Gene 33 is an endogenous inhibitor of epidermal growth factor (EGF) receptor signaling and mediates dexamethasone-induced suppression of EGF function

ERRFI1 exacerbates hepatic ischemia reperfusion injury by promoting hepatocyte apoptosis and ferroptosis in a GRB2-dependent manner

BACKGROUND

Programmed cell death is an important mechanism for the development of hepatic ischemia and reperfusion (IR) injury, and multiple novel forms of programmed cell death are involved in the pathological process of hepatic IR. ERRFI1 is involved in the regulation of cell apoptosis in myocardial IR. However, the function of ERRFI1 in hepatic IR injury and its modulation of programmed cell death remain largely unknown.

METHODS

Here, we performed functional and molecular mechanism studies in hepatocyte-specific knockout mice and ERRFI1-silenced hepatocytes to investigate the significance of ERRFI1 in hepatic IR injury. The histological severity of livers, enzyme activities, hepatocyte apoptosis and ferroptosis were determined.

RESULTS

ERRFI1 expression increased in liver tissues from mice with IR injury and hepatocytes under oxygen-glucose deprivation/reoxygenation (OGD/R) conditions. Hepatocyte-specific ERRFI1 knockout alleviated IR-induced liver injury in mice by reducing cell apoptosis and ferroptosis. ERRFI1 knockdown reduced apoptotic and ferroptotic hepatocytes induced by OGD/R. Mechanistically, ERRFI1 interacted with GRB2 to maintain its stability by hindering its proteasomal degradation. Overexpression of GRB2 abrogated the effects of ERRFI1 silencing on hepatocyte apoptosis and ferroptosis.

CONCLUSIONS

Our results revealed that the ERRFI1-GRB2 interaction and GRB2 stability are essential for ERRFI1-regulated hepatic IR injury, indicating that inhibition of ERRFI1 or blockade of the ERRFI1-GRB2 interaction may be potential therapeutic strategies in response to hepatic IR injury.

METTL14 affects UVB-induced human dermal fibroblasts photoaging via miR-100-3p biogenesis in an m6A-dependent manner

Exposure to ultraviolet radiation can lead to skin photoaging, which increases the risk of skin tumors. This study aims to investigate how microRNA m6A modification contributes to skin photoaging. This study found that skin fibroblasts exposed to a single UVB dose of 30 mJ/cm2 exhibited characteristics of photoaging. The m6A level of total RNA decreased in photoaged cells with a down-regulated level of METTL14, and overexpression of METTL14 displayed a photoprotective function. Moreover, miR-100-3p was a downstream target of METTL14. And METTL14 could affect pri-miR-100 processing to mature miR-100-3p in an m6A-dependent manner via DGCR8. Furthermore, miR-100-3p targeted at 3' end untranslated region of ERRFI1 mRNA with an inhibitory effect on translation. Additionally, photoprotective effects of overexpression of METTL14 were reversed by miR-100-3p inhibitor or overexpression of ERRFI1. In UVB-induced photoaging of human skin fibroblasts, METTL14-dependent m6A can regulate miR-100-3p maturation via DGCR8 and affect skin fibroblasts photoaging through miR-100-3p/ERRFI1 axis.

Role of ErbB and IL-1 signaling pathways in the dermonecrotic lesion induced by Loxosceles sphingomyelinases D

Sphingomyelinase D (SMase D), the main toxic component of Loxosceles venom, has a well-documented role on dermonecrotic lesion triggered by envenomation with these species; however, the intracellular mechanisms involved in this event are still poorly known. Through differential transcriptomics of human keratinocytes treated with L. laeta or L. intermedia SMases D, we identified 323 DEGs, common to both treatments, as well as upregulation of molecules involved in the IL-1 and ErbB signaling. Since these pathways are related to inflammation and wound healing, respectively, we investigated the relative expression of some molecules related to these pathways by RT-qPCR and observed different expression profiles over time. Although, after 24 h of treatment, both SMases D induced similar modulation of these pathways in keratinocytes, L. intermedia SMase D induced earlier modulation compared to L. laeta SMase D treatment. Positive expression correlations of the molecules involved in the IL-1 signaling were also observed after SMases D treatment, confirming their inflammatory action. In addition, we detected higher relative expression of the inhibitor of the ErbB signaling pathway, ERRFI1, and positive correlations between this molecule and pro-inflammatory mediators after SMases D treatment. Thus, herein, we describe the cell pathways related to the exacerbation of inflammation and to the failure of the wound healing, highlighting the contribution of the IL-1 signaling pathway and the ERRFI1 for the development of cutaneous loxoscelism.

The Myc Family and the Metastasis Suppressor NDRG1: Targeting Key Molecular Interactions with Innovative Therapeutics

Cancer is a leading cause of death worldwide, resulting in ∼10 million deaths in 2020. Major oncogenic effectors are the Myc proto-oncogene family, which consists of three members including c-Myc, N-Myc, and L-Myc. As a pertinent example of the role of the Myc family in tumorigenesis, amplification of MYCN in childhood neuroblastoma strongly correlates with poor patient prognosis. Complexes between Myc oncoproteins and their partners such as hypoxia-inducible factor-1α and Myc-associated protein X (MAX) result in proliferation arrest and pro-proliferative effects, respectively. Interactions with other proteins are also important for N-Myc activity. For instance, the enhancer of zest homolog 2 (EZH2) binds directly to N-Myc to stabilize it by acting as a competitor against the ubiquitin ligase, SCFFBXW7, which prevents proteasomal degradation. Heat shock protein 90 may also be involved in N-Myc stabilization since it binds to EZH2 and prevents its degradation. N-Myc downstream-regulated gene 1 (NDRG1) is downregulated by N-Myc and participates in the regulation of cellular proliferation via associating with other proteins, such as glycogen synthase kinase-3β and low-density lipoprotein receptor-related protein 6. These molecular interactions provide a better understanding of the biologic roles of N-Myc and NDRG1, which can be potentially used as therapeutic targets. In addition to directly targeting these proteins, disrupting their key interactions may also be a promising strategy for anti-cancer drug development. This review examines the interactions between the Myc proteins and other molecules, with a special focus on the relationship between N-Myc and NDRG1 and possible therapeutic interventions. SIGNIFICANCE STATEMENT: Neuroblastoma is one of the most common childhood solid tumors, with a dismal five-year survival rate. This problem makes it imperative to discover new and more effective therapeutics. The molecular interactions between major oncogenic drivers of the Myc family and other key proteins; for example, the metastasis suppressor, NDRG1, may potentially be used as targets for anti-neuroblastoma drug development. In addition to directly targeting these proteins, disrupting their key molecular interactions may also be promising for drug discovery.

The increased expression of cytokeratin 13 leads to an increase in radiosensitivity of nasopharyngeal carcinoma HNE-3 cells by upregulating ERRFI1

The main factors contributing to the unfavorable outcome in the clinical treatment of patients with nasopharyngeal carcinoma (NPC) patients are radiation resistance and recurrence. This study aimed to investigate the sensitivity and molecular foundation of cytokeratin 13 (CK13) in the radiotherapy of NPC. To achieve this, a human NPC cell line overexpressing CK13, HNE-3-CK13, was constructed. The effects of CK13 overexpression on cell viability and apoptosis under radiotherapy conditions were evaluated using the CCK-8 assay, immunofluorescence, and western blotting (WB). Next-generation sequencing was performed to identify the downstream genes and signaling pathways of CK13 that mediate radiotherapy response. The potential role of the candidate gene ERRFI1 in CK13-induced enhancement of radiosensitivity was investigated through rescue experiments using clone formation and WB. The effects of ERRFI1 on cell viability, cell apoptosis, cell cycle, and the related key genes were further evaluated using CCK-8, immunofluorescence, flow cytometry, quantitative polymerase chain reaction and WB. The results showed that CK13 overexpression in HNE-3 significantly inhibited cell survival under radiotherapy and promoted apoptosis marker γH2AX expression, leading to a significant increase of ERRFI1. Knockdown of ERRFI1 rescued the decreased cell viability and proliferation and the increased cell apoptosis that were caused by CK13 overexpression-mediated radiotherapy sensitization of NPC cells. In this process, EGFR, AKT, and GSK-3β were found involved. In the end, ERRFI1 was proven to inhibit expression levels of CDK1, CDK2, cyclin B1, and cyclin D1, resulting an increased G2/M cell ratio. Overexpression of CK13 enhances the radiosensitivity of NPC cells, which is characterized by decreased cell viability and proliferation and increased apoptosis. This regulation may affect the survival of HNE-3 cells by increasing the expression of ERRFI1 and activating the EGFR/Akt/GSK-3β signaling pathway, providing new potential therapeutic targets for the treatment of NPC.

