O-linked GlcNAcylation elevated by HPV E6 mediates viral oncogenesis.

High-risk human papillomaviruses (HPVs) are causative agents of anogenital cancers and a fraction of head and neck cancers. The mechanisms involved in the progression of HPV neoplasias to cancers remain largely unknown. Here, we report that O-linked GlcNAcylation (O-GlcNAc) and O-GlcNAc transferase (OGT) were markedly increased in HPV-caused cervical neoplasms relative to normal cervix, whereas O-GlcNAcase (OGA) levels were not altered. Transduction of HPV16 oncogene E6 or E6/E7 into mouse embryonic fibroblasts (MEFs) up-regulated OGT mRNA and protein, elevated the level of O-GlcNAc, and promoted cell proliferation while reducing cellular senescence. Conversely, in HPV-18-transformed HeLa cervical carcinoma cells, inhibition of O-GlcNAc with a low concentration of a chemical inhibitor impaired the transformed phenotypes in vitro. We showed that E6 elevated c-MYC via increased protein stability attributable to O-GlcNAcylation on Thr58. Reduction of HPV-mediated cell viability by a high concentration of O-GlcNAc inhibitor was partially rescued by elevated c-MYC. Finally, knockdown of OGT or O-GlcNAc inhibition in HeLa cells or in TC-1 cells, a mouse cell line transformed by HPV16 E6/E7 and activated K-RAS, reduced c-MYC and suppressed tumorigenesis and metastasis. Thus, we have uncovered a mechanism for HPV oncoprotein-mediated transformation. These findings may eventually aid in the development of effective therapeutics for HPV-associated malignancies by targeting aberrant O-GlcNAc.

Over-expression of BAG-1 in head and neck squamous cell carcinomas (HNSCC) is associated with cisplatin-resistance.

BACKGROUND: In order to improve therapy for head and neck squamous cell carcinoma (HNSCC), biomarkers associated with local and/or distant tumor relapses and cancer drug resistance are urgently needed. This study identified a potential biomarker, Bcl-2 associated athanogene-1 (BAG-1), that is implicated in HNSCC insensitive to cisplatin and tumor progression. METHODS: Primary and advanced (relapsed from parental) University of Michigan squamous cell carcinoma cell lines were tested for sensitivity to cisplatin and gene expression profiles were compared between primary (cisplatin sensitive) and the relapsed (cisplatin resistant) cell lines by using Agilent microarrays. Additionally, differentially expressed genes phosphorylated AKT, and BAG-1, and BCL-xL were evaluated for expression using HNSCC tissue arrays. RESULTS: Advanced HNSCC cells revealed resistant to cisplatin accompanied by increased expression of BAG-1 protein. siRNA knockdown of BAG-1 expression resulted in significant improvement of HNSCC sensitivity to cisplatin. BAG-1 expression enhanced stability of BCL-xL and conferred cisplatin resistant to the HNSCC cells. In addition, high levels of expression of phosphorylated AKT, BAG-1, and BCL-xL were observed in advanced HNSCC compared to in that of primary HNSCC. CONCLUSION: Increased expression of BAG-1 was associated with cisplatin resistance and tumor progression in HNSCC patients and warrants further validation in larger independent studies. Over expression of BAG-1 may be a biomarker for cisplatin resistance in patients with primary or recurrent HNSCCs and targeting BAG-1 could be helpful in overcoming cisplatin resistance.

[Retracted] MicroRNA­491­5p suppresses cervical cancer cell growth by targeting hTERT.

Following the publication of this paper, an interested reader drew to the attention of the Office that the GAPDH control bands shown in Fig. 5 were strikingly similar to data appearing in different form in other articles by different authors. Owing to the fact that the contentious data in the above article had already been published elsewhere, or were already under consideration for publication, prior to its submission to Oncology Reports, the Editor has decided that this paper should be retracted from the Journal. The authors independently contacted the Editorial Office requesting that the paper be retracted. The Editor apologizes to the readership for any inconvenience caused. [the original article was published in Oncology Reports 34: 979­986, 2015; DOI: 10.3892/or.2015.4013].

LKB1 is a DNA damage response protein that regulates cellular sensitivity to PARP inhibitors.

