The role of 5′ untranslated region in translational suppression of OKL38 mRNA in hepatocellular carcinoma

OSGIN1 is a novel TUBB3 regulator that promotes tumor progression and gefitinib resistance in non-small cell lung cancer

BACKGROUND

Oxidative stress induced growth inhibitor 1 (OSGIN1) regulates cell death. The role and underlying molecular mechanism of OSGIN1 in non-small cell lung cancer (NSCLC) are uncharacterized.

METHODS

OSGIN1 expression in NSCLC samples was detected using immunohistochemistry and Western blotting. Growth of NSCLC cells and gefitinib-resistant cells expressing OSGIN1 or TUBB3 knockdown was determined by MTT, soft agar, and foci formation assays. The effect of OSGIN1 knockdown on in vivo tumor growth was assessed using NSCLC patient-derived xenograft models and gefitinib-resistant patient-derived xenograft models. Potentially interacting protein partners of OSGIN1 were identified using IP-MS/MS, immunoprecipitation, PLA, and Western blotting assays. Microtubule dynamics were explored by tubulin polymerization assay and immunofluorescence. Differential expression of signaling molecules in OSGIN1 knockdown cells was investigated using phospho-proteomics, KEGG analysis, and Western blotting.

RESULTS

We found that OSGIN1 is highly expressed in NSCLC tissues and is positively correlated with low survival rates and tumor size in lung cancer patients. OSGIN1 knockdown inhibited NSCLC cell growth and patient-derived NSCLC tumor growth in vivo. Knockdown of OSGIN1 strongly increased tubulin polymerization and re-established gefitinib sensitivity in vitro and in vivo. Additionally, knockdown of TUBB3 strongly inhibited NSCLC cell proliferation. Mechanistically, we found that OSGIN1 enhances DYRK1A-mediated TUBB3 phosphorylation, which is critical for inducing tubulin depolymerization. The results of phospho-proteomics and ontology analysis indicated that knockdown of OSGIN1 led to reduced propagation of the MKK3/6-p38 signaling axis.

CONCLUSIONS

We propose that OSGIN1 modulates microtubule dynamics by enhancing DYRK1A-mediated phosphorylation of TUBB3 at serine 172. Moreover, elevated OSGIN1 expression promotes NSCLC tumor growth and gefitinib resistance through the MKK3/6-p38 signaling pathway. Our findings unveil a new mechanism of OSGIN1 and provide a promising therapeutic target for NSCLC treatment in the clinic.

Docosahexaenoic acid promotes the formation of autophagosomes in MCF-7 breast cancer cells through oxidative stress-induced growth inhibitor 1 mediated activation of AMPK/mTOR pathway

Docosahexaenoic acid (DHA) is known to regulate autophagy in cancer cells. We explored whether oxidative stress-induced growth inhibitor 1 (OSGIN1) is involved in the regulation of autophagy by DHA in breast cancer cells and the possible mechanisms involved. DHA upregulated the levels of OSGIN1, LC3-II and SQSTM1/p62. By contrast, DHA dose-dependently decreased the levels of mTOR and p-mTOR^S2448 expression. Using GFP/RFP-LC3 fluorescence staining, we showed that cells treated with DHA showed a dose-dependent response in autophagic signals. OSGIN1 Overexpression mimicked DHA treatment in that LC3-II and GFP/RFP-LC3 signals as well as the expression of p-AMPKα^T172 and p-Raptor^S792 were significantly increased, whereas mTOR, p-mTOR^S2448, and p-ULK1^S757 expression were decreased. With knockdown of OSGIN1 expression, these outcomes were reversed. Moreover, OSGIN1 overexpression transiently elevated the accumulation of OSGIN1 and reactive oxygen species (ROS) in the mitochondrial fraction and subsequently increased p-AMPKα^T172 and p-Raptor^S792 expression. Upon pretreatment with Mito-TEMPO, a scavenger of mitochondrial ROS, these outcomes were reversed. Taken together, these results suggest that DHA can transiently elevate the generation of ROS in mitochondria and promote autophagosome formation through activation of the p-AMPKα^T172/p-Raptor ^S792 and inactivation of the p-mTOR^S2448/p-ULK1^Ser757 signaling pathways, and these effects depend on OSGIN1 protein in MCF-7 cells.

