Human Bex2 interacts with LMO2 and regulates the transcriptional activity of a novel DNA-binding complex

MSL2 variants lead to a neurodevelopmental syndrome with lack of coordination, epilepsy, specific dysmorphisms, and a distinct episignature

Epigenetic dysregulation has emerged as an important etiological mechanism of neurodevelopmental disorders (NDDs). Pathogenic variation in epigenetic regulators can impair deposition of histone post-translational modifications leading to aberrant spatiotemporal gene expression during neurodevelopment. The male-specific lethal (MSL) complex is a prominent multi-subunit epigenetic regulator of gene expression and is responsible for histone 4 lysine 16 acetylation (H4K16ac). Using exome sequencing, here we identify a cohort of 25 individuals with heterozygous de novo variants in MSL complex member MSL2. MSL2 variants were associated with NDD phenotypes including global developmental delay, intellectual disability, hypotonia, and motor issues such as coordination problems, feeding difficulties, and gait disturbance. Dysmorphisms and behavioral and/or psychiatric conditions, including autism spectrum disorder, and to a lesser extent, seizures, connective tissue disease signs, sleep disturbance, vision problems, and other organ anomalies, were observed in affected individuals. As a molecular biomarker, a sensitive and specific DNA methylation episignature has been established. Induced pluripotent stem cells (iPSCs) derived from three members of our cohort exhibited reduced MSL2 levels. Remarkably, while NDD-associated variants in two other members of the MSL complex (MOF and MSL3) result in reduced H4K16ac, global H4K16ac levels are unchanged in iPSCs with MSL2 variants. Regardless, MSL2 variants altered the expression of MSL2 targets in iPSCs and upon their differentiation to early germ layers. Our study defines an MSL2-related disorder as an NDD with distinguishable clinical features, a specific blood DNA episignature, and a distinct, MSL2-specific molecular etiology compared to other MSL complex-related disorders.

Crotonylated BEX2 interacts with NDP52 and enhances mitophagy to modulate chemotherapeutic agent-induced apoptosis in non-small-cell lung cancer cells

Brain expressed X-linked gene 2 (BEX2) encoded protein was originally identified to promote transcription by interacting with several transcription factors in the DNA-binding complexes. Recently, BEX2 was found to be localized in cytosol and/or mitochondria and regulate apoptosis in cancer cells and tumor growth. However, the molecular mechanism underlying its roles in cancer cells remains unclear. Here, we report that crotonylated BEX2 plays an important role in inhibiting chemotherapeutic agent-induced apoptosis via enhancing mitophagy in human lung cancer cells. BEX2 promotes mitophagy by facilitating interaction between NDP52 and LC3B. Moreover, BEX2 crotonylation at K59 is critical in the BEX2-mediated mitophagy in lung cancer cells. The K59R mutation of BEX2 inhibits mitophagy by affecting the interaction of NDP52 and LC3B. BEX2 expression is elevated after anticancer drug treatment, and its overexpression inhibits chemotherapy-induced apoptosis. In addition, inhibition of BEX2-regulated mitophagy sensitizes tumor cells to apoptosis. Furthermore, BEX2 promotes tumor growth and inhibits apoptosis by regulating mitophagy in vivo. We also confirm that BEX2 is overexpressed in lung adenocarcinoma and is associated with poor prognosis in lymph node metastasis-free cancer. Therefore, combination treatment with pharmaceutical approaches targeting BEX2-induced mitophagy and anticancer drugs may represent a potential strategy for NSCLC therapy.

BEX2 is poor prognostic factor and required for cancer stemness in gastric cancer

Gastric cancer is the fifth most common malignancy worldwide. However, targeted therapy for advanced gastric cancer is still limited. Here, we report BEX2 (Brain expressed X-linked 2) as a poor prognostic factor in two gastric cancer cohorts. BEX2 expression was increased in spheroid cells, and its knockdown decreased aldefluor activity and cisplatin resistance. BEX2 was found to upregulate CHRNB2 (Cholinergic Receptor Nicotinic Beta 2 Subunit) expression, a cancer stemness-related gene, in a transcriptional manner, and the knockdown of which also decreases aldefluor activity. Collectively, these data are suggestive of the role of BEX2 in the malignant process of gastric cancer, and as a promising therapeutic target.

