Inhibition of nonsense-mediated mRNA decay reduces the tumorigenicity of human fibrosarcoma cells

Abstract

Nonsense-mediated mRNA decay (NMD) is a eukaryotic RNA degradation pathway that targets for degradation faulty mRNAs with premature termination codons as well as many physiological mRNAs encoding full-length proteins. Consequently, NMD functions in both, quality control and post-transcriptional regulation of gene expression, and it has been implicated in the modulation of cancer progression. To investigate the role of NMD in cancer, we knocked out SMG7 in the HT1080 human fibrosarcoma cell line. SMG7 is involved in deadenylation-coupled exonucleolytic mRNA decay, one of the two main degradation pathways in mammalian NMD. Genome-wide proteomic and transcriptomic analyses confirmed that NMD is severely compromised in these SMG7-knockout HT1080 cells. We compared the oncogenic properties between the parental, the SMG7-knockout, and a rescue cell line in which we re-introduced both isoforms of SMG7. In parallel, we tested the effect of a drug inhibiting the NMD factor SMG1 on the HT1080 cells to distinguish NMD-dependent effects from putative NMD-independent functions of SMG7. Using cell-based assays as well as a mouse xenograft tumor model, we show that the oncogenic properties of the parental HT1080 cells are severely compromised when NMD is inhibited. Molecular pathway analysis revealed a strong reduction of the matrix metalloprotease 9 (MMP9) gene expression in NMD-suppressed cells. Since MMP9 expression promotes cancer cell migration and invasion, metastasis and angiogenesis, its downregulation in NMD-suppressed cells explains, at least partially, their reduced tumorigenicity. Collectively, our findings emphasize the therapeutic potential of NMD inhibition for the treatment of certain types of cancer. SignificanceNonsense-mediated mRNA decay (NMD) is a eukaryotic RNA decay pathway with reported roles in regulating cellular stress responses, differentiation, and viral defense. NMD has also emerged as a modulator of cancer progression, however, the available evidence supports both, a tumor suppressor as well as a pro-tumorigenic role for NMD. We discovered that NMD inhibition results in impaired tumorigenicity in the HT1080 human fibrosarcoma cell line and uncovered a direct correlation between NMD activity and the expression levels the pro-tumorigenic gene MMP9. Restoring MMP9 expression in NMD-suppressed cells partially improved their oncogenic properties. These results show that the tumorigenicity of the HT1080 fibrosarcoma cells relies on NMD activity and highlights the potential use of NMD inhibition as a therapeutic approach.