Expression of RUNX2 isoforms: Involvement of cap-dependent and cap-independent mechanisms of translation

Narayanasamy Elango, Ye Li, Pooja Shivshankar, Michael S. Katz

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

RUNX2, a major regulator of skeletogenesis, is expressed as type-I and type-II isoforms. Whereas most eukaryotic mRNAs are translated by the cap-dependent scanning mechanism, translation of many mRNAs including type-I and type-II RUNX2 mRNAs has been reported to be initiated by a cap independent internal ribosomal entry site (IRES). Since the dicistronic plasmid assay used to demonstrate IRES has been questioned, we investigated the presence of IRES in RUNX2 mRNAs using dicistronic plasmid and mRNA assays. Our results show that the dicistronic plasmid assay cannot be used to demonstrate IRES in RUNX2 mRNAs because the intercistronic region of dicistronic plasmids containing the 5′-UTRs of both RUNX2 mRNAs operates as a cryptic promoter. In dicistronic mRNA transfection studies the 5′-UTRs of both RUNX2 mRNAs exhibited no IRES activity. When transfected into osteoblastic cells, monocistronic reporter mRNA preceded by the 5′-UTR of type-II RUNX2 (Type-II-FLuc-A100) was translated to a high degree only in the presence of a functional cap (m 7GpppG); in contrast, luciferase mRNA preceded by the 5′-UTR of type-I RUNX2 mRNA (Type-I-FLuc-A100) was translated poorly in the presence of either m7GpppG or a nonfunctional cap (ApppG). Notably, in transfected cells inhibitors of cap-dependent translation suppressed the translation of m7GpppG-capped Type-II-FLuc-A100, but not ApppG-capped reporter mRNA preceded by the IRES-containing hepatitis C virus (HCV) 5′-UTR. Our study demonstrates that type-II RUNX2 mRNA is translated by the cap-dependent mechanism. Although efficient translation of type-I RUNX2 mRNA appears to require a process other than cap-dependent, the mechanism of type-I RUNX2 mRNA translation remains to be resolved.

Original languageEnglish (US)
Pages (from-to)1108-1121
Number of pages14
JournalJournal of Cellular Biochemistry
Volume99
Issue number4
DOIs
StatePublished - Nov 1 2006

Keywords

  • 4E-BP1
  • Cap-dependent translation
  • Internal ribosomal entry site
  • RNA Aptamer-1
  • Type-1 RUNX2
  • Type-II RUNX2

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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