Long non-coding RNA PRNCR1 promotes ovarian cancer cell proliferation, migration and invasion by targeting the miR-653-5p/ELF2 axis

Recent studies have shown that prostate cancer-associated long non-coding RNA, PRNCR1, plays crucial roles in the development of multiple human cancers. However, its role in ovarian cancer is barely known. This study was carried out to investigate the role of PRNCR1 and the underlying mechanisms in OC. The expression of PRNCR1 and miR-653-5p in OC cell lines and tissues were detected by qRT-PCR. The expression of ELF2 protein was evaluated by Western blot analysis. Cell proliferation was measured by colony formation and MTT assay. Cell invasion and migration were evaluated by Transwell and wound healing assay. Luciferase reporter assay and RNA-binding protein immunoprecipitation assay were performed to determine the interaction between miR-653-5p and PRNCR1, as well as between miR-653-5p and ELF2. In vivo tumor xenograft model was established to evaluate the role of PRNCR1 in tumor growth. Our results demonstrated that PRNCR1 was significantly upregulated in both OC cell lines and tissues, and high expression of PRNCR1 was correlated with poor survival of OC patients. Overexpression of PRNCR1 accelerated OC cell invasion, migration and proliferation. Besides, the expression of PRNCR1 was negatively correlated with the expression of miR-653-5p, while positively correlated with the expression of E74-like factor 2 in OC tissues. Importantly, ELF2 could target miR-653-5p, and PRNCR1 increased the expression levels of ELF2 by sponging miR-653-5p in OC cells. Furthermore, the miR-145-5p/ELF2 axis was involved in the regulation of PRNCR1 in OC progression in vivo. PRNCR1 promotes OC tumor progress via the miR-653-5p/ELF2 axis and might be a potential therapeutic target for OC.

Analyzing differentially expressed genes and pathways of Bex2-deficient mouse lung via RNA-Seq

Bex2 is well known for its role in the nervous system, and is associated with neurological disorders, but its role in the lung’s physiology is still not reported. To elucidate the functional role of Bex2 in the lung, we generated a Bex2 knock-out (KO) mouse model using the CRISPR-Cas9 technology and performed transcriptomic analysis. A total of 652 genes were identified as differentially expressed between Bex2^-/- and Bex2^+/+ mice, out of which 500 were downregulated, while 152 were upregulated genes. Among these DEGs, Ucp1, Myh6, Coxa7a1, Myl3, Ryr2, RNaset2b, Npy, Enob1, Krt5, Myl2, Hba-a2, and Nrob2 are the most prominent genes. Myl2, was the most downregulated gene, followed by Npy, Hba-a2, Rnaset2b, nr0b2, Klra8, and Ucp1. Tcte3, Eno1b, Zfp990, and Pcdha9 were the most upregulated DEGs. According to gene enrichment analysis, PPAR pathway, cardiac muscle contraction, and cytokine-cytokine receptor interaction were the most enriched pathways. Besides, the nuclear factor-κB signaling pathway and hematopoietic cell linage pathways were also enriched. Chronic obstructive pulmonary disease (COPD) is enriched among KEGG disease pathways. RT-qPCR assays confirmed the RNA-Seq results. This study opens a new window toward the biological functions of Bex2 in different systems.

BEX2 is required for maintaining dormant cancer stem cell in hepatocellular carcinoma

Cancer stem cells (CSCs) are responsible for therapy resistance and share several properties with normal stem cells. Here, we show that brain‐expressed X‐linked gene 2 (BEX2), which is essential for dormant CSCs in cholangiocarcinoma, is highly expressed in human hepatocellular carcinoma (HCC) lesions compared with the adjacent normal lesions and that in 41 HCC cases the BEX2^high expression group is correlated with a poor prognosis. BEX2 localizes to Ki67‐negative (nonproliferative) cancer cells in HCC tissues and is highly expressed in the dormant fraction of HCC cell lines. Knockdown of BEX2 attenuates CSC phenotypes, including sphere formation ability and aldefluor activity, and BEX2 overexpression enhances these phenotypes. Moreover, BEX2 knockdown increases cisplatin sensitivity, and BEX2 expression is induced by cisplatin treatment. Taken together, these data suggest that BEX2 induces dormant CSC properties and affects the prognosis of patients with HCC.

