Analysis of MUC6 polymorphisms on the clinicopathologic characteristics of Asian patients with oral squamous cell carcinoma.

Head and neck squamous cell carcinomas (HNSCCs) are generally associated with tobacco consumption, alcohol abuse or both. Mucins (MUCs) are high-molecular-weight glycoproteins produced by many epithelial tissues. Many studies have indicated that MUCs play an important role in cancer metastasis. MUC6 expression has been observed in gastric and oncocytic phenotypes and plays an important role during cancer progression. We found that levels of MUC6 are lower in Asian HNCC patients and affect the disease-free survival of HNCC patients. Next, we investigated the combined effect of MUC6 polymorphisms and exposure to environmental carcinogens on the susceptibility to and clinicopathological characteristics of HNCC. Three single-nucleotide polymorphisms (SNPs) of MUC6 (rs7481521, rs6597947 and rs61869016) were analysed using real-time PCR. After adjusting for other co-variants, we found that carrying a CC genotype at MUC6 rs6597947 led to a lower risk of developing oral squamous cell carcinoma (OSCC) than wild-type carriers among non-betel-quid chewers. Moreover, male oral cancer patients who carried the AA + CC genotype at MUC6 rs6597947 had a lower risk of lymph node metastasis than other genotypes, suggesting a significant functional compromise and decompensated disease. Therefore, our findings suggest that genetic variations in MUC6 may correlate to OSCC and indicate the progression in OSCC patients.

The interconnected roles of TRIM21/Ro52 in systemic lupus erythematosus, primary Sjögren's syndrome, cancers, and cancer metabolism.

Protein tripartite motif-containing 21 (TRIM21/Ro52), an E3 ubiquitin ligase, is an essential regulator of innate immunity, and its dysregulation is closely associated with the development of autoimmune diseases, predominantly systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS). TRIM21 /Ro52 also features anti-cancer and carcinogenic functions according to different malignancies. The interconnected role of TRIM21/Ro52 in regulating autoimmunity and cell metabolism in autoimmune diseases and malignancies is implicated. In this review, we summarize current findings on how TRIM21/Ro52 affects inflammation and tumorigenesis, and investigate the relationship between TRIM21/Ro52 expression and the formation of lymphoma and breast cancer in SLE and pSS populations.

EZH2-mediated epigenetic silencing of tumor-suppressive let-7c/miR-99a cluster by hepatitis B virus X antigen enhances hepatocellular carcinoma progression and metastasis.

BACKGROUND: Hepatitis B virus (HBV)-encoded X antigen, HBx, assists in the development of hepatocellular carcinoma (HCC) through complex mechanisms. Our results provide new insights into the EZH2 epigenetic repression of let-7c that promotes HCC migration induced by HBx. Thus, let-7c and HMGA2 represent key diagnostic markers and potential therapeutic targets for the treatment of HBV-related HCC. RESULTS: We investigated the epigenetic regulation of let-7c, an important representative miRNA in liver tumor metastasis, in human HCC cells to verify the effect of HBx. Based on quantitative PCR (qPCR) of mRNA isolated from tumor and adjacent non-tumor liver tissues of 24 patients with HBV-related HCC, EZH2 expression was significantly overexpressed in most HCC tissues (87.5%). We executed a miRNA microarray analysis in paired HBV-related HCC tumor and adjacent non-tumorous liver tissue from six of these patients and identified let-7c, miR-199a-3p, and miR-99a as being downregulated in the tumor tissue. Real-time PCR analysis verified significant downregulation of let-7c and miR-99a in both HepG2X and Hep3BX cells, which stably overexpress HBx, relative to parental cells. HBX enhanced EZH2 expression and attenuated let-7c expression to induce HMGA2 expression in the HCC cells. Knockdown of HMGA2 significantly downregulated the metastatic potential of HCC cells induced by HBx. CONCLUSIONS: The deregulation of let-7c expression by HBx may indicate a potential novel pathway through deregulating cell metastasis and imply that HMGA2 might be used as a new prognostic marker and/or as an effective therapeutic target for HCC.

