Yuqi Guo

Metformin induces ER stress-dependent apoptosis through miR-708-5p/NNAT pathway in prostate cancer

Although the antitumor role of metformin has been widely reported, the molecular mechanism of this biguanide agent in the inhibition of tumor progression remains unclear. Here, we identified miR-708-5p as a novel target of metformin in prostate cancer cells. Metformin promotes increased expression of miR-708-5p, leading to suppression of endoplasmic reticulum (ER) membrane protein neuronatin (NNAT) expression and subsequently induces apoptosis of prostate cancer cells through the ER stress pathway. Further, miR-708-5p-induced knockdown of NNAT is associated with downregulated intracellular calcium levels and induced malformation of ER-ribosome structure revealed by electronic microscopy. Meanwhile, the unfolded protein response regulator CHOP, p-eIF2α, calreticulin, GRP78 and ATP2A1, all of which are also considered as ER stress markers, are upregulated by metformin and miR-708-5p. Taken together, our findings clearly demonstrate that metformin stimulates increased expression of miR-708-5p to target the NNAT-mediated response to ER stress and apoptosis. This novel regulatory mechanism of metformin in prostate cancer cells not only advances our knowledge on the molecular mechanism of metformin but also provides a promising therapeutic strategy by targeting miR-708-5p and NNAT for prostate cancer treatment.

The Pancreatic Cancer Microbiome Promotes Oncogenesis by Induction of Innate and Adaptive Immune Suppression

We found that the cancerous pancreas harbors a markedly more abundant microbiome compared with normal pancreas in both mice and humans, and select bacteria are differentially increased in the tumorous pancreas compared with gut. Ablation of the microbiome protects against preinvasive and invasive pancreatic ductal adenocarcinoma (PDA), whereas transfer of bacteria from PDA-bearing hosts, but not controls, reverses tumor protection. Bacterial ablation was associated with immunogenic reprogramming of the PDA tumor microenvironment, including a reduction in myeloid-derived suppressor cells and an increase in M1 macrophage differentiation, promoting TH1 differentiation of CD4+ T cells and CD8+ T-cell activation. Bacterial ablation also enabled efficacy for checkpoint-targeted immunotherapy by upregulating PD-1 expression. Mechanistically, the PDA microbiome generated a tolerogenic immune program by differentially activating select Toll-like receptors in monocytic cells. These data suggest that endogenous microbiota promote the crippling immune-suppression characteristic of PDA and that the microbiome has potential as a therapeutic target in the modulation of disease progression.Significance: We found that a distinct and abundant microbiome drives suppressive monocytic cellular differentiation in pancreatic cancer via selective Toll-like receptor ligation leading to T-cell anergy. Targeting the microbiome protects against oncogenesis, reverses intratumoral immune tolerance, and enables efficacy for checkpoint-based immunotherapy. These data have implications for understanding immune suppression in pancreatic cancer and its reversal in the clinic. Cancer Discov; 8(4); 403-16. ©2018 AACR.See related commentary by Riquelme et al., p. 386This article is highlighted in the In This Issue feature, p. 371.

Metformin Improves Diabetic Bone Health by Re-Balancing Catabolism and Nitrogen Disposal.

Objective Metformin, a leading drug used to treat diabetic patients, is reported to benefit bone homeostasis under hyperglycemia in animal models. However, both the molecular targets and the biological pathways affected by metformin in bone are not well identified or characterized. The objective of this study is to investigate the bioengergeric pathways affected by metformin in bone marrow cells of mice. Materials and Methods Metabolite levels were examined in bone marrow samples extracted from metformin or PBS -treated healthy (Wild type) and hyperglycemic (diabetic) mice using liquid chromatography-mass spectrometry (LC-MS)-based metabolomics. We applied an untargeted high performance LC-MS approach which combined multimode chromatography (ion exchange, reversed phase and hydrophilic interaction (HILIC)) and Orbitrap-based ultra-high accuracy mass spectrometry to achieve a wide coverage. A multivariate clustering was applied to reveal the global trends and major metabolite players. Results A total of 346 unique metabolites were identified, and they are grouped into distinctive clusters that reflected general and diabetes-specific responses to metformin. As evidenced by changes in the TCA and urea cycles, increased catabolism and nitrogen waste that are commonly associated with diabetes were rebalanced upon treatment with metformin. In particular, we found glutamate and succinate whose levels were drastically elevated in diabetic animals were brought back to normal levels by metformin. These two metabolites were further validated as the major targets of metformin in bone marrow stromal cells. Conclusion Overall using limited sample size, our study revealed the metabolic pathways modulated by metformin in bones which have broad implication in our understanding of bone remodeling under hyperglycemia and in finding therapeutic interventions in mammals.

