The novel primary response gene MyD118 and the proto-oncogenes myb, myc, and bcl-2 modulate transforming growth factor beta 1-induced apoptosis of myeloid leukemia cells

Growth arrest and DNA damage-inducible 45: a new player on inflammatory diseases

Growth arrest and DNA damage-inducible 45 (GADD45) proteins are critical stress sensors rapidly induced in response to genotoxic/physiological stress and regulate many cellular functions. Even though the primary function of the proteins is to block the cell cycle, inhibit cell proliferation, promote cell apoptosis, and repair DNA damage to cope with the damage caused by internal and external stress on the body, evidence has shown that GADD45 also has the function to modulate innate and adaptive immunity and plays a broader role in inflammatory and autoimmune diseases. In this review, we focus on the immunomodulatory role of GADD45 in inflammatory and autoimmune diseases. First, we describe the regulatory factors that affect the expression of GADD45. Then, we introduce its immunoregulatory roles on immune cells and the critical signaling pathways mediated by GADD45. Finally, we discuss its immunomodulatory effects in various inflammatory and autoimmune diseases.

GADD45 in Stress Signaling, Cell Cycle Control, and Apoptosis

GADD45 is a gene family consisting of GADD45A, GADD45B, and GADD45G that is often induced by DNA damage and other stress signals associated with growth arrest and apoptosis. Many of these roles are carried out via signaling mediated by p38 mitogen-activated protein kinases (MAPKs). The GADD45 proteins can contribute to p38 activation either by activation of upstream kinase(s) or by direct interaction, as well as suppression of p38 activity in certain cases. In vivo, there are important tissue and cell type specific differences in the roles for GADD45 in MAPK signaling. In addition to being p53-regulated, GADD45A has also been found to contribute to p53 activation via p38. Like other stress and signaling proteins, GADD45 proteins show complex regulation and numerous effectors. More recently, aberrant GADD45 expression has been found in several human cancers, but the mechanisms behind these findings largely remain to be understood.

miR-148 targets CiGadd45ba and CiGadd45bb to modulate the inflammatory response to bacterial infection in grass carp

In grass carp (Ctenopharyngodon idella), septicemia is a systemic inflammatory response to bacterial infection. Once infected bacteria, a hyper-inflammatory state that could lead to septic shock and death. There is increasing evidence that microRNAs are involved in the regulation of the inflammatory response. Ctenopharyngodon idella growth arrest and DNA damage-inducible 45 ba and bb (CiGadd45ba and CiGadd45bb) are two subtypes of Gadd45b. In the present study, miR-148 was confirmed to be involved in the inflammatory response after infection with Aeromonas hydrophila. Dual-luciferase reporter assays and miRNA expression profiling confirmed that miR-148 targeted both CiGadd45ba and CiGadd45bb. Transfection with miR148 mimics and inhibitors altered the expression levels of proinflammatory genes, suggesting that miRNAs regulate the immune response in grass carp. Our results provide a theoretical basis for studying the molecular mechanism underlying the regulation of inflammation by miR-148 in grass carp.

miR-23a-3p and miR-23a-5p target CiGadd45ab to modulate inflammatory response and apoptosis in grass carp

Ctenopharyngodon idella growth arrest and DNA damage-inducible 45 ab (CiGadd45ab) is a subtype of the Gadd45a gene of the Gadd45 family in grass carp. There is increasing evidence that microRNAs (miRNAs) are involved in the regulation of inflammatory and apoptotic responses. However, little is known about the regulatory effects of miRNAs on CiGadd45ab expression. In the present study, CiGadd45ab was identified as a target gene of miR-23a-3p and miR-23a-5p, based on miRNA expression profiling and a dual-luciferase reporter assay. In addition, miR-23a-3p and miR-23a-5p were both confirmed to be involved in the inflammatory response following infection with Aeromonas hydrophila by targeting CiGadd45ab. Transfection with miR-23a-3p and miR-23a-5p mimics and inhibitor altered proinflammatory gene expression and apoptosis rate, thereby suggesting that miRNAs regulate immune response and anti-apoptosis by targeting CiGadd45ab in grass carp. Our results provide a theoretical basis for exploring the molecular mechanisms by which miR-23a-3p and miR-23a-5p target CiGadd45ab to regulate inflammation and apoptosis against bacterial infection in grass carp.

Effects of microRNA-731 on inflammation and apoptosis by targeting CiGadd45aa in grass carp

Ctenopharyngodon idellagrowth arrest and DNA damage-inducible 45aa (CiGadd45aa) is a member of the Gadd45 family of immune-related proteins in grass carp. There is increasing evidence that microRNAs (miRNAs) are involved in the regulation of inflammatory responses and apoptosis. However, little is known about the regulatory effects of miRNAs on CiGadd45aa expression in grass carp. In the present study, CiGadd45aa was identified as a target gene of miR-731 based on miRNA expression profiling and dual-luciferase reporter assay. Our study revealed that miR-731 targets CiGadd45aa and regulates the expression of proinflammatory factors, thereby regulating immune response in grass carp. In addition, CiGadd45aa and miR-731 were both found induced apoptosis. Hence, our findings provide a theoretical basis for exploring the molecular mechanism by which miR-731 regulates inflammation and apoptosis in grass carp.

Fluorescent labeling of CRISPR/Cas9 RNP for gene knockout in HSPCs and iPSCs reveals an essential role for GADD45b in stress response

CRISPR/Cas9-mediated gene editing of stem cells and primary cell types has several limitations for clinical applications. The direct delivery of ribonucleoprotein (RNP) complexes consisting of Cas9 nuclease and guide RNA (gRNA) has improved DNA- and virus-free gene modifications, but it does not enable the essential enrichment of the gene-edited cells. Here, we established a protocol for the fluorescent labeling and delivery of CRISPR/Cas9-gRNA RNP in primary human hematopoietic stem and progenitor cells (HSPCs) and induced pluripotent stem cells (iPSCs). As a proof of principle for genes with low-abundance transcripts and context-dependent inducible expression, we successfully deleted growth arrest and DNA-damage-inducible β (GADD45B). We found that GADD45B is indispensable for DNA damage protection and survival in stem cells. Thus, we describe an easy and efficient protocol of DNA-free gene editing of hard-to-target transcripts and enrichment of gene-modified cells that are generally difficult to transfect.

Endometrial mesenchymal stem cells isolated from menstrual blood repaired epirubicin-induced damage to human ovarian granulosa cells by inhibiting the expression of Gadd45b in cell cycle pathway

Background

To explore the effect of mesenchymal stem cells isolated from menstrual blood (MB-MSCs) on epirubicin-induced damage to human ovarian granulosa cells (GCs) and its potential mechanisms.

Methods

The estradiol, progesterone, anti-Müllerian hormone, inhibin A, and inhibin B levels were determined using enzyme-linked immunosorbent assay. The proliferation of GCs was detected by Cell Counting Kit-8 assays. The cell cycle distribution was detected by propidiumiodide single staining. The apoptosis of GCs was determined using Annexin V and 7-AAD double staining. The differentially expressed genes of GCs were analyzed with Affymetrix Human Transcriptome Array 2.0 gene chip and verified with Western blot analysis.

Results

Epirubicin inhibited the secretion of estradiol, progesterone, anti-Müllerian hormone, inhibin A, and inhibin B and the proliferation of GCs; arrested these GCs in G2/M phase; and promoted the apoptosis of GCs. However, MB-MSCs repaired epirubicin-induced damage to GCs. Differentially expressed genes of GCs, Gadd45b, CyclinB1, and CDC2, were found by microarray and bioinformatics analysis. Western blot showed that epirubicin upregulated Gadd45b protein expression and downregulated CyclinB1 and CDC2 protein expression, while MB-MSCs downregulated Gadd45b protein expression and upregulated CyclinB1 and CDC2 protein expression.

Conclusions

MB-MSCs repaired epirubicin-induced damage to GCs, which might be related to the inhibition of Gadd45b protein expression.

