ACYP2 Contributes to Malignant Progression of Glioma Through Promoting Ca <sup>2+</sup> Efflux and Subsequently Activating c-Myc and STAT3 Signals

Abstract

Background: Acylphosphatase 2 (ACYP2) is involved in cell differentiation, energy metabolism and hydrolysis of intracellular ion pump. It has been reported as a negative regulator in leukemia and a positive regulator in colon cancer, respectively. However, its biological role in glioma remains unclear. The aim of this study was to clarify the biological functions and related molecular mechanism of ACYP2 in glioma tumorigenesis. Methods: We performed quantitative RT-PCR (qRT-PCR), immunohistochemistry (IHC) and western blot assays to evaluate expression of ACYP2. The functions of ACYP2 in glioma cells were determined by a series of in vitro and in vivo experiments, including cell proliferation, colony formation, cell cycle, apoptosis, migration, invasion and nude mouse tumorigenicity assays. Moreover, western blot and co-immunoprecipitation (co-IP) were used to identify its downstream targets. Findings: Knocking down ACYP2 in glioma cells significantly inhibited cell proliferation, colony formation, migration, invasion and tumorigenic potential in nude mice, and induced cell cycle arrest and apoptosis. Conversely, ectopic expression of ACYP2 in glioma cells dramatically promoted malignant phenotypes of glioma cells. Mechanistically, ACYP2 promoted malignant progression of glioma cells through regulating intracellular Ca2+ homeostasis via its interaction with PMCA4, thereby activating c-Myc and PTP1B/STAT3 signals. This could be effectively reversed by Ca2+ chelator BAPTA-AM or calpain inhibitor calpeptin. Interpretation: Our data demonstrate that ACYP2 functions as an oncogene in glioma through activating c-Myc and STAT3 signals via the regulation of intracellular Ca2+ homeostasis, and indicate that ACYP2 may be a potential therapeutic target and prognostic biomarker in gliomas. Funding Statement: This work was supported by the National Natural Science Foundation of China (No. 81572627 and 81672645), Innovation Talent Promotion Plan in Shaanxi Province (No. 2018TD-006) and The Natural Science Foundation Research Project in Shaanxi Province (No. 2019JQ-230). Declaration of Interests: The authors declare that they have no competing interest. Ethics Approval Statement: All animal procedures were conducted under the approval of the Animal Care and Use Committee of Xi’an Jiaotong University. All patients signed an informed consent before the surgery. The study protocol was approved by the Institutional Review Board and Human Ethics Committee of the First Affiliated Hospital of Xi’an Jiaotong University.