Glucolipotoxic Stress-Induced Mig6 Desensitizes EGFR Signaling and Promotes Pancreatic Beta Cell Death

A loss of functional beta cell mass is a final etiological event in the development of frank type 2 diabetes (T2D). To preserve or expand beta cells and therefore treat/prevent T2D, growth factors have been considered therapeutically but have largely failed to achieve robust clinical success. The molecular mechanisms preventing the activation of mitogenic signaling pathways from maintaining functional beta cell mass during the development of T2D remain unknown. We speculated that endogenous negative effectors of mitogenic signaling cascades impede beta cell survival/expansion. Thus, we tested the hypothesis that a stress-inducible epidermal growth factor receptor (EGFR) inhibitor, mitogen-inducible gene 6 (Mig6), regulates beta cell fate in a T2D milieu. To this end, we determined that: (1) glucolipotoxicity (GLT) induces Mig6, thereby blunting EGFR signaling cascades, and (2) Mig6 mediates molecular events regulating beta cell survival/death. We discovered that GLT impairs EGFR activation, and Mig6 is elevated in human islets from T2D donors as well as GLT-treated rodent islets and 832/13 INS-1 beta cells. Mig6 is essential for GLT-induced EGFR desensitization, as Mig6 suppression rescued the GLT-impaired EGFR and ERK1/2 activation. Further, Mig6 mediated EGFR but not insulin-like growth factor-1 receptor nor hepatocyte growth factor receptor activity in beta cells. Finally, we identified that elevated Mig6 augmented beta cell apoptosis, as Mig6 suppression reduced apoptosis during GLT. In conclusion, we established that T2D and GLT induce Mig6 in beta cells; the elevated Mig6 desensitizes EGFR signaling and induces beta cell death, suggesting Mig6 could be a novel therapeutic target for T2D.

Pancreatic loss of Mig6 alters murine endocrine cell fate and protects functional beta cell mass in an STZ-induced model of diabetes

Background

Maintaining functional beta cell mass (BCM) to meet glycemic demands is essential to preventing or reversing the progression of diabetes. Yet the mechanisms that establish and regulate endocrine cell fate are incompletely understood. We sought to determine the impact of deletion of mitogen-inducible gene 6 (Mig6), a negative feedback inhibitor of epidermal growth factor receptor (EGFR) signaling, on mouse endocrine cell fate. The extent to which loss of Mig6 might protect against loss of functional BCM in a multiple very low dose (MVLD) STZ-induced model of diabetes was also determined.

Methods

Ten-week-old male mice with whole pancreas (Pdx1:Cre, PKO) and beta cell-specific (Ins1:Cre, BKO) knockout of Mig6 were used alongside control (CON) littermates. Mice were given MVLD STZ (35 mg/kg for five days) to damage beta cells and induce hyperglycemia. In vivo fasting blood glucose and glucose tolerance were used to assess beta cell function. Histological analyses of isolated pancreata were utilized to assess islet morphology and beta cell mass. We also identified histological markers of beta cell replication, dedifferentiation, and death. Isolated islets were used to reveal mRNA and protein markers of beta cell fate and function.

Results

PKO mice had significantly increased alpha cell mass with no detectable changes to beta or delta cells. The increase in alpha cells alone did not impact glucose tolerance, BCM, or beta cell function. Following STZ treatment, PKO mice had 18±8% higher BCM than CON littermates and improved glucose tolerance. Interestingly, beta cell-specific loss of Mig6 was insufficient for protection, and BKO mice had no discernable differences compared to CON mice. The increase in BCM in PKO mice was the result of decreased beta cell loss and increased beta cell replication. Finally, STZ-treated PKO mice had more Ins+/Gcg+ bi-hormonal cells compared to controls suggesting alpha to beta cell transdifferentiation.

Conclusions

Mig6 exerted differential effects on alpha and beta cell fate. Pancreatic loss of Mig6 reduced beta cell loss and promoted beta cell growth following STZ. Thus, suppression of Mig6 may provide relief of diabetes.

Sprouty4 at the crossroads of Trk neurotrophin receptor signaling suppression by glucocorticoids

Glucocorticoids (GC) affect neuronal plasticity, development and function of the nervous system by inhibiting neurotrophin-induced Trk signaling. It has been established that pretreatment with dexamethasone (DEX) restricts Neurotrophin-induced neurite outgrowth by inhibiting Trk-dependent activation of Ras-Erk1/2 signaling pathways. However, the precise molecular mechanism through which DEX interferes with neurotrophin signaling and Trk-mediated neurite outgrowth has not been clearly defined yet. Here, we observed that in PC12 cells DEX treatment promotes the transcription of Sprouty4, a regulatory molecule that is part of a negative feedback module that specifically abrogates Ras to Erk1/2 signaling in response to NGF. In line with this, either knockdown of Sprouty4 or overexpression of a dominant negative form of Sprouty4 (Y53A), rescue the inhibition of NGF/TrkA-promoted neurite outgrowth and Erk1/2 phosphorylation induced by DEX. Likewise, treatment of hippocampal neurons with DEX induces the expression of Sprouty4 and its knockdown abrogates the inhibitory effect of DEX on primary neurite formation, dendrite branching and Erk1/2 activation induced by BDNF. Thus, these results suggest that the induction of Sprouty4 mRNA by DEX translates into a significant inhibition of Trk to Erk1/2 signaling pathway. Together, these findings bring new insights into the crosstalk between DEX and neurotrophin signaling and demonstrate that Sprouty4 mediates the inhibitory effects of DEX on neurotrophin function.

Effect of Gene 33/Mig6/ERRFI1 on hexavalent chromium-induced transformation of human bronchial epithelial cells depends on the length of exposure

Hexavalent chromium (Cr(VI)) compounds are environmental and occupational lung carcinogens. The present study followed the chronic effect of Cr(VI) on the neoplastic transformation of BEAS-2B lung bronchial epithelial cells with or without deletion of Gene 33 (Mig6, EFFRI1), a multifunctional adaptor protein. We find that Gene 33-deleted cells exhibit increased anchorage-independent growth compared to control cells after transformed by 8-week but not 24-week Cr(VI) exposure. Gene 33-deleted cells show a higher level of cell proliferation and are more resistant to acute Cr(VI) toxicity compared to control cells after transformed by 8-week but not 24-week Cr(VI) exposure, despite that 24-week-transformed cells have increased resistance to acute Cr(VI) toxicity. However, Gene 33-deleted cells show increased migration after transformed by both 8-week and 24-week Cr(VI) exposures. Furthermore, only cells transformed by 24 weeks of Cr(VI) exposure can form subcutaneous tumors in nude mice. Although no significant difference in the size of tumors formed by the two cell types, there is a marked difference in the histological manifestation and more MMP3 expression in tumors from Gene 33-deleted cells. Our results demonstrate progressive neoplastic transformation of BEAS-2B cells and the adaptation of these cells to Gene 33 deletion during chronic exposure to Cr(VI).

Activity of the nonreceptor tyrosine kinase Ack1 is regulated by tyrosine phosphorylation of its Mig6 homology region

Ack1 is a proto-oncogenic tyrosine kinase with homology to the tumour suppressor Mig6, an inhibitor of the epidermal growth factor receptor (EGFR). The residues critical for binding of Mig6 to EGFR are conserved within the Mig6 homology region (MHR) of Ack1. We tested whether intramolecular interactions between the Ack1 MHR and kinase domain (KD) are regulated by phosphorylation. We identified two Src phosphorylation sites within the MHR (Y859, Y860). Addition of Src-phosphorylated MHR to the Ack1 KD enhanced enzymatic activity. Co-expression of Src in cells led to increased Ack1 activity; mutation of Y859/Y860 blocked this increase. Collectively, the data suggest that phosphorylation of the Ack1 MHR regulates its kinase activity. Phosphorylation of Y859/Y860 occurs in cancers of the brain, breast, colon, and prostate, where genomic amplification or somatic mutations of Ack1 play a role in disease progression. Our findings suggest that MHR phosphorylation could contribute to Ack1 dysregulation in tumours.

The Mechanism of Chaiyin Particles in the Treatment of COVID-19 Based on Network Pharmacology and Experimental Verification

Objective: To explore the potential active components of Chaiyin particles (CYPs) in the treatment of coronavirus disease 2019 (COVID-19) and their mechanism of action using network pharmacology and molecular docking technology. Methods: Based on the components of CYPs, we obtained potential targets of the interaction between CYPs and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The potential targets were analyzed by protein–protein interaction, gene ontology, and Kyoto Encyclopedia of Genes and Genomes pathway analyses. The key active components of CYPs were subjected to molecular docking with 3-chymotrypsin-like protease, angiotensin-converting enzyme II (ACE2), RNA-dependent RNA polymerase, and papain-like protease. The components that may bind to the key target proteins of SARS-CoV-2 were screened to obtain the potential active components, targets and pathways for CYP treatment of COVID-19. The above-described network analysis results were then verified experimentally. Results: CYPs may prevent and treat COVID-19 by inhibiting the release of inflammatory factors such as IL-6 and TNF-α; participating in the AGE-Rage signaling pathway, the HIF-1 signaling pathway, and other anti-inflammatory, antiviral, and immune regulatory signaling pathways; and blocking ACE2 via fortunellin and baicalin. Conclusion: This work illustrated that CYPs mainly play an anti-inflammatory and immunomodulatory role in COVID-19 prevention and treatment. The potential active components and molecular mechanism of CYPs can provide theoretical support and a pharmacological basis for further development and utilization of CYPs in the prevention and treatment of COVID-19. These results provide important insights into future studies of Traditional Chinese medicines (TCMs) modernization and prevention.

