FLLL32 Triggers Caspase-Mediated Apoptotic Cell Death in Human Oral Cancer Cells by Regulating the p38 Pathway

Oral cancer is the most common oral malignant tumor in Taiwan. Although there exist several methods for treatment, oral cancer still has a poor prognosis and high recurrence. FLLL32, a synthetic analog of curcumin with antitumor activity, is currently known to induce melanoma apoptosis and inhibit tumor growth in various cancers. However, few studies have examined the mechanisms of FLLL32 in oral cancer. In this study, we explore whether FLLL32 induces apoptosis in oral cancer. We determined that FLLL32 can inhibit the cell viability of oral cancer. Next, we analyzed the effect of FLLL32 on the cell cycle of oral cancer cells and observed that the proportion of cells in the G2/M phase was increased. Additionally, annexin-V/PI double staining revealed that FLLL32 induced apoptosis in oral cancer cells. Data from the Human Apoptosis Array revealed that FLLL32 increases the expression of cleaved caspase-3 and heme oxygenase-1 (HO-1). FLLL32 activates proteins such as caspase-8, caspase-9, caspase-3, PARP, and mitogen-activated protein kinases (MAPKs) in apoptosis-related molecular mechanisms. Moreover, by using MAPK inhibitors, we suggest that FLLL32 induces the apoptosis of oral cancer cells through the p38 MAPK signaling pathway. In conclusion, our findings suggest that FLLL32 is a potential therapeutic agent for oral cancer by inducing caspase-dependent apoptosis and HO-1 activation through the p38 pathway. We believe that the activation of HO-1 and the p38 pathway by FLLL32 represent potential targets for further research in oral cancer.     

Curcumol Inhibits Growth and Induces Apoptosis of Colorectal Cancer LoVo Cell Line via IGF-1R and p38 MAPK Pathway

Curcumol, isolated from the traditional medical plant Rhizoma Curcumae, is the bioactive component of Zedoary oil, whose potential anti-tumor effect has attracted considerable attention in recent years. Though many researchers have reported curcumol and its bioactivity, the potential molecular mechanism for its anti-cancer effect in colorectal cancer LoVo cells still remains unclear. In the present study, we found that curcumol showed growth inhibition and induced apoptosis of LoVo cells in a dose- and time-dependent manner. The occurrence of its proliferation inhibition and apoptosis came with suppression of IGF-1R expression, and then increased the phosphorylation of p38 mitogen activated protein kinase (MAPK), which might result in a cascade response by inhibiting the CREB survival pathway and finally triggered Bax/Bcl-2 and poly(ADP-ribose) polymerase 1 (PARP-1) apoptosis signals. Moreover, curcumol inhibited colorectal cancer in xenograft models of nude mice. Immunohistochemical and Western blot analysis revealed that curcumol could decrease the expression of ki-67, Bcl-2 as well as CREB1, and increase the expression of Bax and the phosphorylation of p38, which were consistent with our in vitro study. Overall, our in vitro and in vivo data confirmed the anti-cancer activity of curcumol, which was related to a significant inhibition of IGF-1R and activation of p38 MAPKs, indicating that curcumol may be a potential anti-tumor agent for colorectal carcinoma therapy.     

Picrasidine I Triggers Heme Oxygenase-1-Induced Apoptosis in Nasopharyngeal Carcinoma Cells via ERK and Akt Signaling Pathways