Analysis of EZH2 Genetic Variants on Triple-Negative Breast Cancer Susceptibility and Pathology.

Triple-negative breast cancer (TNBC) is the third most common female cancer in Taiwan. EZH2 plays an important role in cancer development through transcriptional repression by chromatin remodeling. However, the expression of EZH2 in breast cancer is highly correlated with tumorigenesis, and patient survival is not matched to TNBC. Furthermore, it has not been determined if specific EZH2 genetic variants are associated with breast cancer risk. In this paper, we evaluated the survival of different types of breast cancer. The results indicated that a lower expression of EZH2 led to poor survival of TNBC patients. Therefore, we aimed at studying the relationship between genetic polymorphisms of EZH2 and susceptibility to TNBC in Taiwan. Four single-nucleotide polymorphisms (SNPs) of EZH2 (rs6950683, rs2302427, rs3757441, and rs41277434) were analyzed by real-time PCR genotyping in 176 patients with TNBC and 1000 cancer-free controls. The results showed that TNBC patients under 60 years old who carried a TC or CC genotype at EZH2 rs6950683 and re3757441 had a tumor size of 20 mm or smaller (T1). Thus, this study is the first to examine the age and mutant genes associated with EZH2 SNPs in TNBC progression and development in Taiwan.

Epigenetic regulation of the miR142-3p/interleukin-6 circuit in glioblastoma.

Epigenetic regulation plays a critical role in glioblastoma (GBM) tumorigenesis. However, how microRNAs (miRNAs) and cytokines cooperate to regulate GBM tumor progression is still unclear. Here, we show that interleukin-6 (IL-6) inhibits miR142-3p expression and promotes GBM propagation by inducing DNA methyltransferase 1-mediated hypermethylation of the miR142-3p promoter. Interestingly, miR142-3p also suppresses IL-6 secretion by targeting the 3' UTR of IL-6. In addition, miR142-3p also targets the 3' UTR and suppresses the expression of high-mobility group AT-hook 2 (HMGA2), leading to inhibition of Sox2-related stemness. We further show that HMGA2 enhances Sox2 expression by directly binding to the Sox2 promoter. Clinically, GBM patients whose tumors present upregulated IL-6, HMGA2, and Sox2 protein expressions and hypermethylated miR142-3p promoter also demonstrate poor survival outcome. Orthotopic delivery of miR142-3p blocks IL-6/HMGA2/Sox2 expression and suppresses stem-like properties in GBM-xenotransplanted mice. Collectively, we discovered an IL-6/miR142-3p feedback-loop-dependent regulation of GBM malignancy that could be a potential therapeutic target.

TRIM21 Polymorphisms are associated with Susceptibility and Clinical Status of Oral Squamous Cell Carcinoma patients.

Squamous cell cancer of head and neck (HNSCC) is the sixth most common malignancy worldwide. One of the most common HNSCC types is oral squamous cell carcinoma (OSCC), which is the fifth leading cause of cancer death in Taiwan. Tripartite motif 21 (TRIM21) has been reported to play an important role in different cancer types. We found a correlation between TRIM21 and survival of HNSCC patients, but little information exists about how altered TRIM21 expression contributes to tumorigenesis. Thus, we investigated the combined effect of TRIM21 polymorphisms and exposure to environmental carcinogens on the susceptibility and clinicopathological characteristics of OSCC. Two single-nucleotide polymorphisms (SNPs) of TRIM21 (rs4144331, rs915956) from 1194 healthy controls and 1192 OSCC patients were analyzed by real-time PCR. Among 1632 smokers, TRIM21 polymorphism carriers with the betel-nut chewing habit had a ~4.8-fold greater risk of OSCC than TRIM21 wild-type carriers without the betel-nut chewing habit. After adjusting for other covariants, OSCC patients with G/T at TRIM21 rs4144331 had a high risk for distant metastasis compared with G/G homozygotes. This study is the first to examine the risk factors associated with TRIM21 SNPs in OSCC progression and development. Thus, our findings suggest that this study is the first to examine the risk factors associated with TRIM21 SNPs in OSCC progression and development and suggest that interactions between mutant genes may alter the susceptibility to OSCC.