The glucocorticoid receptor associates with RAS complexes to inhibit cell proliferation and tumor growth

Mutations that activate members of the RAS family of GTPases are associated with various cancers and drive tumor growth. The glucocorticoid receptor (GR), a member of the nuclear receptor family, has been proposed to interact with and inhibit the activation of components of the PI3K-AKT and MAPK pathways downstream of RAS. In the absence of activating ligands, we found that GR was present in cytoplasmic KRAS-containing complexes and inhibited the activation of wild-type and oncogenic KRAS in mouse embryonic fibroblasts and human lung cancer A549 cells. The DNA binding domain of GR was involved in the interaction with KRAS, but GR-dependent inhibition of RAS activation did not depend on the nuclear translocation of GR. The addition of ligand released GR-dependent inhibition of RAS, AKT, the MAPK p38, and the MAPKK MEK. CRISPR-Cas9-mediated deletion of GR in A549 cells enhanced tumor growth in xenografts in mice. Patient samples of non-small cell lung carcinomas showed lower expression of NR3C1, the gene encoding GR, compared to adjacent normal tissues and lower NR3C1 expression correlated with a worse disease outcome. These results suggest that glucocorticoids prevent the ability of GR to limit tumor growth by inhibiting RAS activation, which has potential implications for the use of glucocorticoids in patients with cancer.

Glucocorticoids Inhibit EGFR Signaling Activation in Podocytes in Anti-GBM Crescentic Glomerulonephritis

Glucocorticoids are commonly used to treat anti-GBM crescentic glomerulonephritis, however, the mechanism underlying its therapeutic effectiveness is not completely understood. Since podocyte EGFR/STAT3 signaling is known to mediate the development of anti-GBM glomerulonephritis, we investigated the effect of glucocorticoids on EGFR/STAT3 signaling in podocytes. We found that the levels of phosphorylated (activated) EGFR and STAT3 in podocytes were markedly elevated in anti-GBM patients without glucocorticoids treatment, but were normalized in patients with glucocorticoids treatment. In a rat model of anti-GBM glomerulonephritis, glucocorticoids treatment significantly attenuated the proteinuria, crescent formation, parietal epithelial cell (PEC) activation and proliferation, accompanied by elimination of podocyte EGFR/STAT3 signaling activation. In cultured podocytes, glucocorticoids were found to inhibit HB-EGF-induced EGFR and STAT3 activation. The conditioned medium from podocytes treated with HB-EGF in the absence but not presence of glucocorticoids was capable of activating Notch signaling (which is known to be involved in PEC proliferation and crescent formation) and enhancing proliferative activity in primary PECs, suggesting that glucocorticoids prevent podocytes from producing secreted factors that cause PEC proliferation and crescent formation. Furthermore, we found that glucocorticoids can downregulate the expression of EGFR ligands, EGF and HB-EGF, while upregulate the expression of EGFR inhibitor, Gene 33, explaining how glucocorticoids suppress EGFR signaling. Taken together, glucocorticoids exert therapeutic effect on anti-GBM crescentic glomerulonephritis through inhibiting podocyte EGFR/STAT3 signaling and the downstream pathway that leads to PEC proliferation and crescent formation.

Gene 33/Mig6/ERRFI1, an Adapter Protein with Complex Functions in Cell Biology and Human Diseases

Gene 33 (also named Mig6, RALT, and ERRFI1) is an adapter/scaffold protein with a calculated molecular weight of about 50 kD. It contains multiple domains known to mediate protein–protein interaction, suggesting that it has the potential to interact with many cellular partners and have multiple cellular functions. The research over the last two decades has confirmed that it indeed regulates multiple cell signaling pathways and is involved in many pathophysiological processes. Gene 33 has long been viewed as an exclusively cytosolic protein. However, recent evidence suggests that it also has nuclear and chromatin-associated functions. These new findings highlight a significantly broader functional spectrum of this protein. In this review, we will discuss the function and regulation of Gene 33, as well as its association with human pathophysiological conditions in light of the recent research progress on this protein.

Stress-induced differential gene expression in cardiac tissue

The stress response is adaptive and aims to guarantee survival. However, the persistence of a stressor can culminate in pathology. Catecholamines released as part of the stress response over activate beta adrenoceptors (β-AR) in the heart. Whether and how stress affects the expression of components of the intracellular environment in the heart is still, however, unknown. This paper used microarray to analyze the gene expression in the left ventricle wall of rats submitted to foot shock stress, treated or not treated with the selective β₂-AR antagonist ICI118,551 (ICI), compared to those of non-stressed rats also treated or not with ICI, respectively. The main findings were that stress induces changes in gene expression in the heart and that β₂-AR plays a role in this process. The vast majority of genes disregulated by stress were exclusive for only one of the comparisons, indicating that, in the same stressful situation, the profile of gene expression in the heart is substantially different when the β₂-AR is active or when it is blocked. Stress induced alterations in the expression of such a large number of genes seems to be part of stress-induced adaptive mechanism.

Docosahexaenoic acid differentially modulates the cell cycle and metabolism- related genes in tumor and pre-malignant prostate cells

Prostate cancer (PCa) has different molecular features along progression, including androgen profile, which is associated to therapy inefficiency leading to more aggressive phenotype. Docosahexaenoic acid (DHA) has antiproliferative and pro-apoptotic properties in different cancers associated to cell metabolism modulation. The latter is of particular interest since metabolic reprogramming is one of PCa hallmarks, but is not clear how this occurs among disease progression. Therefore, we evaluated DHA antiproliferative potential in distinct androgenic backgrounds associated to metabolism modulation and androgen-regulated genes. For this purpose, pre-malignant PNT1A and tumor AR-positive 22rv1, and AR-negative PC3 cells were incubated with DHA at 100 μM-48 h. DHA reduced at least 26% cell number for all lineages due to S-phase decrease in AR-positive and G2/M arrest in AR-negative. Mitochondrial metabolic rate decreased in PNT1A (~38%) and increased in tumor cells (at least 40%). This was associated with ROS overproduction (1.6-fold PNT1A; 2.1 22rv1; 2.2 PC3), lipid accumulation (3-fold PNT1A; 1.8 22rv1; 3.6 PC3) and mitochondria damage in all cell lines. AKT, AMPK and PTEN were not activated in any cell line, but p-ERK1/2 increased (1.5-fold) in PNT1A. Expression of androgen-regulated and nuclear receptors genes showed that DHA affected them in a distinct pattern in each cell line, but most converged to metabolism regulation, response to hormones, lipids and stress. In conclusion, regardless of androgenic or PTEN background DHA exerted antiproliferative effect associated to cell cycle impairment, lipid deregulation and oxidative stress, but differentially regulated gene expression probably due to distinct molecular features of each pathologic stage.

Differential Glucocorticoid-Dependent Regulation and Function of the ERRFI1 Gene in Triple-Negative Breast Cancer

Glucocorticoids (GCs; eg, hydrocortisone [CORT]) are routinely used as chemotherapeutic, anti-emetic, and palliative agents in breast cancer (BCa) therapy. The effects of GC signaling on BCa progression, however, remain a contentious topic as GC treatment seems to be beneficial for receptor-positive subtypes but elicits unfavorable responses in triple-negative BCa (TNBC). The mechanistic basis for these conflicting effects of GC in BCa is poorly understood. In this study, we sought to decipher the molecular mechanisms that govern the GC-dependent induction of the tumor suppressor ERRFI1 gene, an inhibitor of epidermal growth factor receptor (EGFR) signaling, and characterize the role of the GC-ERRFI1 regulatory axis in TNBC. Treatment of TNBC cell lines with a protein synthesis inhibitor or GC receptor (GR) antagonist followed by gene expression analysis suggests that ERRFI1 is a direct GR target. Using in silico analysis coupled with enhancer-reporter assays, we identified a putative ERRFI1 enhancer that supports CORT-dependent transactivation. In orthogonal assays for cell proliferation, survival, migration, and apoptosis, CORT mostly facilitated an oncogenic phenotype regardless of malignancy status. Lentiviral knockdown and overexpression of ERRFI1 showed that the CORT-enhanced oncogenic phenotype is restricted by ERRFI1 in the normal breast epithelial model MCF10A and to a lesser degree in the metastatic TNBC line MDA-MB-468. Conversely, ERRFI1 conferred pro-tumorigenic effects in the highly metastatic TNBC model MDA-MB-231. Taken together, our findings suggest that the progressive loss of the GC-dependent regulation and anti-tumorigenic function of ERRFI1 influences BCa progression and may contribute to the unfavorable effects of GC therapy in TNBC.