Nasopharyngeal carcinoma (NPC) has a higher incidence in Taiwan than worldwide. Although it is a radiosensitive malignancy, cancer recurrence is still high in the advanced stages because of its ability to induce lymph node metastasis. Picrasidine I from Picrasma quassioides has been reported as a potential drug for targeting multiple signaling pathways. The present study aimed to explore the role of picrasidine I in the apoptosis of NPC cells. Our results show that picrasidine I induced cytotoxic effects in NPC cells and caused cell cycle arrest in the sub-G1, S, and G2/M phases. Western blot analysis further demonstrated that the modulation of apoptosis through the extrinsic and intrinsic pathways was involved in picrasidine I-induced cell death. Downregulation of the ERK1/2 and Akt signaling pathways was also found in picrasidine I-induced apoptosis. Additionally, the apoptosis array showed that picrasidine I significantly increased heme oxygenase-1 (HO-1) expression, which could act as a critical molecule in picrasidine I-induced apoptosis in NPC cells. The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets also revealed that the HMOX1 mRNA level (HO-1) is lower in patients with head and neck squamous carcinoma (HNSCC) and NPC than in patients without cancer. Our study indicated that picrasidine I exerts anticancer effects in NPC by modulating HO-1 via the ERK and Akt signaling pathways.     

Canagliflozin Inhibits Human Endothelial Cell Inflammation through the Induction of Heme Oxygenase-1

Sodium-glucose co-transporter 2 (SGLT2) inhibitors improve cardiovascular outcomes in patients with type 2 diabetes mellitus (T2DM). Studies have also shown that canagliflozin directly acts on endothelial cells (ECs). Since heme oxygenase-1 (HO-1) is an established modulator of EC function, we investigated if canagliflozin regulates the endothelial expression of HO-1, and if this enzyme influences the biological actions of canagliflozin in these cells. Treatment of human ECs with canagliflozin stimulated a concentration- and time-dependent increase in HO-1 that was associated with a significant increase in HO activity. Canagliflozin also evoked a concentration-dependent blockade of EC proliferation, DNA synthesis, and migration that was unaffected by inhibition of HO-1 activity and/or expression. Exposure of ECs to a diabetic environment increased the adhesion of monocytes to ECs, and this was attenuated by canagliflozin. Knockdown of HO-1 reduced the anti-inflammatory effect of canagliflozin which was restored by bilirubin but not carbon monoxide. In conclusion, this study identified canagliflozin as a novel inducer of HO-1 in human ECs. It also found that HO-1-derived bilirubin contributed to the anti-inflammatory action of canagliflozin, but not the anti-proliferative and antimigratory effects of the drug. The ability of canagliflozin to regulate HO-1 expression and EC function may contribute to the clinical profile of the drug.     

Hyperglycemia in Pregnancy-Associated Oxidative Stress Augments Altered Placental Glucose Transporter 1 Trafficking via AMPKα/p38MAPK Signaling Cascade

GLUT1, being a ubiquitous transporter isoform, is considered primarily responsible for glucose uptake during glycolysis. However, there is still uncertainty about the regulatory mechanisms of GLUT1 in hyperglycemia in pregnancy (HIP, PGDM, and GDM) accompanied by abnormal oxidative stress responses. In the present study, it was observed that the glycolysis was enhanced in GDM and PGDM pregnancies. In line with this, the antioxidant system was disturbed and GLUT1 expression was increased due to diabetes impairment in both placental tissues and in vitro BeWo cells. GLUT1 responded to high glucose stimulation through p38MAPK in an AMPKα-dependent manner. Both the medical-mediated and genetic depletion of p38MAPK in BeWo cells could suppress GLUT1 expression and OS-induced proapoptotic effects. Furthermore, blocking AMPKα with an inhibitor or siRNA strategy promoted p38MAPK, GLUT1, and proapoptotic molecules expression and vice versa. In general, a new GLUT1 regulation pathway was identified, which could exert effects on placental transport function through the AMPKα-p38MAPK pathway. AMPKα may be a therapeutic target in HIP for alleviating diabetes insults.     

