Internal cap-initiated translation for efficient protein production from circular mRNA

  • Nat Biotechnol. 2026 Jan;44(1):120-132. doi: 10.1038/s41587-025-02561-8.
Kosuke Fukuchi  #  1 ,  Yuko Nakashima  #  1 ,  Naoko Abe  #  2 ,  Seigo Kimura  3 ,  Fumitaka Hashiya  4 ,  Yuichi Shichino  5 ,  Yiwei Liu  1 ,  Ryoko Ogisu  1 ,  Satomi Sugiyama  1 ,  Daisuke Kawaguchi  1 ,  Masahito Inagaki  1 ,  Zheyu Meng  1 ,  Shiryu Kajihara  1 ,  Mizuki Tada  1 ,  Satoshi Uchida  6  7 ,  Ting-Ting Li  1 ,  Ramkrishna Maity  1 ,  Tairin Kawasaki  1 ,  Yasuaki Kimura  1 ,  Shintaro Iwasaki  5  8 ,  Hiroshi Abe  9  10
Affiliations
  • 1. Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan.
  • 2. Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan. [email protected].
  • 3. Integrated Research Consortium on Chemical Sciences (IRCCS), Nagoya University, Nagoya, Japan.
  • 4. Research Center for Materials Science, Nagoya University, Nagoya, Japan.
  • 5. RNA Systems Biochemistry Laboratory, RIKEN Cluster for Pioneering Research, Saitama, Japan.
  • 6. Medical Research Institute, Tokyo Medical and Dental University (TMDU), Tokyo, Japan.
  • 7. Innovation Center of NanoMedicine (iCONM), Kawasaki Institute of Industrial Promotion, Kawasaki, Japan.
  • 8. Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Chiba, Japan.
  • 9. Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan. [email protected].
  • 10. Institute for Glyco-core Research (iGCORE), Nagoya University, Nagoya, Japan. [email protected].
  • # Contributed equally.
PMID: 39972222 DOI: 10.1038/s41587-025-02561-8
Abstract

Circular mRNA faces challenges in enhancing its translation potential as an RNA therapeutic. Here we introduce two molecular designs that bolster circular mRNA translation through an internal cap-initiated mechanism. The first consists of a circular mRNA with a covalently attached N7-methylguanosine (m7G) cap through a branching structure (cap-circ mRNA). This modification allows circular mRNA to recruit translation machinery and produce proteins more efficiently than internal ribosome entry site (IRES)-containing circular mRNAs. Combining with an N1-methylpseudouridine (m1Ψ) modification, cap-circ mRNA exhibits a lower acute immunostimulatory effect, maintaining high translation in mice. The second design features the non-covalent attachment of an m7G cap to a circular mRNA through hybridization with an m7G cap-containing oligonucleotide, enhancing translation by more than 50-fold. This setup allows circular mRNAs to synthesize reporter proteins upon hybridizing with capped mRNAs or long non-coding RNAs and to undergo rolling circle-type translation. These advancements broaden the therapeutic applications of circular mRNAs by minimizing their molecular size, elevating translation efficiency and facilitating cell-type-selective translation.

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