circRNAs arise from back splicing events during mRNA processing, and when deregulated can play an active role in cancer. Here we characterize a new circRNA (circPOK) encoded by the Zbtb7a gene (also kown as POKEMON, LRF) in the context of mesenchymal tumor progression. circPOK functions as a non-coding proto-oncogenic RNA independently and antithetically to its linear transcript counterpart, which acts as a tumor suppressor by encoding the Pokemon transcription factor. We find that circPOK regulates pro-proliferative and pro-angiogenic factors by co-activation of the ILF2/3 complex. Importantly, the expression of Pokemon protein and circRNA is aberrantly uncoupled in cancer through differential post-transcriptional regulation. Thus, we identify a novel type of genetic unit, the iRegulon, that yields biochemically distinct RNA products, circular and linear, with diverse and antithetical functions. Our findings further expand the cellular repertoire towards the control of normal biological outputs, while aberrant expression of such components may underlie disease pathogenesis including cancer.
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We thank Lauren Southwood and Elizabeth Stack for their insightful editing, and all members of the Pandolfi lab for critical discussion. Jlenia Guarnerio was supported by the K99/R00 grant (CA212200) for the execution of this work. Mona Batish was supported by the grant 5 DP5 OD012160. This work was supported by the grant NIH/NCI-R35CA197529 and the grant GP009/2014 from the Human Frontier Science Program Organization to Pier Paolo Pandolfi. The collection of osteosarcoma samples was possible thanks to the NIH grant R01CA178908 to Dr. Spentzos Dimitrios.
P.P.P. and J.G. conceived the hypothesis and designed the experiments. J.G., Y.Z., G.C., R.P. and J.M.K. performed the experiments. P.P.P., J.G., and J.G.C. wrote the paper. M.S. and M.B. performed the circFISH presented in the paper. A.M., A.P. and C.L. helped to perform the experiments. A.P. and S.K. helped with LNA-GapmeRs. C.G., G.P.N., V.D. and S.D. provided osteosarcoma samples; S.D. helped to design experiments with osteosarcoma samples. M.C.M. and C.C.C. provided undifferentiated sarcoma samples.
The authors declare no competing interests.