Induced pluripotent stem cells established from a female patient with Xq22 deletion confirm that BEX2 escapes from X-chromosome inactivation

Large deletions in Xq22 are responsible for neurodevelopmental disorders, including severe intellectual disability and behavioral abnormalities. Although the deletion regions contain PLP1, the gene related to Pelizaeus-Merzbacher disease (PMD), patients with Xq22 deletions show no clinical features of PMD such as paraplegia and white matter abnormalities. This could be due to skewed X-chromosome inactivation (XCI) occurring predominantly in the affected allele. Isogenic pairs of wild type and mutant induced pluripotent stem cells (iPSCs) were established from the patient. In the iPSC line in which the wild type allele was inactivated, PLP1 was not expressed, but biallelic expression of BEX2 was identified. This suggests that BEX2 escaped from XCI and haploinsufficiency of BEX2 may be related to the phenotype of Xq22 deletions.

Molecular functions of brain expressed X-linked 2 (BEX2) in malignancies

Over the last decade there has been growing evidence that Brain Expressed X-Linked 2 (BEX2) has a significant role in the process of carcinogenesis. Collectively, available studies suggest a pro-oncogenic function for this gene in multiple malignancies, including breast, colorectal and hepatocellular cancers in addition to brain tumors. The identification of BEX2 in breast cancer resulted from gene expression microarray studies. Subsequent studies showed that BEX2 promotes breast cancer cell growth and survival by modulating the mitochondrial apoptotic pathway and G1 cell cycle. In this process, BEX2 has cross-talk with the NF-κB, c-Jun/JNK and ErbB2 pathways. Of note, several studies have found a pro-oncogenic function for BEX2 in other malignancies associated with a similar signaling function to that observed in breast cancer. In brain tumors, BEX2 promotes cell migration and invasion in oligodendroglioma and glioblastoma cells. In addition, BEX2 expression protects glioma cells against apoptosis mediated through the JNK pathway and is required for glioma cell proliferation through the NF-κB p65. Furthermore, it has been shown that BEX2 promotes cell proliferation through the JNK/c-Jun pathway and regulates JNK/c-Jun phosphorylation in colorectal cancer. Most recently, it has been demonstrated that BEX2 expression is required for cell proliferation and Hepatitis B Virus-mediated development of hepatocellular carcinoma. Therefore, a pro-oncogenic function for BEX2 is supported by reproducible data in multiple malignancies and the NF-κB and JNK/c-Jun pathways are commonly regulated by BEX2 in this process. In view of these findings, targeting BEX2 may provide an attractive therapeutic strategy in multiple malignancies.

STAT6, PBX2, and PBRM1 Emerge as Predicted Regulators of 452 Differentially Expressed Genes Associated With Puberty in Brahman Heifers

The liver plays a central role in metabolism and produces important hormones. Hepatic estrogen receptors and the release of insulin-like growth factor 1 (IGF1) are critical links between liver function and the reproductive system. However, the role of liver in pubertal development is not fully understood. To explore this question, we applied transcriptomic analyses to liver samples of pre- and post-pubertal Brahman heifers and identified differentially expressed (DE) genes and genes encoding transcription factors (TFs). Differential expression of genes suggests potential biological mechanisms and pathways linking liver function to puberty. The analyses identified 452 DE genes and 82 TF with significant contribution to differential gene expression by using a regulatory impact factor metric. Brain-derived neurotrophic factor was observed as the most down-regulated gene (P = 0.003) in post-pubertal heifers and we propose this gene influences pubertal development in Brahman heifers. Additionally, co-expression network analysis provided evidence for three TF as key regulators of liver function during pubertal development: the signal transducer and activator of transcription 6, PBX homeobox 2, and polybromo 1. Pathway enrichment analysis identified transforming growth factor-beta and Wnt signaling pathways as significant annotation terms for the list of DE genes and TF in the co-expression network. Molecular information regarding genes and pathways described in this work are important to further our understanding of puberty onset in Brahman heifers.

BEX2 promotes tumor proliferation in colorectal cancer

BEX2 has been suggested to promote the tumor growth in breast cancer and glioblastoma, while inhibit the proliferation of glioma cells. Thus, the role of BEX2 in tumor was still in debate. Additionally, the biological functions of BEX2 in colorectal cancer (CRC) have not yet been clarified. Here, we reported that BEX2 was overexpressed in advanced CRC from both the GSE14333 database and fresh CRC tissue specimens, and positively correlated with clinical staging. Knockdown of BEX2 significantly decreased the in vitro proliferation of SW620 colorectal cancer cells, suppressed subcutaneous xenograft growth and enhanced the survival of mice with cecal tumors. These effects were mainly mediated by the JNK/c-Jun pathway. Knockdown of BEX2 inhibited JNK/c-Jun phosphorylation, while BEX2 overexpression activated JNK/c-Jun phosphorylation. Moreover, the administration of the JNK-specific inhibitor SP600125 to SW620 with BEX2 overexpression abolished the effect of BEX2 on SW620 cell proliferation. This study reveals that BEX2 promotes colorectal cancer cell proliferation via the JNK/c-Jun pathway, suggesting BEX2 as a potential candidate target for the treatment of CRC.

