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Creators: School of Life Sciences

Differential Activation of Unfolded Protein Response in Two Osteosarcoma Cell Lines Following Hypoxic and Chemotherapeutic Stress

Description

Osteosarcoma (OS) is the most prevalent primary tumor of bone in the pediatric age group [1]. The long-term cancer free survival has improved in patients with localized cancer; however, less than 20% of patients diagnosed with metastatic disease survive without relapse [2]. While these findings emphasize the urgent need for new therapeutic agents, the lack of understanding of the factors and the tumor microenvironment that lead to therapy resistance in OS has significantly hampered progress towards improved prognosis. Recent clinical reports have shown a negative correlation between tumor hypoxia and overall survival in OS patients [4]. In addition to the up-regulation of hypoxia inducible factors (HIFs), it has been shown that hypoxia can trigger an adaptive response such as the unfolded protein response (UPR) that allows tumor cells to avoid therapy-induced death [3,4,7,10].
Using in vitro experimental models of both SAOS-2 (non-metastatic) and 143-b (metastatic) osteosarcoma cell lines and Western blot analysis, we have demonstrated that basal levels of molecular chaperone BiP (Binding immunoglobulin protein, or GRP-78) and peIF2α (phospho-eukaryotic initiation factor 2 alpha), both markers of the UPR, were higher in SAOS-2 than 143-b cells. We also show that both these markers were further up-regulated upon exposure to hypoxia, as evidenced by the increase in banding intensity in both SAOS-2 and 143-b cells. Furthermore, analysis of another UPR marker, ATF6 (activating transcription factor 6) showed that basal levels of active nuclear ATF6 were slightly higher in SAOS-2 cells than in 143-b cells. However, unlike the other UPR markers these levels were significantly reduced upon exposure to hypoxia (0.1% O2). In addition to hypoxia, treatment with Cisplatin also had similar effects on the expression of aforementioned UPR markers: BiP and peIF2α. We found that the 143-b OS cells were more sensitive to the Cisplatin treatment than the SAOS-2 OS cells, and thus more prone to cell-mediated death.
Our findings shed light on the unknown mechanisms underlying chemotherapeutic drug resistance in osteosarcoma patients. Our research may lead to novel therapies that seek out and destroy the chemoresistant OS cells within the hypoxia core of tumors, thereby preventing survival and metastasis, and ultimately improving the chances of survival amongst OS patients.

ContributorsFaraj, Janine Jean (Author) / Chandler, Douglas (Thesis director) / Sertil, Aparna (Committee member) / Sweazea, Karen (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor) / School of Historical, Philosophical and Religious Studies (Contributor)

Created2014-05

Flight performance and thermal tolerance of flies acclimated to hypoxia or hyperoxia

Description

Animals are thought to die at high temperatures because proteins and cell membranes lose their structural integrity. Alternatively, a newer hypothesis (the oxygen and capacity limitation of thermal tolerance, or OCLTT) states that death occurs because oxygen supply becomes limited at high temperatures. Consequently, animals exposed to hypoxia are more sensitive to heating than those exposed to normoxia or hyperoxia. We hypothesized that animals raised in hypoxia would acclimate to the low oxygen supply, thereby making them less sensitive to heating. Such acclimation would be expressed as greater heat tolerance and better flight performance in individuals raised at lower oxygen concentrations. We raised flies (Drosophila melanogaster) from eggs to adults under oxygen concentrations ranging from 10% to 31% and measured two aspects of thermal tolerance: 1) the time required for flies to lose motor function at 39.5°C at normoxia (21%), referred to as knock-down time, and 2) flight performance at 37°, 39°, or 41°C and 12%, 21%, or 31% oxygen. Contrary to our prediction, flies from all treatments had the same knock-down time. However, flight performance at hypoxia was greatest for flies raised in hypoxia, but flight performance at normoxia and hyperoxia was greatest for flies raised at hyperoxia. Thus, flight performance acclimated to oxygen supply during development, but heat tolerance did not. Our data does not support the OCLTT hypothesis, but instead supports the beneficial acclimation hypothesis, which proposes that acclimation improves the function of an organism during environmental change.

ContributorsShiehzadegan, Shayan (Co-author) / VadenBrooks, John (Co-author) / Le, Jackie (Co-author) / Smith, Colton (Co-author) / Shiehzadegan, Shima (Co-author) / Angilletta, Michael (Co-author, Thesis director) / VandenBrooks, John (Committee member) / Klok, C. J. (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)

Created2016-05

High-Altitude Metabolic Enzyme Activity in Gelada Monkeys

Description

Our cells need constant fuel and oxygen for the body to work properly and maintain cellular function. In high altitudes tissue oxygen levels fall and the body must work against this hypoxic challenge to maintain energetics and limit oxidative stress. Mammals living at high altitudes are challenged to sustain thermogenesis and aerobic exercise despite reduced amounts of available oxygen. Enhancements in oxidative capacity and oxygen diffusion capacity of skeletal muscle may be necessary to compensate for insufficient oxygen supply in tissues. Hypoxic conditions can cause a switch from aerobic metabolism to anaerobic metabolism. Due to previous research of Graham Scott and colleagues on “Adaptive Modifications of Muscle Phenotype in High-Altitude Deer Mice” and the SMack Lab at Arizona State University, the question of how low atmospheric oxygen levels affects the enzymatic activity in the gastrocnemius muscle of Gelada Monkeys compared to Rhesus Macaque Monkeys was researched. Lactate Dehydrogenase (LDH) activity was measured in the gastrocnemius tissue of 6 Gelada Monkeys (highland) and 6 Rhesus Macaque monkeys (lowland). LDH was expected to be greater in Gelada tissue samples due to heightened anaerobic metabolism in the presence of limited available oxygen in high altitude environments. Results showed higher LDH in Rhesus Macaque samples compared to Gelada samples, but this difference was not statistically significant. Despite nonsignificant data, this experiment is insightful into the effects of Hypoxic adaptation in skeletal muscle enzymatic activity in primates.

ContributorsSalehi, Yasmine (Author) / Snyder-Mackler, Noah (Thesis director) / Trumble, Ben (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor) / School of Human Evolution & Social Change (Contributor)

Created2023-05