LINE-1 ORF1 Protein Localizes in Stress Granules with Other RNA-Binding Proteins, Including Components of RNA Interference RNA-Induced Silencing Complex

Abstract

LINE-1 retrotransposons constitute one-fifth of human DNA and have helped shape our genome. A full-length L1 encodes a 40-kDa RNA-binding protein (ORF1p) and a 150-kDa protein (ORF2p) with endonuclease and reverse transcriptase activities. ORF1p is distinctive in forming large cytoplasmic foci, which we identified as cytoplasmic stress granules. A phylogenetically conserved central region of the protein is critical for wild-type localization and retrotransposition. Yeast two-hybrid screens revealed several RNA-binding proteins that coimmunoprecipitate with ORF1p and colocalize with ORF1p in foci. Two of these proteins, YB-1 and hnRNPA1, were previously reported in stress granules. We identified additional proteins associated with stress granules, including DNA-binding protein A, 9G8, and plasminogen activator inhibitor RNA-binding protein 1 (PAI-RBP1). PAI-RBP1 is a homolog of VIG, a part of the Drosophila melanogaster RNA-induced silencing complex (RISC). Other RISC components, including Ago2 and FMRP, also colocalize with PAI-RBP1 and ORF1p. We suggest that targeting ORF1p, and possibly the L1 RNP, to stress granules is a mechanism for controlling retrotransposition and its associated genetic and cellular damage.

SUPPLEMENTAL MATERIAL

We greatly appreciate the reagents sent by the many researchers listed in the Materials and Methods section. We thank Eric Ostertag for critical reading of the manuscript. Special thanks to Gary Swain and the fabulous Morphology Core (Center Grant P30 DK50306), Division of Gastroenterology, University of Pennsylvania.

This work was supported by NIH/NIGMS grant 1R01GM45398-16 to H.H.K. and DOD/CDMRP grant BC051386 to J.L.G.