Oncogenic microtubule hyperacetylation through BEX4-mediated sirtuin 2 inhibition

Five brain-expressed X-linked (BEX) gene members (BEX1–5) are arranged in tandem on chromosome X, and are highly conserved across diverse species. However, little is known about the function and role of BEX. This study represents a first attempt to demonstrate the molecular details of a novel oncogene BEX4. Among BEX proteins, BEX4 localizes to microtubules and spindle poles, and interacts with α-tubulin (α-TUB) and sirtuin 2 (SIRT2). The overexpression of BEX4 leads to the hyperacetylation of α-TUB by inhibiting SIRT2-mediated deacetylation. Furthermore, we found BEX4 expression conferred resistance to apoptotic cell death but led to acquisition of aneuploidy, and also increased the proliferating potential and growth of tumors. These results suggest that BEX4 overexpression causes an imbalance between TUB acetylation and deacetylation by SIRT2 inhibition and induces oncogenic aneuploidy transformation.

LMO2 at 25 years: a paradigm of chromosomal translocation proteins

LMO2 was first discovered through proximity to frequently occurring chromosomal translocations in T cell acute lymphoblastic leukaemia (T-ALL). Subsequent studies on its role in tumours and in normal settings have highlighted LMO2 as an archetypical chromosomal translocation oncogene, activated by association with antigen receptor gene loci and a paradigm for translocation gene activation in T-ALL. The normal function of LMO2 in haematopoietic cell fate and angiogenesis suggests it is a master gene regulator exerting a dysfunctional control on differentiation following chromosomal translocations. Its importance in T cell neoplasia has been further emphasized by the recurrent findings of interstitial deletions of chromosome 11 near LMO2 and of LMO2 as a target of retroviral insertion gene activation during gene therapy trials for X chromosome-linked severe combined immuno-deficiency syndrome, both types of event leading to similar T cell leukaemia. The discovery of LMO2 in some B cell neoplasias and in some epithelial cancers suggests a more ubiquitous function as an oncogenic protein, and that the current development of novel inhibitors will be of great value in future cancer treatment. Further, the role of LMO2 in angiogenesis and in haematopoietic stem cells (HSCs) bodes well for targeting LMO2 in angiogenic disorders and in generating autologous induced HSCs for application in various clinical indications.

Brain-Expressed X-linked (BEX) proteins in human cancers

The Brain-Expressed X-linked (BEX) family proteins are comprised of five human proteins including BEX1, BEX2, BEX3, BEX4 and BEX5. BEX family proteins are expressed in a wide range of tissues and are known to play a role in neuronal development. Recent studies suggest a role of BEX family proteins in cancers. BEX1 expression is lost in a subgroup of patients with acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). Expression of BEX1 controls cell surface receptor signaling and restores imatinib response in resistant cells. BEX2 is overexpressed in a group of breast cancer patients and also in gliomas. Increased BEX2 expression led to enhanced NF-κB signaling as well as cell proliferation. Although BEX2 acts as tumor promoter in a subset of breast cancer, BEX3 expression displayed an opposite role. Overexpression of BEX3 resulted in inhibition of tumor formation in breast cancer mouse xenograft models. The role of BEX4 and BEX5 in cancer has not yet been defined. Collectively this suggests that BEX family members have distinct roles in cancers. While BEX1 and BEX3 act as tumor suppressors, BEX2 seems to act as an oncogene.