Praeruptorin A reduces metastasis of human hepatocellular carcinoma cells by targeting ERK/MMP1 signaling pathway.

Praeruptorin A (PA) is one of the active ingredients found in the dried root of Peucedanum praeruptorum Dunn, has been reported to possess anticancer effects against various types of cancer. However, the effect of PA on human hepatocellular carcinoma (HCC) remains uncleared. In this study, our results indicated that PA did not induce cytotoxicity or alter cell cycle distribution in human HCC cells (Huh-7, SK-Hep-1, and PLC/PRF/5 cells). Instead, PA inhibited the migration and invasion of human HCC cells while downregulating the expression of matrix metalloproteinase-1 (MMP1) and activating the extracellular signal-regulated kinase (ERK) signaling pathways. Furthermore, blocking the ERK signaling pathway through siERK restored the expression of MMP1 and the invasive ability of PA-treated HCC cells. In conclusion, our results demonstrate the antimetastatic activity of PA against human HCC cells, supporting its potential as a therapeutic agent of HCC treatments.

α-Mangostin attenuates stemness and enhances cisplatin-induced cell death in cervical cancer stem-like cells through induction of mitochondrial-mediated apoptosis.

Cancer stem cells (CSCs) exhibit specific characteristics including decontrolled self-renewal, tumor-initiating, promoting, and metastatic potential, abnormal stemness signaling, and chemotherapy resistance. Thus, targeting CSC is becoming an emerging cancer treatment. α-Mangostin has been shown to have potent and multiple anticancer activities. Accordingly, we hypothesized that α-mangostin may diminish the stemness and proliferation of CSC-like cervical cancer cells. In our results, comparing to the parent cells, CSC-like SiHa and HeLa cells highly expressed CSC marker Sox2, Oct4, Nanog, CK-17, and CD49f. α-Mangostin significantly reduced the cell viability, sphere-forming ability, and expression of the CSC stemness makers of CSC-like cervical cancer cells. Further investigation showed that α-mangostin induced mitochondrial depolarization and mitochondrial apoptosis signaling, including upregulation of Bax, downregulation of Mcl-1 and Bcl-2, and activation of caspase-9/3. Moreover, α-mangostin synergically enhanced the cytotoxicity of cisplatin on CSC-like SiHa cells by promoting mitochondrial apoptosis and inhibiting the expression of CSC markers. Consistent with in vitro findings, in vivo tumor growth assay revealed that α-mangostin administration significantly inhibited the growth of inoculated CSC-like SiHa cells and synergically enhanced the antitumor effect of cisplatin. Our findings indicate that α-mangostin can reduce the stemness and proliferation of CSC-like SiHa and HeLa cells and promote the cytotoxicity of cisplatin, which may attribute to the mitochondrial apoptosis activation. Thus, it suggests that α-mangostin may have clinical potential to improve chemotherapy for cervical cancer by targeting cervical CSC.

Anti-cancer therapeutic benefit of red guava extracts as a potential therapy in combination with doxorubicin or targeted therapy for triple-negative breast cancer cells.