Loss of Gadd45b accelerates BCR-ABL-driven CML

Gadd45b is a member of Gadd45 stress sensor protein family that also includes Gadd45a & Gadd45g. To investigate the effect of Gadd45b in bcr-abl oncogene driven chronic myeloid leukemia (CML) development, syngeneic wild type lethally irradiated mice were reconstituted with either wild type or Gadd45b null myeloid progenitors transduced with a retroviral vector expressing BCR-ABL. Loss of Gadd45b was observed to accelerate BCR-ABL driven CML development with shortened median mouse survival time. BCR-ABL Gadd45b deficient CML progenitors exhibited increased proliferation and decreased apoptosis, associated with hyper-activation of c-Jun NH₂-terminal kinase and Stat5. These results provide novel evidence that gadd45b, like gadd45a, functions as a suppressor of BCR-ABL driven leukemia, albeit via a different mechanism.

Molecular cloning and functional analysis of Growth arrest and DNA damage-inducible 45 aa and ab (Gadd45aa and Gadd45 ab) in Ctenopharyngodon idella

The Gadd45aa and Gadd45 ab genes are members of the Gadd45 family, which are critically involved in immunological and apoptosis functions. In this study, we isolated and characterized Gadd45aa and Gadd45 ab cDNA from grass carp (Ctenopharyngodon idella) (designated CiGadd45aa and CiGadd45 ab). The CiGadd45aa and CiGadd45 ab fragments spanned 1272 bp/1248 bp, which contained 474 bp/480 bp open reading frames encoding 157/159 amino acid proteins. BLAST analysis revealed that CiGadd45aa and CiGadd45 ab shared high similarity with known Gadd45a sequences. qRT-PCR analysis showed widespread and abundant expression of CiGadd45aa in gill, intestine, kidney, brain, blood, skin and fin, but low in liver, spleen, head kidney, heart, and muscle. CiGadd45 ab was expressed highly in liver, spleen and blood but at low levels in gill, intestine, kidney, head kidney, heart, brain, skin, muscle, and fin. Following challenge of grass carp with Aeromonas hydrophila, CiGadd45aa and CiGadd45 ab expression was upregulated. In immune-relevant tissues and MAPK family genes (p38, JNK and ERK) were upregulated by CiGadd45aa and CiGadd45 ab overexpression and partly downregulated by interfered in the CIK grass carp kidney cell line. In addition, transcription of the cytokine-encoding il-8 gene was upregulated/downregulated by CiGadd45aa and CiGadd45 ab overexpression and interference. These results suggest that CiGadd45aa and CiGadd45 ab play roles in innate immune responses against A. hydrophila in grass carp.

Genetic variants of GADD45A, GADD45B and MAPK14 predict platinum-based chemotherapy-induced toxicities in Chinese patients with non-small cell lung cancer

The JNK and P38α pathways play a crucial role in tissue homeostasis, apoptosis and autophagy under genotoxic stresses, but it is unclear whether single nucleotide polymorphisms (SNPs) of genes in these pathways play a role in platinum-based chemotherapy-induced toxicities in patients with advanced non-small cell lung cancer (NSCLC). We genotyped 11 selected, independent, potentially functional SNPs of nine genes in the JNK and P38α pathways in 689 patients with advanced NSCLC treated with platinum-combination chemotherapy regimens. Associations between these SNPs and chemotherapy toxicities were tested in a discovery group of 345 patients and then validated in a replication group of 344 patients. In both discovery and validation groups as well as their pooled analysis, carriers of GADD45B rs2024144T variant allele had a significantly higher risk for severe hematologic toxicity and carriers of MAPK14 rs3804451A variant allele had a significantly higher risk for both overall toxicity and gastrointestinal toxicity. In addition, carriers of GADD45A rs581000C had a lower risk of anemia, while carriers of GADD45B rs2024144T had a significantly higher risk for leukocytopenia or agranulocytosis. The present study provides evidence that genetic variants in genes involved in the JNK and P38α pathways may predict platinum-based chemotherapy toxicity outcomes in patients with advanced NSCLC. Larger studies of other patient populations are needed to validate our findings.

κ-opioid receptor is involved in the cardioprotection induced by exercise training

The present study was designed to test the hypothesis that exercise training elicited a cardioprotective effect against ischemia and reperfusion (I/R) via the κ-opioid receptor (κ-OR)-mediated signaling pathway. Rats were randomly divided into four groups: the control group, the moderate intensity exercise (ME) group, the high intensity exercise (HE) group, and the acute exercise (AE) group. For the exercise training protocols, the rats were subjected to one week of adaptive treadmill training, while from the second week, the ME and HE groups were subjected to eight weeks of exercise training, and the AE group was subjected to three days of adaptive treadmill training and one day of vigorous exercise. After these protocols, the three exercise training groups were divided into different treatment groups, and the rats were subjected to 30 min of ischemia and 120 min of reperfusion. Changes in infarct size and serum cTnT (cardiac troponin T) caused by I/R were reduced by exercise training. Moreover, cardiac dysfunction caused by I/R was also alleviated by exercise training. These effects of exercise training were reversed by nor-BNI (a selective κ-OR antagonist), Compound C (a selective AMPK inhibitor), Akt inhibitor and L-NAME (a non-selective eNOS inhibitor). Expression of κ-OR and phosphorylation of AMPK, Akt and eNOS were significantly increased in the ME, HE and AE groups. These findings demonstrated that the cardioprotective effect of exercise training is possibly mediated by the κ-OR-AMPK-Akt-eNOS signaling pathway.

Cell death caused by the synergistic effects of zinc and dopamine is mediated by a stress sensor gene Gadd45b - implication in the pathogenesis of Parkinson's disease

The pathogenesis of Parkinson's disease (PD) is not completely understood, Zinc (Zn(2+) ) and dopamine (DA) have been shown to involve in the degeneration of dopaminergic cells. By microarray analysis, we identified Gadd45b as a candidate molecule that mediates Zn(2+) and DA-induced cell death; the mRNA and protein levels of Gadd45b are increased by Zn(2+) treatment and raised to an even higher level by Zn(2+) plus DA treatment. Zn(2+) plus DA treatment-induced PC12 cell death was enhanced when there was over-expression of Gadd45b and was decreased by knock down of Gadd45b. MAPK p38 and JNK signaling was able to cross-talk with Gadd45b during Zn(2+) and DA treatment. The synergistic effects of Zn(2+) and DA on PC12 cell death can be accounted for by an activation of the Gadd45b-induced cell death pathway and an inhibition of p38/JNK survival pathway. Furthermore, the in vivo results show that the levels of Gadd45b protein expression and phosphorylation of p38 were increased in the substantia nigra by the infusion of Zn(2+) /DA in the mouse brain and the level of Gadd45b mRNA is significantly higher in the substantia nigra of male PD patients than normal controls. The novel role of Gadd45b and its interactions with JNK and p38 will help our understanding of the pathogenesis of PD and help the development of future treatments for PD. Zinc and dopamine are implicated in the degeneration of dopaminergic neurons. We previously demonstrated that zinc and dopamine induced synergistic effects on PC12 cell death. Results from this study show that these synergistic effects can be accounted for by activation of the Gadd45b-induced cell death pathway and inhibition of the p38/JNK survival pathway. We provide in vitro and in vivo evidence to support a novel role for Gadd45b in the pathogenesis of Parkinson's disease.

Early transcriptional responses of internalization defective Brucella abortus mutants in professional phagocytes, RAW 264.7

Background

Brucella abortus is an intracellular zoonotic pathogen which causes undulant fever, endocarditis, arthritis and osteomyelitis in human and abortion and infertility in cattle. This bacterium is able to invade and replicate in host macrophage instead of getting removed by this defense mechanism. Therefore, understanding the interaction between virulence of the bacteria and the host cell is important to control brucellosis. Previously, we generated internalization defective mutants and analyzed the envelope proteins. The present study was undertaken to evaluate the changes in early transcriptional responses between wild type and internalization defective mutants infected mouse macrophage, RAW 264.7.