Liver kinase B1 (LKB1) functions as a tumor suppressor encoded by STK11, a gene that mutated in Peutz-Jeghers syndrome and in sporadic cancers. Previous studies showed that LKB1 participates in IR- and ROS-induced DNA damage response (DDR). However, the impact of LKB1 mutations on targeted cancer therapy remains unknown. Herein, we demonstrated that LKB1 formed DNA damage-induced nuclear foci and co-localized with ataxia telangiectasia mutated kinase (ATM), γ-H2AX, and breast cancer susceptibility 1 (BRCA1). ATM mediated LKB1 phosphorylation at Thr 363 following the exposure of cells to ionizing radiation (IR). LKB1 interacted with BRCA1, a downstream effector in DDR that is recruited to sites of DNA damage and functions directly in homologous recombination (HR) DNA repair. LKB1 deficient cells exhibited delayed DNA repair due to insufficient HR. Notably, LKB1 deficiency sensitized cells to poly (ADP-ribose) polymerase (PARP) inhibitors. Thus, we have demonstrated a novel function of LKB1 in DNA damage response. Cancer cells lacking LKB1 are more susceptible to DNA damage-based therapy and, in particular, to drugs that further impair DNA repair, such as PARP inhibitors.

MicroRNA-491-5p suppresses cervical cancer cell growth by targeting hTERT.

MicroRNAs (miRNAs) are small non-coding RNAs that have been shown to regulate a variety of biological processes by targeting messenger RNA. MicroRNA-491-5p (miR-491-5p), an important miRNA, has been demonstrated to be involved in the processes of initiation and progression in several tumors. However, the precise biological function of miR-491-5p and its molecular mechanism in cervical cancer cells remain elusive. The present study was carried out to investigate the clinical significance and prognostic value of miR-491-5p expression in cervical cancer, and to evaluate the role of miR-491-5p and the underlying molecular mechanisms involved in cervical cancer. The results showed that miR-491-5p expression was significantly downregulated in cervical cancer tissues when compared with the corresponding adjacent normal tissues (P<0.001), and the value was negatively associated with advanced International Federation of Gynecology and Obstetrics (FIGO) stage, high histological grading and lymph node metastasis (P<0.01). The enforced expression of miR-491-5p in cervical cancer cells significantly inhibited proliferation, migration and invasion, induced cell apoptosis, and suppressed the tumor growth of the mouse model of HeLa cells. In addition, the dual-luciferase reporter assay revealed that human telomerase reverse transcriptase (hTERT) was identified as a novel target gene of miR-491-5p. Notably, it was found that miR-491-5p regulated the PI3K/AKT signaling pathway. These results suggested that targeting miR-491-5p is a strategy for blocking the development of cervical cancer.

Expression of human telomerase reverse transcriptase mediates the senescence of mesenchymal stem cells through the PI3K/AKT signaling pathway.

Multipotent mesenchymal stem cells (MSCs) are widely used as seed cells in studies of tissue engineering and regenerative medicine; however, their clinical application is limited due to replicative senescence. It has been demonstrated that telomerase expression extends the lifespan and maintains the bone-forming ability of MSCs; however, the detailed role and the underlying molecular mechanisms in MSCs remain largely unknown. In the present study, we found that senescence was associated with human telomerase reverse transcriptase (hTERT) expression, and telomere length and telomerase activity. We established a short interfering RNA (siRNA) targeting hTERT and a gene expression vector carrying hTERT and transfected these into the MSCs to investigate the detailed role and the underlying molecular mechanisms of action of hTERT in MSCs. We found that the downregulation of hTERT by siRNA markedly decreased telomere length and telomerase activity in the MSCs, whereas the overexpression of hTERT increased telomere length and telomerase activity in the MSCs. The downregulation of hTERT inhibited cell proliferation and promoted the senescence and apoptosis of MSCs, whereas the upregulation of hTERT increased cell proliferation and decreased the senescence and apoptosis of MSCs. Of note, we also found that the activation of the PI3K/AKT signaling pathway was mediated by hTERT and that blocking this pathway using LY294002 inhibited hTERT expression, induced senescence and decreased the proliferation of MSCs. These findings reveal a previously unknown regulatory mechanism of hTERT, indicating that hTERT mediates the senescence of MSCs through the PI3K/AKT signaling pathway.