HIF-1α Accumulation In Cells Research Articles

Abstract 2435: ST6Gal-I sialylation potentiates hypoxia adaptation by enhancing HIF-1a signaling

Abstract Aberrant surface glycosylation is a well-known hallmark of a tumor cell, however the functional role of glycans in cancer cell biology remains unclear. Tumor cells frequently display an increase in surface α2-6 sialylation, a modification added to N-glycosylated proteins by the ST6Gal-I sialyltransferase. ST6Gal-I sialylates a select cohort of surface receptors, which correspondingly modulates receptor-induced intracellular signaling cascades. Emerging evidence suggests that ST6Gal-I-mediated sialylation promotes the survival of tumor cells exposed to a variety of cell stressors. In the current study we identify a new function for ST6Gal-I in protecting against hypoxic stress. In response to low oxygen tension, the hypoxia inducible factor, HIF-1α, becomes stabilized in tumor cells. In turn, HIF-1α stimulates the transcription of genes important for cell survival. To interrogate a role for ST6Gal-I in hypoxic response, we evaluated HIF-1α accumulation in ovarian and pancreatic cancer cells with ST6Gal-I overexpression or knockdown. We find that ST6Gal-I activity augments HIF-1α accumulation in cells treated with chemical hypoxia mimetics (DFO and DMOG), or alternatively grown in a hypoxic environment. Furthermore, hypoxic cells with high ST6Gal-I expression have increased mRNA levels of HIF-1α transcriptional targets including the glucose transporters, GLUT1 GLUT3, and the glycolytic enzyme, PDHK1. Interestingly, cells with high ST6Gal-I expression also have an increased pool of HIF-1α mRNA, suggesting that ST6Gal-I may influence the biosynthesis of HIF-1α. Finally, cells grown in hypoxia for several weeks display an enrichment in ST6Gal-I expression, consistent with the concept that ST6Gal-I acts as a pro-survival factor. Taken together, these findings highlight a novel, glycosylation-dependent mechanism that facilitates tumor cell adaptation to a hypoxic milieu. Citation Format: Robert B. Jones, Kaitlyn A. Dorsett, Anita B. Hjelmeland, Susan L. Bellis. ST6Gal-I sialylation potentiates hypoxia adaptation by enhancing HIF-1a signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2435.

The ST6Gal-I sialyltransferase protects tumor cells against hypoxia by enhancing HIF-1α signaling

Aberrant cell surface glycosylation is prevalent in tumor cells, and there is ample evidence that glycans have functional roles in carcinogenesis. Nonetheless, many molecular details remain unclear. Tumor cells frequently exhibit increased α2-6 sialylation on N-glycans, a modification that is added by the ST6Gal-I sialyltransferase, and emerging evidence suggests that ST6Gal-I-mediated sialylation promotes the survival of tumor cells exposed to various cell stressors. Here we report that ST6Gal-I protects cancer cells from hypoxic stress. It is well known that hypoxia-inducible factor 1α (HIF-1α) is stabilized in hypoxic cells, and, in turn, HIF-1α directs the transcription of genes important for cell survival. To investigate a putative role for ST6Gal-I in the hypoxic response, we examined HIF-1α accumulation in ovarian and pancreatic cancer cells in ST6Gal-I overexpression or knockdown experiments. We found that ST6Gal-I activity augmented HIF-1α accumulation in cells grown in a hypoxic environment or treated with two chemical hypoxia mimetics, deferoxamine and dimethyloxalylglycine. Correspondingly, hypoxic cells with high ST6Gal-I expression had increased mRNA levels of HIF-1α transcriptional targets, including the glucose transporter genes GLUT1 and GLUT3 and the glycolytic enzyme gene PDHK1 Interestingly, high ST6Gal-I-expressing cells also had an increased pool of HIF-1α mRNA, suggesting that ST6Gal-I may influence HIF-1α expression. Finally, cells grown in hypoxia for several weeks displayed enriched ST6Gal-I expression, consistent with a pro-survival function. Taken together, these findings unravel a glycosylation-dependent mechanism that facilitates tumor cell adaptation to a hypoxic milieu.