Bex3 Dimerization Regulates NGF-Dependent Neuronal Survival and Differentiation by Enhancing trkA Gene Transcription

The development of the nervous system is a temporally and spatially coordinated process that relies on the proper regulation of the genes involved. Neurotrophins and their receptors are directly responsible for the survival and differentiation of sensory and sympathetic neurons; however, it is not fully understood how genes encoding Trk neurotrophin receptors are regulated. Here, we show that rat Bex3 protein specifically regulates TrkA expression by acting at the trkA gene promoter level. Bex3 dimerization and shuttling to the nucleus regulate the transcription of the trkA promoter under basal conditions and also enhance nerve growth factor (NGF)-mediated trkA promoter activation. Moreover, qChIP assays indicate that Bex3 associates with the trkA promoter within a 150 bp sequence, immediately upstream from the transcription start site, which is sufficient to mediate the effects of Bex3. Consequently, the downregulation of Bex3 using shRNA increases neuronal apoptosis in NGF-dependent sensory neurons deprived of NGF and compromises PC12 cell differentiation in response to NGF. Our results support an important role for Bex3 in the regulation of TrkA expression and in NGF-mediated functions through modulation of the trkA promoter.

Brain expressed and X-linked (Bex) proteins are intrinsically disordered proteins (IDPs) and form new signaling hubs

Intrinsically disordered proteins (IDPs) are abundant in complex organisms. Due to their promiscuous nature and their ability to adopt several conformations IDPs constitute important points of network regulation. The family of Brain Expressed and X-linked (Bex) proteins consists of 5 members in humans (Bex1-5). Recent reports have implicated Bex proteins in transcriptional regulation and signaling pathways involved in neurodegeneration, cancer, cell cycle and tumor growth. However, structural and biophysical data for this protein family is almost non-existent. We used bioinformatics analyses to show that Bex proteins contain long regions of intrinsic disorder which are conserved across all members. Moreover, we confirmed the intrinsic disorder by circular dichroism spectroscopy of Bex1 after expression and purification in E. coli. These observations strongly suggest that Bex proteins constitute a new group of IDPs. Based on these findings, together with the demonstrated promiscuity of Bex proteins and their involvement in different signaling pathways, we propose that Bex family members play important roles in the formation of protein network hubs.

Bex2 controls proliferation of human glioblastoma cells through NF-κB signaling pathway

Glioblastoma is the most common and fatal human brain malignancy in adults with highly proliferative capacity. Despite advances in surgery and adjuvant therapy, the median survival of patients has changed little over recent decades. Identifying molecules critical for glioma development is significant for devising effective targeted therapy. We previously reported that Bex2, a member of the brain expressed X-linked gene family, promoted the progression of glioma by promoting cell proliferation. In the present study, we investigated the main mechanism of Bex2 promoting the proliferation of glioblastoma cells. We found that Bex2 downregulation inhibited glioma cell proliferation and the expression of NF-κB p65, but Bex2 overexpression promoted them. Similarly, the proliferation of glioma cells was inhibited by p65 downregulation but increased by p65 overexpression. In addition, Bex2 overexpression-induced cell proliferation was abolished by p65 downregulation. Furthermore, Bex2 with nuclear localization signal deleted no longer promoted p65 expression. In conclusion, this study demonstrates that Bex2 promotes proliferation of human glioblastoma cells via NF-κB signaling pathway and Bex2 nuclear location is critical for p65 expression.

Hepatocytes response to interferon alpha levels recorded after liver resection

Extensive damage of liver parenchyma stimulates hepatic cells to transit from quiescence to proliferation with eventual restoration of liver mass and function. Our recent studies have revealed upregulated expression of interferon (IFN)-α and its antiviral activity during the early hours after partial hepatectomy. In this study, we analyzed the response of primary hepatocytes from intact liver to IFN-α mimicking its levels (250 U/mL) during the transition period of liver restoration. The gene expression profile was analyzed with rat genome array 230 2.0 (Affymetrix). After 3- and 6-h treatment we identified respectively 28 and 124 differentially expressed genes responsible for autonomous changes in hepatocytes and those involving non-parenchymal cells in a concerted response to IFN-α. The response has an energy sparing character and affects all levels of gene expression. The factors activating T cells and apoptosis are opposed by those restricting the signal propagation, inhibiting T cells activation, and promoting survival. The partial resemblance between the specific in vitro response to IFN-α and the processes in regenerating liver is discussed. Our study opens the way to a more focused investigation of the liver cell response to quasiphysiological dose of IFN-α.