Results

Both of the wild type and mutant infected macrophages showed increased expression levels in proinflammatory cytokines, chemokines, apoptosis and G-protein coupled receptors (Gpr84, Gpr109a and Adora2b) while the genes related with small GTPase which mediate intracellular trafficking was decreased. Moreover, cytohesin 1 interacting protein (Cytip) and genes related to ubiquitination (Arrdc3 and Fbxo21) were down-regulated, suggesting the survival strategy of this bacterium. However, we could not detect any significant changes in the mutant infected groups compared to the wild type infected group.

Conclusions

In summary, it was very difficult to clarify the alterations in host cellular transcription in response to infection with internalization defective mutants. However, we found several novel gene changes related to the GPCR system, ubiquitin-proteosome system, and growth arrest and DNA damages in response to B. abortus infection. These findings may contribute to a better understanding of the molecular mechanisms underlying host-pathogen interactions and need to be studied further.

Gadd45 in modulation of solid tumors and leukemia

The stress response gadd45 gene family participates in cell cycle control, cell survival, apoptosis, maintenance of genomic stability, DNA repair, and active DNA demethylation, in response to environmental and physiological stress including oncogenic stress. Given these diverse functions, it is anticipated that gadd45 genes can influence the initiation and progression of malignancy and the response to different treatments. This chapter will provide an overview of how the different members of the gadd45 gene family are expressed in different tumors and leukemia, how this may impact on progression of disease, and what happens when expression is manipulated. Studies from human tumor/leukemia samples, cell lines, and animal models are included in this review. An overriding theme is that each of the gadd45 genes has both tumor suppressor and tumor promoter functions, dependent on the tissue/cell type and transforming event.

Gadd45 proteins in immunity

The vertebrate immune system protects the host against invading pathogens such as viruses, bacteria and parasites. It consists of an innate branch and an adaptive branch that provide immediate and long-lasting protection, respectively. As the immune system is composed of different cell types and distributed throughout the whole body, immune cells need to communicate with each other. Intercellular communication in the immune system is mediated by cytokines, which bind to specific receptors on the cell surface and activate intracellular signalling networks. Growth arrest and DNA damage-inducible 45 (Gadd45) proteins are important components of these intracellular signalling networks. They are induced by a number of cytokines and by bacterial lipopolysaccharide. Within the innate immune system, Gadd45 proteins are crucial for the differentiation of myeloid cells as well as for the function of granulocytes and macrophages. Moreover, Gadd45β regulates autophagy, a catabolic pathway that also degrades intracellular pathogens. Regarding adaptive immunity, Gadd45 proteins are especially well characterized in T cells. For instance, Gadd45β and Gadd45γ regulate cytokine expression and Th1 differentiation, while Gadd45α inhibits p38 kinase activation downstream of the T cell receptor. Due to their many functions in the immune system, deficiency in Gadd45 proteins causes autoimmune diseases and less efficient tumour immunosurveillance.

Gadd45 proteins: relevance to aging, longevity and age-related pathologies

The Gadd45 proteins have been intensively studied, in view of their important role in key cellular processes. Indeed, the Gadd45 proteins stand at the crossroad of the cell fates by controlling the balance between cell (DNA) repair, eliminating (apoptosis) or preventing the expansion of potentially dangerous cells (cell cycle arrest, cellular senescence), and maintaining the stem cell pool. However, the biogerontological aspects have not thus far received sufficient attention. Here we analyzed the pathways and modes of action by which Gadd45 members are involved in aging, longevity and age-related diseases. Because of their pleiotropic action, a decreased inducibility of Gadd45 members may have far-reaching consequences including genome instability, accumulation of DNA damage, and disorders in cellular homeostasis - all of which may eventually contribute to the aging process and age-related disorders (promotion of tumorigenesis, immune disorders, insulin resistance and reduced responsiveness to stress). Most recently, the dGadd45 gene has been identified as a longevity regulator in Drosophila. Although further wide-scale research is warranted, it is becoming increasingly clear that Gadd45s are highly relevant to aging, age-related diseases (ARDs) and to the control of life span, suggesting them as potential therapeutic targets in ARDs and pro-longevity interventions.

MYBBP1A: a new Ipr1's binding protein in mice

Infection with mycobacterium tuberculosis (MTB) can cause different outcomes in hosts with variant genetic backgrounds. Previously, we identified an intracellular pathogen resistance 1 (Ipr1) gene with the role of resistance of MTB infection in mice model. However, until now, its binding proteins have been little known even for its human homology, SP110. In this study, the homology for mouse Ipr1 in canines was found to have an extra domain structure, h.1.5.1. And 30 potential candidate proteins were predicted to bind canine Ipr1, which were characterized of the interacting structure with the h.1.5.1. Among them, MYBBP1A was verified to bind with both Ipr1 and eGFP-Ipr1 in mouse macrophage J774A.1 clone 21 cells using co-immunoprecipitation method. And with the constructed high-confidence Ipr1-involved network, we suggested that Ipr1 might be involved in apoptosis pathway via MYBBP1A.

Gadd45β expression in chondrosarcoma: a pilot study for diagnostic and biological implications in histological grading

Background

Although the diagnosis of chondrosarcoma, especially the distinction between enchondroma and low-grade chondrosarcoma or low-grade chondrosarcoma and high-grade chondrosarcoma, is pathologically difficult, differential diagnosis is very important because the treatment strategies for these diseases are completely different. The grading system is crucial in predicting biologic behavior and prognosis, however, exact pathological grading is difficult using only routine examinations because the criteria of the grading system are not necessarily definitive. Growth arrest and DNA damage-inducible protein 45β (GADD45β) is an essential molecule for chondrocytes during terminal differentiation. In the present study, we investigated the immunohistochemical expression of GADD45β in enchondroma, and chondrosarcoma of histological grades I, II, and III, to clarify the diagnostic significance of GADD45β in pathological grading of chondrosarcoma.

Methods

Twenty samples (enchondroma = 6, chondrosarcoma grade I = 7, grade II = 6, grade III = 1) were used for immunohistochemical analysis to investigate the expression of GADD45β. Quantitative analysis was performed to compare the number of GADD45β positive cells and pathological grading.

Results

Over 70% of the cells in enchondromas expressed GADD45β. On the other hand, the expression of GADD45β decreased significantly according to the histological grade of chondrosarcoma (grade I: 45%; grade II: 13.8%; and grade III: 3.8%).

Conclusions

The association of GADD45β expression and pathological grading of chondrosarcoma in the present study suggests that the immunohistochemical study of GADD45β may be a specific diagnostic parameter for chondrosarcoma cell differentiation.

TGF-beta enforces senescence in Myc-transformed hematopoietic tumor cells through induction of Mad1 and repression of Myc activity

Inhibition of tumor growth factor (TGF)-beta-mediated cell cycle exit is considered an important tumorigenic function of Myc oncoproteins. Here we found that TGF-beta1 enforced G(1) cell cycle arrest and cellular senescence in human U-937 myeloid tumor cells ectopically expressing v-Myc, which contains a stabilizing mutation frequently found in lymphomas. This correlated with induced expression of the Myc antagonist Mad1, resulting in replacement of Myc for Mad1 at target promoters, reduced histone acetylation and strong repression of Myc-driven transcription. The latter was partially reversed by histone deacetylase (HDAC) inhibitors, consistent with involvement of Mad1. Importantly, knockdown of MAD1 expression prevented TGF-beta1-induced senescence, underscoring that Mad1 is a crucial component of this process. Enforced Mad1 expression sensitized U-937-myc cells to TGF-beta and restored phorbol ester-induced cell cycle exit, but could not alone induce G(1) arrest, suggesting that Mad1 is required but not sufficient for cellular senescence. Our results thus demonstrate that TGF-beta can override Myc activity despite a stabilizing cancer mutation and induce senescence in myeloid tumor cells, at least in part by induction of Mad1. TGF-beta-induced senescence, or signals mimicking this pathway, could therefore potentially be explored as a therapeutic principle for treating hematopoietic and other tumors with deregulated MYC expression.