Guava extracts purified from leaf and bark have many bio-active molecules with anti-cancer activities. In addition, lycopene-rich extracts obtained from red guava fruit can induce apoptosis in estrogen receptor-positive breast cancers. Triple-negative breast cancer (TNBC) lacks estrogen receptors, progesterone receptors and human epidermal growth factor receptor 2 (HER2) and, therefore, hormone therapy and targeted therapy are not used in the clinic. The purpose of this study was to determine whether red guava fruit extracts can affect the proliferation of TNBC cells. In this study, cell viability was determined by using the MTT assay. Apoptosis and necrosis were analyzed using flow cytometry. Cleaved caspase-3 and PARP were analyzed by western blotting. We found that red guava extracts can, through caspase-3 activation and PARP cleavage signaling, induce apoptotic and necrotic death in TNBC cells. Our results thus show the therapeutic benefit of red guava extracts as a potential cancer treatment for TNBC in combination with doxorubicin or targeted therapy.

Water-Extracted Ganoderma lucidum Induces Apoptosis and S-Phase Arrest via Cyclin-CDK2 Pathway in Glioblastoma Cells.

Glioblastoma is one of the most common and most aggressive brain cancers. The current treatment is mainly surgery, chemotherapy, and radiation therapy, but the results are not satisfactory. Ganoderma lucidum (G. lucidum), also called "Lingzhi", is a medicinal mushroom that has been used as a therapeutic agent for the treatment of numerous diseases, including cancer. However, whether it is effective for treating cancer is still unclear. In the present study, the anti-tumor effect of a water extract of G. lucidum was investigated using brain tumor cells. We used an analysis of cell viability, flow cytometry, the IncuCyte live-cell analysis system, and Western blotting to study its effects. The water extract from G. lucidum inhibited cell proliferation in a dose- and time-dependent manner, and it induced mitochondria-mediated apoptosis and cell cycle arrest at S phase via the cyclin-CDK2 pathway in human brain tumor cells. In addition, the G. lucidum extract significantly inhibited cell migration and mesenchymal marker expression based on the IncuCyte live-cell assay and qRT-PCR analysis. In summary, these anti-tumor effects in brain tumor cells suggest that G. lucidum may be useful for treating brain tumors.

Antiproliferative and Antimetastatic Effects of Praeruptorin C on Human Non-Small Cell Lung Cancer Through Inactivating ERK/CTSD Signalling Pathways.

Praeruptorin C (PC) reportedly has beneficial effects in terms of antiinflammation, antihypertension, and antiplatelet aggregation, and it potentially has anticancer activity. However, the effect of PC on human non-small cell lung cancer (NSCLC) is largely unknown. Compared with the effects of praeruptorin A and praeruptorin B, we observed that PC significantly suppressed cell proliferation, colony formation, wound closure, and migration and invasion of NSCLC cells. It induced cell cycle arrest in the G0/G1 phase, downregulated cyclin D1 protein, and upregulated p21 protein. PC also significantly reduced the expression of cathepsin D (CTSD). In addition, the phosphorylation/activation of the ERK1/2 signalling pathway was significantly suppressed in PC-treated NSCLC cells. Cotreatment with PC and U0126 synergistically inhibited CTSD expression, cell migration, and cell invasion, which suggests that the ERK1/2 signalling pathway is involved in the downregulation of CTSD expression and invasion activity of NSCLC cells by PC. These findings are the first to demonstrate the inhibitory effects of PC in NSCLC progression. Therefore, PC may represent a novel strategy for treating NSCLC.

Anti-Cancer Effects of Sulfasalazine and Vitamin E Succinate in MDA-MB 231 Triple-Negative Breast Cancer Cells.

Aim: Sulfasalazine (SSZ) displayed anti-cancer activities. Vitamin E succinate (VES) could inhibit cell growth in various cancer cells. However, chemical therapies were often not useful for triple-negative breast cancer cells (TNBCs) treatment. Here, this study investigated the anti-cancer effects and the mechanisms on TNBCs under combination treatment with SSZ and VES. Methods: Cell viability was analyzed by using the MTT assay. The H2O2 levels were determined by using lucigenin-amplified chemiluminescence method. In addition, caspase and MAPs signals were studied by using western blotting. Results: Low-dose VES antagonized the SSZ-induced cytotoxicity effects while high-dose VES promoted the SSZ-induced cytotoxicity effects on TNBCs. In addition, SSZ alone treatment activated both caspase-3 and ERK signals, however, VES alone treatment only activated JNK signals. On the other hand, activation of caspase-3, JNK, and ERK were found in SSZ plus VES-treated cells. Conclusion: Combined SSZ and VES has synergistic or antagonistic cytotoxic effects depending on VES concentration. In addition, different cytotoxic signals are induced on SSZ-treated, VES-treated and SSZ plus VES-treated cells.