Glucocorticoid Receptor Modulates EGFR Feedback upon Acquisition of Resistance to Monoclonal Antibodies

Evidences of a crosstalk between Epidermal Growth Factor Receptor (EGFR) and Glucocorticoid Receptor (GR) has been reported, ranging from the modulation of receptor levels or GR mediated transcriptional repression of EGFR target genes, with modifications of epigenetic markers. The present study focuses on the involvement of EGFR positive and negative feedback genes in the establishment of cetuximab (CTX) resistance in metastatic Colorectal Cancer (CRC) patients. We evaluated the expression profile of the EGFR ligands TGFA and HBEGF, along with the pro-inflammatory cytokines IL-1B and IL-8, which were previously reported to be negatively associated with monoclonal antibody response, both in mice and patient specimens. Among EGFR negative feedback loops, we focused on ERRFI1, DUSP1, LRIG3, and LRIG1. We observed that EGFR positive feedback genes are increased in CTX-resistant cells, whereas negative feedback genes are reduced. Next, we tested the expression of these genes in CTX-resistant cells upon GR modulation. We unveiled that GR activation leads to an increase in ERRFI1, DUSP1, and LRIG1, which were shown to restrict EGFR activity, along with a decrease in the EGFR activators (TGFA and IL-8). Finally, in a cohort of xenopatients, stratified for response to cetuximab, we observed an inverse association between the expression level of LRIG1 and CRC progression upon CTX treatment. Our model implies that combining GR modulation to EGFR inhibition may yield an effective treatment strategy in halting cancer progression.

The metastasis suppressor NDRG1 down-regulates the epidermal growth factor receptor via a lysosomal mechanism by up-regulating mitogen-inducible gene 6

The metastasis suppressor, N-Myc downstream-regulated gene-1 (NDRG1) inhibits a plethora of oncogenic signaling pathways by down-regulating the epidermal growth factor receptor (EGFR). Herein, we examined the mechanism involved in NDRG1-mediated EGFR down-regulation. NDRG1 overexpression potently increased the levels of mitogen-inducible gene 6 (MIG6), which inhibits EGFR and facilitates its lysosomal processing and degradation. Conversely, silencing NDRG1 in multiple human cancer cell types decreased MIG6 expression, demonstrating the regulatory role of NDRG1. Further, NDRG1 overexpression facilitated MIG6-EGFR association in the cytoplasm, possibly explaining the significantly (p <0.001) increased half-life of MIG6 from 1.6 ± 0.2 h under control conditions to 7.9 ± 0.4 h after NDRG1 overexpression. The increased MIG6 levels enhanced EGFR co-localization with the late endosome/lysosomal marker, lysosomal-associated membrane protein 2 (LAMP2). An increase in EGFR levels after MIG6 silencing was particularly apparent when NDRG1 was overexpressed, suggesting a role for MIG6 in NDRG1-mediated down-regulation of EGFR. Silencing phosphatase and tensin homolog (PTEN), which facilitates early to late endosome maturation, decreased MIG6, and also increased EGFR levels in both the presence and absence of NDRG1 overexpression. These results suggest a role for PTEN in regulating MIG6 expression. Anti-tumor drugs of the di-2-pyridylketone thiosemicarbazone class that activate NDRG1 expression also potently increased MIG6 and induced its cytosolic co-localization with NDRG1. This was accompanied by a decrease in activated and total EGFR levels and its redistribution to late endosomes/lysosomes. In conclusion, NDRG1 promotes EGFR down-regulation through the EGFR inhibitor MIG6, which leads to late endosomal/lysosomal processing of EGFR.

Glucocorticoids, genes and brain function

The identification of key genes in transcriptomic data constitutes a huge challenge. Our review of microarray reports revealed 88 genes whose transcription is consistently regulated by glucocorticoids (GCs), such as cortisol, corticosterone and dexamethasone, in the brain. Replicable transcriptomic data were combined with biochemical and physiological data to create an integrated view of the effects induced by GCs. The most frequently reported genes were Errfi1 and Ddit4. Their up-regulation was associated with the altered transcription of genes regulating growth factor and mTORC1 signaling (Gab1, Tsc22d3, Dusp1, Ndrg2, Ppp5c and Sesn1) and progression of the cell cycle (Ccnd1, Cdkn1a and Cables1). The GC-induced reprogramming of cell function involves changes in the mRNA level of genes responsible for the regulation of transcription (Klf9, Bcl6, Klf15, Tle3, Cxxc5, Litaf, Tle4, Jun, Sox4, Sox2, Sox9, Irf1, Sall2, Nfkbia and Id1) and the selective degradation of mRNA (Tob2). Other genes are involved in the regulation of metabolism (Gpd1, Aldoc and Pdk4), actin cytoskeleton (Myh2, Nedd9, Mical2, Rhou, Arl4d, Osbpl3, Arhgef3, Sdc4, Rdx, Wipf3, Chst1 and Hepacam), autophagy (Eva1a and Plekhf1), vesicular transport (Rhob, Ehd3, Vps37b and Scamp2), gap junctions (Gjb6), immune response (Tiparp, Mertk, Lyve1 and Il6r), signaling mediated by thyroid hormones (Thra and Sult1a1), calcium (Calm2), adrenaline/noradrenaline (Adcy9 and Adra1d), neuropeptide Y (Npy1r) and histamine (Hdc). GCs also affected genes involved in the synthesis of polyamines (Azin1) and taurine (Cdo1). The actions of GCs are restrained by feedback mechanisms depending on the transcription of Sgk1, Fkbp5 and Nr3c1. A side effect induced by GCs is increased production of reactive oxygen species. Available data show that the brain's response to GCs is part of an emergency mode characterized by inactivation of non-core activities, restrained inflammation, restriction of investments (growth), improved efficiency of energy production and the removal of unnecessary or malfunctioning cellular components to conserve energy and maintain nutrient supply during the stress response.

Inhibition of Cdc42 is essential for Mig-6 suppression of cell migration induced by EGF

The adaptor protein Mig-6 is a negative regulator of EGF signaling. It is shown that Mig-6 inhibits cell migration via direct interaction with the ErbB receptors, thereby inhibiting cross-phosphorylation or targeting the receptors for degradation. Mig-6 has also been shown to bind to and inhibit the Rho GTPase Cdc42 to suppress cytoskeletal rearrangement. However, the molecular mechanism(s) by which Mig-6 inhibits cell migration via Cdc42 is still not entirely clear. Here, we show that Mig-6 binding to Cdc42 is necessary and sufficient to inhibit EGF-induced filopodia formation and migration. This binding, mediated by four specific residues (I11, R12, M26, R30) in the Mig-6 CRIB domain, is essential for Mig-6 function. In addition, ectopic expression of Cdc42 reverses Mig-6 inhibition of cell migration. Mig-6 CRIB domain, alone, is sufficient to inhibit cell migration. Conversely, Mig-6 binding to EGFR is dispensable for Mig-6-mediated inhibition of cell migration. Moreover, we found that decreased Mig-6 expression correlates with cancer progression in breast and prostate cancers. Together, our results demonstrate that Mig-6 inhibition of Cdc42 signaling is critical in Mig-6 function to suppress cell migration and that dysregulation of this pathway may play a critical role in cancer development.

The role of small adaptor proteins in the control of oncogenic signalingr driven by tyrosine kinases in human cancer

Protein phosphorylation on tyrosine (Tyr) residues has evolved as an important mechanism to coordinate cell communication in multicellular organisms. The importance of this process has been revealed by the discovery of the prominent oncogenic properties of tyrosine kinases (TK) upon deregulation of their physiological activities, often due to protein overexpression and/or somatic mutation. Recent reports suggest that TK oncogenic signaling is also under the control of small adaptor proteins. These cytosolic proteins lack intrinsic catalytic activity and signal by linking two functional members of a catalytic pathway. While most adaptors display positive regulatory functions, a small group of this family exerts negative regulatory functions by targeting several components of the TK signaling cascade. Here, we review how these less studied adaptor proteins negatively control TK activities and how their loss of function induces abnormal TK signaling, promoting tumor formation. We also discuss the therapeutic consequences of this novel regulatory mechanism in human oncology.

Phosphorylation of Mig6 negatively regulates the ubiquitination and degradation of EGFR mutants in lung adenocarcinoma cell lines

Activating mutations in the kinase domain of epidermal growth factor receptor (EGFR) leads to the constitutively active kinase, improves the EGFR stability and promotes malignant transformation in lung adenocarcinoma. Despite the clinical significance, the mechanism by which the increased kinase activity stabilizes the receptor is not completely understood. Using SILAC phosphoproteomic approach, we identify that Mig6 is highly phosphorylated at S256 in EGFR mutants (19del and L858R). Loss of Mig6 contributes to the efficient degradation of EGFR wildtype and mutants in lung cancer cells. Mig6 regulates the recruitment of c-Cbl to EGFR as the ablation of Mig6 enables efficient ubiquitination of the EGFR mutants through elevated recruitment of c-Cbl. We show that the cells with activating mutants of EGFR inactivate Mig6 through phosphorylation at S256. Inactivated Mig6 causes inefficient ubiquitination of EGFR, leading to defective degradation of the receptor thus contributing to the increased stability of the receptor. Taken together, we show a novel function of Mig6 in regulating the ubiquitination of EGFR.