Genetic analysis of radiation-induced changes in human gene expression

Humans are exposed to radiation through the environment and in medical settings. To deal with radiation-induced damage, cells mount complex responses that rely on changes in gene expression. These gene expression responses differ greatly between individuals and contribute to individual differences in response to radiation. Here we identify regulators that influence expression levels of radiation-responsive genes. We treated radiation-induced changes in gene expression as quantitative phenotypes, and conducted genetic linkage and association studies to map their regulators. For more than 1,200 of these phenotypes there was significant evidence of linkage to specific chromosomal regions. Nearly all of the regulators act in trans to influence the expression of their target genes; there are very few cis-acting regulators. Some of the trans-acting regulators are transcription factors, but others are genes that were not known to have a regulatory function in radiation response. These results have implications for our basic and clinical understanding of how human cells respond to radiation.

Gadd45 modulation of intrinsic and extrinsic stress responses in myeloid cells

Gadd45 proteins modulate signaling in response to physiological and environmental stressors. Expression of gadd45 genes is rapidly induced by different stressors, including differentiation-inducing cytokines and genotoxic stress. Induction of gadd45 genes at the onset of myeloid differentiation suggested that Gadd45 protein(s) play a role in hematopoiesis, yet no apparent abnormalities were observed in either the bone marrow (BM) or peripheral blood compartments of mice deficient for either gadd45a or gadd45b. However, under conditions of hematological stress, including acute stimulation with cytokines, myelo-ablation and inflammation, both gadd45a-deficient and gadd45b-deficient mice exhibited deficiencies. This is discussed within the context of what is known about Gadd45 proteins in stress signaling, hematopoietic development and the innate immune response. Furthermore, myeloid enriched BM cells from gadd45a and gadd45b deficient mice were observed to be more sensitive to ultraviolet radiation (UVC), VP-16 and daunorubicin (DNR) induced apoptosis compared to wild-type (WT) cells, displaying defective G2/M arrest following exposure to UVC and VP-16, but not to DNR. Novel mechanisms that mediate the pro-survival functions of Gadd45 in hematopoietic cells following UV irradiation were demonstrated, involving activation of the Gadd45a-p38-NF-kappaB survival pathway and Gadd45b mediated inhibition of the stress response MKK4-JNK apoptotic pathway. The ramifications regarding the pathogenesis of different leukemias and the response of normal and malignant hematopoietic cells to chemo- and radiation-therapy, as well as other challenges to the hematopoietic compartment, are discussed.

Stress sensor Gadd45 genes as therapeutic targets in cancer

Gadd45 genes have been implicated in stress signaling responses to various physiological or environmental stressors, resulting in cell cycle arrest, DNA repair, cell survival and senescence, or apoptosis. Evidence accumulated up to date suggests that Gadd45 proteins function as stress sensors, mediating their activity through a complex interplay of physical interactions with other cellular proteins that are implicated in cell cycle regulation and the response of cells to stress. These include PCNA, p21, cdc2/cyclinB1, and the p38 and JNK stress response kinases. Disregulated expression of Gadd45 has been observed in multiple types of solid tumors as well as in hematopoietic malignancies. Also, evidence has accumulated that Gadd45 proteins are intrinsically associated with the response of tumor cells to a variety of cancer therapeutic agents. Thus, Gadd45 proteins may represent a novel class of targets for therapeutic intervention in cancer. Additional research is needed to better understand which of the Gadd45 stress response functions may be targeted for chemotherapeutic drug design in cancer therapy.

Differential expression of GADD45beta in normal and osteoarthritic cartilage: potential role in homeostasis of articular chondrocytes

OBJECTIVE

Our previous study suggested that growth arrest and DNA damage-inducible protein 45beta (GADD45beta) prolonged the survival of hypertrophic chondrocytes in the developing mouse embryo. This study was undertaken, therefore, to investigate whether GADD45beta plays a role in adult articular cartilage.

METHODS

Gene expression profiles of cartilage from patients with late-stage osteoarthritis (OA) were compared with those from patients with early OA and normal controls in 2 separate microarray analyses. Histologic features of cartilage were graded using the Mankin scale, and GADD45beta was localized by immunohistochemistry. Human chondrocytes were transduced with small interfering RNA (siRNA)-GADD45beta or GADD45beta-FLAG. GADD45beta and COL2A1 messenger RNA (mRNA) levels were analyzed by real-time reverse transcriptase-polymerase chain reaction, and promoter activities were analyzed by transient transfection. Cell death was detected by Hoechst 33342 staining of condensed chromatin.

RESULTS

GADD45beta was expressed at higher levels in cartilage from normal donors and patients with early OA than in cartilage from patients with late-stage OA. All chondrocyte nuclei in normal cartilage immunostained for GADD45beta. In early OA cartilage, GADD45beta was distributed variably in chondrocyte clusters, in middle and deep zone cells, and in osteophytes. In contrast, COL2A1, other collagen genes, and factors associated with skeletal development were up-regulated in late OA, compared with early OA or normal cartilage. In overexpression and knockdown experiments, GADD45beta down-regulated COL2A1 mRNA and promoter activity. NF-kappaB overexpression increased GADD45beta promoter activity, and siRNA-GADD45beta decreased cell survival per se and enhanced tumor necrosis factor alpha-induced cell death in human articular chondrocytes.

CONCLUSION

These observations suggest that GADD45beta might play an important role in regulating chondrocyte homeostasis by modulating collagen gene expression and promoting cell survival in normal adult cartilage and in early OA.

The incorporation of poly(lactic-co-glycolic) acid nanoparticles into porcine small intestinal submucosa biomaterials

Small intestinal submucosa (SIS) derived from porcine small intestine has been intensively studied for its capacity in repairing and regenerating wounded and dysfunctional tissues. However, SIS suffers from a large spectrum of heterogeneity in microarchitecture leading to inconsistent results. In this study, we introduced nanoparticles (NPs) to SIS with an intention of decreasing the heterogeneity and improving the consistency of this biomaterial. As determined by scanning electron microscopy and urea permeability, the optimum NP size was estimated to be between 200 nm and 500 nm using commercial monodisperse latex spheres. The concentration of NPs that is required to alter pore sizes of SIS as determined by urea permeability was estimated to be 1 mg/ml 260 nm poly(lactic-co-glycolic) acid (PLGA) NPs. The 1mg/ml PLGA NPs loaded in the SIS did not change the tensile properties of the unmodified SIS or even alter pH values in a cell culture environment. More importantly, PLGA NP modified SIS did not affect human mammary endothelial cells (HMEC-1) morphology or adhesion, but actually enhanced HEMC-1 cell growth.

Phosphatidylinositol 3-kinase signaling in proliferating cells maintains an anti-apoptotic transcriptional program mediated by inhibition of FOXO and non-canonical activation of NFkappaB transcription factors

BACKGROUND

Phosphatidylinositol (PI) 3-kinase is activated by a variety of growth factor receptors and the PI 3-kinase/Akt signaling pathway is a key regulator of cell proliferation and survival. The downstream targets of PI 3-kinase/Akt signaling include direct regulators of cell cycle progression and apoptosis as well as a number of transcription factors. Growth factor stimulation of quiescent cells leads to robust activation of PI 3-kinase, induction of immediate-early genes, and re-entry into the cell cycle. A lower level of PI 3-kinase signaling is also required for the proliferation and survival of cells maintained in the presence of growth factors, but the gene expression program controlled by PI 3-kinase signaling in proliferating cells has not been elucidated.

