Expression and function of APELA : a potential regulator of cell growth in human cancers

Apela, a novel gene identified by our laboratory, is expressed in mouse definitive endoderm, neural tube, and mouse embryonic stem cells (mESCs). In humans, APELA is expressed in embryonic stem cells, induced adult pluripotent stem cells (iPSCs) as well as adult kidney and prostate. APELA peptide signals through the G-protein coupled receptor, the APJ receptor, to regulate zebrafish definitive endoderm migration and cardiac development. Interestingly, the mRNA of Apela can mediate p53-dependent mESCs cell apoptosis. These findings suggest that Apela can functions as a peptide or as a lncRNA. Signaling pathways that are critical during embryogenesis are also important in cancer development and progression. However, thus far, whether APELA exerts any biological functions that regulate cancer progression is completely unknown. In this study, analysis of the cancer genome atlas (TCGA) RNA sequencing datasets reveals that APELA mRNA is expressed in different human cancer including in ovarian cancer. Real-time quantitative PCR analyses of clinical human ovarian cancer samples show that APELA mRNA levels are higher in ovarian clear cell carcinoma (OCCC), than other subtypes. Using a CRISPR/Cas9-mediated knockout approach, I have demonstrated that APELA knockout suppresses cell growth in the ovarian clear cell carcinoma cell line, OVISE. Decreased cell growth induced by APELA knockout can be partially attenuated by treating cells with recombinant human APELA protein. In addition, flow cytometry analyses show that APELA knockout induces G2/M phase arrest in OVISE cells. Western blot results show that the phosphorylation levels of ERK1/2, AKT, and cyclin B1 expression levels are significantly down-regulated in the APELA deficient OVISE cells. Moreover, our results indicate that in the APELA knockout cells, decreased cell growth is dependent on the expression of wildtype p53. Unexpectedly, knockout APELA does not affect cell growth in Ewing sarcoma cell line A673, which has high expression of APELA at mRNA level. Interestingly, the APJ receptor is expressed in A673 cells but not in OVISE cells, which strongly suggests that APELA can exert its function through APJ-independent pathway in OVISE cells. In summary, our study demonstrates that APLEA may be an important factor that mediates the progression of OCCC.Medicine, Faculty ofGraduat