Title：CHSY1 promotes the tumorigenesis and progression of ovarian cancer. Running title：CHSY1 in ovarian cancer

Abstract Background Chondroitin synthase-1 (CHSY1) is an enzyme responsible for the biosynthesis of chondroitin sulfate, and it has been reported to be involved in tumorigenesis and progression in several cancer types. However, little is known about CHSY1 in ovarian cancer (OC). Methods CHSY1 expression was analysed on a tissue microarray (TMA) including tumour and peritumour tissues of OC patients, and the correlations between CHSY1 and clinicopathological features and prognosis. Gene sequencing analysis and qRT‒PCR were used to identify downstream genes and pathways. Cell function assays were used to assess cell proliferation, invasion and metastasis. Results The study revealed that CHSY1 expression was increased in OC vs. peritumour tissues and positively correlated with prognosis. In vitro cell function assays revealed high CHSY1 expression in OC cells, and CHSY1 was able to promote tumour cell proliferation and tumour cell invasion. Gene sequencing analysis and qRT‒PCR confirmed that CHSY1 promotes OC tumorigenesis through the downstream gene TIAM1 and the ERK signalling pathway. Conclusion Our study revealed a novel role of CHSY1 in OC tumorigenesis and offered a possible therapeutic target for OC.