Optimization of 5' Untranslated Region of Modified mRNA for Use in Cardiac or Hepatic Ischemic Injury

Modified mRNA (modRNA) is a gene-delivery platform for transiently introducing a single gene or several genes of interest to different cell types and tissues. modRNA is considered to be a safe vector for gene transfer, as it negligibly activates the innate immune system and does not compromise the genome integrity. The use of modRNA in basic and translational science is rising, due to the clinical potential of modRNA. We are currently using modRNA to induce cardiac regeneration post-ischemic injury. Major obstacles in using modRNA for cardiac ischemic disease include the need for the direct and single administration of modRNA to the heart and the inefficient translation of modRNA due to its short half-life. Modulation of the 5' untranslated region (5' UTR) to enhance translation efficiency in ischemic cardiac disease has great value, as it can reduce the amount of modRNA needed per delivery and will achieve higher and longer protein production post-single delivery. Here, we identified that 5' UTR, from the fatty acid metabolism gene carboxylesterase 1D (Ces1d), enhanced the translation of firefly luciferase (Luc) modRNA by 2-fold in the heart post-myocardial infarction (MI). Moreover, we identified, in the Ces1d, a specific RNA element (element D) that is responsible for the improvement of modRNA translation and leads to a 2.5-fold translation increment over Luc modRNA carrying artificial 5' UTR, post-MI. Importantly, we were able to show that 5' UTR Ces1d also enhances modRNA translation in the liver, but not in the kidney, post-ischemic injury, indicating that Ces1d 5' UTR and element D may play a wider role in translation of protein under an ischemic condition.

Bone marrow stromal cell-derived growth inhibitor serves as a stress sensor to induce autophagy

Autophagy is an evolutionarily conserved stress response that promotes the lysosomal degradation of intracellular components. The bone marrow stromal cell-derived growth inhibitor (BDGI) functions as a stress sensor which is upregulated by oxidative stress and DNA damage. However, the role of BDGI in autophagic response to certain stresses remains unknown. Here, our results demonstrate that BDGI defines the impact of autophagy induction under stresses. Overexpression of BDGI promotes, while knockdown of BDGI impairs, autophagy. Mechanistically, BDGI localizes to the nucleus and interacts with the transcription factor transcription factor EB to increase the expression of multiple autophagy- and lysosome-related genes. In addition, BDGI regulates autophagy in a p53-dependent manner. Furthermore, BDGI-induced autophagy enables cell survival under stress conditions. Taken together, our study demonstrates that BDGI is a stress sensor that positively regulates autophagy.

MAFB mediates the therapeutic effect of sleeve gastrectomy for obese diabetes mellitus by activation of FXR expression

Farnesoid X receptor (FXR) and related pathways are involved in the therapeutic effect of sleeve gastrectomy for overweight or obese patients with diabetes mellitus. This study aimed to investigate the mechanism of FXR expression regulation during the surgical treatment of obese diabetes mellitus by sleeve gastrectomy. Diabetic rats were established by combined streptozotocin and high-fat diet induction. Data collection included body weight, chemical indexes of glucose and lipid metabolism, liver function, and the expression levels of musculoaponeurotic fibrosarcoma oncogene family B (MAFB), FXR, and related genes induced by sleeve gastrectomy. Chang liver cells overexpressing MAFB gene were established to confirm the expression of related genes. The binding and activation of FXR gene by MAFB were tested by Chip and luciferase reporter gene assays. Vertical sleeve gastrectomy induced significant weight loss and decreased blood glucose and lipids in diabetic rat livers, as well as decreased lipid deposition and recovered lipid function. The expression of MAFB, FXR, and FXR-regulated genes in diabetic rat livers were also restored by sleeve gastrectomy. Overexpression of MAFB in Chang liver cells led to FXR gene expression activation and the alteration of multiple FXR-regulated genes. Chip assay showed that MAFB could directly bind with FXR promoter, and the activation of FXR expression was confirmed by luciferase reporter gene analysis. The therapeutic effect of sleeve gastrectomy for overweight or obese patients with diabetes mellitus was mediated by activation of FXR expression through the binding of MAFB transcription factor.

Role of OSGIN1 in mediating smoking-induced autophagy in the human airway epithelium

