wild-type mice and the healing process was analyzed. Macroscopic wound closure and the re-epithelialization rate were accelerated in 8-week-old Med1^epi−/− mice compared with age-matched wild-type mice. Increased lengths of migrating epithelial tongues and numbers of Ki67-positive cells at the wounded epidermis were observed in 8-week-old Med1^epi−/− mice, whereas wound contraction and the area of α-SMA-positive myofibroblasts in the granulation tissue were unaffected. Migration was enhanced in Med1^epi−/− keratinocytes compared with wild-type keratinocytes in vitro. Immunoblotting revealed that the expression of follistatin was significantly decreased in Med1^epi−/− keratinocytes. Moreover, the mitogen-activated protein kinase pathway was enhanced before and after treatment of Med1^epi−/− keratinocytes with activin A in vitro. Cell-cycle analysis showed an increased ratio of S phase cells after activin A treatment of Med1^epi−/− keratinocytes compared with wild-type keratinocytes. These findings indicate that the activin-follistatin system is involved in this acceleration of skin wound healing in 8-week-old Med1^epi−/− mice. On the other hand, skin wound healing in 6-month-old Med1^epi−/− mice was significantly delayed with decreased numbers of Ki67-positive cells at the wounded epidermis as well as BrdU-positive label retaining cells in hair follicles compared with age-matched wild-type mice. These results agree with our previous observation that hair follicle bulge stem cells are reduced in older Med1^epi−/− mice, indicating a decreased contribution of hair follicle stem cells to epidermal regeneration after wounding in 6-month-old Med1^epi−/− mice. This study sheds light on the novel function of MED1 in keratinocytes and suggests a possible new therapeutic approach for skin wound healing and aging.

Beyond cell replacement: unresolved roles of NG2-expressing progenitors

NG2-expressing parenchymal precursors (NG2+p) serve as primary source of myelinating oligodendrocytes in both the developing and adult Central Nervous System (CNS). However, their abundance, limited differentiation potential at adult stages along with stereotypic reaction to injury independent of the extent of myelin loss suggest that NG2+p exert functions additional to myelin production. In support of this view, NG2+p express a complex battery of molecules known to exert neuromodulatory and neuroprotective functions. Further, they establish intimate physical associations with the other CNS cell types, receive functional synaptic contacts and possess ion channels apt to constantly sense the electrical activity of surrounding neurons. These latter features could endow NG2+p with the capability to affect neuronal functions with potential homeostatic outcomes. Here we summarize and discuss current evidence favoring the view that NG2+p can participate in circuit formation, modulate neuronal activity and survival in the healthy and injured CNS, and propose perspectives for studies that may complete our understanding of NG2+p roles in physiology and pathology.

The effect of activin A on signal transduction pathways in PC12 cells subjected to oxygen and glucose deprivation

The processes and mechanisms underlying brain injuries due to ischemia and anoxia have yet to be determined. Additionally, few clinical treatements are currently available. Activins have a protective role in the restoration, differentiation, and survival of injured cells, including Activin A (ActA), which acts as a neuroprotectant. However, its exact mechanism of action remains to be determined. ActA has been shown to protect neurons following ischemic brain injury. In this study, PC12 cells were differentiated into neuron-like cells after stimulation with nerve growth factor to prepare an oxygen/glucose deprivation (OGD) model in neurons. The differentiated PC12 cells, subjected to the OGD model, were exposed to ActA. Results showed that the PC12 survival rate decreased after OGD, leading to an increase in caspase-3 expression in these cells. Pretreatment with ActA was able to partially prevent OGD-induced apoptosis, likely through the downregulation of caspase-3. Futhermore, ActA pretreatment increased the expression of key proteins in the ActA/Smads signal transduction pathway, which may promote neuroprotection after OGD. Therefore, exogenous ActA may function as a neuroprotectant and provide a novel therapeutic treatment for ischemic brain injury.