RESULTS

We used microarray analyses to characterize the changes in gene expression resulting from inhibition of PI 3-kinase in proliferating cells. The genes regulated by inhibition of PI 3-kinase in proliferating cells were distinct from genes induced by growth factor stimulation of quiescent cells and highly enriched in genes that regulate programmed cell death. Computational analyses followed by chromatin immunoprecipitations demonstrated FOXO binding to both previously known and novel sites in promoter regions of approximately one-third of the up-regulated genes, consistent with activation of FOXO1 and FOXO3a in response to inhibition of PI 3-kinase. NFkappaB binding sites were similarly identified in promoter regions of over one-third of the down-regulated genes. RelB was constitutively bound to promoter regions in cells maintained in serum, however binding decreased following PI 3-kinase inhibition, indicating that PI 3-kinase signaling activates NFkappaB via the non-canonical pathway in proliferating cells. Approximately 70% of the genes targeted by FOXO and NFkappaB regulate cell proliferation and apoptosis, including several regulators of apoptosis that were not previously known to be targeted by these transcription factors.

CONCLUSION

PI 3-kinase signaling in proliferating cells regulates a novel transcriptional program that is highly enriched in genes that regulate apoptosis. At least one-third of these genes are regulated either by FOXO transcription factors, which are activated following PI 3-kinase inhibition, or by RelB, which is activated by PI 3-kinase via the non-canonical pathway in proliferating cells.

Role of gadd45 in myeloid cells in response to hematopoietic stress

The gadd45 family of genes is rapidly induced by different stressors, including differentiation-inducing cytokines, and there is a large body of evidence that their cognate proteins are key players in cellular stress responses. Induction of gadd45 genes at the onset of myeloid differentiation suggested that Gadd45 protein(s) play a role in hematopoiesis, yet no apparent abnormalities were observed in either the bone marrow or peripheral blood compartments of mice deficient for either gadd45a or gadd45b. However, under conditions of hematological stress, including acute stimulation with cytokines, myelo-ablation and inflammation, both gadd45a-deficient and gadd45b-deficient mice exhibited deficiencies. This topic is discussed within the context of what is known about Gadd45 proteins in stress signaling, hematopoietic development and the innate immune response.

Gadd45 in the response of hematopoietic cells to genotoxic stress

Gadd45 genes have been implicated in stress signaling in response to physiological or environmental stressors, which results in either cell cycle arrest, DNA repair, cell survival and senescence, or apoptosis. Evidence accumulated implies that Gadd45 proteins function as stress sensors is mediated by a complex interplay of physical interactions with other cellular proteins that are implicated in cell cycle regulation and the response of cells to stress. These include PCNA, p21, cdc2/cyclinB1, and the p38 and JNK stress response kinases. Recently we have taken advantage of gadd45a and gadd45b deficient mice to determine the role gadd45a and gadd45b play in the response of bone marrow (BM) cells to genotoxic stress. Myeloid enriched BM cells from gadd45a and gadd45b deficient mice were observed to be more sensitive to ultraviolet radiation (UVC), VP-16, and daunorubicin (DNR)-induced apoptosis compared to wild-type (wt) cells. The increased apoptosis in gadd45a and gadd45b deficient cells was evident also by enhanced activation of caspase-3 and PARP cleavage and decreased expression of cIAP-1, Bcl-2, and Bcl-xL compared to wt cells. Reintroduction of gadd45 into gadd45 deficient BM cells restored the wt apoptotic phenotype. Both gadd45a and gadd45b deficient BM cells also displayed defective G2/M arrest following exposure to UVC and VP-16, but not to DNR, indicating the existence of different G2/M checkpoints that are either dependent or independent of gadd45. Additional work conducted in this laboratory has shown that in hematopoietic cells exposed to UV radiation gaddd45a and gadd45b cooperate to promote cell survival via two distinct signaling pathways involving activation of the Gadd45a-p38-NF-kB-mediated survival pathway and Gadd45b-mediated inhibition of the stress response MKK4-JNK pathway [O. Kovalsky, F.D. Lung, P.P. Roller, A.J. Fornace, Jr. Oligomerization of human Gadd45a protein. J Biol Chem. 276 (42) (2001) 39330-39339]. These data reveal novel mechanisms that mediate the pro-survival functions of gadd45a and gadd45b in hematopoietic cells following UV irradiation. Taken together, these findings identify gadd45a and gadd45b as anti-apoptotic genes that increase the survival of hematopoietic cells following exposure to UV radiation and certain anticancer drugs. This knowledge should contribute to a greater understanding of the genetic events involved in the pathogenesis of different leukemias and response of normal and malignant hematopoietic cells to chemo and radiation therapy. These observations set the stage to evaluate, in clinically relevant settings, the impact that the status of gadd45a and gadd45b might have on the efficacy of DNR or VP-16 in killing leukemic cells.

Gadd45 beta is a pro-survival factor associated with stress-resistant tumors

Tumors that acquire resistance against death stimuli constitute a severe problem in the context of cancer therapy. To determine genetic alterations that favor the development of stress-resistant tumors in vivo, we took advantage of polyclonal tumors generated after retroviral infection of newborn Elambda-MYC mice, in which the retroviral integration acts as a mutagen to enhance tumor progression. Tumor cells were cultivated ex vivo and exposed to gamma-irradiation prior to their transplantation into syngenic recipients, thereby providing a strong selective pressure for pro-survival mutations. Secondary tumors developing from stress-resistant tumor stem cells were analysed for retroviral integration sites to reveal candidate genes whose dysregulation confer survival. In addition to the gene encoding the antiapoptotic Bcl-x(L) protein, we identified the gadd45b locus to be a novel common integration site in these tumors, leading to enhanced expression. In accord with a thus far undocumented role of Gadd45beta in tumorigenesis, we showed that NIH3T3 cells overexpressing Gadd45beta form tumors in NOD/SCID mice. Interestingly and differently to other known 'classical' antiapoptotic factors, high Gadd45beta levels did not protect against MYC-, UV- or gamma-irradiation-induced apoptosis, but conferred a strong and specific survival advantage to serum withdrawal.

Effects of transforming growth factor-beta in the development of inflammatory pseudotumour-like lesions in a murine model

Alterations in transforming growth factor (TGF)-beta signalling have been frequently implicated in human cancer, and an important mechanism underlying its pro-oncogenic nature is suppression of the host antitumour immune response. Considering the immunosuppressive effect of TGF-beta, we asked whether human tumour cells, known to secrete TGF-beta in culture, would survive and grow when implanted into the peritoneal cavity of immunocompetent mice. Therefore, we developed a xenogeneic model where mice were intraperitoneally (i.p.) injected with a TGF-beta-secreting human colorectal adenocarcinoma cell line, LISP-A10. Although animals did not develop macroscopic tumours, the recovery and isolation of human tumour cells was achieved when an inflammatory environment was locally induced by the administration of complete Freund's adjuvant (CFA). This procedure significantly increased TGF-beta concentrations in the peritoneal fluid and was accompanied by impaired activation of the host-specific immune response against LISP-A10 cells. Furthermore, inflammatory lesions resembling human inflammatory pseudotumours (IPTs) were observed on the surface of i.p. organs. These lesions could be induced by either injection of LISP-A10 cells, cells-conditioned medium or recombinant TGF-beta but only after administration of CFA. In addition, host cyclooxygenase-2 and kinin receptors played an important role in the induction of TGF-beta-mediated IPT-like lesions in our experimental model.