Over-expression of lysyl oxidase is associated with poor prognosis and response to therapy of patients with lower grade gliomas.

Lower grade gliomas (LGGs) have highly diverse clinical phenotypes. The histological grade and type are insufficient to accurately predict the clinical outcomes of patients with LGGs. Therefore, identification of biomarkers that can facilitate the prediction of clinical outcomes in LGGs is urgently needed. Gene expression of LOX has been identified as a biomarker for various cancers. However, the clinical significance of LOX expression in LGGs has not been investigated. In this study, we analyzed the glioma RNA-seq dataset from TCGA (The Cancer Genome atlas) and identified lysyl oxidase (LOX) as a potential biomarker for LGGs. Kaplan-Meier survival analysis revealed that high LOX expression is associated with worse overall survival and recurrence free survival in LGG patients. Besides, high LOX expression is associated with poor response to primary therapy, follow-up treatment, targeted molecular therapy, and radiation therapy. Univariate and multivariate Cox regression analyses further confirmed LOX expression as an independent prognostic factor for LGG patients. Finally, we observed that LOX expression is significantly correlated with EMT (epithelial to mesenchymal transition) and IDH1 status in LGGs. In conclusion, our analyses suggest that LOX expression is a potential biomarker for prognosis and therapeutic response in LGGs.

FUT2 genetic variants as predictors of tumor development with hepatocellular carcinoma.

Lewis antigens related to the ABO blood group are fucosylated oligosaccharides and are synthesized by specific glycosyltransferases (FUTs). FUTs are involved in various biological processes including cell adhesion and tumor progression. The fucosyltransferase-2 gene (FUT2) encodes alpha (1,2) fucosyltransferase, which is responsible for the addition of the alpha (1,2)-linkage of fucose to glycans. Aberrant fucosylation occurs frequently during the development and progression of hepatocellular carcinoma (HCC). However, the association of FUT2 polymorphisms with HCC development has not been studied. Therefore, we aimed to investigate the association of FUT2 polymorphisms with demographic, etiological, and clinical characteristics and with susceptibility to HCC. In this study, a total of 339 patients and 720 controls were recruited. The genotypes of FUT2 at four single-nucleotide polymorphisms (SNPs; rs281377, rs1047781, rs601338, and rs602662) were detected by real-time polymerase chain reaction from these samples. Compared with the wild-type genotype at SNP rs1047781, which is homozygous for nucleotides AA, at least one polymorphic T allele (AT or TT) displayed significant association with clinical stage (p = 0.048) and tumor size (p = 0.022). Our study strongly implicates the polymorphic locus rs1047781 of FUT2 as being associated with HCC development.

Combinations of FUT2 gene polymorphisms and environmental factors are associated with oral cancer risk.

In humans, fucosyltransferase-2 (FUT2) plays an important role in α1,2- linkage of fucose and participates in complex cellular processes such as fertilization, embryogenesis, and immune responses. However, little information is available concerning the FUT2 expression in tumorigenesis. The aim of this work was to investigate the combined effect of FUT2 gene polymorphisms and exposure to environmental carcinogens on the susceptibility and clinic pathological characteristics of oral cancer. Four SNPs of the FUT2 gene (rs281377, rs1047781, rs601338, and rs602662) from 1200 non-cancer controls and 700 oral squamous cell carcinoma (OSCC) patients were analyzed by real-time polymerase chain reaction (PCR). The samples were further analyzed to clarify the associations between these gene polymorphisms and the risk of OSCC, and the impact of these SNPs on the susceptibility and clinic pathological characteristics of OSCC. After adjusting for other covariant, we observed that betel quid chewing among 1255 smokers who carrying at least one C genotype (TC and CC) at rs281377 and least one T genotype (TA and TT) at rs1047781 were exhibited synergistic effects of environmental factors (betel quid and cigarette use) on the susceptibility of oral cancer. Taken together, our results support gene-environment interactions of FUT2 polymorphisms with smoking and betel quid chewing habits possibly altering oral cancer susceptibility. Furthermore, to our knowledge, this is the first study of association between FUT2 gene variants and OSCC risk.