Activin A induction of erythroid differentiation sensitizes K562 chronic myeloid leukemia cells to a subtoxic concentration of imatinib

Chronic myeloid leukemia (CML) is a hematopoietic stem/progenitor cell disorder in which Bcr-Abl oncoprotein inhibits cell differentiation. Differentiation induction is considered an alternative strategy for treating CML. Activin A, a member of the transforming growth factor-β superfamily, induces erythroid differentiation of CML cells through the p38 MAPK pathway. In this study, treatment of the K562 CML stem/progenitor cell line with activin A followed by a subtoxic concentration of the Bcr-Abl inhibitor imatinib strongly induced growth inhibition and apoptosis compared with simultaneous treatment with activin A and imatinib. Imatinib-induced growth inhibition and apoptosis following activin A pretreatment were dose- and time-dependent. Imatinib-induced growth inhibition and apoptosis were also dependent on the pretreatment dose of activin A. More than 90% of the activin A-induced increases in glycophorin A-positive cells were sensitive to imatinib. However, only some of original glycophorin A-positive cells in the activin A treatment group were sensitive to imatinib. Sequential treatment with activin A and imatinib decreased Bcr-Abl, procaspase-3, Mcl-1, and Bcl-xL and also induced cleavage of procaspase-3/poly(ADP-ribose)polymerase. The reduction of erythroid differentiation in p38 MAPK dominant-negative mutants or by short hairpin RNA knockdown of p38 MAPK decreased the growth inhibition and apoptosis mediated by sequential treatment with activin A and imatinib. Furthermore, the same inhibition level of multidrug resistance 1 expression was observed in cells treated with activin A alone, treated sequentially with activin A and imatinib, or treated simultaneously with activin A and imatinib. The p38 MAPK inhibitor SB-203580 can restore activin A-inhibited multidrug resistance 1 expression. Taken together, our results suggest that a subtoxic concentration of imatinib could exhibit strong cytotoxicity against erythroid-differentiated K562 CML cells.

Molecular and cellular mechanisms of bone morphogenetic proteins and activins in the skin: potential benefits for wound healing

Bone morphogenetic proteins (BMPs) and activins are phylogenetically conserved proteins, belonging to the transforming growth factor-β superfamily, that signal through the phosphorylation of receptor-regulated Smad proteins, activating different cell responses. They are involved in various steps of skin morphogenesis and wound repair, as can be evidenced by the fact that their expression is increased in skin injuries. BMPs play not only a role in bone regeneration but are also involved in cartilage, tendon-like tissue and epithelial regeneration, maintain vascular integrity, capillary sprouting, proliferation/migration of endothelial cells and angiogenesis, promote neuron and dendrite formation, alter neuropeptide levels and are involved in immune response modulation, at least in animal models. On the other hand, activins are involved in wound repair through the regulation of skin and immune cell migration and differentiation, re-epithelialization and granulation tissue formation, and also promote the expression of collagens by fibroblasts and modulate scar formation. This review aims at enunciating the effects of BMPs and activins in the skin, namely in skin development, as well as in crucial phases of skin wound healing, such as inflammation, angiogenesis and repair, and will focus on the effects of these proteins on skin cells and their signaling pathways, exploring the potential therapeutic approach of the application of BMP-2, BMP-6 and activin A in chronic wounds, particularly diabetic foot ulcerations.

Neuroprotective effects of exogenous activin A on oxygen-glucose deprivation in PC12 cells

Ischemic cerebrovascular disease is one of the most common causes of death in the World. Exogenous activin A (ActA) protects neurons against toxicity and plays a central role in regulating the brain's response to injury. In the present study, we investigated the mechanisms involved in the neuroprotective effects of ActA in a model of hypoxic-ischemic brain disease. We found that ActA could effectively increase the survival rate of PC12 cells and relieve oxygen-glucose deprivation (OGD) damage. To clarify the neuroprotective mechanisms of ActA, the effects of ActA on the ActA/Smad pathway and on the up-regulation of inducible nitric oxide synthase (NOS) and superoxide dismutase (SOD) were investigated using OGD in PC12 cells. The results showed that ActA could increase the expression of activin receptor IIA (ActRIIA), Smad3 and Smad4 and that 50 ng/mL and 100 ng/mL of ActA could reduce NO levels and increase SOD activity by 78.9% and 79.9%, respectively. These results suggested that the neuroprotective effects of ActA in ischemia could be related to the activation of the ActA/Smad signaling pathway and to its anti-oxidant activities.

