The Role of Sp1-Regulated Neurosteroidogenesis in Glioma Development(2/2)

Background and objective: Steroidogenesis-mediated production of neurosteroids is important for brain homeostasis. The enzymes responsible for steroidogenesis are abundantly expressed in the brain, including in neurons and astrocytes. Neurosteroids not only protect neurons and astrocytes from oxidative stress but also maintain the survival of astrocytes. Nevertheless, whether neurosteroids cause aberrant hyperplasia of astrocytes, and even astrocyte-derived glioma, is totally unknown. Glioblastoma multiforme (GBM) is a Grade IV astrocytoma and is a highly aggressive brain tumor for which no effective treatment is available. Temozolomide (TMZ), the only chemotherapeutic drug for the treatment of GBM, does not benefit all patients, and GBM tumors always develop resistance to TMZ. Therefore, we attempt to investigate whether aberrant levels of neurosteroids possibly serve as a biomarker for glioma diagnosis. Additionally, we like to clarify whether neurosteroidogenic enzymes are overexpressed in glioma and identify its underlying mechanism. Specific aims: The purpose of this study is to clarify the importance of neurosteroidogenesis in glioma development. Five aims are designed to achieve our goal. Aim 1: To investigate whether neurosteroid and neurosteroidogenic enzymes are aberrantly upregulated in glioblastoma and their clinical relevance. Aim 2: To investigate the mechanisms underlying neurosteroids upregulation in glioblastoma and the involvement of the Sp1 transcription factor. Aim 3: To determine the effect of neurosteroids on glioblastoma. Aim 4: To determine whether neurosteroids affect TMZ-induced DNA damage and their underlying mechanism. Aim 5: To investigate the effect of the inhibitor targeting a neurosteroidogenic enzyme on GBM in vivo. Preliminary results: We initially found that secretions of three neurosteroids, including dehydroepiandrosterone (DHEA), allopregnanolone, and androstanediol, were significantly increased in glioma cells compared with those in normal astrocytes. DHEA was further increased in TMZ-resistant glioma. Overexpression of both Sp1 and cytochrome P450 (CYP) 17A1 overexpression in glioma contributed to DHEA upregulation. In particular, Sp1 increased DHEA through CYP17A1 expression. We found that Sp1 transcriptionally increased CYP17A1 expression by associating with the -300/+1 region of the promoter. Furthermore, DHEA promoted glioma proliferation and induced TMZ resistance by enhancing DNA repair activity. Novelty and application: Glioma is difficult to treat due to accelerated progression to GBM, which always develops TMZ resistance for recurrence. Many reports have struggled to identify biomarkers for diagnosis and for evaluating chemotherapeutic responses. Our study will clarify whether the upregulation of neurosteroids, such as DHEA, is a potential indicator for glioma and TMZ-resistant GBM. We will also identify the key neurosteroidogenic enzymes, such as CYP17A1, for overactivated neurosteroid biosynthesis. The mechanism for the overexpression of enzymes will be dissected by elucidating Sp1-mediated transcription. The above findings have never been reported; thus, we will provide a pioneering study on the role of neurosteroids in glioma development. Accordingly, we will identify a novel therapeutic strategy targeting neurosteroidogenesis and will test our proposed strategy in the preclinical models, including a spontaneous GBM mouse model. Finally, we hope that we can provide a reliable clue and evidence for treating glioma.