AK4P1 is a cancer-promoting pseudogene in pancreatic adenocarcinoma cells whose transcripts can be transmitted by exosomes

Abstract

Adenylate kinase 4 pseudogene 1 (AK4P1) is a processed pseudogene whose function in cancer biology remains largely underexplored. Bioinformatics analysis suggested an association between the expression levels of adenylate kinase 4 (AK4) gene and AK4P1, as well as a clinical significance in relation to the increased transcription levels of AK4P1 in pancreatic adenocarcinoma (PAAD). In the present study, the expression levels of AK4P1 and AK4 were compared by RT-qPCR and western blotting between PAAD tissue and paired adjacent tissue. The level of AK4P1 transcript was compared between the circulating exosomes derived from patients with PAAD and those derived from healthy donors. Overall survival of the patients with PAAD with high or low expression levels of AK4P1 or AK4 was compared. AK4 gene expression level, in vitro cell viability and gemcitabine-induced apoptosis in PAAD cells with or without AK4P1 overexpression were also assessed using Cell Counting Kit-8 and TUNEL assays. It was identified that the transcription level of AK4P1 and the expression level of AK4 in PAAD tissue were significantly higher compared with those in paired non-cancerous tissue specimens. Transcription levels of AK4P1 and AK4 showed a significant relationship in PAAD. Circulating exosomes derived from patients with PAAD showed significantly higher level of AK4P1 transcript compared with that from circulating exosomes derived from blood samples of healthy donors. Patients with high expression of AK4P1 or AK4 exhibited significantly reduced overall survival compared with those with low expression. AK4P1 overexpression significantly upregulated the expression levels of AK4 in PAAD cells and rescued the viability and survival under gemcitabine challenge decreased by AK4 knockdown but not that by AK4 knockout. Treatment with exosomes secreted by AK4P1-overexpressing PAAD cells but not with those secreted by wild-type PAAD cells significantly increased the viability and survival under gemcitabine challenge of the recipient cells. These results suggested that AK4P1 affects the cellular biological functions of PAAD cells in vitro by upregulating the expression level of AK4. AK4P1 transcripts with elevated expression levels can be transmitted between PAAD cells through exosomes and exert pro-oncogenic effects in recipient cells.

Keywords: adenylate kinase 4; adenylate kinase 4 pseudogene 1; exosome; pancreatic adenocarcinoma; pseudogene.