Hematopoietic cells from gadd45a-deficient and gadd45b-deficient mice exhibit impaired stress responses to acute stimulation with cytokines, myeloablation and inflammation

The gadd45 family of gene(s) is rapidly induced by genotoxic stress or by differentiation-inducing cytokines. Using bone marrow (BM) from gadd45a-/-, gadd45b-/- and wild-type (wt) mice, we investigated their role in stress responses of myeloid cells to acute stimulation with differentiating cytokines, myelotoxic agents and inflammatory substances. Bone marrow cells from gadd45a-/- and gadd45b-/- mice displayed compromised myeloid differentiation and higher apoptosis in vitro, following acute stimulation with a variety of differentiating cytokines. Intriguingly, gadd45a-/- and gadd45b-/- colony forming units granulocyte/macrophage progenitors displayed prolonged proliferation capacity compared to wt controls upon re-plating in methylcellulose supplemented with interleukin-3. The recovery of the BM myeloid compartment following 5-Fluorouracil-induced myelo-ablation was much slower in gadd45a-/- and gadd45b-/- mice compared to wt controls. Furthermore, the response of myeloid cells to inflammatory stress, inflicted via intraperitoneal administration of sodium caseinate was impaired in gadd45a-/- and gadd45b-/- mice compared to age-matched wt mice, as indicated by lower percentage of Gr-1-positive cells in the BM and lower number of myeloid cells in peritoneal exudates. Overall, these data indicate that both gadd45a and gadd45b play a role in modulating physiological stress responses of myeloid cells to acute stimulation with differentiating cytokines, myelo-ablation and inflammation. These findings should aid in understanding the response of normal and malignant hematopoietic cells to physiological and chemical stressors including anticancer agents.

Hematopoietic cells from Gadd45a- and Gadd45b-deficient mice are sensitized to genotoxic-stress-induced apoptosis

Gadd45a, gadd45b and gadd45g (Gadd45/MyD118/CR6) are genes that are rapidly induced by genotoxic stress. However, the exact function of Gadd45 proteins in the response of mammalian cells to genotoxic stress is unclear. Here, advantage was taken of gadd45a- and gadd45b-deficient mice to determine the role gadd45a and gadd45b play in the response of bone marrow (BM) cells to genotoxic stress. BM cells from gadd45a- and gadd45b-deficient mice were observed to be more sensitive to ultraviolet radiation chemotherapy (UVC), VP-16 and daunorubicin (DNR)-induced apoptosis compared to wild-type (wt) cells. The increased apoptosis in gadd45a- and gadd45b-deficient cells was evident also by enhanced activation of caspase-3 and poly-ADP-ribose polymerase cleavage and decreased expression of c-inhibitor of apoptotic protein-1, Bcl-2, Bcl-xL compared to wt cells. Reintroduction of gadd45 into gadd45-deficient BM cells restored the wt apoptotic phenotype. Both gadd45a- and gadd45b-deficient BM cells also displayed defective G2/M arrest following exposure to UVC and VP-16, but not to DNR, indicating the existence of different G2/M checkpoints that are either dependent or independent of gadd45. Taken together, these findings identify gadd45a and gadd45b as anti-apoptotic genes that increase the survival of hematopoietic cells following exposure to UV radiation and certain anticancer drugs.

Hypermethylation of growth arrest DNA damage-inducible gene 45 beta promoter in human hepatocellular carcinoma

Growth arrest DNA damage-inducible gene 45 beta (GADD45beta) has been known to regulate cell growth, apoptotic cell death, and cellular response to DNA damage. Down-regulation of GADD45beta has been verified to be specific in hepatocellular cancer (HCC) and consistent with the p53 mutant, and degree of malignancy of HCC. This observation was further confirmed by eight HCC cell lines and paired human normal and HCC tumor tissues by Northern blot and immunohistochemistry. To better understand the transcription regulation, we cloned and characterized the active promoter region of GADD45beta in luciferase-expressing vector. Using the luciferase assay, three nuclear factor-kappaB binding sites, one E2F-1 binding site, and one putative inhibition region were identified in the proximal promoter of GADD45beta from -865/+6. Of interest, no marked putative binding sites could be identified in the inhibition region between -520/-470, which corresponds to CpG-rich region. The demethylating agent 5-Aza-dC was used and demonstrated restoration of the GADD45beta expression in HepG2 in a dose-dependent manner. The methylation status in the promoter was further examined in one normal liver cell, eight HCC cell lines, eight HCC tissues, and five corresponding nonneoplastic liver tissues. Methylation-specific polymerase chain reaction and sequencing of the sodium bisulfite-treated DNA from HCC cell lines and HCC samples revealed a high percentage of hypermethylation of the CpG islands. Comparatively, the five nonneoplastic correspondent liver tissues demonstrated very low levels of methylation. To further understand the functional role of GADD45beta under-expression in HCC the GADD45beta cDNA constructed plasmid was transfected into HepG2 (p53 WT) and Hep3B (p53 null) cells. The transforming growth factor-beta was assayed by enzyme-linked immunosorbent assay, which revealed a decrease to 40% in transfectant of HepG2, but no significant change in Hep3B transfectant. Whereas, Hep3B co-transfected with p53 and GADD45beta demonstrated significantly reduced transforming growth factor-beta. The colony formation was further examined and revealed a decrease in HepG2-GADD45beta transfectant and Hep3B-p53/GADD45beta co-transfectant. These findings suggested that methylation might play a crucial role in the epigenetic regulation of GADD45beta in hepatocyte transformation that may be directed by p53 status. Thus, our results provided a deeper understanding of the molecular mechanism of GADD45beta down-regulation in HCC.

DNA microarray screening of differential gene expression in bone marrow samples from AML, non-AML patients and AML cell lines

This study used cDNA microarray technology to compare gene expression profiles in acute myeloblastic leukaemia (AML) with cDNA dot-blot and real time PCR analysis of cDNA transcripts to confirm array data. Patient AML marrow samples and AML cell lines were compared with normal/non-AML samples. Screening revealed five particular genes to be significantly differentially expressed across the sample groups. The migration-inhibitory factor-related-proteins 8 and 14 (MRP-8 and MRP-14) genes, the products of which inhibit cell migration and differentiation were the most highly expressed in non-malignant cells. The high-mobility-group-protein gene (HMG-1) was up regulated in leukaemic samples and cell lines, which may be associated with aggressive disease. Also upregulated in malignant samples were genes encoding c-myc and glutathione-S-transferase pi (GSTP), the latter implicated in chemotherapy resistance. Faulty expression of such genes may contribute to the pathogenesis of AML and resistance to treatment.

Identification of a β 3′ Enhancer That Mediates SMAD3- and SMAD4-dependent Transcriptional Induction by Transforming Growth Factor β

GADD45beta regulates cell growth, differentiation, and cell death following cellular exposure to diverse stimuli, including DNA damage and transforming growth factor-beta (TGFbeta). We examined how cells transduce the TGFbeta signal from the cell surface to the gadd45beta genomic locus and describe how GADD45beta contributes to TGFbeta biology. Following an alignment of gadd45beta genomic sequences from multiple organisms, we discovered a novel TGFbeta-responsive enhancer encompassing the third intron of the gadd45beta gene. Using three different experimental approaches, we found that SMAD3 and SMAD4, but not SMAD2, mediate transcription from this enhancer. Three lines of evidence support our conclusions. First, overexpression of SMAD3 and SMAD4 activated the transcriptional activity from this enhancer. Second, silencing of SMAD protein levels using short interfering RNAs revealed that TGFbeta-induced activation of the endogenous gadd45beta gene required SMAD3 and SMAD4 but not SMAD2. In contrast, we found that the regulation of plasminogen activator inhibitor type I depended upon all three SMAD proteins. Last, SMAD3 and SMAD4 reconstitution in SMAD-deficient cancer cells restored TGFbeta induction of gadd45beta. Finally, we assessed the function of GADD45beta within the TGFbeta response and found that GADD45beta-deficient cells arrested in G2 following TGFbeta treatment. These data support a role for SMAD3 and SMAD4 in activating gadd45beta through its third intron to facilitate G2 progression following TGFbeta treatment.