Activin B promotes epithelial wound healing in vivo through RhoA-JNK signaling pathway

Background

Activin B has been reported to promote the proliferation and migration of keratinocytes in vitro via the RhoA-JNK signaling pathway, whereas its in vivo role and mechanism in wound healing process has not yet been elucidated.

Principal Findings

In this study, we explored the potential mechanism by which activin B induces epithelial wound healing in mice. Recombinant lentiviral plasmids, with RhoA (N19) and RhoA (L63) were used to infect wounded KM mice. The wound healing process was monitored after different treatments. Activin B-induced cell proliferation on the wounded skin was visualized by electron microscopy and analyzed by 5′-bromodeoxyuridine (BrdU) incorporation assay. Protein expression of p-JNK or p-cJun was determined by immunohistochemical staining and immunoblotting analysis. Activin B efficiently stimulated the proliferation of keratinocytes and hair follicle cells at the wound area and promoted wound closure. RhoA positively regulated activin B-induced wound healing by up-regulating the expression of p-JNK and p-cJun. Moreover, suppression of RhoA activation delayed activin B-induced wound healing, while JNK inhibition recapitulated phenotypes of RhoA inhibition on wound healing.

Conclusion

These results demonstrate that activin B promotes epithelial wound closure in vivo through the RhoA-Rock-JNK-cJun signaling pathway, providing novel insight into the essential role of activin B in the therapy of wound repair.

Activin A inhibits vascular endothelial cell growth and suppresses tumour angiogenesis in gastric cancer

Background:

Activin A is a multi-functional cytokine belonging to the transforming growth factor-β (TGF-β) superfamily; however, the effect of activin A on angiogenesis remains largely unclear. We found that inhibin β A subunit (INHBA) mRNA is overexpressed in gastric cancer (GC) specimens and investigated the effect of activin A, a homodimer of INHBA, on angiogenesis in GC.

Methods:

Anti-angiogenic effects of activin A via p21 induction were evaluated using human umbilical vein endothelial cells (HUVECs) in vitro and a stable INHBA-introduced GC cell line in vivo.

Results:

Compared with TGF-β, activin A potently inhibited the cellular proliferation and tube formation of HUVECs with induction of p21. A promoter assay and a chromatin immunoprecipitation assay revealed that activin A directly regulates p21 transcriptional activity through Smads. Stable p21-knockdown significantly enhanced the cellular proliferation of HUVECs. Notably, stable p21-knockdown exhibited a resistance to activin-mediated growth inhibition in HUVECs, indicating that p21 induction has a key role on activin A-mediated growth inhibition in vascular endothelial cells. Finally, a stable INHBA-introduced GC cell line exhibited a decrease in tumour growth and angiogenesis in vivo.

Conclusion:

Our findings highlight the suppressive role of activin A, unlike TGF-β, on tumour growth and angiogenesis in GC.

Activin A binds to perlecan through its pro-region that has heparin/heparan sulfate binding activity