Negative Regulation of Receptor Tyrosine Kinase (RTK) Signaling: A Developing Field

Trophic factors control cellular physiology by activating specific receptor tyrosine kinases (RTKs). While the over activation of RTK signaling pathways is associated with cell growth and cancer, recent findings support the concept that impaired down-regulation or deactivation of RTKs may also be a mechanism involved in tumor formation. Under this perspective, the molecular determinants of RTK signaling inhibition may act as tumor-suppressor genes and have a potential role as tumor markers to monitor and predict disease progression. Here, we review the current understanding of the physiological mechanisms that attenuate RTK signaling and discuss evidence that implicates deregulation of these events in cancer.

Glucocorticoid mediates prenatal caffeine exposure-induced endochondral ossification retardation and its molecular mechanism in female fetal rats

Our previous studies discovered that prenatal caffeine exposure (PCE) could induce intrauterine growth retardation (IUGR) and long-bone dysplasia in offspring rats, accompanied by maternal glucocorticoid over-exposure. This study is to explore whether intrauterine high glucocorticoid level can cause endochondral ossification retardation and clarify its molecular mechanism in PCE fetal rats. Pregnant Wistar rats were intragastrically administered 30 and 120 mg/kg day of caffeine during gestational days (GDs) 9–20, then collected fetal serum and femurs at GD20. In vitro, primary chondrocytes were treated with corticosterone (0–1250 nM), caffeine (0–100 μM), mitogen-inducible gene 6 (Mig-6) siRNA and epidermal growth factor receptor (EGFR) siRNA, respectively, or together. Results showed that the hypertrophic chondrocytes zone (HZ) of PCE fetal femur was widened. Meanwhile, the expression levels of chondrocytes terminal differentiation genes in the HZ were decreased, and the chondrocytes apoptosis rate in the HZ was decreased too. Furthermore, PCE upregulated Mig-6 and suppressed EGFR expression in the HZ. In vitro, a high-concentration corticosterone (1250 nM) upregulated Mig-6 expression, inhibit EGFR/c-Jun N-terminal kinase (JNK) signaling pathway and terminal differentiation genes expression in chondrocytes and reduced cell apoptosis, and these above alterations could be partly reversed step-by-step after Mig-6 and EGFR knockdown. However, caffeine concentration dependently increased chondrocyte apoptosis without significant changes in the expression of terminal differentiation genes. Collectively, PCE caused endochondral ossification retardation in the female fetal rats, and its main mechanism was associated with glucocorticoid (rather than caffeine)-mediated chondrocyte terminal differentiation suppression by the upregulation of Mig-6 and then inhibition of EGFR/JNK pathway-mediated chondrocyte apoptosis.

Nuclear Gene 33/Mig6 regulates the DNA damage response through an ATM serine/threonine kinase-dependent mechanism

Gene 33 (Mig6, ERRFI1) is an adaptor protein with multiple cellular functions. We recently linked Gene 33 to the DNA damage response (DDR) induced by hexavalent chromium (Cr(VI)), but the molecular mechanism remains unknown. Here we show that ectopic expression of Gene 33 triggers DDR in an ATM serine/threonine kinase (ATM)-dependent fashion and through pathways dependent or not dependent on ABL proto-oncogene 1 non-receptor tyrosine kinase (c-Abl). We observed the clear presence of Gene 33 in the nucleus and chromatin fractions of the cell. We also found that the nuclear localization of Gene 33 is regulated by its 14-3-3-binding domain and that the chromatin localization of Gene 33 is partially dependent on its ErbB-binding domain. Our data further indicated that Gene 33 may regulate the targeting of c-Abl to chromatin. Moreover, we observed a clear association of Gene 33 with histone H2AX and that ectopic expression of Gene 33 promotes the interaction between ATM and histone H2AX without triggering DNA damage. In summary, our results reveal nuclear functions of Gene 33 that regulate DDR. The nuclear localization of Gene 33 also provides a spatial explanation of the previously reported regulation of apoptosis by Gene 33 via the c-Abl/p73 pathway. On the basis of these findings and our previous studies, we propose that Gene 33 is a proximal regulator of DDR that promotes DNA repair.

Single-cell RNA sequencing reveals an altered gene expression pattern as a result of CRISPR/cas9-mediated deletion of Gene 33/Mig6 and chronic exposure to hexavalent chromium in human lung epithelial cells

Gene 33 (Mig6, ERRFI1) is an adaptor protein with multiple cellular functions. We recently reported that depletion of this protein promotes lung epithelial cell transformation induced by hexavalent chromium [Cr(VI)]. However, the early molecular events that mediate this process are not clear. In the present study, we used single-cell RNA sequencing to compare gene expression profiles between BEAS-2B lung epithelial cells chronically exposed to a sublethal dose of Cr(VI) with or without CRISPR/cas9-mediated deletion of Gene 33. Our data reveal 83 differentially expressed genes. The most notable changes are genes associated with cell adhesion, oxidative stresses, protein ubiquitination, epithelial-mesenchymal transition/metastasis, and WNT signaling. Up-regulation of some neuro-specific genes is also evident, particularly ubiquitin carboxyl-terminal hydrolase L1 (UCHL1), a deubiquitinase and potential biomarker for lung cancer. Gene 33 deletion and/or Cr(VI) exposure did not cause discernable changes in cell morphology. However, Gene 33 deletion led to a modest but significant reduction of cells in the G2/M phase of the cell cycle regardless of Cr(VI) exposure. Gene 33 deletion also significantly reduced cell proliferation. Interestingly, Cr(VI) exposure eliminated the difference in cell proliferation between the two genotypes. Gene 33 deletion also significantly elevated cell migration. Our data indicate that combined Gene 33 deletion and chronic Cr(VI) exposure produces a gene expression pattern and a phenotype resemble those of the transformed lung epithelial cells. Given the known association of UCHL1 with lung cancer, we propose that UCHL1 is an important player in the early stage of lung epithelial cell transformation and tumorigenesis.

Recent developments in emerging therapeutic targets of osteoarthritis

Purpose of review

Despite the tremendous individual suffering and socioeconomic burden caused by osteoarthritis, there are currently no effective disease-modifying treatment options. This is in part because of our incomplete understanding of osteoarthritis disease mechanism. This review summarizes recent developments in therapeutic targets identified from surgical animal models of osteoarthritis that provide novel insight into osteoarthritis pathology and possess potential for progression into preclinical studies.

Recent findings

Several candidate pathways and processes that have been identified include chondrocyte autophagy, growth factor signaling, inflammation, and nociceptive signaling. Major strategies that possess therapeutic potential at the cellular level include inhibiting autophagy suppression and decreasing reactive oxygen species (ROS) production. Cartilage anabolism and prevention of cartilage degradation has been shown to result from growth factor signaling modulation, such as TGF-β, TGF-α, and FGF; however, the results are context-dependent and require further investigation. Pain assessment studies in rodent surgical models have demonstrated potential in employing anti-NGF strategies for minimizing osteoarthritis-associated pain.

Summary

Studies of potential therapeutic targets in osteoarthritis using animal surgical models are helping to elucidate osteoarthritis pathology and propel therapeutics development. Further studies should continue to elucidate pathological mechanisms and therapeutic targets in various joint tissues to improve overall joint health.

Gene 33/Mig6 inhibits hexavalent chromium-induced DNA damage and cell transformation in human lung epithelial cells

Hexavalent Chromium [Cr(VI)] compounds are human lung carcinogens and environmental/occupational hazards. The molecular mechanisms of Cr(VI) carcinogenesis appear to be complex and are poorly defined. In this study, we investigated the potential role of Gene 33 (ERRFI1, Mig6), a multifunctional adaptor protein, in Cr(VI)-mediated lung carcinogenesis. We show that the level of Gene 33 protein is suppressed by both acute and chronic Cr(VI) treatments in a dose- and time-dependent fashion in BEAS-2B lung epithelial cells. The inhibition also occurs in A549 lung bronchial carcinoma cells. Cr(VI) suppresses Gene 33 expression mainly through post-transcriptional mechanisms, although the mRNA level of gene 33 also tends to be lower upon Cr(VI) treatments. Cr(VI)-induced DNA damage appears primarily in the S phases of the cell cycle despite the high basal DNA damage signals at the G2M phase. Knockdown of Gene 33 with siRNA significantly elevates Cr(VI)-induced DNA damage in both BEAS-2B and A549 cells. Depletion of Gene 33 also promotes Cr(VI)-induced micronucleus (MN) formation and cell transformation in BEAS-2B cells. Our results reveal a novel function of Gene 33 in Cr(VI)-induced DNA damage and lung epithelial cell transformation. We propose that in addition to its role in the canonical EGFR signaling pathway and other signaling pathways, Gene 33 may also inhibit Cr(VI)-induced lung carcinogenesis by reducing DNA damage triggered by Cr(VI).

