SEPTIN14P20 encodes RBRP (RNA-binding regulatory peptide), a 71-amino-acid peptide translated from a transcript of the septin 14 pseudogene 20 locus on chromosome 20q13.33, which was previously annotated as the long non-coding RNA LINC00266-1 (C20orf69). The peptide is the retained septin-14 reading frame of this pseudogene: residues 1-47 are identical to the C-terminal coiled-coil region of SEPTIN14 (residues 383-429), and only a 24-residue C-terminal tail is unique. RBRP has been reported in colorectal, breast, ovarian and nasopharyngeal cancer cells and in colorectal tissue, at higher levels in tumours than in adjacent normal tissue, but independent confirmation of the endogenous product is lacking. In the single functional study, RBRP bound the KH3-KH4 di-domain of the m6A reader IGF2BP1 in an RNA-independent manner (abolished by a G19A substitution), increased IGF2BP1 binding to m6A-modified RNA in vitro and in cells, and increased the association of IGF2BP1 and the RNA stabilisers ELAVL1/HuR, MATR3 and PABPC1 with m6A-marked MYC mRNA. This stabilised MYC mRNA and promoted colorectal cancer cell proliferation, migration, invasion and xenograft growth.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005515 protein binding | IPI PMID:32245947 An oncopeptide regulates m(6)A recognition by the m(6)A read... | MODIFY | Summary: Co-immunoprecipitation of RBRP with IGF2BP1 (UniProtKB:Q9NZI8), RNase resistant, mapped to the IGF2BP1 KH3-KH4 di-domain and abolished by RBRP G19A. Reason: Bare protein binding carries no functional information. The same paper shows what the binding does - recombinant RBRP increases the binding of recombinant IGF2BP1 to m6A-methylated RNA, and the binding-defective G19A mutant does not - so the interaction is better captured as an activator of IGF2BP1's m6A-RNA-binding activity (GO:0140677 molecular function activator activity). The evidence comes from one laboratory on a PE5 pseudogene product whose first 47 residues are identical to SEPTIN14, so the replacement is offered on the strength of the in vitro data, not as a settled function. Proposed replacements: molecular function activator activity Supporting Evidence: PMID:32245947 indicating that the binding of RBRP to IGF2BP1 was RNA independent PMID:32245947 Similar to endogenous RBRP peptides, a recombinant RBRP oncopeptide increased the binding of the recombinant IGF2BP1 protein to m6A-methylated RNA oligos, whereas a recombinant G19A-mutated RBRP oncopeptide did not |
| GO:0048255 mRNA stabilization | IDA PMID:32245947 An oncopeptide regulates m(6)A recognition by the m(6)A read... | ACCEPT | Summary: RBRP overexpression lengthens MYC mRNA half-life in an IGF2BP1-, METTL14- and m6A-site-dependent way; knockdown of the host transcript shortens it, and only wild-type RBRP (not G19A) rescues. Reason: Full text read. RBRP acts as a cofactor of the IGF2BP1 stabilising complex (it increases IGF2BP1 and HuR/MATR3/PABPC1 occupancy on m6A-marked MYC mRNA), so it contributes to the process rather than merely being required for it. The data are locus-specific (ORF constructs, start-codon mutants, 3'-UTR shRNA with shRNA-resistant rescue), so the doubtful-existence rule for inherited annotations does not apply. Caveats are recorded on the reference - single laboratory, UniProt PE5, HGNC pseudogene, and the peptide shares residues 1-47 with SEPTIN14. Supporting Evidence: PMID:32245947 Knockdown of LINC00266-1 significantly decreased the c-Myc mRNA stability and level, cell growth, colony formation, migration, and invasion, whereas these alterations were restored to the control levels in cells cotransfected with WT RBRP but not with the IGF2BP1-binding-defective mutant RBRP G19A PMID:32245947 Thus, RBRP strengthens the recruitment of the RNA stabilizers HuR, MATR3, and PABPC1 to m6A-c-Myc CRD RNAs, to promote the stability of c-Myc mRNA and upregulate the c-Myc levels. |
| GO:1902416 positive regulation of mRNA binding | IDA PMID:32245947 An oncopeptide regulates m(6)A recognition by the m(6)A read... | ACCEPT | Summary: RBRP increases binding of IGF2BP1 to m6A-modified RNA oligos and MYC CRD RNA, in vitro with recombinant proteins and in cells by RIP-qPCR, in a G19-dependent and m6A-dependent manner. Reason: This is the central, best-controlled result of the paper (recombinant proteins, a binding-dead point mutant, and m6A-site mutants in the target). It is the process-side description of the activator activity proposed for the protein binding row. Same single-laboratory and existence caveats as the mRNA stabilization row. Supporting Evidence: PMID:32245947 Collectively, RBRP enhances the m6A recognition by IGF2BP1 on RNAs. |
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Download this section (compressed HTML)Q: GO:0140677 molecular function activator activity records that RBRP activates another molecular function but not which one or of what. Should GO provide a scoped term (or a has-input extension) for activating IGF2BP1 binding to m6A-modified mRNA, so the target and the activated activity are machine-readable?
Q: Which tryptic peptides were observed in the endogenous MS identification of RBRP? Only peptides from the unique C-terminal tail (residues 48-71, e.g. HPDPYEFLLLR or HPGFNEELSPC) distinguish RBRP from SEPTIN14, and the search was run against a custom RBRP-only database.
Q: Does the C-terminal coiled-coil region of SEPTIN14 itself, which contains the same Gly-19-equivalent residue (SEPTIN14 Gly-401), bind IGF2BP1? If so, the binding surface is a septin property rather than a novel peptide function.
Q: Has the RBRP-IGF2BP1 interaction or the MYC mRNA stabilisation effect been reproduced by an independent laboratory?
Experiment: Targeted mass spectrometry for the unique C-terminal tryptic peptides, searched against the full human proteome, in colorectal cancer cells; plus CRISPR knock-in of an epitope tag at the endogenous RBRP C-terminus and ribosome profiling across the ORF.
Hypothesis: The endogenous SEPTIN14P20 ORF is translated into the 71-residue RBRP peptide.
Type: proteomics / genome editing
Experiment: Mutate the endogenous start codon or introduce a frameshift in the RBRP ORF (leaving the transcript intact), then measure MYC mRNA half-life and IGF2BP1 RIP enrichment on MYC CRD RNA.
Hypothesis: RBRP knockout (not transcript knockdown) reduces MYC mRNA stability.
Type: genome editing with mRNA decay assay
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