Activin A, a member of the transforming growth factor-β family, plays important roles in hormonal homeostasis and embryogenesis. In this study, we produced recombinant human activin A and examined its abilities to bind to extracellular matrix proteins. Recombinant activin A expressed in 293-F cells was purified as complexes of mature dimeric activin A with its pro-region. Among a panel of extracellular matrix proteins tested, recombinant activin A bound to perlecan and agrin, but not to laminins, nidogens, collagens I and IV, fibronectin, and nephronectin. The binding of recombinant activin A to perlecan was inhibited by heparin and high concentrations of NaCl and abolished by heparitinase treatment of perlecan, suggesting that activin A binds to the heparan sulfate chains of perlecan. In support of this possibility, recombinant activin A was capable of directly binding to heparin and heparan sulfate chains. Site-directed mutagenesis of recombinant activin A revealed that clusters of basic amino acid residues, Lys(259)-Lys(263) and Lys(270)-Lys(272), in the pro-region were required for binding to perlecan. Interestingly, deletion of the peptide segment Lys(259)-Gly(277) containing both basic amino acid clusters from the pro-region did not impair the activity of activin A to stimulate Smad-dependent gene expressions, although it completely ablated the perlecan-binding activity. The binding of activin A to basement membrane heparan sulfate proteoglycans through the basic residues in the pro-region was further confirmed by in situ activin A overlay assays using frozen tissue sections. Taken together, the present results indicate that activin A binds to heparan sulfate proteoglycans through its pro-region and thereby regulates its localization within tissues.

Synthesis, purification and bioactivity of recombinant human activin A expressed in the yeast Pichia pastoris

The transforming growth factor-beta (TGF-beta) superfamily member, activin A, plays a central role in the regulation of multiple physiological processes including cell differentiation, mitogenesis, embryogenesis, apoptosis and inflammation. In normal cells, activin A signalling is regulated to maintain cellular and tissue health and suppress tumour growth. Disruption of activin A signalling has been implicated in tumour formation and progression. Hence, the availability of activin A is an important target for the development of diagnostics and drugs for therapeutic intervention. To this end, we have expressed human activin A in Pichia pastoris, permitting its secretion into culture medium and purification as the mature homodimer. A construct was engineered encoding the monomeric precursor protein with a N-terminal FLAG affinity tag (DYKDDDDK) and a cleavage site (EKR) for Kex2p protease. Procedures for the two-step purification of human activin A by ion-exchange and anti-FLAG antibody affinity chromatography, and for the removal of the FLAG affinity tag from purified recombinant human activin A by enteropeptidase, are described. The molecular weights of the FLAG-tagged and de-tagged human activin A were confirmed by MALDI-TOF mass spectroscopy. The biological activity of these recombinant activins was assessed for their effects on modulating the secretion of Endothelin-1 (ET-1) by human umbilical vein endothelial cells (HUVECs). The recombinant human activin A containing the intact FLAG tag resulted in a reduced ET-1 secretion from HUVECs, whereas upon removal of this affinity purification tag the purified recombinant human activin A restored ET-1 secretion to levels comparable to the positive control. These results document an approach of considerable potential for the simple, large-scale expression and purification of this important human growth factor for use in diagnostic and therapeutic purposes.

The neuroprotective effect of Activin A and B: implication for neurodegenerative diseases

Activin is a member of the transforming growth factor-beta superfamily which comprises a growing list of multifunctional proteins that function as modulators of cell proliferation, differentiation, hormone secretion and neuronal survival. This study examined the neuroprotective effect of both Activin A and B in serum withdrawal and oxidative stress apoptotic cellular models and investigated the expression of pro- and anti-apoptotic proteins, which may account for the mechanism of Activin-induced neuroprotection. Here, we report that recombinant Activin A and B are neuroprotective against serum deprivation- and toxin- [either the parkinsonism-inducing neurotoxin, 6-hydroxydopamine (6-OHDA) or the peroxynitrite donor, 3-(4-morpholinyl) sydnonimine hydrochloride (SIN-1)] induced neuronal death in human SH-SY5Y neuroblastoma cells. Furthermore, we demonstrate for the first time that transient transfection with Activin betaA or betaB significantly protect SH-SY5Y and rat pheochromocytoma PC12 cells against serum withdrawal-induced apoptosis. This survival effect is mediated by the Bcl-2 family members and involves inhibition of caspase-3 activation; reduction of cleaved poly-ADP ribose polymerase and phosphorylated H2A.X protein levels and elevation of tyrosine hydroxylase expression. These results indicate that both Activin-A and -B share the potential to induce neuroprotective activity and thus may have positive impact on aging and neurodegenerative diseases to retard the accelerated rate of neuronal degeneration.