Increased FOXM1 Expression by Cisplatin Inhibits Paclitaxel-Related Apoptosis in Cisplatin-Resistant Human Oral Squamous Cell Carcinoma (OSCC) Cell Lines

Cisplatin and paclitaxel are commonly used to treat oral cancer, but their use is often limited because of acquired drug resistance. Here, we tested the effects of combined cisplatin and paclitaxel on three parental (YD-8, YD-9, and YD-38) and three cisplatin-resistant (YD-8/CIS, YD-9/CIS, and YD-38/CIS) oral squamous cell carcinoma (OSCC) cell lines using cell proliferation assays and combination index analysis. We detected forkhead box protein M1 (FOXM1) mRNA and protein expression via real-time qPCR and Western blot assays. Cell death of the cisplatin-resistant cell lines in response to these drugs with or without a FOXM1 inhibitor (forkhead domain inhibitory compound 6) was then measured by propidium iodide staining and TdT dUTP nick end labeling (TUNEL) assays. In all six OSCC cell lines, cell growth was more inhibited by paclitaxel alone than combination therapy. Cisplatin-induced overexpression of FOXM1 showed the same trend only in cisplatin-resistant cell lines, indicating that it was associated with inhibition of paclitaxel-related apoptosis. In summary, these results suggest that, in three cisplatin-resistant cell lines, the combination of cisplatin and paclitaxel had an antagonistic effect, likely because cisplatin blocks paclitaxel-induced apoptosis. Cisplatin-induced FOXM1 overexpression may explain the failure of this combination.     

Lablab purpureus Protects HaCaT Cells from Oxidative Stress-Induced Cell Death through Nrf2-Mediated Heme Oxygenase-1 Expression via the Activation of p38 and ERK1/2

Ultraviolet B (UV-B) radiation induces the extreme production of either reactive oxygen species (ROS) or inflammatory mediators. The aim of this study was to evaluate the antioxidant activities of 70% ethanolic extract of Lablab purpureus (LPE) and the underlying mechanisms using HaCaT cells exposed to UV-B. High-performance liquid chromatography (HPLC) confirmed the presence of gallic acid, catechin, and epicatechin in LPE. LPE was shown to have a very potent capacity to scavenge free radicals. The results showed that LPE prevented DNA damage and inhibited the generation of ROS in HaCaT cells without causing any toxicity. LPE increased the expression of endogenous antioxidant enzymes such as superoxide dismutase-1 and catalase. Furthermore, LPE treatment facilitates the nuclear translocation of nuclear factor (erythroid-derived 2)-like 2 (Nrf-2), boosting the phase II detoxifying enzyme heme oxygenase-1 (HO-1) leading to the combatting of oxidative stress. However, pretreatment of LPE also caused the phosphorylation of mitogen-activated protein kinases (MAPK kinase) (p38 kinase) and extracellular signal-regulated kinase (ERK), whereas treatment with p38 and ERK inhibitors substantially suppressed LPE-induced Nrf2 and heme oxygenase (HO)-1 expression. These findings suggest that LPE exhibits antioxidant activity via Nrf-2-mediated HO-1 signaling through the activation of p38 and ERK, indicating that LPE can potentially be used as a remedy to combat oxidative stress-induced disorder.     

Heme Oxygenase-1 Induction by Cobalt Protoporphyrin Ameliorates Cholestatic Liver Disease in a Xenobiotic-Induced Murine Model

Cholestatic liver diseases can progress to end-stage liver disease and reduce patients’ quality of life. Although their underlying mechanisms are still incompletely elucidated, oxidative stress is considered to be a key contributor to these diseases. Heme oxygenase-1 (HO-1) is a cytoprotective enzyme that displays antioxidant action. It has been found that this enzyme plays a protective role against various inflammatory diseases. However, the role of HO-1 in cholestatic liver diseases has not yet been investigated. Here, we examined whether pharmacological induction of HO-1 by cobalt protoporphyrin (CoPP) ameliorates cholestatic liver injury. To this end, a murine model of 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet feeding was used. Administration of CoPP ameliorated liver damage and cholestasis with HO-1 upregulation in DDC diet-fed mice. Induction of HO-1 by CoPP suppressed the DDC diet-induced oxidative stress and hepatocyte apoptosis. In addition, CoPP attenuated cytokine production and inflammatory cell infiltration. Furthermore, deposition of the extracellular matrix and expression of fibrosis-related genes after DDC feeding were also decreased by CoPP. HO-1 induction decreased the number of myofibroblasts and inhibited the transforming growth factor-β pathway. Altogether, these data suggest that the pharmacological induction of HO-1 ameliorates cholestatic liver disease by suppressing oxidative stress, hepatocyte apoptosis, and inflammation.     