Mig-6 Mouse Model of Endometrial Cancer

Endometrial cancer is a frequently occurring gynecological disorder. Estrogen-dependent endometrioid carcinoma is the most common type of gynecological cancer. One of the major pathologic phenomena of endometrial cancer is the loss of estrogen (E2) and progesterone (P4) control over uterine epithelial cell proliferation. P4 antagonizes the growth-promoting properties of E2 in the uterus. P4 prevents the development of endometrial cancer associated with unopposed E2 by blocking E2 actions. Mitogen inducible gene 6 (Mig-6, Errfi1, RALT, or gene 33) is an immediate early response gene that can be induced by various mitogens and common chronic stress stimuli. Mig-6 has been identified as an important component of P4-mediated inhibition of E2 signaling in the uterus. Decreased expression of MIG-6 is observed in human endometrial carcinomas. Transgenic mice with Mig-6 ablation in the uterus develop endometrial hyperplasia and E2-dependent endometrial cancer. Thus, MIG-6 has a tumor suppressor function in endometrial tumorigenesis. The following discussion summarizes our current knowledge of Mig-6 mouse models and their role in understanding the molecular mechanisms of endometrial tumorigenesis and in the development of therapeutic approaches for endometrial cancer.

Type I γ Phosphatidylinositol Phosphate 5-Kinase i5 Controls the Ubiquitination and Degradation of the Tumor Suppressor Mitogen-inducible Gene 6

Mitogen-inducible gene 6 (Mig6) is a tumor suppressor, and the disruption of Mig6 expression is associated with cancer development. Mig6 directly interacts with epidermal growth factor receptor (EGFR) to suppress the activation and downstream signaling of EGFR. Therefore, loss of Mig6 enhances EGFR-mediated signaling and promotes EGFR-dependent carcinogenesis. The molecular mechanism modulating Mig6 expression in cancer remains unclear. Here we demonstrate that type I γ phosphatidylinositol phosphate 5-kinase i5 (PIPKIγi5), an enzyme producing phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P₂), stabilizes Mig6 expression. Knockdown of PIPKIγi5 leads to the loss of Mig6 expression, which dramatically enhances and prolongs EGFR-mediated cell signaling. Loss of PIPKIγi5 significantly promotes Mig6 protein degradation via proteasomes, but it does not affect the Mig6 mRNA level. PIPKIγi5 directly interacts with the E3 ubiquitin ligase neuronal precursor cell-expressed developmentally down-regulated 4-1 (NEDD4-1). The C-terminal domain of PIPKIγi5 and the WW1 and WW2 domains of NEDD4-1 are required for their interaction. The C2 domain of NEDD4-1 is required for its interaction with PtdIns(4,5)P₂ By binding with NEDD4-1 and producing PtdIns(4,5)P₂, PIPKIγi5 perturbs NEDD4-1-mediated Mig6 ubiquitination and the subsequent proteasomal degradation. Thus, loss of NEDD4-1 can rescue Mig6 expression in PIPKIγi5 knockdown cells. In this way, PIPKIγi5, NEDD4-1, and Mig6 form a novel molecular nexus that controls EGFR activation and downstream signaling.

Context-specific protection of TGFα null mice from osteoarthritis

Transforming growth factor alpha (TGFα) is a growth factor involved in osteoarthritis (OA). TGFα induces an OA-like phenotype in articular chondrocytes, by inhibiting matrix synthesis and promoting catabolic factor expression. To better understand TGFα’s potential as a therapeutic target, we employed two in vivo OA models: (1) post-traumatic and (2) aging related OA. Ten-week old and six-month old male Tgfa null mice and their heterozygous (control) littermates underwent destabilization of the medial meniscus (DMM) surgery. Disease progression was assessed histologically using the Osteoarthritis Research Society International (OARSI) scoring system. As well, spontaneous disease progression was analyzed in eighteen-month-old Tgfa null and heterozygous mice. Ten-week old Tgfa null mice were protected from OA progression at both seven and fourteen weeks post-surgery. No protection was seen however in six-month old null mice after DMM surgery, and no differences were observed between genotypes in the aging model. Thus, young Tgfa null mice are protected from OA progression in the DMM model, while older mice are not. In addition, Tgfa null mice are equally susceptible to spontaneous OA development during aging. Thus, TGFα might be a valuable therapeutic target in some post-traumatic forms of OA, however its role in idiopathic disease is less clear.

Mitogen-inducible gene-6 partly mediates the inhibitory effects of prenatal dexamethasone exposure on endochondral ossification in long bones of fetal rats

BACKGROUND AND PURPOSE

Prenatal exposure to dexamethasone slows down fetal linear growth and bone mineralization but the regulatory mechanism remains unknown. Here we assessed how dexamethasone regulates bone development in the fetus.

EXPERIMENTAL APPROACH

Dexamethasone (1 mg·kg(-1) ·day(-1) ) was injected subcutaneously every morning in pregnant rats from gestational day (GD)9 to GD20. Fetal femurs and tibias were harvested at GD20 for histological and gene expression analysis. Femurs of 12-week-old female offspring were harvested for microCT (μCT) measurement. Primary chondrocytes were treated with dexamethasone (10, 50, 250 and 1000 nM).

KEY RESULTS

Prenatal dexamethasone exposure resulted in accumulation of hypertrophic chondrocytes and delayed formation of the primary ossification centre in fetal long bone. The retardation was accompanied by reduced maturation of hypertrophic chondrocytes, decreased osteoclast number and down-regulated expression of osteocalcin and bone sialoprotein in long bone. In addition, the mitogen-inducible gene-6 (Mig6) and osteoprotegerin (OPG) expression were stimulated, and the receptor activator of NF-κB ligand (RANKL) expression was repressed. Moreover, dexamethasone activated OPG and repressed RANKL expression in both primary chondrocytes and primary osteoblasts, and the knockdown of Mig6 abolished the effect of dexamethasone on OPG expression. Further, μCT measurement showed loss of bone mass in femur of 12-week-old offspring with prenatal dexamethasone exposure.

CONCLUSIONS AND IMPLICATIONS

Prenatal dexamethasone exposure delays endochondral ossification by suppressing chondrocyte maturation and osteoclast differentiation, which may be partly mediated by Mig6 activation in bone. Bone development retardation in the fetus may be associated with reduced bone mass in later life.

Circadian Clocks, Stress, and Immunity

In mammals, molecular circadian clocks are present in most cells of the body, and this circadian network plays an important role in synchronizing physiological processes and behaviors to the appropriate time of day. The hypothalamic-pituitary-adrenal endocrine axis regulates the response to acute and chronic stress, acting through its final effectors - glucocorticoids - released from the adrenal cortex. Glucocorticoid secretion, characterized by its circadian rhythm, has an important role in synchronizing peripheral clocks and rhythms downstream of the master circadian pacemaker in the suprachiasmatic nucleus. Finally, glucocorticoids are powerfully anti-inflammatory, and recent work has implicated the circadian clock in various aspects and cells of the immune system, suggesting a tight interplay of stress and circadian systems in the regulation of immunity. This mini-review summarizes our current understanding of the role of the circadian clock network in both the HPA axis and the immune system, and discusses their interactions.

Fatty Liver and Insulin Resistance in the Liver-Specific Knockout Mice of Mitogen Inducible Gene-6

Mitogen inducible gene-6 (Mig-6) is a feedback inhibitor of epidermal growth factor receptor (EGFR) signaling pathway. The liver-specific knockout mice of the Mig-6 gene (Mig-6 ^d/d ) showed hepatomegaly and increased hypercholesterolemia. In this study, the biomarkers of insulin resistance and the effects of high-fat diets in the wild (Mig-6 ^f/f ) and Mig-6 ^d/d mice were analyzed. The fasting plasma concentrations of glucose, triglyceride, cholesterols, free fatty acids, and HOMA-IR were measured and the glucose tolerance and insulin resistance tests were performed in the 25-week-old Mig-6 ^f/f and the Mig-6 ^d/d mice. The protein levels of active insulin receptor, glucose 6-phosphatase, and phosphoenolpyruvate carboxykinase were analyzed in the liver and fat. The fasting plasma cholesterol and glucose concentration were higher in the Mig-6 ^d/d mice than the Mig-6 ^f/f mice with increased fat deposition in the liver. But the Mig-6 ^d/d mice had the improved glucose intolerance and insulin resistance without increased amount of phosphoinsulin receptor after insulin infusion in the liver. The hepatic concentration of phosphoenolpyruvate carboxykinase was increased in fasting Mig-6 ^d/d mice. The feeding of high-fat diet accelerated the plasma lipids profiles and HOMA-IR in the Mig-6 ^d/d mice but had no differential effects in oral glucose tolerance test and insulin tolerance test in both genotypes. These results suggest that the activated EGFR signaling might increase the fasting plasma glucose concentration through inducing the hepatic steatosis and the improved whole-body insulin resistance in the KO mice be caused by decreased adipogenesis in fat tissues.