Activin is a neuronal survival factor that is rapidly increased after transient cerebral ischemia and hypoxia in mice

One approach for developing targeted stroke therapies is to identify the neuronal protective and destructive signaling pathways and gene expression that follow ischemic insult. In some neural injury models, the transforming growth factor-beta family member activin can provide neuroprotective effects in vivo and promote neuronal survival. This study tests if activin supports cortical neurons after ischemic challenge in vitro and if signals after cerebral ischemia involve activin in vivo. In a defined cell culture model that uses hydrogen peroxide (H(2)O(2))-free radical stress, activin addition maintained neuronal survival. H(2)O(2) treatment increased activin mRNA twofold in surviving cortical neurons, and inhibition of activin with neutralizing antibodies caused neuronal death. These data identify activin gene changes as a rapid response to oxidative stress, and indicate that endogenous activin acts as a protective factor for cortical neurons in vitro. Similarly, after transient focal cerebral ischemia in adult mice, activin mRNA increased at 1 and 4 h ipsilateral to the infarct but returned to control values at 24 h after reperfusion. Intracellular activated smad signals were detected in neurons adjacent to the infarct. Activin was also increased after 2 h of 11% hypoxia. Activin mRNA increased at 1 h but not 4 or 24 h after hypoxia, similar to the time course of erythropoietin and vascular endothelial growth factor induction. These findings identify activin as an early-regulated gene response to transient ischemia and hypoxia, and its function in cortical neuron survival during oxidative challenge provides a basis to test activin as a potential therapeutic in stroke injury.

Cg-TGF-beta, a TGF-beta/activin homologue in the Pacific Oyster Crassostrea gigas, is involved in immunity against Gram-negative microbial infection

Transforming growth factor-beta (TGF-beta) members represent a widespread protein superfamily in the animal kingdom, but few members have been characterised in lophotrochozoans, a major clade of invertebrates. Here, we report the identification of Crassostrea gigas-TGF-beta (Cg-TGF-beta), a homologue of vertebrate TGF-beta and activin, from the bivalve mollusc C. gigas. Phylogenetic analysis suggests an early ancestral origin of this subgroup of TGF-beta superfamily member. Investigation of the spatio-temporal expression of Cg-TGF-beta gene by real-time quantitative RT-PCR showed a ubiquitous pattern in all adult tissues. These findings imply that Cg-TGF-beta has multiple functions as described for its vertebrate counterparts. Moreover, Cg-TGF-beta was upregulated in haemocytes during infection by a Gram-negative bacterium, suggesting that it could act as a cytokine involved in immunity in molluscs.

Expression of bone morphogenetic proteins (BMPs), their receptors, and activins in normal and scarred conjunctiva: Role of BMP-6 and activin-A in conjunctival scarring?

Bone morphogenetic proteins (BMPs) and activins are multifunctional growth factors, which also affect wound healing and tissue fibrosis. To determine their putative role in conjunctival wound healing and scarring, we investigated the expression of various BMPs, BMP receptors, and activins in normal and scarred human conjunctival tissue and in cultured human Tenon's capsule fibroblasts on the mRNA and protein level. Messenger RNA expression of BMP-2, BMP-3, BMP-4, BMP-5, BMP-6, BMP-7, the BMP receptors type I (BMPR-IA, BMPR-IB) and II (BMPR-II), and of activin A and B was investigated by semi-quantitative RT-PCR in normal conjunctival specimens and in scarred filtering blebs as well as in cultured Tenon's capsule fibroblasts obtained from patients with primary open-angle glaucoma (POAG), pseudoexfoliation (PEX) glaucoma and cataract. Immunohistochemistry was used to study the protein expression of BMP-2, BMP-4, BMP-6, BMP-7, and activin A in normal and scarred conjunctival tissue as well as in cultured Tenon's capsule fibroblasts. BMP-2, BMP-3, BMP-4, BMP-6, BMP-7, all BMP receptors, and activin A were expressed on the mRNA and protein level in conjunctival biopsies without showing any differences between groups of patients. The mRNA and protein expression of both BMP-6 and activin A was found to be significantly increased in scar tissue compared with normal conjunctiva and could be immunolocalized to epithelial cells, vascular endothelia, stromal fibroblasts, and macrophage-like cells. However, no significant increase in receptor gene expression was observed in scar tissue. With the exception of BMP-7, all growth factors and receptors were also expressed in cultured Tenon's fibroblasts without showing any differences between cultures derived from normal and scarred conjunctival specimens. These findings suggest various BMPs and activin A as components of the conjunctival cytokine meshwork regulating tissue homeostasis and wound healing and provide evidence that alterations in the expression of BMP-6 and activin A, in particular, are associated with conjunctival scarring. Modulation of BMP/activin activities may, therefore, be explored as new approaches for managing postoperative conjunctival scarring responses in glaucoma patients.