Ionizing radiation sensitizes bone cells to apoptosis

Osteoradionecrosis is a common sequelae of radiation therapy for head and neck cancer. To test the hypothesis that radiation induces osteoradionecrosis by induction of bone cell apoptosis, we exposed MC3T3-E1 osteoblast-like cells to gamma-radiation and evaluated cell viability. Twenty-four hours postirradiation, measurement of osteoblast dehydrogenase activity suggested that there was a small decrease in cell viability. However, TUNEL and flow cytometric analysis indicated that the viability loss was caused by inhibition of cell proliferation and not by induction of apoptosis. The effect of irradiation on osteoblast function was examined by Western blot and flow cytometric analysis. It was found that irradiated osteoblasts underwent G2 cell cycle arrest. In addition, we observed changes in expression of molecules that regulate the cell cycle. Thus, there was an increase in p53 transcription, a raised level of MDM2 dephosphorylation, and elevation in p21 and GADD153 protein levels. Since these proteins are concerned with the regulation of the cell cycle, the observed changes in expression would be expected to disturb cyclin activity and cause G2M arrest. The arrested cells displayed a dramatic increase in sensitivity to specific apoptogens. Thus, when irradiated, and then treated with Ca2+Pi or staurosporine, agents that cause mitochondrial dysfunction, more osteoblasts underwent apoptosis than with the apoptogen alone. In contrast, irradiated cells treated with anti-Fas antibody showed no change in apoptotic sensitivity; apoptosis was inhibited when osteoblasts were treated with etoposide. Similar alterations in sensitivity were observed when cells were arrested in G2/M by pretreatment with colchicine and then challenged with apoptogens. It was concluded that activation of radiation-induced G2 arrest sensitizes osteoblasts to agents that mediate apoptosis through a mitochondrial-dependent death pathway.

Transforming growth factor-beta-induced apoptosis is mediated by Smad-dependent expression of GADD45b through p38 activation

Transforming growth factor-beta (TGF-beta)-dependent apoptosis is important in the elimination of damaged or abnormal cells from normal tissues in vivo. In this report, we identify GADD45b as an effector of TGF-beta-induced apoptosis. GADD45b has been shown to be a positive mediator of apoptosis induced by certain cytokines and oncogenes. We show that Gadd45b is an immediateearly response gene for TGF-beta and that the proximal Gadd45b promoter is activated by TGF-beta through the action of Smad2, Smad3, and Smad4. We show that ectopic expression of GADD45b in AML12 murine hepatocytes is sufficient to activate p38 and to trigger apoptotic cell death, whereas antisense inhibition of Gadd45b expression blocks TGF-beta-dependent p38 activation and apoptosis. Furthermore, we also show that TGF-beta can activate p38 and induce apoptosis in mouse primary hepatocytes from wild-type mice, but not from Gadd45b-/- mice. All of these findings suggest that GADD45b participates in TGF-beta-induced apoptosis by acting upstream of p38 activation.

Comparative analysis of the genetic structure and chromosomal mapping of the murine Gadd45g/CR6 gene

Gadd45g/CR6, Gadd45b/MyD118, and Gadd45a/Gadd45 are members of a gene family that displays distinct patterns of gene expression in response to stimuli that induce differentiation, growth arrest, and/or apoptosis. All three of these highly conserved proteins interact with a number of critical cell cycle and cell survival regulatory proteins such as PCNA, p21(WAF1/CIP1), CDK1 (cdc2-p34), and MTK1/MEKK4, and have been reported to influence the activity of the p38 and JNK kinases. Species-blot analysis showed that Gadd45g is an evolutionarily conserved gene and sequence analysis showed that Gadd45g has a gene structure conserved with that of other members of its gene family. A comparison of the putative transcription factor binding sites found in the sequences of the gene family members suggests, that like Gadd45b, NF-kappaB and STATs may be responsible for the differences in regulation of expression observed between Gadd45g and Gadd45a. Analysis of the Gadd45b/MyD118 promoter shows that there are three different enhanceosome-like regions that may allow cell-type specific responses to TGF-beta1 by the Gadd45b/MyD118 promoter. Fluorescent in situ hybridization (FISH) confirmed the localization of the Gadd45g gene to mouse chromosome band 13A5-B, which has been reported to contain a quantitative trait locus that regulates body weight in mice. This suggests that alleles of the Gadd45g gene may function in the regulation of body weight, in addition to its currently recognized roles in differentiation and stress responses.

Co-localization of apoptosis-regulating proteins in mouse mammary epithelial HC11 cells exposed to TGF-beta1

TGF-beta1 is an apoptogenic agent for mammary epithelial cells (MEC). The molecular mechanism of the TGF-beta1-induced apoptosis remains, however, obscure. In the present study we used laser scanning cytometry, confocal microscopy and immunogold electron microscopy to analyze the expression, aggregation and co-localization of caspase-8, Bid, Bax and VDAC-1. These proteins are regarded as the most important factors involved in the regulatory phase of TGF-beta1-induced apoptosis. Apoptosis in HC11 mouse MEC manifested with a simultaneous increase in expression and subcellular aggregation of caspase-8, Bid, Bax and VDAC-1. Confocal microscopy revealed a strong pattern of co-localization of examined proteins during both early and late apoptosis. Experiments with double- and triple-staining immunoelectron microscopy showed a co-localization of Bax/Bid, caspase-8/Bax/Bid, and Bax/VDAC-1, on the membranes of mitochondria, Golgi apparatus, rough endoplasmic reticulum, nuclear envelope, nuclear pore, and within the nucleus. In conclusion, the observed pattern of changes in aggregation and subcellular localization of caspase-8, Bid, Bax and VDAC-1 during TGF-beta1-induced apoptosis in HC11 mouse MEC suggests an interaction between these proteins and formation of multimeric complexes on organellar membranes, thus controlling their permeability for intracellular mediators of apoptosis.

Down-regulation of growth arrest DNA damage-inducible gene 45beta expression is associated with human hepatocellular carcinoma

In this study, we describe the growth arrest DNA damage-inducible gene 45beta (GADD45beta), whose expression was significantly down-regulated in the hepatocellular carcinoma (HCC) microarray study and confirmed by Northern blot analysis. The results suggested that expression of GADD45beta was decreased in human liver cancer cell lines HepG2 and Hep3B, but not in normal human embryonic liver cell line CL-48 or normal liver tissue. Histochemistry study and real-time PCR further confirmed that GADD45beta staining in HCC was significantly decreased when compared to surrounding non-neoplastic liver tissue. In further studies of multiple human cancer tissues, GADD45beta strongly stained tissues such as colon cancer, breast cancer, prostate cancer, squamous cell cancer, lymphoma, and leiomyosarcoma, suggesting that the decreased expression of GADD45beta is specific to HCC. Eighty-five cases of primary HCC were further examined by immunohistochemistry and statistical analyses demonstrated that HCC scored lower than matched non-neoplastic liver tissues consistently and significantly. No staining occurred in 12.94% of HCC cases (score = 0, n = 11); 42.35% had weak staining (score = 1, n = 36); 27.06% had moderate staining (score = 2, n = 23); and 17.65% had staining as strong as normal tissue (score = 3, n = 15). Overall, surrounding non-neoplastic liver tissue was highly positive for GADD45beta compared to adjacent neoplastic liver tissues (P < 0.01). We further observed that down-regulation of GADD45beta expression was strongly correlated with differentiation (P < 0.01) and high nuclear grade (P < 0.01). Moreover, we found that expression of GADD45beta was inversely correlated to the presence of mutant p53 in HCC tissue (P < 0.05). Thus, the results of our study suggest that GADD45beta, which is down-regulated in most cases of HCC, remains an ideal candidate for development as a molecular marker in the diagnosis of HCC and as a potential therapeutic target.