蛋白酶体抑制剂诱导的PC12细胞帕金森病模型中血红素加氧酶-1的差异表达

目的探讨蛋白酶体抑制剂(Proteasome inhibitor,PSI)诱导的PC12细胞帕金森病(Parkinson disease,PD)模型中血红素加氧酶-1(Hemeoxygenase-1,HO-1)的差异表达,为深入研究PD的发病机制提供理论依据。方法取培养的PC12细胞,加入终浓度为10μmol/L的PSI,建立PSI诱导的PC12细胞模型,以加入终浓度为10μmol/L的二甲基亚砜(DMSO)为对照组。经HE、AO&EB及α-SYN染色进行鉴定;PSI作用48h后提取蛋白,应用荧光差异凝胶电泳(DIGE)系统获得差异蛋白点,运用基质辅助激光解吸/电离飞行时间质谱仪(MALDI-TOFProMS)鉴定差异蛋白。结果模型组与对照组比较,PSI作用48h可见细胞内嗜酸性类Lewy小体形成及细胞凋亡,凋亡率达(24.74±4.55)%。模型组与对照组比较,HO-1表达量显著增加。结论在泛素-蛋白酶体系统(Ubiquitin-proteasome system,UPS)功能障碍诱发PD过程中,氧化应激反应发挥着一定的作用。     

Curcumin Induces Apoptosis of Chemoresistant Lung Cancer Cells via ROS-Regulated p38 MAPK Phosphorylation

This study aimed to challenge chemoresistance by curcumin (CUR) with drug-selected human lung cancer A549 sublines that continuously proliferate in the present of docetaxel (DOC) and vincristine (VCR). Their sensitivities to CUR were measured by MTT assay and the particular intracellular reactive oxygen species (ROS) was detected by fluorescence activated cell sorting (FACS) analysis. Apoptosis was analyzed by Annexin V assay of the flow cytometry. Inhibitors and RNA interference were used to examine the signaling pathway regulated by the kinases. The obtained data demonstrated that CUR induces chemoresistant cell apoptosis by generating ROS and application of N-acetylcysteine (NAC) blocks ROS production, resulting in apoptosis suppression. Phosphorylation of extracellular regulated kinase (ERK), p38 MAPK, and eIF-2α were increased but c-Jun N-terminal kinase (JNK) did not increase when chemoresistant cells were treated with CUR. Downregulation of ERK and p38 MAPK phosphorylation by their inhibitors had no effect on CUR-induced apoptosis. Interestingly, the knockdown of p38 MAPK with shRNA significantly reduced CUR-induced apoptosis on the chemoresistant sublines. Phosphorylation of the eIF-2α protein was inhibited when p38 MAPK was knocked down in DOC-resistant A549 cells, but a high level of phosphorylated eIF-2α protein remained on the VCR-resistant A549 cells when p38 MAPK was knocked down. These data confirmed that CUR-augmented ROS potently induced apoptosis via upregulated p38 MAPK phosphorylation. Therefore, activated p38 MAPK is considered a pro-apoptotic signal for CUR-induced apoptosis of chemoresistant human lung cancer cells.     

