Multimodal regulation of SOD2 during ovarian cancer transcoelomic metastasis
Open Access
- Author:
- Kim, Yeon Soo
- Graduate Program:
- Biomedical Sciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 21, 2021
- Committee Members:
- Nadine Hempel, Dissertation Advisor/Co-Advisor
Nadine Hempel, Committee Chair/Co-Chair
Katherine M Aird, Committee Member
Shengyu Yang, Committee Member
James Robert Connor, Outside Member
Jong Kak Yun, Committee Member
Ralph Lauren Keil, Program Head/Chair - Keywords:
- ovarian cancer
transcoelomic metastasis
anchorage-independence
matrix detachment
oxidative stress
stress response
post-translational regulation
post-transcriptional regulation
SOD2
SIRT3
HuR - Abstract:
- Despite recent advancements targeting cancer-specific signatures associated with aggressive phenotypes and chemoresistance, the 5-year survival rate of ovarian cancer patients has remained relatively low. Epithelial ovarian cancer (EOC) is a deadly gynecological malignancy accounting for 90% of ovarian cancer cases, of which 75% are diagnosed at stages III and IV primarily due to the asymptomatic progression of the disease. Most advanced stage patients present widespread metastasis throughout the peritoneal cavity and ascites accumulation. Ascites provides a unique environment in which cancer cells, passively disseminated from the primary tumor, undergo metastatic colonization of the peritoneal cavity known as transcoelomic metastasis. Matrix detachment-induced oxidative stress is a huge hurdle that cancer cells must overcome for anoikis resistance. Accumulating evidence suggests that antioxidant capacity determines the metastatic potential of cancer cells in vivo, and thus achieving redox homeostasis is a key adaptation process during metastasis. The aim of this dissertation was to investigate how cancer cells restore redox balance after oxidative insults caused by matrix detachment and promote survival in anchorage-independence. Superoxide dismutase 2 (SOD2, also known as manganese superoxide dismutase [MnSOD]) is one of many antioxidant enzymes essential for protecting cells from reactive oxygen species (ROS) generated in the mitochondrial matrix, where partial reduction of oxygen (O2) into superoxide anion (O2•−) occurs during electron transfer for ATP synthesis. Unless scavenged by SOD2, O2•− can elicit deleterious consequences, including mitochondrial dysfunction and excess generation of highly reactive oxidants. SOD2 acts as a tumor suppressor in early tumorigenesis but enhances tumor progression in later stages, illustrating its context-dependent role in cancer. I demonstrate that ovarian cancer cells require SOD2 for anchorage-independent survival and metastasis. Hence, both activity and expression of SOD2 are upregulated during early anchorage-independence through two key regulatory mechanisms: post-translational and post-transcriptional levels. In anchorage-independent conditions, dual regulation of SOD2 occurs simultaneously in different cellular compartments. In the mitochondria, the existing pool of SOD2 protein is rapidly activated by SIRT3-mediated deacetylation at Lys68 following matrix detachment. SIRT3 silencing results in elevated levels of acetyl-Lys68 and decreased SOD2 dismutase activity, even though SOD2 protein expression is increased in anchorage-independence. This suggests that SOD2 must be deacetylated by SIRT3 for its functional activity. The SIRT3-SOD2 axis enhances the ability of mitochondrial oxidant scavenging, promotes cell survival in anchorage-independence. Not only is mitochondrial SOD2 protein activated, but increased translation of SOD2 mRNA also occurs shortly after placing ovarian cancer cells in anchorage-independence. Matrix detachment stimulates the stress-activated protein kinase p38 MAPK, leading to increased association of SOD2 mRNA with RNA binding protein HuR in the cytosol. HuR-bound SOD2 mRNA displays an increased translational efficiency in anchorage-independent conditions as measured by polysome profiling. The shift of SOD2 mRNA from light to heavy polysomal fractions is abrogated in HuR silencing, indicating that HuR enhances the translation efficiency of SOD2 mRNA in anchorage-independence. This rapid upregulation of SOD2 protein synthesis is thought to be part of stress adaptation pathways employed by anchorage-independent ovarian cancer cells to increase mitochondrial antioxidant capacity by making an additional SOD2 protein pool in the cytosol. In summary, this dissertation provides insights into multimodal regulation of SOD2 during metastasis, and further identifies a previously unexplored regulatory mechanism of SOD2 at the post-transcriptional level.