A novel tumour suppressor protein encoded by circMAPK14 inhibits progression and metastasis of colorectal cancer by competitively binding to MKK6

Abstract

Background The mitogen‐activated protein kinase (MAPK) pathway is highly associated with the progression and metastasis of various solid tumours. MAPK14, a core molecule of the MAPK pathway, plays vital roles in the colorectal cancer (CRC). Recent studies have shown that circRNAs can affect tumour progression by encoding peptides. However, little is known regarding the potential protein translated from circMAPK14 and whether it plays a role in the carcinogenesis of colorectal cancer. Methods The RNA level and translatable potential of circMAPK14 in CRC was verified using qRT‐PCR and public databases. RNase R digestion assay, qRT‐PCR, sanger sequencing and FISH assays were utilised to verify the circular characteristics and subcellular localisation of circMAPK14. The suppressive role of circMAPK14 on the progression and metastasis of CRC was verified in vivo and in vitro. LC/MS analysis combined with western blotting demonstrated the presence and relative expression of circMAPK14‐175aa. The underlying mechanism of circMAPK14‐175aa action to inhibit CRC was identified by co‐IP analysis. The binding of U2AF2 within the flanking introns of circMAPK14 was evaluated by RNA pull‐down assay and RIP assay. Ultimately, luciferase reporter gene assays and ChIP assays confirmed that FOXC1 suppressed transcription of U2AF2 by binding to the U2AF2 promoter in the –400 bp to –100 bp region. Results We identified that hsa_circ_0131663 (termed circMAPK14) showed significantly decreased expression level in cells and tissue samples of CRC, and was primarily localised in the cytoplasm. A series of function experiments demonstrated that circMAPK14 influenced CRC progression and metastasis by encoding a peptide of 175 amino acids (termed circMAPK14‐175aa). We also found that circMAPK14‐175aa reduced nuclear translocation of MAPK14 by competitively binding to MKK6, thus facilitating ubiquitin‐mediated degradation of FOXC1. Moreover, we described a positive feedback loop in CRC in which elevated FOXC1 expression was caused by reduced circMAPK14‐175aa expression. This, in turn, decreased circMAPK14 biogenesis by suppressing U2AF2 transcription. Conclusion In summary, we reported for the first time that circMAPK14 functioned as a tumour‐suppressor by encoding circMAPK14‐175aa, which blocked the progression and metastasis of colorectal cancer.

Non-Coding RNAs in Colorectal Cancer: Their Functions and Mechanisms

“…For example, it has been reported that lncRNA HOXB-AS3 encodes a conserved 53-aa peptide that inhibits CRC growth by regulating the reprogramming of tumor metabolism and alternative splicing of pyruvate kinase ( 167 ). Additionally, function experiments have revealed that circMAPK14-175aa (a 175 amino acid peptide) encoded by circRNA MAPK14 can suppress the CRC malignant phenotype, thus affecting CRC progression and metastasis ( 168 ). Currently, some lncRNAs and circRNAs have been shown to encode proteins or peptides, and studies on the coding functions of miRNAs are emerging.…”

NcRNAs: Multi‑angle participation in the regulation of glioma chemotherapy resistance (Review)

“…Wu et al ( 168 ) confirmed that circ_SMO is able to encode a novel protein, SMO-193a.a., which is critical for Hh signal transduction and drives malignant progression of glioblastoma. CircMAPK14-175aa, a novel tumour suppressor protein encoded by circRNA_mitogen-activated protein kinase 14 (circ_MAPK14), inhibits colorectal cancer progression and metastasis by reducing the nuclear translocation of MAPK14 via competitively binding to MAPK kinase 6 to facilitate ubiquitin-mediated degradation of FOXC1 ( 169 ). N 6 -methyladenosine (m 6 A) methylation is the most prevalent post-transcriptional RNA modification in the transcriptome.…”

circRNA: A New Biomarker and Therapeutic Target for Esophageal Cancer

“…This truncated protein prevents the full-length SHPRH protein from degradation by the ubiquitin-proteasome and functions as a tumor suppressor in glioblastoma. CircMAPK14-175aa, a peptide of 175 amino acids encoded by the circMAPK14 gene, reduces the nuclear translocation of MAPK14 by competitively binding to MKK6 and blocking the progression of colorectal cancer [ 56 ]. Recent studies have shown that N6-methladenosine (m6A) RNA methylation can drive translation initiation in circRNAs [ 57 ].…”