Abstract 1529: Scutellaria baicalensis targets the hypoxia-inducible factor-1α and attenuates ovarian cancer growth

Abstract Hypoxia-inducible factor-1alpha (HIF-1α), a transcription factor important for maintaining cellular oxygen homeostasis, is aberrantly upregulated in many tumors and implicated in angiogenesis, metastasis and drug resistance. Therefore, developing treatments that target HIF-1α may be a viable therapeutic approach. For centuries, traditional Chinese medicine has used herbs, such as Scutellaria baicalensis (SB), as a natural remedy for tumors. However, the mechanisms by which SB inhibits tumor growth are not known. We have previously reported that SB inhibits cancer cell proliferation and targets NF-κB in endometrial and ovarian cancers and TGF-β in endometrial cancers. In this study, we examined the effects of SB on HIF-1α protein levels in three ovarian cancer cell lines, SKOV3, OVCA 429, and OVCA 420, grown under normoxic and hypoxic conditions. When treated daily with SB, cancer cells showed a decrease in HIF-1α expression after 48 hours. Investigation into the molecular mechanisms of SB-induced inhibition revealed a significant reduction of HIF-1α accumulation in cells treated with cycloheximide, a protein synthesis inhibitor. Further decrease of HIF-1α accumulation was seen when cycloheximide was combined with SB. Additionally, SB- induced HIF-1α proteasomal degradation was prevented by treatment of cells with proteasomal inhibitor MG132 and chloroquine, lysosome inhibitor, abrogated SB-induced inhibition of HIF-1α. Activation of PI3K/AKT and MAPK/ERK is shown in cancers. SB reduced levels of phospho-AKT and phospho-extracellular signal-related kinase (ERK) in ovarian cancer cells. Furthermore, pretreatment of cells with LY294002 (phosphoinositide 3-kinase inhibitor) and PD98059 (mitogen-activated protein kinase kinase inhibitor) reduced HIF-1α expression comparable to SB-treated cells. Hypoxia-induced cisplatin resistance is a major challenge in therapy of ovarian tumors. SB reduces the proliferation and reverses cisplatin resistance in ovarian cancer cells by attenuating the expression of HIF-1α. Taken together, the findings suggest that targeting HIF-1α with SB could be an effective treatment strategy for ovarian cancer and that SB can improve the sensitivity of cells to cisplatin. Note: This abstract was not presented at the meeting. Citation Format: Imran Hussain, Sana Waheed, Kashif A. Ahmad, John E. Pirog, Viqar Syed. Scutellaria baicalensis targets the hypoxia-inducible factor-1α and attenuates ovarian cancer growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1529. doi:10.1158/1538-7445.AM2017-1529

Selenium protects the hypoxia induced apoptosis in neuroblastoma cells through upregulation of Bcl-2

Selenium (Se) is an essential micronutrient as well as a toxic trace element in animal and human nutrition. The effects of Se in the immune system and some diseases are well documented. The objective of the present study was to examine the role of Se in reducing the hypoxia induced apoptosis in neuroblastoma cell line. Hypoxia showed an enhanced cytotoxicity, increased free radical production and apoptosis ( p < 0.001) which was measured in terms of DNA break down by comet assay. Hypoxia has decreased reduced Glutathione (GSH) content, Glutathione Reductase (GR), Glutathione peroxidase (GPx) and Superoxide Dismutase (SOD) activities as compared to control cells. During hypoxic condition the expression of cytochrome C, pro and active caspase-3 levels were enhanced significantly followed by nonsignificant upregulation of Bcl-2. But, the Se supplementation inhibited the cytotoxicity, free radical generation and stabilized the HIF-1α accumulation in cells under hypoxia. The GSH content, GR, GPx and SOD activities increased significantly in Se-treated hypoxic cells, as compared to control. Further there was an appreciable inhibition of apoptosis by upregulation of Bcl-2 proteins, in the presence of Se under hypoxia. Selenium supplementation to cells significantly inhibited the hypoxia induced DNA fragmentation and restored the antioxidant status back to control levels. This study suggests that Se supplementation prevented the cells from hypoxia induced apoptosis by triggering upregulation of Bcl-2 protein and reducing the oxidative stress.