Towards the emerging crosstalk: ERBB family and steroid hormones

Growth factors acting through receptor tyrosine kinases (RTKs) of ERBB family, along with steroid hormones (SH) acting through nuclear receptors (NRs), are critical signalling mediators of cellular processes. Deregulations of ERBB and steroid hormone receptors are responsible for several diseases, including cancer, thus demonstrating the central role played by both systems. This review will summarize and shed light on an emerging crosstalk between these two important receptor families. How this mutual crosstalk is attained, such as through extensive genomic and non-genomic interactions, will be addressed. In light of recent studies, we will describe how steroid hormones are able to fine-tune ERBB feedback loops, thus impacting on cellular output and providing a new key for understanding the complexity of biological processes in physiological or pathological conditions. In our understanding, the interactions between steroid hormones and RTKs deserve further attention. A system biology approach and advanced technologies for the analysis of RTK-SH crosstalk could lead to major advancements in molecular medicine, providing the basis for new routes of pharmacological intervention in several diseases, including cancer.

Thymosin beta 4 up-regulates miR-200a expression and induces differentiation and survival of rat brain progenitor cells

Thymosin beta 4 (Tβ4), a secreted 43 amino acid peptide, promotes oligodendrogenesis, and improves neurological outcome in rat models of neurologic injury. We demonstrated that exogenous Tβ4 treatment up-regulated the expression of the miR-200a in vitro in rat brain progenitor cells and in vivo in the peri-infarct area of rats subjected to middle cerebral artery occlusion (MCAO). The up-regulation of miR-200a down-regulated the expression of the following targets in vitro and in vivo models: (i) growth factor receptor-bound protein 2 (Grb2), an adaptor protein involved in epidermal growth factor receptor (EGFR)/Grb2/Ras/MEK/ERK1/c-Jun signaling pathway, which negatively regulates the expression of myelin basic protein (MBP), a marker of mature oligodendrocyte; (ii) ERRFI-1/Mig-6, an endogenous potent kinase inhibitor of EGFR, which resulted in activation/phosphorylation of EGFR; (iii) friend of GATA 2, and phosphatase and tensin homolog deleted in chromosome 10 (PTEN), which are potent inhibitors of the phosphatidylinositol-3-kinase (PI3K)/AKT signaling pathway, and resulted in marked activation of AKT; and (iv) transcription factor, p53, which induces pro-apoptotic genes, and possibly reduced apoptosis of the progenitor cells subjected to oxygen glucose deprivation (OGD). Anti-miR-200a transfection reversed all the effects of Tβ4 treatment in vitro. Thus, Tβ4 up-regulated MBP synthesis, and inhibited OGD-induced apoptosis in a novel miR-200a dependent EGFR signaling pathway. Our findings of miR-200a-mediated protection of progenitor cells may provide a new therapeutic importance for the treatment of neurologic injury. Tβ4-induced micro-RNA-200a (miR-200a) regulates EGFR signaling pathways for MBP synthesis and apoptosis: up-regulation of miR-200a after Tβ4 treatment, increases MBP synthesis after targeting Grb2 and thereby inactivating c-Jun from inhibition of MBP synthesis; and also inhibits OGD-mediated apoptosis after targeting EGFR inhibitor (Mig-6), PI3K inhibitors (FOG2 and Pten) and an inducer (p53) of pro-apoptotic genes, for AKT activation and down-regulation of p53. These findings may contribute the therapeutic benefits for stroke and other neuronal diseases associated with demyelination disorders.

The antitumorigenic function of EGFR in metastatic breast cancer is regulated by expression of Mig6

Numerous studies by our lab and others demonstrate that epidermal growth factor receptor (EGFR) plays critical roles in primary breast cancer (BC) initiation, growth and dissemination. However, clinical trials targeting EGFR function in BC have lead to disappointing results. In the current study we sought to identify the mechanisms responsible for this disparity by investigating the function of EGFR across the continuum of the metastatic cascade. We previously established that overexpression of EGFR is sufficient for formation of in situ primary tumors by otherwise nontransformed murine mammary gland cells. Induction of epithelial-mesenchymal transition (EMT) is sufficient to drive the metastasis of these EGFR-transformed tumors. Examining growth factor receptor expression across this and other models revealed a potent downregulation of EGFR through metastatic progression. Consistent with diminution of EGFR following EMT and metastasis EGF stimulation changes from a proliferative to an apoptotic response in in situ versus metastatic tumor cells, respectively. Furthermore, overexpression of EGFR in metastatic MDA-MB-231 BC cells promoted their antitumorigenic response to EGF in three dimensional (3D) metastatic outgrowth assays. In line with the paradoxical function of EGFR through EMT and metastasis we demonstrate that the EGFR inhibitory molecule, Mitogen Induced Gene-6 (Mig6), is tumor suppressive in in situ tumor cells. However, Mig6 expression is absolutely required for prevention of apoptosis and ultimate metastasis of MDA-MB-231 cells. Further understanding of the paradoxical function of EGFR between primary and metastatic tumors will be essential for application of its targeted molecular therapies in BC.

Structure and mechanism of activity-based inhibition of the EGF receptor by Mig6

Mig6 is a feedback inhibitor that directly binds, inhibits and drives internalization of ErbB-family receptors. Mig6 selectively targets activated receptors. Here we found that the epidermal growth factor receptor (EGFR) phosphorylates Mig6 on Y394 and that this phosphorylation is primed by prior phosphorylation of an adjacent residue, Y395, by Src. Crystal structures of human EGFR-Mig6 complexes reveal the structural basis for enhanced phosphorylation of primed Mig6 and show how Mig6 rearranges after phosphorylation by EGFR to effectively irreversibly inhibit the same receptor that catalyzed its phosphorylation. This dual phosphorylation site allows Mig6 to inactivate EGFR in a manner that requires activation of the target receptor and that can be modulated by Src. Loss of Mig6 is a driving event in human cancer; analysis of 1,057 gliomas reveals frequent focal deletions of ERRFI1, the gene that encodes Mig6, in EGFR-amplified glioblastomas.

Mig-6 gene knockout induces neointimal hyperplasia in the vascular smooth muscle cell

Although advances in vascular interventions can reduce the mortality associated with cardiovascular disease, neointimal hyperplasia remains a clinically significant obstacle limiting the success of current interventions. Identification of signaling pathways involved in migration and proliferation of vascular smooth muscle cells (SMCs) is an important approach for the development of modalities to combat this disease. Herein we investigate the role of an immediate early response gene, mitogen-inducible gene-6 (Mig-6), in the development of neointimal hyperplasia using vascular smooth muscle specific Mig-6 knockout mice. We induced endoluminal injury to one side of femoral artery by balloon dilatation in both Mig-6 knockout and control mice. Four weeks following injury, the artery of Mig-6 knockout mice demonstrated a 5.3-fold increase in the neointima/media ratio compared with control mice (P = 0.04). In addition, Mig-6 knockout vascular SMCs displayed an increase in both cell migration and proliferation compared with wild-type SMCs. Taken together, our data suggest that Mig-6 plays a critical role in the development of atherosclerosis. This finding provides new insight into the development of more effective ways to treat and prevent neointimal hyperplasia, particularly in-stent restenosis after percutaneous vascular intervention.

Mig6 haploinsufficiency protects mice against streptozotocin-induced diabetes

AIMS/HYPOTHESIS

EGF and gastrin co-administration reverses type 1 diabetes in rodent models. However, the failure of this to translate into a clinical treatment suggests that EGF-mediated tissue repair is a complicated process and warrants further investigation. Thus, we aimed to determine whether EGF receptor (EGFR) feedback inhibition by mitogen-inducible gene 6 protein (MIG6) limits the effectiveness of EGF therapy and promotes type 1 diabetes development.

METHODS

We treated Mig6 (also known as Errfi1) haploinsufficient mice (Mig6 (+/-)) and their wild-type littermates (Mig6 (+/+)) with multiple low doses of streptozotocin (STZ), and monitored diabetes development via glucose homeostasis tests and histological analyses. We also investigated MIG6-mediated cytokine-induced desensitisation of EGFR signalling and the DNA damage repair response in 832/13 INS-1 beta cells.

RESULTS

Whereas STZ-treated Mig6 (+/+) mice became diabetic, STZ-treated Mig6 (+/-) mice remained glucose tolerant. In addition, STZ-treated Mig6 (+/-) mice exhibited preserved circulating insulin levels following a glucose challenge. As insulin sensitivity was similar between Mig6 (+/-) and Mig6 (+/+) mice, the preserved glucose tolerance in STZ-treated Mig6 (+/-) mice probably results from preserved beta cell function. This is supported by elevated Pdx1 and Irs2 mRNA levels in islets isolated from STZ-treated Mig6 (+/-) mice. Conversely, MIG6 overexpression in isolated islets compromises glucose-stimulated insulin secretion. Studies in 832/13 cells suggested that cytokine-induced MIG6 hinders EGFR activation and inhibits DNA damage repair. STZ-treated Mig6 (+/-) mice also have increased beta cell mass recovery.