The role of activin in neuropeptide induction and pain sensation

Signals from target tissues play critical roles in the functional differentiation of neuronal cells, and in their subsequent adaptations to peripheral changes in the adult. Sensory neurons in the dorsal root ganglia (DRG) provide an excellent model system for the study of signals that regulate the development of neuronal diversity. DRG have been well characterized and contain both neurons that convey information from muscles about limb position, as well as other neurons that provide sensations from skin about pain information. Sensory neurons involved in pain sensation can be distinguished physiologically and antigenically, and one hallmark characteristic is that these neurons contain neuropeptides important for their functions. The transforming growth factor (TGF) beta family member activin A has recently been implicated in neural development and response to injury. During sensory neuron development, peripheral target tissues containing activin or activin itself can regulate pain neuropeptide expression. Long after development has ceased, skin target tissues retain the capacity to signal neurons about changes or injury, to functionally refine synapses. This review focuses on the role of activin as a target-derived differentiative factor in neural development that has additional roles in response to cutaneous injuries in the adult.

Rat activin-betaE mRNA expression during development and in acute and chronic liver injury

Activin-βE mRNA expression was investigated in male and female rats using gel-based and quantitative RT-PCR, in fetal and post-natal liver during development and in a variety of tissues from 200 gm adult animals. Activin-βE expression was also assessed in rat liver after partial hepatectomy, and after repeated toxic insult. Male Sprague Dawley rats were subjected to partial hepatectomy or sham operations. Samples were collected from the caudate liver lobe during regeneration, from 12 to 240 hr after surgery. Three groups of 5 male rats were treated with CCl₄ for 0 (control), 5 or 10 weeks, to induce liver fibrosis and cirrhosis. Activin-βE mRNA was predominantly expressed in liver, with much lower amounts of mRNA observed in pituitary, adrenal gland and spleen, in both males and females. Low activin-βE expression was observed in liver at fetal day 16, with higher levels seen between post-natal days 3 and 35 and a further increase noted by day 47, in both males and females. Liver activin-βE mRNA concentrations did not change from control values 12-72 hr after PHx, but significantly increased over six fold, 168 hr post-hepatectomy, when liver mass was restored. Activin-βE mRNA was up-regulated after 5 weeks of CCl₄ treatment, but not after 10 weeks. The changes in activin-βE mRNA concentrations after liver insult did not always parallel those reported for the activin-βC subunit, suggesting activin-βE may have an independent role in liver under certain conditions.

