Cytochrome P450 17A1 (CYP17A1) Attenuates Oxidative Stress through Regulating Protein Stability of SAR1a/b in Glioblastoma
Authors: Hsu Tsung-I 
Published: April 2020

IntroductionCytochrome P450 (CYP) 17A1, known as steroid 17a‐hydrolase, plays an important role in steroid hormone metabolism through converting pregnenolone to dehydroepiandrosterone (DHEA). Previously, we found that CYP17A1 expression was dramatically increased in glioblastoma compared with normal astrocytes, and showed that upregulated CYP17A1 contributed to the induction of resistance in response to temozolomide (TMZ) which is a chemotherapeutic drug used for glioblastoma patients. Via the upregulation of DHEA synthesis, CYP17A1 obviously attenuated apoptosis. However, in addition to steroid metabolism, the physiological functions of CYP17A1 in cellular homeostasis are still not clear. Moreover, whether the inhibition of CYP17A1 is potential for treating glioblastoma is also unknown.AimsWe attempt to elucidate effect of abiraterone, the inhibitor targeting CYP17A1, on glioblastoma, and to clarify how CYP17A1 maintains cellular health.MethodsCell viability assay and brain tumor orthotropic mouse model were employed to evaluate the tumor‐suppressive effect of abiraterone in vitro and in vivo, respectively. Western blotting was used to estimate the occurrence of ER stress. The production of superoxide was estimated by fluorescence‐based flow cytometry, and the accumulation of oxidative stress was evaluated by H2O2 levels and the ratio of GSH/GSSG. Mass spectrophotometry‐based proteomics was used to clarify effect of CYP17A1 overexpression on cellular protein levels.ResultsAbiraterone obviously inhibited the survival of glioblastoma and induced multiple oxidative stresses, including superoxide production, H2O2 accumulation and dysfunction of glutathione. In contrast, overexpression of CYP17A1 significantly prevented H2O2‐induced ER stress and oxidative stresses. Further, proteomics revealed that CYP17A1 increased the expression of SRP14 and SAR1, both of which are responsible for ER‐mediated protein processing and trafficking to Golgi apparatus, respectively. In addition, abiraterone obviously decreased the expression of SRP14, SAR1A and SAR1B. Interestingly, CYP17A1 positively regulated SRP14 and SAR1 expression through extending protein half‐life. Moreover, overexpression of SRP14 or SAR1 prevented abiraterone‐impaired cellular homeostasis.DiscussionThe current study identified the novel function of CYP17A1 in addition to regulating steroid hormone synthesis. The evidence in this study showing that CYP17A1 mediates redox optimization has never been demonstrated well. Additionally, CYP17A1 also participates in regulating protein processing in ER and protein trafficking to Golgi apparatus. However, the further mechanism underlying CYP17A1‐regulated protein maturation needs to be elucidated in the future.ConclusionBased on our findings, inhibition of CYP17A1 significantly inhibits glioblastoma through inducing ER stress and multiple oxidative stresses. Particularly, CYP17A1 prevents oxidative stresses through maintaining SRP14‐ and SAR1‐mediated protein maturation.Support or Funding InformationThis study was supported by the Ministry of Science and Technology of Taiwan (MOST 108‐2628‐B‐038‐005‐).