Antiproliferative and apoptotic effect of TGF-beta 1 in bovine mammary epithelial BME-UV1 cells

Transforming growth factor beta1 (TGF-beta(1)) is regarded as an important auto/paracrine regulator of mammary gland involution, however, its apoptotic effect and inhibition of growth in bovine mammary epithelial cells (MEC) has not been documented. In the present study, laser scanning cytometry, confocal and immunoelectron microscopy techniques were used for quantitative and qualitative analyzes of apoptosis, cell cycle and expression, subcellular redistribution and interactions of apoptosis-related proteins in bovine BME-UV1 MEC exposed to TGF-beta(1). TGF-beta(1) exerted both antiproliferative and apoptotic action. The antiproliferative effect was manifested by increase of cell number in G1 phase with simultaneous decrease of cell number in S and G2/M phases. It resulted in significant increase of G1/S ratio in TGF-beta(1) treated cells, indicating partial cell cycle arrest at the G1-S transition. Apoptosis induced by TGF-beta(1) manifested by characteristic morphological changes. Among biochemical features of TGF-beta(1)-induced apoptosis in BME-UV1 cells we found: (1) an increase of cell number with lowered DNA content and condensed chromatin, (2) enhanced expression of caspase-3 and m-calpain, (3) elevated number of 89 kDa PARP degradation fragments, and (4) aggregation of Bax and its interactions with voltage dependant anion channel-1. In conclusion, antiproliferative and apoptotic action of TGF-beta(1), observed in the culture of BME-UV1 cells, suggests an essential role of this cytokine in the regulation of mammary gland involution in cow.

Transient activation of NF-kappaB through a TAK1/IKK kinase pathway by TGF-beta1 inhibits AP-1/SMAD signaling and apoptosis: implications in liver tumor formation

NF-kappaB has been implicated in the regulation of apoptosis, a key mechanism of normal and malignant growth control. Previously, we demonstrated that inhibition of NF-kappaB activity by TGF-beta1 leads directly to induction of apoptosis of murine B-cell lymphomas and hepatocytes. Thus, we were surprised to determine that NF-kappaB is transiently activated in response to TGF-beta1 treatment. Here we elucidate the mechanism of TGF-beta1-mediated regulation of NF-kappaB and induction of apoptosis in epithelial cells. We report that TGF-beta1 activates IKK kinase, which mediates IkappaB-alpha phosphorylation. In turn, the activation of IKK following TGF-beta1 treatment is mediated by the TAK1 kinase. As a result of NF-kappaB activation, IkappaB-alpha mRNA and protein levels are increased leading to postrepression of NF-kappaB and induction of cell death. Inhibition of NF-kappaB following TGF-beta1 treatment increased AP-1 complex transcriptional activity through sustained c-Jun phosphorylation, thereby potentiating AP-1/SMADs-mediated cell killing. Furthermore, TGF-beta1-mediated upregulation of Smad7 appeared independent of NF-kappaB. In hepatocellular carcinomas of TGF-beta1 or TGF-alpha/c-myc transgenic mice, we observed constitutive activation of NF-kappaB that led to inhibition of JNK signaling. Overall, our data illustrate an autocrine mechanism based on the ability of IKK/NF-kappaB/IkappaB-alpha signaling to negatively regulate NF-kappaB levels thereby permitting TGF-beta1-induced apoptosis through AP-1 activity.

Activin/TGF-beta induce apoptosis through Smad-dependent expression of the lipid phosphatase SHIP

Members of the transforming growth factor beta (TGF-beta) family regulate fundamental physiological processes, such as cell growth, differentiation and apoptosis, in almost all cell types. As a result, defects in TGF-beta signalling pathways have been linked to uncontrolled cellular proliferation and carcinogenesis. Here, we explored the signal transduction mechanisms downstream of the activin/TGF-beta receptors that result in cell growth arrest and apoptosis. We show that in haematopoietic cells, TGF-beta family members regulate apoptosis through expression of the inositol phosphatase SHIP (Src homology 2 (SH2) domain-containing 5' inositol phosphatase), a central regulator of phospholipid metabolism. We also demonstrated that the Smad pathway is required in the transcriptional regulation of the SHIP gene. Activin/TGF-beta-induced expression of SHIP results in intracellular changes in the pool of phospholipids, as well as in inhibition of both Akt/PKB (protein kinase B) phosphorylation and cell survival. Our results link phospholipid metabolism to activin/TGF-beta-mediated apoptosis and define TGF-beta family members as potent inducers of SHIP expression.

Microarray analysis of bone morphogenetic protein, transforming growth factor beta, and activin early response genes during osteoblastic cell differentiation

Bone morphogenetic protein (BMP) 2, a member of the transforming growth factor (TGF) beta family, is a potent regulator of osteoblast differentiation. In addition, both TGF-beta and activin A can either induce bone formation or inhibit bone formation depending on cell type and differentiation status. Although much is known about the receptors and intracellular second messengers involved in the action of TGF-beta family members, little is known about how selectivity in the biological response of individual family members is controlled. In this study, we have investigated selective gene induction by BMP-2, TGF-beta1 and activin A in relation to their ability to control differentiation of mouse mesenchymal precursor cells C2C12 into osteoblastic cells. TGF-beta1 can inhibit BMP-2-induced differentiation of these cells, whereas activin A was found to be without morphogenetic effect. Using a gene expression microarray approach covering 8636 sequences, we have identified a total of 57 established genes and expressed sequence tags (ESTs) that were either up-regulated or down-regulated 2 h after treatment with at least one of these three stimuli. With respect to the established genes, 15 new target genes for TGF-beta family members thus were identified. Furthermore, a set of transcripts was identified, which was oppositely regulated by TGF-beta1 and BMP-2. Based on the inverse biological effects of TGF-beta1 and BMP-2 on C2C12 cells, these genes are important candidates for controlling the process of growth factor-induced osteoblast differentiation.

Xiro homeoproteins coordinate cell cycle exit and primary neuron formation by upregulating neuronal-fate repressors and downregulating the cell-cycle inhibitor XGadd45-gamma

The iroquois (iro) homeobox genes participate in many developmental processes both in vertebrates and invertebrates, among them are neural plate formation and neural patterning. In this work, we study in detail Xenopus Iro (Xiro) function in primary neurogenesis. We show that misexpression of Xiro genes promotes the activation of the proneural gene Xngnr1 but suppresses neuronal differentiation. This is probably due to upregulation of at least two neuronal-fate repressors: XHairy2A and XZic2. Accordingly, primary neurons arise at the border of the Xiro expression domains. In addition, we identify XGadd45-gamma as a new gene repressed by Xiro. XGadd45-gamma encodes a cell-cycle inhibitor and is expressed in territories where cells will exit mitosis, such as those where primary neurons arise. Indeed, XGadd45-gamma misexpression causes cell cycle arrest. We conclude that, during Xenopus primary neuron formation, in Xiro expressing territories neuronal differentiation is impaired, while in adjacent cells, XGadd45-gamma may help cells stop dividing and differentiate as neurons.

Expression profiling confirms the role of endocytic receptor megalin in renal vitamin D3 metabolism

BACKGROUND

The endocytic receptor megalin constitutes the major pathway for clearance of low-molecular weight plasma proteins from the glomerular filtrate into the renal proximal tubules. Furthermore, the receptor has been implicated in a number of other functions in the kidney including uptake and activation of 25-(OH) vitamin D3, calcium and sodium reabsorption as well as signal transduction.

METHODS

We used genome-wide expression profiling by microarray technology to detect changes in the gene expression pattern in megalin knockout mouse kidneys and to uncover some of the renal pathways affected by megalin deficiency.

RESULTS

Alterations were identified in several (patho)physiologic processes in megalin-deficient kidneys including the renal vitamin D metabolism, transforming growth factor (TGF)-beta1 signal transduction, lipid transport and heavy metal detoxification. Most importantly, changes were detected in the mRNA levels of 25-(OH) vitamin D-24-hydroxylase and 25-(OH) vitamin D-1alpha-hydroxylase as well as strong up-regulation of TGF-beta1 target genes. Both findings indicate plasma vitamin D deficiency and lack of vitamin D signaling in renal tissues.

CONCLUSIONS

Expression profiling confirms a crucial role for megalin in renal vitamin D metabolism.