Stroke injury in rats causes an increase in activin A gene expression which is unaffected by oestradiol treatment

Activins are members of the transforming growth factor-beta superfamily that exert neurotrophic and neuroprotective effects on various neuronal populations. To determine the possible function of activin in stroke injury, we assessed which components of the activin signalling pathway were modulated in response to middle cerebral artery occlusion (MCAO). Furthermore, because oestradiol replacement protects against MCAO-induced cell death, we explored whether oestradiol replacement influences activin gene expression. Female Sprague-Dawley rats underwent permanent MCAO and the expression of activins and their corresponding receptors was determined by semiquantitative reverse transcriptase-polymerase chain reaction at 24 h after onset of ischaemia. We observed up-regulation of activin betaA and activin type I receptor A mRNA in response to injury. Dual-label immunocytochemistry followed by confocal z-stack analysis showed that the activin A expressing cells comprised neurones. Next, we monitored the time course of activin betaA mRNA expression in oestradiol- or vehicle-treated rats at 4, 8, 16 and 24 h after MCAO via in situ hybridisation. Starting at 4 h after injury, activin betaA mRNA was up-regulated in cortical and striatal areas in the ipsilateral hemisphere. Activin betaA mRNA levels in the cortex increased dramatically with time and were highest at 24 h after the insult, and oestradiol replacement did not influence this increase.

Activin A suppresses neuroblastoma xenograft tumor growth via antimitotic and antiangiogenic mechanisms

The tumor suppressor function of activin A, together with our findings that activin A is an inhibitor of angiogenesis, which is down-regulated by the N-MYC oncogene, prompted us to investigate in more detail its role in the malignant transformation process of neuroblastomas. Indeed, neuroblastoma cells with restored activin A expression exhibited a diminished proliferation rate and formed smaller xenograft tumors with reduced vascularity, whereas lung metastasis rate remained unchanged. In agreement with the decreased vascularity of the xenograft tumors, activin A inhibited several crucial angiogenic responses of cultured endothelial cells, such as proteolytic activity, migration, and proliferation. Endothelial cell proliferation, activin A, or its constitutively active activin receptor-like kinase 4 receptor (ALK4T206D), increased the expression of CDKN1A (p21), CDKN2B (p15), and CDKN1B (p27) CDK inhibitors and down-regulated the expression of vascular endothelial growth factor receptor-2, the receptor of a key angiogenic factor in cancer. The constitutively active forms of SMAD2 and SMAD3 were both capable of inhibiting endothelial cell proliferation, whereas the dominant-negative forms of SMAD3 and SMAD4 released the inhibitory effect of activin A on endothelial cell proliferation by only 20%. Thus, the effects of activin A on endothelial cell proliferation seem to be conveyed via the ALK4/SMAD2-SMAD3 pathways, however, non-SMAD cascades may also contribute. These results provide novel information regarding the role of activin A in the malignant transformation process of neuroblastomas and the molecular mechanisms involved in regulating angiogenesis thereof.

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.

Dynamics and localization of activin A expression in rat gastric ulcers

BACKGROUND

Activin A, the homodimer of the activin/inhibin betaA subunit, has been shown to participate in cutaneous wound healing. In this study we intended to determine its part in gastric ulceration.

METHODS

Activin A expression was studied by immunohistochemistry and in situ hybridization in acetic-acid-induced chronic gastric ulcers in rat. The dynamics of this process were also assessed by quantitative real time RT-PCR and RNase protection assays (RPA). The effects of different doses of this cytokine on epithelial and mesenchymal cell proliferation were quantitated in vitro.

RESULTS

Low amounts of activin A and its mRNA were expressed by epithelia, endothelia and fibroblasts in intact gastric tissue. Granulation tissue of gastric ulcers and gastric glands adjacent to the ulcer rim expressed markedly increased amounts of activin protein as well as activin/inhibin betaA mRNA. RPA and RT-PCR studies revealed a more than 3-fold increase in the relative abundance of this mRNA. Activin A did not affect the proliferation rate of fibroblasts and epithelial cells in vitro.

CONCLUSIONS

Activin A participates in gastric ulcer healing in a similar fashion as in cutaneous wounding. Its expression on protein and mRNA level is markedly increased in ulcer base and rim.