Enhanced macroautophagy/autophagy is recognized as a component of the pathogenesis of smoking-induced airway disease. Based on the knowledge that enhanced autophagy is linked to oxidative stress and the DNA damage response, both of which are linked to smoking, we used microarray analysis of the airway epithelium to identify smoking upregulated genes known to respond to oxidative stress and the DNA damage response. This analysis identified OSGIN1 (oxidative stress induced growth inhibitor 1) as significantly upregulated by smoking, in both the large and small airway epithelium, an observation confirmed by an independent small airway microarray cohort, TaqMan PCR of large and small airway samples and RNA-Seq of small airway samples. High and low OSGIN1 expressors have different autophagy gene expression patterns in vivo. Genome-wide correlation of RNAseq analysis of airway basal/progenitor cells showed a direct correlation of OSGIN1 mRNA levels to multiple classic autophagy genes. In vitro cigarette smoke extract exposure of primary airway basal/progenitor cells was accompanied by a dose-dependent upregulation of OSGIN1 and autophagy induction. Lentivirus-mediated expression of OSGIN1 in human primary basal/progenitor cells induced puncta-like staining of MAP1LC3B and upregulation of MAP1LC3B mRNA and protein and SQSTM1 mRNA expression level in a dose and time-dependent manner. OSGIN1-induction of autophagosome, amphisome and autolysosome formation was confirmed by colocalization of MAP1LC3B with SQSTM1 or CD63 (endosome marker) and LAMP1 (lysosome marker). Both OSGIN1 overexpression and knockdown enhanced the smoking-evoked autophagic response. Together, these observations support the concept that smoking-induced upregulation of OSGIN1 is one link between smoking-induced stress and enhanced-autophagy in the human airway epithelium.

The NRF2 transcriptional target, OSGIN1, contributes to monomethyl fumarate-mediated cytoprotection in human astrocytes

Dimethyl fumarate (DMF) is indicated for the treatment of relapsing multiple sclerosis and may exert therapeutic effects via activation of the nuclear factor (erythroid-derived 2)-like 2 (NRF2) pathway. Following oral DMF administration, central nervous system (CNS) tissue is predominantly exposed to monomethyl fumarate (MMF), the bioactive metabolite of DMF, which can stabilize NRF2 and induce antioxidant gene expression; however, the detailed NRF2-dependent mechanisms modulated by MMF that lead to cytoprotection are unknown. Our data identify a mechanism for MMF-mediated cytoprotection in human astrocytes that functions in an OSGIN1-dependent manner, specifically via upregulation of the OSGIN1-61 kDa isoform. NRF2-dependent OSGIN1 expression induced P53 nuclear translocation following MMF administration, leading to cell-cycle inhibition and cell protection against oxidative challenge. This study provides mechanistic insight into MMF-mediated cytoprotection via NRF2, OSGIN1, and P53 in human CNS-derived cells and contributes to our understanding of how DMF may act clinically to ameliorate pathological processes in neurodegenerative disease.

Pharmacodynamics of Dimethyl Fumarate Are Tissue Specific and Involve NRF2-Dependent and -Independent Mechanisms

AIMS

Gastro-resistant dimethyl fumarate (DMF) is an oral therapeutic indicated for the treatment of relapsing multiple sclerosis. Recent data suggest that a primary pharmacodynamic response to DMF treatment is activation of the nuclear factor (erythroid-derived 2)-like 2 (NRF2) pathway; however, the gene targets modulated downstream of NRF2 that contribute to DMF-dependent effects are poorly understood.

RESULTS

Using wild-type and NRF2 knockout mice, we characterized DMF transcriptional responses throughout the brain and periphery to understand DMF effects in vivo and to explore the necessity of NRF2 in this process. Our findings identified tissue-specific expression of NRF2 target genes as well as NRF2-dependent and -independent gene regulation after DMF administration. Furthermore, using gene ontology, we identified common biological pathways that may be regulated by DMF and contribute to in vivo functional effects.

INNOVATION

Together, these data suggest that DMF modulates transcription through multiple pathways, which has implications for the cytoprotective, immunomodulatory, and clinical properties of DMF.

CONCLUSION

These findings provide further understanding of the DMF mechanism of action and propose potential therapeutic targets that warrant further investigation for treating neurodegenerative diseases. Antioxid. Redox Signal. 24, 1058-1071.

Genomic analysis of xCT-mediated regulatory network: Identification of novel targets against AIDS-associated lymphoma

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of primary effusion lymphoma (PEL), a rapidly progressing malignancy mostly arising in HIV-infected patients. Even under conventional chemotherapy, PEL continues to portend nearly 100% mortality within several months, which urgently requires novel therapeutic strategies. We have previously demonstrated that targeting xCT, an amino acid transporter for cystine/glutamate exchange, induces significant PEL cell apoptosis through regulation of multiple host and viral factors. More importantly, one of xCT selective inhibitors, Sulfasalazine (SASP), effectively prevents PEL tumor progression in an immune-deficient xenograft model. In the current study, we use Illumina microarray to explore the profile of genes altered by SASP treatment within 3 KSHV⁺ PEL cell-lines, and discover that many genes involved in oxidative stress/antioxidant defense system, apoptosis/anti-apoptosis/cell death, and cellular response to unfolded proteins/topologically incorrect proteins are potentially regulated by xCT. We further validate 2 downstream candidates, OSGIN1 (oxidative stress-induced growth inhibitor 1) and XRCC5 (X-ray repair cross-complementing protein 5), and evaluate their functional relationship with PEL cell survival/proliferation and chemoresistance, respectively. Together, our data indicate that targeting these novel xCT-regulated downstream genes may represent a promising new therapeutic strategy against PEL and/or other AIDS-related lymphoma.