Bex2 regulates cell proliferation and apoptosis in malignant glioma cells via the c-Jun NH2-terminal kinase pathway

The function of Bex2, a member of the Brain Expressed X-linked gene family, in glioma is controversial and its mechanism is largely unknown. We report here that Bex2 regulates cell proliferation and apoptosis in malignant glioma cells via the c-Jun NH2-terminal kinase (JNK) pathway. The expression level of Bex2 is markedly increased in glioma tissues. We observed that Bex2 over-expression promotes cell proliferation, while down-regulation of Bex2 inhibits cell growth. Furthermore, Bex2 down-regulation promotes cell apoptosis and activates the JNK pathway; these effects were abolished by administration of the JNK specific inhibitor, SP600125. Thus, Bex2 may be an important player during the development of glioma.

Melanocortin 4 receptor is a transcriptional target of nescient helix-loop-helix-2

Melanocortin 4 receptor (Mc4r/MC4R) is a G-Protein coupled receptor that is expressed in the hypothalamus and implicated in body weight control. Mutations in MC4R are the most frequent cause of monogenetic forms of human obesity. Despite its importance, the MC4R signaling pathways and transcriptional regulation underlying the melanocortin pathway are far from being fully understood. The transcription factor nescient helix-loop-helix 2 (Nhlh2) influences the melanocortin pathway through transcriptional regulation of prohormone convertase I, which influences the production of melanocortin peptides. In the present study, Nhlh2's role as a transcriptional regulator of Mc4r has been demonstrated. Nhlh2 knockout mice have reduced hypothalamic expression of Mc4r mRNA, suggesting that it could be a direct or indirect transcriptional regulator of the Mc4r promoter. To demonstrate direct transcriptional regulation, chromatin immunoprecipitation and electrophoretic gel shift assays show that Nhlh2 binds to the E-Boxes located at -551, -366 and +54 on the Mc4r promoter. Leptin-induced transactivation of the Mc4r promoter is significantly higher in the presence of exogenously added Nhlh2. siRNA knockdown of Nhlh2 leads to significantly reduced endogenous Mc4r mRNA expression levels in N29/2 cell line. Transactivation using promoters with mutations in each of the E-Boxes results in significantly reduced transactivation efficiency compared to the WT Mc4r promoter, suggesting that Nhlh2 regulates Mc4r transcription through these sites. Findings from these studies, combined with previous work implicating Nhlh2 as a transcriptional regulator of both the Mc4r gene and the melanocortin pathway, suggest that Nhlh2's transcriptional activity directly influences the human and rodent body weight control pathways.

BEX2 has a functional interplay with c-Jun/JNK and p65/RelA in breast cancer

Background

We have previously demonstrated that BEX2 is differentially expressed in breast tumors and has a significant role in promoting cell survival and growth in breast cancer cells. BEX2 expression protects breast cancer cells against mitochondrial apoptosis and G1 cell cycle arrest. In this study we investigated the transcriptional regulation of BEX2 and feedback mechanisms mediating the cellular function of this gene in breast cancer.

Results

We found a marked induction of BEX2 promoter by c-Jun and p65/RelA using luciferase reporter assays in MCF-7 cells. Furthermore, we confirmed the binding of c-Jun and p65/RelA to the BEX2 promoter using a chromatin immunoprecipitation assay. Importantly, transfections of c-Jun or p65/RelA in MCF-7 cells markedly increased the expression of BEX2 protein. Overall, these results demonstrate that BEX2 is a target gene for c-Jun and p65/RelA in breast cancer. These findings were further supported by the presence of a strong correlation between BEX2 and c-Jun expression levels in primary breast tumors. Next we demonstrated that BEX2 has a feedback mechanism with c-Jun and p65/RelA in breast cancer. In this process BEX2 expression is required for the normal phosphorylation of p65 and IκBα, and the activation of p65. Moreover, it is necessary for the phosphorylation of c-Jun and JNK kinase activity in breast cancer cells. Furthermore, using c-Jun stable lines we showed that BEX2 expression is required for c-Jun mediated induction of cyclin D1 and cell proliferation. Importantly, BEX2 down-regulation resulted in a significant increase in PP2A activity in c-Jun stable lines providing a possible underlying mechanism for the regulatory effects of BEX2 on c-Jun and JNK.

Conclusions

This study shows that BEX2 has a functional interplay with c-Jun and p65/RelA in breast cancer. In this process BEX2 is a target gene for c-Jun and p65/RelA and in turn regulates the phosphorylation/activity of these proteins. These suggest that BEX2 is involved in a novel feedback mechanism with significant implications for the biology of breast cancer.