Succinate and its G-protein-coupled receptor stimulates osteoclastogenesis

The mechanism underlying bone impairment in patients with diabetes mellitus, a metabolic disorder characterized by chronic hyperglycaemia and dysregulation in metabolism, is unclear. Here we show the difference in the metabolomics of bone marrow stromal cells (BMSCs) derived from hyperglycaemic (type 2 diabetes mellitus, T2D) and normoglycaemic mice. One hundred and forty-two metabolites are substantially regulated in BMSCs from T2D mice, with the tricarboxylic acid (TCA) cycle being one of the primary metabolic pathways impaired by hyperglycaemia. Importantly, succinate, an intermediate metabolite in the TCA cycle, is increased by 24-fold in BMSCs from T2D mice. Succinate functions as an extracellular ligand through binding to its specific receptor on osteoclastic lineage cells and stimulates osteoclastogenesis in vitro and in vivo. Strategies targeting the receptor activation inhibit osteoclastogenesis. This study reveals a metabolite-mediated mechanism of osteoclastogenesis modulation that contributes to bone dysregulation in metabolic disorders.

Metformin inhibits SUV39H1-mediated migration of prostate cancer cells

Prostate cancer (PCa) is a leading cause of cancer-related death among men, largely due to incurable distant metastases. Metformin, the most common used anti-type-2 diabetes medicine, has been linked to reduced cancer risk and better diagnosis. We found that metformin was able to inhibit PCa cell migration, which correlates with tumor metastatic capability. The pathogenesis and progression of tumors are closely related to dysregulated gene expression in tumor cells through epigenetic alterations such as DNA methylation and histone modifications. We found that the level of SUV39H1, a histone methyltransferase of H3 Lys9, was reduced in metformin-treated PCa cells in a time-dependent manner. SUV39H1 overexpression increased PCa migration, whereas SUV39H1 depletion suppressed PCa cell migration. There is a positive correlation between SUV39H1 expression and PCa pathological stages. We further showed that both metformin treatment and SUV39H1 knockout in PCa cells can reduce integrin αV and β1 proteins, as well as their downstream phosphorylated focal adhesion kinase (FAK) levels, which is essential for functional adhesion signaling and tumor cell migration. Taken together, metformin reduced SUV39H1 to inhibit migration of PCa cells via disturbing the integrin-FAK signaling. Our study suggests SUV39H1 as a novel target to inhibit PCa cell migration.

Inhibition of KPNA4 attenuates prostate cancer metastasis

Prostate cancer (PCa) is a common cancer in men. Although current treatments effectively palliate symptoms and prolong life, the metastatic PCa remains incurable. It is important to find biomarkers and targets to improve metastatic PCa diagnosis and treatment. Here we report a novel correlation between karyopherin α4 (KPNA4) and PCa pathological stages. KPNA4 mediates the cytoplasm-to-nucleus translocation of transcription factors, including nuclear factor kappa B, although its role in PCa was largely unknown. We find that knockdown of KPNA4 reduces cell migration in multiple PCa cell lines, suggesting a role of KPNA4 in PCa progression. Indeed, stable knockdown of KPNA4 significantly reduces PCa invasion and distant metastasis in mouse models. Functionally, KPNA4 alters tumor microenvironment in terms of macrophage polarization and osteoclastogenesis by modulating tumor necrosis factor (TNF)-α and -β. Further, KPNA4 is proved as a direct target of miR-708, a tumor-suppressive microRNA. We disclose the role of miR-708-KPNA4-TNF axes in PCa metastasis and KPNA4’s potential as a novel biomarker for PCa metastasis.

Abstract 3492: Metformin inhibits salivary gland tumor growth through cell cycle arrest and apoptosis

Human salivary gland cancer (SGC) is one of the common malignancies found in the head and neck area. The limitation of the treatment and poor prognosis are calling for more investigations into novel intervention to improve the treatment modality in SGCs. Metformin as a widely used anti-type-2 diabetes medicine had demonstrated its anti-tumor potential in many different types of cancers. Our previous work demonstrated that metformin effectively targeted c-Myc oncogene to prevent the initiation and progression of prostate cancer. Interestingly, the overexpression of c-Myc has also been shown in some SGCs, such as salivary gland adenoid cystic carcinoma. Therefore, it is intriguing to explore metformin9s anti-neoplastic efficacy of metformin in SGC. In this study, we used a human salivary adenocarcinoma cell line, HSY cell line as a model for salivary gland tumor. Our in vitro results show metformin prominently suppresses the growth of HSY cell through stimulation of cell cycle arrest and apoptosis. Meanwhile, metformin significantly down-regulates cMyc expression and rescues p53 tumor suppressor gene expression. Considering that mTOR inhibitors resistance could occur when tumors over-express cMYC. PP242, a novel and potent mTOR inhibitor was used in combination with metformin to inhibit HSY cell growth. As expected, metformin enhanced the inhibitory effects of PP242 associated with reduced c-MYC levels in vitro. Further in HSY xenograft tumors, massive necrotic areas were observed inside the tumors from metformin treated mice while only limited necrotic area in the core of tumors from PBS treated mice. Staining of proliferation marker Ki-67 confirmed lower proliferation rate in tumors from metformin treated group compare to that from the PBS group. In conclusion, our novel finding of metformin efficacy in SGC not only proves metformin plays a pivotal role in suppressing SGCs through cell cycle arrest and apoptosis, but also suggest that a combination treatment using metformin and mTOR inhibitors together may yield better inhibitory efficacy. Citation Format: Yuqi Guo. Metformin inhibits salivary gland tumor growth through cell cycle arrest and apoptosis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3492. doi:10.1158/1538-7445.AM2015-3492

