CPSF2-mediated 3' UTR truncation of MTERF3 drives mitochondrial dysfunction and osteosarcoma progression.

Alternative polyadenylation (APA), an important post-transcriptional regulatory mechanism, is aberrantly activated in cancer, but how APA functions in tumorigenesis remains elusive. We analyzed APA events in osteosarcoma (OS) tissues and identified 3' UTR alterations associated with both OS patient prognosis and gene expression changes involving loss of tumor-suppressive miRNA binding sites. In OS tumors, MTERF3 3' UTRs were recurrently shortened and MTERF3 mRNA levels were upregulated, and indicated poor prognosis. OS cells with shorter MTERF3 3' UTRs displayed elevated proliferation, migration, and invasion ability compared to the cells with control or longer MTERF3 3' UTR. Moreover, system correlation analysis revealed that CPSF2 is a candidate upstream regulator of MTERF3 3' UTR length. Mechanistically, CPSF2 favored use of the proximal poly (A) site in the 3' UTR of MTERF3, resulting in a short-3' UTR MTERF3 isoform that produced more MTERF3 protein due to loss of miR-182-5p binding sites. The shortened MTERF3 3' UTR disrupted competing endogenous RNA (ceRNA) cross-talk, resulting in downregulation of the tumor suppressor gene ADCY6. Collectively, these findings demonstrate that CPSF2-mediates MTERF3 3' UTR shortening through APA to promote OS tumor progression.