Galectin 1 proangiogenic and promigratory effects in the Hs683 oligodendroglioma model are partly mediated through the control of BEX2 expression

We have previously reported that galectin 1 (Gal-1) plays important biological roles in astroglial as well as in oligodendroglial cancer cells. As an oligodendroglioma model, we make use of the Hs683 cell line that has been previously extensively characterized at cell biology, molecular biology, and genetic levels. Galectin 1 has been shown to be involved in Hs683 oligodendroglioma chemoresistance, neoangiogenesis, and migration. Down-regulating Gal-1 expression in Hs683 cells through targeted small interfering RNA provokes a marked decrease in the expression of the brain-expressed X-linked gene: BEX2. Accordingly, the potential role of BEX2 in Hs683 oligodendroglioma cell biology has been investigated. The data presented here reveal that decreasing BEX2 expression in Hs683 cells increases the survival of Hs683 orthotopic xenograft-bearing mice. Furthermore, this decrease in BEX2 expression impairs vasculogenic mimicry channel formation in vitro and angiogenesis in vivo, and modulates glioma cell adhesion and invasive features through the modification of several genes previously reported to play a role in cancer cell migration, including MAP2, plexin C1, SWAP70, and integrin beta(6). We thus conclude that BEX2 is implicated in oligodendroglioma biology.

Nescient helix-loop-helix 2 interacts with signal transducer and activator of transcription 3 to regulate transcription of prohormone convertase 1/3

Mechanisms controlling body weight involve gene regulation through the activation of signal transduction pathways. The Janus kinase/signal transducer and activator of transcription (STAT) signal transduction pathway is the mechanism primarily used by leptin in the hypothalamus. The transcription factor nescient helix-loop-helix 2 (Nhlh2) is a downstream target of leptin signaling and is expressed in proopiomelanocortin arcuate neurons. Proopiomelanocortin is cleaved by prohormone convertase 1/3 (PC1/3) to produce peptides that regulate the body's response to energy availability. Previous studies show that the PC1/3 promoter contains STAT3 sites mediating leptin-induced PC1/3 expression, and that Nhlh2 is required for hypothalamic PC1/3 expression because Nhlh2 knockout mice have reduced PC1/3 mRNA levels. Studies herein reveal that leptin-induced PC1/3 gene expression is abrogated in N2KO mice, and that in a hypothalamic cell line both STAT3 and Nhlh2 are required for the full transcriptional response of a PC1/3 reporter gene after leptin stimulation. Furthermore, it is shown that Nhlh2 binds to E-box motifs found adjacent to STAT3 sites in the PC1/3 promoter both in vitro and in chromatin immunoprecipitation assays. Finally, two different protein-protein interaction assays confirm the presence of a STAT3:Nhlh2 heterodimer on the PC1/3 promoter. The Nhlh2:STAT3 heterodimer may be an important transcriptional regulator of other hypothalamic genes in the leptin signaling pathway. These data confirm Nhlh2 as an integral element of the Janus kinase/STAT signaling pathway and are the first to demonstrate coordinated control of PC1/3 transcription by Nhlh2 and STAT3 after leptin stimulation.

BEX2 is overexpressed in a subset of primary breast cancers and mediates nerve growth factor/nuclear factor-kappaB inhibition of apoptosis in breast cancer cell lines

We have identified a novel subtype of estrogen receptor (ER)-positive breast cancers with improved outcome after tamoxifen treatment and characterized by overexpression of the gene BEX2. BEX2 and its homologue BEX1 have highly correlated expression and are part of a cluster enriched for ER response and apoptosis genes. BEX2 expression is induced after estradiol (E2) treatment with a peak at 3 h, suggesting BEX2 is an estrogen-regulated gene. BEX2 belongs to a family of genes, including BEX1, NGFRAP1 (alias BEX3), BEXL1 (alias BEX4), and NGFRAP1L1 (alias BEX5). Both BEX1 and NGFRAP1 interact with p75NTR and modulate nerve growth factor (NGF) signaling through nuclear factor-kappaB (NF-kappaB) to regulate cell cycle, apoptosis, and differentiation in neural tissues. In breast cancer cells, NGF inhibits C2-induced apoptosis through binding of p75NTR and NF-kappaB activation. Here, we show that BEX2 expression is necessary and sufficient for the NGF-mediated inhibition (through NF-kappaB activation) of C2-induced apoptosis. We also show that BEX2 modulates apoptosis of breast cancer cells in response to E2 (50 nmol/L) and tamoxifen (5 and 10 micromol/L). Furthermore, BEX2 overexpression enhances the antiproliferative effect of tamoxifen at pharmacologic dose (1 micromol/L). These data suggest that a NGF/BEX2/NF-kappaB pathway is involved in regulating apoptosis in breast cancer cells and in modulating response to tamoxifen in primary tumors.