Abstract 3814: Metformin induces ER stress-dependent apoptosis through miR-708-5p/NNAT pathway in prostate cancer

Previous studies showed that metformin is associated with lower risk of tumorigenesis for several cancer types including prostate cancer. However, the molecular basis of anti-tumor effect induced by this biguanide agent is still unclear. In this study, we identified miR-708-5p as a novel downstream effector of metformin in prostate cancer. By increasing the expression of miR-708-5p, metformin suppresses the expression of endoplasmic reticulum (ER) membrane protein neuronatin (NNAT) and subsequently induces apoptosis of prostate cancer cells through ER stress pathway. Notably, down-regulated NNAT is associated with down-regulated intracellular calcium level and induces malformation of endoplasmic reticulum-ribosome structure which is revealed by electronic microscopy. Furthermore, western blot shows that the unfolded-protein response (UPR) proteins including CHOP, p-eIF2α, Calreticulin, GRP78 and ATP2A1, all of which are also considered as the ER stress markers, were up-regulated by metformin and miR-708-5p. Importantly, an increased apoptosis of prostate cancer cells is also observed when miR-708-5p mimic or NNAT siRNA was introduced. In summary, our findings clearly reveals that metformin stimulates miR-708-5p to target on NNAT mediated response to ER stress and apoptosis. This novel regulatory mechanism of metformin in prostate cancer cells not only advances our knowledge on the molecular mechanism of metformin in cancer progression, but also provide a promising therapeutic target for prostate cancer treatment. Citation Format: Jian Yang, Juncheng Wei, Yushi Wu, Zhilin Wang, Yuqi Guo, Xin Li. Metformin induces ER stress-dependent apoptosis through miR-708-5p/NNAT pathway in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3814. doi:10.1158/1538-7445.AM2015-3814

Abstract 14: Nucleolin phosphorylation by CK2 is important for its role in regulating apoptosis

Nucleolar phosphoprotein nucleolin integrates critical cellular processes including gene expression, ribosome biogenesis, proliferation and the cellular response to stress. Elevated levels of nucleolin are found in a variety of tumors. Nucleolin has distinct mechanisms in p53 regulation to influence cell survival: In “normal unstressed” cells (with hyper-proliferative signals but no obvious DNA damage), nucleolin stabilizes p53 and induces apoptosis. Under DNA-damage however, nucleolin can cause translational repression. The translational repression is overcome upon DNA damage in part, possibly due to nucleolin translocation to the nucleoplasm, altered interactions with ribosomal protein, RPL26 and/or p53-antagonist, HDM2. In contrast, nucleolin binding to AU rich elements (AREs) of anti-apoptotic BCL2-mRNA stabilizes BCL2, leading to cell survival. Importantly, increased nucleolin phosphorylation by the interphase kinase CK2 is finely regulated in exponentially dividing cells; however, role of nucleolin phosphorylation remains largely unexplored in cell survival. We recently demonstrated that phosphorylation deficient nucleolin mutant confers dominant negative effect on cell proliferation. In this study, we dissect the role of nucleolin phosphorylation in regulating p53-signaling pathway. Our pathway specific qRT-PCR-array analyses indicate that expression of phosphorylation-deficient nucleolin mutant resulted in an increased gene expression in the apoptosis, DNA damage and repair pathways that are downstream to p53 activation. We further elucidate that targeting nucleolin phosphorylation by CK2 initiates an increased expression of BH3-only proteins: p53-transcriptional targets e.g. BID and PUMA. Interestingly, an increased expression of BIM, a p53-independent target that is required during DNA damage induced cell death is evident with NCL expression regardless of its phosphorylation status. This is the first step in understanding nucleolin-phosphorylation mediated regulation of gene expression in the p53-pathway to control cell proliferation. This information will be useful in identifying new targets that can be either directly (via RNA binding) or indirectly (through other proteins or gene expression) regulated by nucleolin phosphorylation. Citation Format: Esther Akinwunmi, Shu Xiao, Yuqi Guo, Xin Li, Anjana D. Saxena. Nucleolin phosphorylation by CK2 is important for its role in regulating apoptosis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 14. doi:10.1158/1538-7445.AM2015-14