Crosstalk between p38 MAPK and GR Signaling

The p38 MAPK is a signaling pathway important for cells to respond to environmental and intracellular stress. Upon activation, the p38 kinase phosphorylates downstream effectors, which control the inflammatory response and coordinate fundamental cellular processes such as proliferation, apoptosis, and differentiation. Dysregulation of this signaling pathway has been linked to inflammatory diseases and cancer. Secretion of glucocorticoids (GCs) is a classical endocrine response to stress. The glucocorticoid receptor (GR) is the primary effector of GCs and plays an important role in the regulation of cell metabolism and immune response by influencing gene expression in response to hormone-dependent activation. Its ligands, the GCs or steroids, in natural or synthetic variation, are used as standard therapy for anti-inflammatory treatment, severe asthma, autoimmune diseases, and several types of cancer. Several years ago, the GR was identified as one of the downstream targets of p38, and, at the same time, it was shown that glucocorticoids could influence p38 signaling. In this review, we discuss the role of the crosstalk between the p38 and GR in the regulation of gene expression in response to steroids and comprehend the importance and potential of this interplay in future clinical applications.     

Curcumin-Induced Heme Oxygenase-1 Expression Prevents H2O2-Induced Cell Death in Wild Type and Heme Oxygenase-2 Knockout Adipose-Derived Mesenchymal Stem Cells

Mesenchymal stem cell (MSC) administration is a promising adjuvant therapy to treat tissue injury. However, MSC survival after administration is often hampered by oxidative stress at the site of injury. Heme oxygenase (HO) generates the cytoprotective effector molecules biliverdin/bilirubin, carbon monoxide (CO) and iron/ferritin by breaking down heme. Since HO-activity mediates anti-apoptotic, anti-inflammatory, and anti-oxidative effects, we hypothesized that modulation of the HO-system affects MSC survival. Adipose-derived MSCs (ASCs) from wild type (WT) and HO-2 knockout (KO) mice were isolated and characterized with respect to ASC marker expression. In order to analyze potential modulatory effects of the HO-system on ASC survival, WT and HO-2 KO ASCs were pre-treated with HO-activity modulators, or downstream effector molecules biliverdin, bilirubin, and CO before co-exposure of ASCs to a toxic dose of H₂O₂. Surprisingly, sensitivity to H₂O₂-mediated cell death was similar in WT and HO-2 KO ASCs. However, pre-induction of HO-1 expression using curcumin increased ASC survival after H₂O₂ exposure in both WT and HO-2 KO ASCs. Simultaneous inhibition of HO-activity resulted in loss of curcumin-mediated protection. Co-treatment with glutathione precursor N-Acetylcysteine promoted ASC survival. However, co-incubation with HO-effector molecules bilirubin and biliverdin did not rescue from H₂O₂-mediated cell death, whereas co-exposure to CO-releasing molecules-2 (CORM-2) significantly increased cell survival, independently from HO-2 expression. Summarizing, our results show that curcumin protects via an HO-1 dependent mechanism against H₂O₂-mediated apoptosis, and likely through the generation of CO. HO-1 pre-induction or administration of CORMs may thus form an attractive strategy to improve MSC therapy.     

UVB Inhibits Proliferation,Cell Cycle and Induces Apoptosis via p53, E2F1 and Microtubules System in Cervical Cancer Cell Lines

Ultraviolet (UV) exposure has been linked to skin damage and carcinogenesis, but recently UVB has been proposed as a therapeutic approach for cancer. Herein, we investigated the cellular and molecular effects of UVB in immortal and tumorigenic HPV positive and negative cells. Cells were irradiated with 220.5 to 1102.5 J/m² of UVB and cell proliferation was evaluated by crystal violet, while cell cycle arrest and apoptosis analysis were performed through flow cytometry. UVB effect on cells was recorded at 661.5 J/m² and it was exacerbated at 1102.5 J/m². All cell lines were affected by proliferation inhibition, cell cycle ablation and apoptosis induction, with different degrees depending on tumorigenesis level or HPV type. Analysis of the well-known UV-responsive p53, E2F1 and microtubules system proteins was performed in SiHa cells in response to UVB through Western-blotting assays. E2F1 and the Microtubule-associated protein 2 (MAP2) expression decrease correlated with cellular processes alteration while p53 and Microtubule-associated Protein 1S (MAP1S) expression switch was observed since 882 J/m², suggesting they were required under more severe cellular damage. However, expression transition of α-Tubulin3C and β-Tubulin was abruptly noticed until 1102.5 J/m² and particularly, γ-Tubulin protein expression remained without alteration. This study provides insights into the effect of UVB in cervical cancer cell lines.     