The significance of LMO2 expression in the progression of prostate cancer

LIM domain only 2 (LMO2) proteins are important regulators in determining cell fate and controlling cell growth and differentiation. This study has investigated LMO2 expression in human prostatic tissue specimens, prostate cancer cell lines, and xenografts; and has assessed the possible role and mechanism of LMO2 in prostate carcinogenesis. Immunohistochemical analysis on a tissue microarray consisting of 91 human prostate specimens, including normal, prostatic hyperplasia, high-grade prostatic intraepithelial neoplasia, and invasive carcinoma, revealed that overexpression of LMO2 was significantly associated with advanced tumour stage, as measured by Gleason score (p = 0.012), as well as with the development of distant metastasis (p = 0.018). These data were supported by quantitative real-time PCR experiments, where LMO2 mRNA levels were found to be significantly higher in prostate tumour specimen than in normal epithelium (p = 0.037). The expression of LMO2 in cell lines and xenografts representing androgen-dependent (AD) and androgen-independent (AI) prostate cancer stages was further studied. Consistent with the in vivo data, LMO2 mRNA and protein were found to be overexpressed in the more aggressive AI cells (PC3, DU145, and AI CWR22 xenografts) compared with less aggressive AD cells (LNCaP and AD CWR22 xenografts). Furthermore, stable introduction of LMO2 into LNCaP cells conferred enhanced cell motility and invasiveness in vitro, accompanied by down-regulation of E-cadherin expression. Taken together, these findings provide the first evidence to support the hypothesis that LMO2 may play an important role in prostate cancer progression, possibly via repression of E-cadherin expression.

Identification of the Key LMO2-binding Determinants on Ldb1

The overexpression of LIM-only protein 2 (LMO2) in T-cells, as a result of chromosomal translocations, retroviral insertion during gene therapy, or in transgenic mice models, leads to the onset of T-cell leukemias. LMO2 comprises two protein-binding LIM domains that allow LMO2 to interact with multiple protein partners, including LIM domain-binding protein 1 (Ldb1, also known as CLIM2 and NLI), an essential cofactor for LMO proteins. Sequestration of Ldb1 by LMO2 in T-cells may prevent it binding other key partners, such as LMO4. Here, we show using protein engineering and enzyme-linked immunosorbent assay (ELISA) methodologies that LMO2 binds Ldb1 with a twofold lower affinity than does LMO4. Thus, excess LMO2 rather than an intrinsically higher binding affinity would lead to sequestration of Ldb1. Both LIM domains of LMO2 are required for high-affinity binding to Ldb1 (K(D) = 2.0 x 10(-8) M). However, the first LIM domain of LMO2 is primarily responsible for binding to Ldb1 (K(D) = 2.3 x 10(-7) M), whereas the second LIM domain increases binding by an order of magnitude. We used mutagenesis in combination with yeast two-hybrid analysis, and phage display selection to identify LMO2-binding "hot spots" within Ldb1 that locate to the LIM1-binding region. The delineation of this region reveals some specific differences when compared to the equivalent LMO4:Ldb1 interaction that hold promise for the development of reagents to specifically bind LMO2 in the treatment of leukemia.

Inhibitory regulation of EGF receptor degradation by sorting nexin 5

Endosomal trafficking of EGF receptor (EGFR) upon stimulation is a highly regulated process during receptor-mediated signaling. Recently, the sorting nexin (SNX) family has emerged as an important regulator in the membrane trafficking of EGFR. Here, we report the identification of a novel interaction between two members of the family, SNX1 and SNX5, which is mediated by the newly defined BAR domain of both SNXs. We have also shown that the PX domain of SNX5 binds specifically to PtdIns other than to PtdIns(3)P. Furthermore, the BAR domain but not the PX domain of SNX5 is sufficient for its subcellular membrane association. Functionally, overexpression of SNX5 inhibits the degradation of EGFR. This process appears to be independent of its interaction with SNX1. However, overexpression of SNX1 is able to attenuate the effect of SNX5 on EGFR degradation, suggesting the two proteins may play antagonistic roles in regulating endosomal trafficking of the receptor.