Downregulation of microRNA-15b by hepatitis B virus X enhances hepatocellular carcinoma proliferation via fucosyltransferase 2-induced Globo H expression.

Globo H, a cancer-associated carbohydrate antigen, is highly expressed in various types of cancers. However, the role of Globo H in hepatocellular carcinoma (HCC) remains elusive. In our study, we performed glycan microarray analysis of 134 human serum samples to explore anti-Globo H antibody changes and found that Globo H is upregulated in hepatitis B virus (HBV)-positive HCC. Similarly, immunohistochemistry showed that Globo H expression was higher in tumors compared to normal tissues. In addition, fucosyltransferase 2 (FUT2), the main synthetic enzyme of Globo H, was also increased in HCC cells overexpressing HBV X protein (HBX). HBX plays an important role in promoting cell proliferation and may be related to increased levels of FUT2 and Globo H. Furthermore, using microRNA profiling, we observed that microRNA-15b (miR-15b) was downregulated in patients with HCC and confirmed association of FUT2 expression with expression of its product, Globo H. Therefore, our results suggest that HBX suppressed the expression of miR-15b, which directly targeted FUT2 and then increased levels of Globo H to enhance HCC cell proliferation. Additionally, proliferation of HBX-overexpressing HCC cells was significantly inhibited by treatment with Globo H antibody in vitro. In xenograft animal experiments, we found that overexpression of miR-15b effectively suppressed tumor growth. The newly identified HBX/miR-15b/FUT2/Globo H axis suggests one possible molecular mechanism of HCC cell proliferation and represents a new potential therapeutic target for HCC treatment.

Terminalia catappa attenuates urokinase-type plasminogen activator expression through Erk pathways in Hepatocellular carcinoma.

BACKGROUND: The survival rate of malignant tumors, and especially hepatocellular carcinoma (HCC), has not improved primarily because of uncontrolled metastasis. In our previous studies, we have reported that Terminalia catappa leaf extract (TCE) exerts antimetastasis effects on HCC cells. However, the molecular mechanisms of urokinase-type plasminogen activator (u-PA) in HCC metastasis have not been thoroughly investigated, and remain poorly understood. METHODS: The activities and protein levels of u-PA were determined by casein zymography and western blotting. Transcriptional levels of u-PA were detected by real-time PCR and promoter assays. RESULTS: We found that treatment of Huh7 cells with TCE significantly reduced the activities, protein levels and mRNA levels of u-PA. A chromatin immunoprecipitation (ChIP) assay showed that TCE inhibited the transcription protein of nuclear factors SP-1 and NF-κB. TCE also did inhibit the effects of u-PA by reducing the phosphorylation of ERK1/2 pathway. CONCLUSIONS: These results show that u-PA expression may be a potent therapeutic target in the TCE-mediated suppression of HCC metastasis.