The Inhibition of RANKL-Induced Osteoclastogenesis through the Suppression of p38 Signaling Pathway by Naringenin and Attenuation of Titanium-Particle-Induced Osteolysis

The aim of this study was to assess the effect of naringenin on osteoclastogenesis and titanium particle-induced osteolysis. Osteolysis from wear-induced particles and aseptic loosening are the most frequent late complications of total joint arthroplasty leading to revision of the prosthesis. Osteolysis during aseptic loosening is most likely due to increased bone resorption by osteoclasts. Through in vitro studies, we demonstrated that naringenin, a naturally occurring flavanone in grapefruit and tomatoes, exerts potent inhibitory effects on the ligand of the receptor activator of nuclear factor-κB (RANKL)-induced osteoclastogenesis and revealed that the mechanism of action of naringenin, which inhibited osteoclastogenesis by suppression of the p38 signaling pathway. Through in vivo studies, we proved that naringenin attenuated titanium particle-induced osteolysis in a mouse calvarial model. In general, we demonstrated that naringenin inhibited osteoclastogenesis via suppression of p38 signaling in vitro and attenuated titanium particle-induced osteolysis in vivo. This study also suggested that naringenin has significant potential for the treatment of osteolysis-related diseases caused by excessive osteoclast formation and activity.     

Chronic Alcohol Exposure Promotes Cancer Stemness and Glycolysis in Oral/Oropharyngeal Squamous Cell Carcinoma Cell Lines by Activating NFAT Signaling

Alcohol consumption is associated with an increased risk of several cancers, including oral/oropharyngeal squamous cell carcinoma (OSCC). Alcohol also enhances the progression and aggressiveness of existing cancers; however, its underlying molecular mechanism remains elusive. Especially, the local carcinogenic effects of alcohol on OSCC in closest contact with ingestion of alcohol are poorly understood. We demonstrated that chronic ethanol exposure to OSCC increased cancer stem cell (CSC) populations and their stemness features, including self-renewal capacity, expression of stem cell markers, ALDH activity, and migration ability. The ethanol exposure also led to a significant increase in aerobic glycolysis. Moreover, increased aerobic glycolytic activity was required to support the stemness phenotype of ethanol-exposed OSCC, suggesting a molecular coupling between cancer stemness and metabolic reprogramming. We further demonstrated that chronic ethanol exposure activated NFAT (nuclear factor of activated T cells) signaling in OSCC. Functional studies revealed that pharmacological and genetic inhibition of NFAT suppressed CSC phenotype and aerobic glycolysis in ethanol-exposed OSCC. Collectively, chronic ethanol exposure promotes cancer stemness and aerobic glycolysis via activation of NFAT signaling. Our study provides a novel insight into the roles of cancer stemness and metabolic reprogramming in the molecular mechanism of alcohol-mediated carcinogenesis.     