CONCLUSIONS/INTERPRETATION

Reducing Mig6 expression promotes beta cell repair and abates the development of experimental diabetes, suggesting that MIG6 may be a novel therapeutic target for preserving beta cells.

Whole genome sequencing of glioblastoma multiforme identifies multiple structural variations involved in EGFR activation

Next generation sequencing has become a powerful tool in dissecting and identifying mutations and genomic structural variants that accompany tumourigenesis. Sequence analysis of glioblastoma multiforme (GBM) illustrates the ability to rapidly identify mutations that may affect phenotype. Approximately 50% of human GBMs overexpress epidermal growth factor receptor (EGFR) which renders the EGFR protein a compelling therapeutic target. In brain tumours, attempts to target EGFR as a cancer therapeutic, however, have achieved little or no benefit. The mechanisms that drive therapeutic resistance to EGFR inhibitors in brain tumours are not well defined, and drug resistance contributes to the deadly and aggressive nature of the disease. Whole genome sequencing of four primary GBMs revealed multiple pathways by which EGFR protein abundance becomes deregulated in these tumours and will guide the development of new strategies for treating EGFR overexpressing tumours. Each of the four tumours displayed a different mechanism leading to increased EGFR protein levels. One mechanism is mediated by gene amplification and tandem duplication of the kinase domain. A second involves an intragenic deletion that generates a constitutively active form of the protein. A third combines the loss of a gene which encodes a protein that regulates EGFR abundance as well as an miRNA that modulates EGFR expression. A fourth mechanism entails loss of an ubiquitin ligase docking site in the C-terminal part of the protein whose absence inhibits turnover of the receptor.

Pathways driving the endocytosis of mutant and wild-type EGFR in cancer

EGFR (epidermal growth factor receptor) is activated through changes in expression or mutations in a number of tumors and is a driving force in cancer progression. EGFR is targeted by numerous inhibitors, including chimeric antibodies targeting the extracellular domain and small molecule kinase domain inhibitors. The kinase domain inhibitors are particularly active against mutant forms of the receptor, and subsequent mutations drive resistance to the inhibitors. Here, we review recent developments on the trafficking of wild-type and mutant EGFR, focusing on the roles of MIG6, SPRY2, ITSN, SHP2, S2R^PGRMC1 and RAK. Some classes of EGFR regulators affect wild-type and mutant EGFR equally, while others are specific for either the wild-type or mutant form of the receptor. Below we summarize multiple signaling-associated pathways that are important in trafficking wild-type and mutant EGFR with the goal being stimulation of new approaches for targeting the distinct forms of the receptor.

Mig-6 participates in the regulation of cell senescence and retinoblastoma protein phosphorylation

Mitogen-inducible gene-6 (Mig-6) is a cytosolic multiadaptor protein that is best known for its role as a negative feedback regulator of epidermal growth factor receptor (EGFR) mediated signalling. Alternative roles of Mig-6 are becoming increasingly recognised. Consistently with this, Mig-6 was demonstrated to be involved in a broad spectrum of cellular events including tumour suppression which may include the induction of cellular senescence. Here, we investigated the mechanisms of Mig-6 induced premature cell senescence. Endogenous Mig-6 is poorly expressed in young fibroblasts, whilst its expression rises in cells presenting with typical features of senescence. Overexpression of Mig-6 is sufficient to trigger premature cellular senescence of early passage diploid lung fibroblasts (WI-38). Interestingly, Mig-6 overexpression reduced retinoblastoma protein (pRb) phosphorylation at the inactivating Ser249/Thr252 sites. We also found that phosphorylation of these sites in pRb is increased in the presence of the B-Raf V600E oncogenic mutation. We further show that Mig-6 overexpression reduces B-Raf V600E mediated pRb inactivation and preserves pRb function.

The mitogen-inducible gene-6 is involved in regulation of cellular senescence in normal diploid fibroblasts

BACKGROUND INFORMATION

The mitogen-inducible gene-6 (Mig-6) is a non-kinase scaffolding adaptor protein. It has been shown that Mig-6 may play important roles in regulating stress response, maintaining homeostasis and functioning as a tumour suppressor. In this study, we investigated the role of Mig-6 in cellular senescence.

RESULTS

Our results showed that Mig-6 is up-regulated during the senescence process. Functional analysis indicated that cells over-expressing Mig-6 have reduced DNA synthesis and showed the signs of senescence. Knockdown of Mig-6 delayed the initiation of Ras-induced cellular senescence. These results suggest that the increase of Mig-6 expression contributes to establishment of cellular senescence. Furthermore, our results showed that Mig-6 induction of senescence is related to its inhibition of EGF receptor (EGFR)/Erb B signalling. Subsequent analysis of the mechanism responsible for the up-regulation of its expression showed that FOXO3A transcriptionally up-regulates Mig-6 expression via directly binding to the FOXO response element in Mig-6 5'-flanking regulatory sequences.

CONCLUSIONS

Mig-6 induces premature senescence via functioning in regulation of cellular senescence in normal diploid fibroblasts.

Emerging roles for intersectin (ITSN) in regulating signaling and disease pathways

Intersectins (ITSNs) represent a family of multi-domain adaptor proteins that regulate endocytosis and cell signaling. ITSN genes are highly conserved and present in all metazoan genomes examined thus far. Lower eukaryotes have only one ITSN gene, whereas higher eukaryotes have two ITSN genes. ITSN was first identified as an endocytic scaffold protein, and numerous studies reveal a conserved role for ITSN in endocytosis. Subsequently, ITSNs were found to regulate multiple signaling pathways including receptor tyrosine kinases (RTKs), GTPases, and phosphatidylinositol 3-kinase Class 2beta (PI3KC2β). ITSN has also been implicated in diseases such as Down Syndrome (DS), Alzheimer Disease (AD), and other neurodegenerative disorders. This review summarizes the evolutionary conservation of ITSN, the latest research on the role of ITSN in endocytosis, the emerging roles of ITSN in regulating cell signaling pathways, and the involvement of ITSN in human diseases such as DS, AD, and cancer.

Inflammation and Hras signaling control epithelial-mesenchymal transition during skin tumor progression

Epithelial-mesenchymal transition (EMT) is thought to be an important, possibly essential, component of the process of tumor dissemination and metastasis. About 20%-30% of Hras mutant mouse skin carcinomas induced by chemical initiation/promotion protocols have undergone EMT. Reduced exposure to TPA-induced chronic inflammation causes a dramatic reduction in classical papillomas and squamous cell carcinomas (SCCs), but the mice still develop highly invasive carcinomas with EMT properties, reduced levels of Hras and Egfr signaling, and frequent Ink4/Arf deletions. Deletion of Hras from the mouse germline also leads to a strong reduction in squamous tumor development, but tumors now acquire activating Kras mutations and exhibit more aggressive metastatic properties. We propose that invasive carcinomas can arise by different genetic and biological routes dependent on exposure to chronic inflammation and possibly from different target cell populations within the skin. Our data have implications for the use of inhibitors of inflammation or of Ras/Egfr pathway signaling for prevention or treatment of invasive cancers.

Glucocorticoid-induced suppression of β-cell proliferation is mediated by Mig6

Glucocorticoids can cause steroid-induced diabetes or accelerate the progression to diabetes by creating systemic insulin resistance and decreasing functional β-cell mass, which is influenced by changes in β-cell function, growth, and death. The synthetic glucocorticoid agonist dexamethasone (Dex) is deleterious to functional β-cell mass by decreasing β-cell function, survival, and proliferation. However, the mechanism by which Dex decreases β-cell proliferation is unknown. Interestingly, Dex induces the transcription of an antiproliferative factor and negative regulator of epidermal growth factor receptor signaling, Mig6 (also known as gene 33, RALT, and Errfi1). We, therefore, hypothesized that Dex impairs β-cell proliferation by increasing the expression of Mig6 and thereby decreasing downstream signaling of epidermal growth factor receptor. We found that Dex induced Mig6 and decreased [(3)H]thymidine incorporation, an index of cellular replication, in mouse, rat, and human islets. Using adenovirally delivered small interfering RNA targeted to Mig6 in rat islets, we were able to limit the induction of Mig6 upon exposure to Dex, compared with islets treated with a control virus, and completely rescued the Dex-mediated impairment in replication. We demonstrated that both Dex and overexpression of Mig6 attenuated the phosphorylation of ERK1/2 and blocked the G(1)/S transition of the cell cycle. In conclusion, Mig6 functions as a molecular brake for β-cell proliferation during glucocorticoid treatment in β-cells, and thus, Mig6 may be a novel target for preventing glucocorticoid-induced impairments in functional β-cell mass.