The Antioxidative Mechanism Of PGRN-Promoted Survival Of Cervical Cancer Cells Under Serum Deprivation

Cervical cancer is one of the most common malignant tumors in female reproductive system. Statistics show that cervical cancer is the fourth-most common cause of death from cancer in women, and it is the second reason induced women death behind breast cancer. In 2012, an estimated 528,000 cases of cervical cancer occurred, with 266,000 deaths, lead a mortality of 50.3%. About 85% of cervical cancers occur in developing countries.High-risk Human papillomavirus(HPV) infection is the primary etiology of cervical cancer. Not all of the individuals who have had HPV infections would develop to cervical cancer. It is hinted that other risk factors involved as well in the progress of cervical cancer.The main characteristics of cancer cells include 1) sensitivity to growth signals 2) tolerance to growth-inhibitory signals 3) evasion of programmed cell death or apoptosis 4) the ability of limitless replication 5) sustained angiogenesis and tissue invasion and metastasis.When cancer cells appeared in human body, they may suffer from disadvantageous microenvironment such as hypoxia, hypoglycemia, lack of cell-cell/cell-ECM contact, serum deprivation and lack of growth factor. Only if they adapt themselves to this microenvironment stress can they acquire the ability of anti-apoptosis proliferation, maintainance of the angiogenesis and biochemical characteristics of invasion and metastasis.The regulation of redox homeostasis is fundamental to maintaining normal cellular functions and ensuring cell survival. There are many factors that can induce Reactive oxygen species (ROS) including metabolic defects, ER stress, hypoxia and activation of oncogenes. Growth factor-actived PI3K/Akt signaling pathway promotes glucose transport and glycolysis. Lack of growth factor results in reduction of PI3K/Akt signaling, the intake of glucose and abnormality of glucose metabolism, which in turn gives rise to the production of ROS.The excess ROS may cause lipid oxidation, protein oxidation and DNA damage.The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) is arguably the most important regulator of antioxidant functions in the cell. Under resting conditions, Nrf2 is constitutively degraded by the Kelch-like ECH-associated protein 1(Keap1)-Cullin3 (CUL3) E3 ligase complex. When oxidative stress occurs, Keapl is oxidized and dissociated from Nrf2, thereby leading to the stabilization of Nrf2 and its translocation to nucleus. In nucleus it combines ARE area of Phase II detoxification enzyme gene with various anti-oxidation proteins, which drives the expression of related genes and executes the ability of anti-oxidation.Progranulin (PGRN) is an autocrine growth factor. It is composed of 7.5 tandem repeats of a 12 cysteine motif. PGRN plays an important role in various physiologic and pathology procedure including early embryogenesis, tissue repair, inflammation, host defense and tumorigenesis. Our previous study demonstrates that PGRN is overexpressed in cervical cancer cells and tissues. It contributes to cervical cancer cell proliferation and transformation through PI3K/Akt and Erk signaling pathway. It is a well-known survival factor for normal and cancer cells for its preventing ECM attachment induced anoikis in cancer cells, inhibiting hypoxia and acidosis-induced apoptosis in fibroblast and promoting neuronal cell survival in condition of serum deprivation. So far, the mechanism of PGRN in cancer cell survival with microenvironment stress is still ambiguous.PGRN plays an important role in the mechanism of carcinogenesis in cervical cancer. In this study we used serum deprivation to simulate oxidative stress in cervical cancer cells. We analyzed the function of PGRN in cervical cancer cells with microenvironment stress and further explored the mechanism of PGRN-promoted survival of cervical cancer cells under serum deprivation. The main findings of this study include(1)PGRN is a serum response protein because serum deprivation fastly decreased the intracellular protein level of PGRN in cervical cancer cells.(2)PGRN protected cervical cancer cells against serum deprivation-induced cell death and apoptosis, which suggests the contribution of PGRN in the adaption of cervical cancer cells to microenvironmental stress. (3)PGRN decreased the ROS levels and attenuated protein and lipid oxidation, DNA damage and mitochondrial dysfunction in cervical cancer cells with serum deprivation, which demonstrates the antioxidative function of PGRN in cancer cells with physiological stress. (4)PGRN exerted its antioxidative function through enhancing the levels of ROS scavengers in cervical cancer cells with serum deprivation. (5)PGRN enhanced the expression of antioxidation transcriptional factor Nrf2 by inducing disassociation of Nrf2 from Keapl and promoting the translocation of Nrf2 to nucleus. These subsequently elevated the transcriptional activity of Nrf2. (6)The promotion of cell survival and antioxidation roles of PGRN depended on Nrf2/ARE signaling pathway in cervical cancer cells with serum deprivation.This study firstly reveals the sharply reduction of PGRN in cervical cancer cells with serum deprivation; data in this study shows that PGRN protects cervical cancer cells from serum deprivation-induced cell death via enhancing the levels of ROS scavengers system. These study demonstrates that PGRN not only promotes cell proliferation and migration, but also facilitates cancer cells to adapt to the environment stress. This study reveals the mechanism of PGRN in mediating the malignant progress. Based on these results, PGRN would be a potential target in finding new treatment strategies for not only cervical cancer, but also for those cancers involved PGRN and Nrf2/ARE signaling pathway. At the same time, this study highlights on antioxidant mechanism for PGRN in inflammatory response, neurodegenerative diseases and other physiological and pathological process.