Genomic Landscape And Chemoresistance Related Mechanism Of Ovarian Yolk Sac Tumor

Objectives:To explore the genomic landscape,evolutionary pattern and chemoresistance related mechanism of ovarian yolk sac tumor(YST).Methods:We performed whole-exome sequencing on 41 tumor samples and related peripheral blood samples from 30 YST patients,which were categorized as chemosensitive and chemoresistant group based on the relapse-free survival.There were 19 primary and one relapse tumor samples in the former group,seven primary and 14 relapse tumor samples in the latter group.Meanwhile,we performed transcriptome sequencing on three chemosensitive and nine chemoresistant tumor samples to screen differentially expressed genes.We also investigated the function of OVOL2 on cisplatin chemosensitivity in the human yolk sac tumor cell line(NOY1)by using siRNA knockdown,cell viability,apoptosis rate and the expression level of apoptosis-associated protein were analyzed.Results:Ovarian YST exhibited a moderate level of tumor mutation burden(1.34 mutations/Mb),which was significantly higher than that of testicular germ cell tumors in TCGA.We analyzed sequencing data from 24 primary tumor samples and five genes were predicted as driver genes,in which KRAS and KIT have been reported in the previous study,and the others included ZNF708,FRG1,NPAS1.We identified significant somatic copy number alteration(SCNA)including 18 amplifications and 15 deletions,and SCNA-associated genes such as deleted ARID1A and PARK2,and amplified ZNF217,CDKN1B,and KRAS.Compared with primary chemosensitive tumor samples,the level of chromosome 7q22.1 copy number amplification,microsatellite instability score and the percentage of COSMIC Signature 1 were significantly higher in primary chemoresistant tumor samples.Compared with primary tumor samples,tumor mutation burden,COSMIC Signature 4 and 23 were significantly higher in relapse tumor samples.There existed two evolutionary models in YST,which were linear and branched.A total of 153 significant differentially expressed genes were identified in three chemosensitive and nine chemoresistant tumor samples and they were enriched in the KRAS signal pathway.The expression of OVOL2 was significantly increased in chemoresistant YST samples.Knockdown of OVOL2 in NOY1 by using siRNA,compared with the negative control group,the cell viability in the transfection group was significantly decreased at the same time after treating with 20?M cisplatin,while apoptosis rate,the level of Caspase 3 and Cleaved Caspase 3 was significantly increased.Conclusions:In this study,we portrayed the genomic landscape of ovarian YST and identified five driver genes including already known KRAS,KIT,and novel ZNF708,FRG1,NPAS1.Chromosome 7q22.1 copy number alteration,microsatellite instability status and COSMIC Signature 1 could be applied as predictive markers for chemotherapy response of primary YST.Clonal evolution was complicated in YST and both linear and branched evolutionary models existed.OVOL2 was a chemoresistance related gene in YST,the expression level of OVOL2 influenced the response of NOY1 to cisplatin.