Atypical p38 Signaling,Activation, and Implications for Disease

The mitogen-activated protein kinase (MAPK) p38 is an essential family of kinases, regulating responses to environmental stress and inflammation. There is an ever-increasing plethora of physiological and pathophysiological conditions attributed to p38 activity, ranging from cell division and embryonic development to the control of a multitude of diseases including retinal, cardiovascular, and neurodegenerative diseases, diabetes, and cancer. Despite the decades of intense investigation, a viable therapeutic approach to disrupt p38 signaling remains elusive. A growing body of evidence supports the pathological significance of an understudied atypical p38 signaling pathway. Atypical p38 signaling is driven by a direct interaction between the adaptor protein TAB1 and p38α, driving p38 autophosphorylation independent from the classical MKK3 and MKK6 pathways. Unlike the classical MKK3/6 signaling pathway, atypical signaling is selective for just p38α, and at present has only been characterized during pathophysiological stimulation. Recent studies have linked atypical signaling to dermal and vascular inflammation, myocardial ischemia, cancer metastasis, diabetes, complications during pregnancy, and bacterial and viral infections. Additional studies are required to fully understand how, when, where, and why atypical p38 signaling is induced. Furthermore, the development of selective TAB1-p38 inhibitors represents an exciting new opportunity to selectively inhibit pathological p38 signaling in a wide array of diseases.     

Dysregulated Autophagy and Mitophagy in a Mouse Model of Duchenne Muscular Dystrophy Remain Unchanged Following Heme Oxygenase-1 Knockout

Dysregulation of autophagy may contribute to the progression of various muscle diseases, including Duchenne muscular dystrophy (DMD). Heme oxygenase-1 (HO-1, encoded by Hmox1), a heme-degrading enzyme, may alleviate symptoms of DMD, inter alia, through anti-inflammatory properties. In the present study, we determined the role of HO-1 in the regulation of autophagy and mitophagy in mdx animals, a commonly used mouse model of the disease. In the gastrocnemius of 6-week-old DMD mice, the mRNA level of mitophagy markers: Bnip3 and Pink1, as well as autophagy regulators, e.g., Becn1, Map1lc3b, Sqstm1, and Atg7, was decreased. In the dystrophic diaphragm, changes in the latter were less prominent. In older, 12-week-old dystrophic mice, diminished expressions of Pink1 and Sqstm1 with upregulation of Atg5, Atg7, and Lamp1 was depicted. Interestingly, we demonstrated higher protein levels of autophagy regulator, LC3, in dystrophic muscles. Although the lack of Hmox1 in mdx mice influenced blood cell count and the abundance of profibrotic proteins, no striking differences in mRNA and protein levels of autophagy and mitophagy markers were found. In conclusion, we demonstrated complex, tissue, and age-dependent dysregulation of mitophagic and autophagic markers in DMD mice, which are not affected by the additional lack of Hmox1.     

Downregulation of miR-506-3p Facilitates EGFR-TKI Resistance through Induction of Sonic Hedgehog Signaling in Non-Small-Cell Lung Cancer Cell Lines

Non-small-cell lung cancer (NSCLC) patients with epidermal growth factor receptor (EGFR) mutation eventually develop resistance to EGFR-targeted tyrosine kinase inhibitors (TKIs). Treatment resistance remains the primary obstacle to the successful treatment of NSCLC. Although drug resistance mechanisms have been studied extensively in NSCLC, the regulation of these mechanisms has not been completely understood. Recently, increasing numbers of microRNAs (miRNAs) are implicated in EGFR-TKI resistance, indicating that miRNAs may serve as novel targets and may hold promise as predictive biomarkers for anti-EGFR therapy. MicroRNA-506 (miR-506) has been identified as a tumor suppressor in many cancers, including lung cancer; however, the role of miR-506 in lung cancer chemoresistance has not yet been addressed. Here we report that miR-506-3p expression was markedly reduced in erlotinib-resistant (ER) cells. We identified Sonic Hedgehog (SHH) as a novel target of miR-506-3p, aberrantly activated in ER cells. The ectopic overexpression of miR-506-3p in ER cells downregulates SHH signaling, increases E-cadherin expression, and inhibits the expression of vimentin, thus counteracting the epithelial–mesenchymal transition (EMT)-mediated chemoresistance. Our results advanced our understanding of the molecular mechanisms underlying EGFR-TKI resistance and indicated that the miR-506/SHH axis might represent a novel therapeutic target for future EGFR mutated lung cancer treatment.