Allele-specific imbalance of oxidative stress-induced growth inhibitor 1 associates with progression of hepatocellular carcinoma

BACKGROUND & AIMS

Although there are a few highly penetrant mutations that are linked directly to cancer initiation, more less-penetrant susceptibility alleles have been associated with cancer risk and progression. We used RNA sequence analysis to search for genetic variations associated with pathogenesis of hepatocellular carcinoma (HCC).

METHODS

We analyzed 400 paired HCC and adjacent nontumor tissues, along with clinical information, from patients who underwent surgery at Sun Yat-Sen University in Guangzhou, China. Total RNA was extracted from tissues and sequenced, and variations with allele imbalance were identified. Effects of variants on cell functions were investigated in HCC cell lines and tumor xenografts in mice. Variants were associated with patient outcomes.

RESULTS

We found a high proportion of allele imbalance in genes related to cellular stress. A nucleotide variation in the Oxidative Stress-Induced Growth Inhibitor 1 (OSGIN1) gene (nt 1494: G-A) resulted in an amino acid substitution (codon 438: Arg-His). The variant form of OSGIN1 was specifically retained in the tumor tissues. Functional assays showed that the common form of OSGIN1 functioned as a tumor suppressor, sensitizing HCC cells to chemotherapeutic agents by inducing apoptosis. However, the variant form of OSGIN1 was less effective. It appeared to affect the translocation of OSGIN1 from the nucleus to mitochondria, which is important for its apoptotic function. The expression pattern and localization of OSGIN1 was altered in HCC specimens, compared with adjacent liver tissue. Levels of OSGIN1 messenger RNA were reduced in 24.7% of HCC specimens, and down-regulation was associated with shorter overall and disease-free survival times of patients. Patients with the OSGIN1 1494A variant had the shortest mean survival time (32.68 mo) among patient subgroups, and their tumor samples had the lowest apoptotic index.

CONCLUSIONS

We identified OSGIN1 as a tumor suppressor that is down-regulated or altered in human HCCs. Variants of OSGIN1 detected in HCC samples reduce apoptosis and are associated with shorter survival times of patients.

Interaction of OKL38 and p53 in regulating mitochondrial structure and function

The tumor suppressor p53 is a well-known transcription factor controlling the expression of its target genes involved in cell cycle and apoptosis. In addition, p53 also plays a direct proapoptotic role in mitochondria by regulating cytochrome c release. Recently, we identified a novel downstream target of p53, OKL38, which relocalizes from nucleus to mitochondria upon forced expression to induce apoptosis. However, the mechanism underlying OKL38 targeting to mitochondria and apoptosis induction remains unclear. Here, we found that OKL38 interacts with p53 to regulate mitochondria function. After DNA damage, OKL38 colocalizes with p53 to mitochondria in U2OS cells. Further, p53 and OKL38 are targeted to mitochondria in synergy: forced expression of OKL38 leads to p53 localization to mitochondria while the expression of a mitochondria enriched p53 polymorphic variant, p53^R72, leads to OKL38 enrichment in mitochondria. Biochemical analyses found that OKL38 and p53 interact in vivo and in vitro via multiple domains. In cell biological assays, multiple regions of OKL38 mediate its mitochondria localization and induce mitochondria morphology changes. OKL38 induces formation of megamitochondria and increases cellular levels of reactive oxygen species. Furthermore, OKL38 induces cytochrome c release upon incubation with mitochondria. Taken together, our studies suggest that OKL38 regulates mitochondria morphology and functions during apoptosis together with p53.

Histone Arg modifications and p53 regulate the expression of OKL38, a mediator of apoptosis

Protein Arg methyltransferases function as coactivators of the tumor suppressor p53 to regulate gene expression. Peptidylarginine deiminase 4 (PAD4/PADI4) counteracts the functions of protein Arg methyltransferases in gene regulation by deimination and demethylimination. Here we show that the expression of a tumor suppressor gene, OKL38, is activated by the inhibition of PAD4 or the activation of p53 following DNA damage. Chromatin immunoprecipitation assays showed a dynamic change of p53 and PAD4 occupancy and histone Arg modifications at the OKL38 promoter during DNA damage, suggesting a direct role of PAD4 and p53 in the expression of OKL38. Furthermore, we found that OKL38 induces apoptosis through localization to mitochondria and induction of cytochrome c release. Together, our studies identify OKL38 as a novel p53 target gene that is regulated by PAD4 and plays a role in apoptosis.