Background: Ovarian carcinoma is one of the most fatal malignancies in females. From the analysis of RNA-seq we have previously conducted to study the transcriptome of ovarian carcinoma upon knockdown of transcription factor hepatic nuclear factor 1β (HNF-1β), PRR5-ARHGAP8 was identified as the only read-through transcript not targeted for the nonsense-mediated decay pathway. Read-through transcription refers to the splicing of the intergenic region from two adjacent genes resulting in a chimeric transcript comprising of one or more exons from both genes. Although several of such transcripts are found in the transcriptome, their significance remains an enigma. Our aim was to ascertain the differential expression of the read-through transcript PRR5-ARHGAP8 in ovarian cancers and to determine its molecular functions.

Materials & Methods: The deregulation of PRR5-ARHGAP8 was validated by RT-qPCR in several ovarian carcinoma cell lines. The expression of this fusion transcript and the individual genes were studied in immortalised human ovarian surface epithelial (HOSE) cell lines, ovarian carcinoma cell lines, and matched tumour and non-tumour pairs from frozen patient samples. Overexpression of this transcript was achieved by transient transfection in HEK293T cells to study its effect on proliferation using MTT assays. RNA and protein lysates were also obtained at several time points to evaluate the pathways affected by RT-qPCR and western blot, respectively.

Results: There was an approximate 3- to 9-fold upregulation of PRR5-ARHGAP8 transcript with a decrease in the expression of PRR5 and ARHGAP8 transcripts in OVMANA, OVISE and KK ovarian carcinoma cell lines upon the knockdown of HNF-1β. Moreover, higher transcript levels of PRR5, ARHGAP8 and PRR5-ARHGAP8 were observed in ovarian carcinoma cell lines compared to HOSE cell lines and in ovarian cancer samples compared to the non-tumour counterparts. Overexpression of PRR5-ARHGAP8 in HEK293T cells resulted in the decrease of phosphorylated Akt protein expression and a reduction of cell viability. RT-qPCR analysis showed a decrease in E-cadherin and an increase in vimentin expression upon PRR5-ARHGAP8 overexpression.

Discussion: The present data suggests PRR5-ARHGAP8 is highly abundant in ovarian carcinomas and may mediate its effects on proliferation via the MAPK pathway and on migration by regulating the epithelial to mesenchymal transition. Overall, this study provides novel insights into the biological relevance of read-through transcription in carcinogenesis.

Citation Format: Jasmeen K. Sethi, Oscar G. Wong, Esther S. Wong, Annie N. Cheung. Molecular function of the read-through transcript PRR5-ARHGAP8 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1490.