Analysis of ZNF208 Polymorphisms on the Clinicopathologic Characteristics of Asian Patients with Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC), a major form of liver cancer, is characterized by high lethality and a multifactorial etiology that includes hepatitis virus infections, lifestyle factors, and genetic predispositions. This study aimed to explore the impact of ZNF208 gene polymorphisms on the clinicopathological features of Taiwanese HCC patients, focusing on three specific single nucleotide polymorphisms (SNPs): rs2188971, rs2188972, and rs8105767. Our cohort consisted of 438 HCC patients and 1193 control individuals. Clinical staging was determined using the tumor/node/metastasis (TNM) system, and various clinical indicators were collected. Our analysis revealed a statistically significant increase in ZNF208 expression in HCC patients compared to controls, indicating a potential role in HCC progression. Although no substantial association was observed between ZNF208 SNPs and increased HCC risk, specific clinical features such as distant metastasis and vascular invasion showed significant associations with these SNPs, suggesting their influence on disease aggressiveness. Demographic analyses highlighted the importance of factors like alcohol consumption and viral hepatitis markers in HCC. Our study underscores the complexity of genetic influences on HCC, with ZNF208 polymorphisms potentially affecting tumor progression and patient outcomes.

Lapatinib-mediated cyclooxygenase-2 expression via epidermal growth factor receptor/HuR interaction enhances the aggressiveness of triple-negative breast cancer cells.

Lapatinib, a dual epidermal growth factor receptor (EGFR)/human epidermal growth factor receptor 2 (HER2) kinase inhibitor, showed clinical benefits in advanced HER2-positive breast cancer patients. Because some triple-negative breast cancers (TNBCs) frequently overexpress EGFR, the antitumor activity of lapatinib in such diseases was also tested. However, the results showed a worse event-free survival rate. It remains unknown whether and how lapatinib elicits the aggressiveness of such cancer cells. In this study, our results demonstrated that lapatinib facilitated axillary and lung metastases of triple-negative MDA-MB-231 breast cancer cells without affecting their viability, leading to worse survival in orthotopic xenograft mice. The lapatinib-increased motility was attributed by the elevation of EGFR through the downregulation of microRNA-7 and by the subsequent overexpression of cyclooxygenase-2 (COX-2). Strikingly, independent of its kinase activity, the elevated EGFR at least partly stabilized COX-2 expression by enhancing the binding of HuR to COX-2 mRNA. Our results suggest that lapatinib may increase the migration and invasion of MDA-MB-231 cells by upregulating EGFR and COX-2 through the downregulation of microRNA-7, providing a potential explanation for the worse clinical outcome of TNBC patients who receive lapatinib-based treatment. These findings also shed new light on the molecular mechanism of COX-2 mRNA stabilization by EGFR in a kinase-independent manner.

Nuclear EGFR suppresses ribonuclease activity of polynucleotide phosphorylase through DNAPK-mediated phosphorylation at serine 776.

Nuclear existence of epidermal growth factor receptor (EGFR) has been documented for more than two decades. Resistance of cancer to radiotherapy is frequently correlated with elevated EGFR expression, activity, and nuclear translocation. However, the role of nuclear EGFR (nEGFR) in radioresistance of cancers remains elusive. In the current study, we identified a novel nEGFR-associated protein, polynucleotide phosphorylase (PNPase), which possesses 3' to 5' exoribonuclease activity toward c-MYC mRNA. Knockdown of PNPase increased radioresistance. Inactivation or knock-down of EGFR enhanced PNPase-mediated c-MYC mRNA degradation in breast cancer cells, and also increased its radiosensitivity. Interestingly, the association of nEGFR with PNPase and DNA-dependent protein kinase (DNAPK) increased significantly in breast cancer cells after exposure to ionizing radiation (IR). We also demonstrated that DNAPK phosphorylates PNPase at Ser-776, which is critical for its ribonuclease activity. The phospho-mimetic S776D mutant of PNPase impaired its ribonuclease activity whereas the nonphosphorylatable S776A mutant effectively degraded c-MYC mRNA. Here, we uncovered a novel role of nEGFR in radioresistance, and that is, upon ionizing radiation, nEGFR inactivates the ribonuclease activity of PNPase toward c-MYC mRNA through DNAPK-mediated Ser-776 phosphorylation, leading to increase of c-MYC mRNA, which contributes to radioresistance of cancer cells.