Bone morphogenetic proteins and their antagonists in skin and hair follicle biology

Bone morphogenetic proteins (BMP) are members of the transforming growth factor-beta superfamily regulating a large variety of biologic responses in many different cells and tissues during embryonic development and postnatal life. BMP exert their biologic effects via binding to two types of serine/threonine kinase BMP receptors, activation of which leads to phosphorylation and translocation into the nucleus of intracellular signaling molecules, including Smad1, Smad5, and Smad8 ("canonical" BMP signaling pathway). BMP effects are also mediated by activation of the mitogen-activated protein (MAP) kinase pathway ("noncanonical" BMP Signaling pathway). BMP activity is regulated by diffusible BMP antagonists that prevent BMP interactions with BMP receptors thus modulating BMP effects in tissues. During skin development, BMPs its receptors and antagonists show stringent spatiotemporal expressions patterns to achieve proper regulation of cell proliferation and differentiation in the epidermis and in the hair follicle. In normal postnatal skin, BMP are involved in the control of epidermal homeostasis, hair follicle growth, and melanogenesis. Furthermore, BMP are implicated in a variety of pathobiologic processes in skin, including wound healing, psoriasis, and carcinogenesis. Therefore, BMPs represent new important players in the molecular network regulating homeostasis in normal and diseased skin. Pharmacologic modulation of BMP signaling may be used as a new approach for managing skin and hair disorders.

Activins, inhibins, and follistatins: from endocrinology to signaling. A paradigm for the new millennium

It has been 70 years since the name inhibin was used to describe a gonadal factor that negatively regulated pituitary hormone secretion. The majority of this period was required to achieve purification and definitive characterization of inhibin, an event closely followed by identification and characterization of activin and follistatin (FS). In contrast, the last 15-20 years saw a virtual explosion of information regarding the biochemistry, physiology, and biosynthesis of these proteins, as well as identification of activin receptors, and a unique mechanism for FS action-the nearly irreversible binding and neutralization of activin. Many of these discoveries have been previously summarized; therefore, this review will cover the period from the mid 1990s to present, with particular emphasis on emerging themes and recent advances. As the field has matured, recent efforts have focused more on human studies, so the endocrinology of inhibin, activin, and FS in the human is summarized first. Another area receiving significant recent attention is local actions of activin and its regulation by both FS and inhibin. Because activin and FS are produced in many tissues, we chose to focus on a few particular examples with the most extensive experimental support, the pituitary and the developing follicle, although nonreproductive actions of activin and FS are also discussed. At the cellular level, it now seems that activin acts largely as an autocrine and/or paracrine growth factor, similar to other members of the transforming growh factor beta superfamily. As we discuss in the next section, its actions are regulated extracellularly by both inhibin and FS. In the final section, intracellular mediators and modulators of activin signaling are reviewed in detail. Many of these are shared with other transforming growh factor beta superfamily members as well as unrelated molecules, and in a number of cases, their physiological relevance to activin signal propagation remains to be elucidated. Nevertheless, taken together, recent findings suggest that it may be more appropriate to consider a new paradigm for inhibin, activin, and FS in which activin signaling is regulated extracellularly by both inhibin and FS whereas a number of intracellular proteins act to modulate cellular responses to these activin signals. It is therefore the balance between activin and all of its modulators, rather than the actions of any one component, that determines the final biological outcome. As technology and model systems become more sophisticated in the next few years, it should become possible to test this concept directly to more clearly define the role of activin, inhibin, and FS in reproductive physiology.

The gene expression sequence of radiated mucosa in an animal mucositis model

Oral mucositis is a common, dose-limiting, acute toxicity of radiation therapy administered for the treatment of cancers of the head and neck. Accumulating data would suggest that the pathogenesis of mucositis is complex and involves the sequential interaction of all cell types of the oral mucosa, as well as a number of cytokines and elements of the oral environment. While a number of studies have reported on gene expression of particular cell types in response to radiation, the overall response of irradiated mucosa has only been evaluated in a limited way. The present study was undertaken to evaluate the expression of a target group of genes using RNA quantification assays and, more broadly, to assess patterns of mucosal gene expression using DNA microarray hybridization. Our results demonstrate the sequential upregulation of a series of genes that, when taken collectively, suggest an intricate functional interaction.