Htra2-β1 stimulates an exonic splicing enhancer and can restore full-length SMN expression to survival motor neuron 2 (SMN2)

Htra2-β1 stimulates an exonic splicing enhancer and can restore full-length SMN expression to survival motor neuron 2 (SMN2)

^*Institute of Human Genetics, University of Bonn, 53111 Bonn, Germany; ^‡Department of Dermatology, New England Medical Center and Tufts University School of Medicine, Boston, MA 02111; and ^§Max-Planck-Institute of Neurobiology, 82152 Martinsried, Germany

Edited by Louis M. Kunkel, Harvard Medical School, Boston, MA, and approved June 14, 2000 (received for review April 20, 2000)

Abstract

Spinal muscular atrophy (SMA), a common motor neuron disease in humans, results from loss of functional survival motor neuron (SMN1) alleles. A nearly identical copy of the gene, SMN2, fails to provide protection from SMA because of a single translationally silent nucleotide difference in exon 7. This likely disrupts an exonic splicing enhancer and causes exon 7 skipping, leading to abundant production of a shorter isoform, SMN2Δ 7. The truncated transcript encodes a less stable protein with reduced self-oligomerization activity that fails to compensate for the loss of SMN1. This report describes the identification of an in vivo regulator of SMN mRNA processing. Htra2-β1, an SR-like splicing factor and ortholog of Drosophila melanogaster transformer-2, promoted the inclusion of SMN exon 7, which would stimulate full-length SMN2 expression. Htra2-β1 specifically functioned through and bound an AG-rich exonic splicing enhancer in SMN exon 7. This effect is not species-specific as expression of Htra2-β1 in human or mouse cells carrying an SMN2 minigene dramatically increased production of full-length SMN2. This demonstrates that SMN2 mRNA processing can be modulated in vivo. Because all SMA patients retain at least one SMN2 copy, these results show that an in vivo modulation of SMN RNA processing could serve as a therapeutic strategy to prevent SMA.

Footnotes

↵ † Y.H. and C.L.L. contributed equally to this work.
↵ ¶ To whom reprint requests should be addressed. E-mail: bwirth{at}uni-bonn.de.
This paper was submitted directly (Track II) to the PNAS office.
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.160181697.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.160181697
Abbreviations:

SMA,

spinal muscular atrophy;

SMN,

survival motor neuron gene;

ESE,

exonic splicing enhancer;

FL,

full-length;

SR,

serine/arginine-rich splicing factor;

GFP,

green fluorescent protein;

HA,

hemagglutinin;

HPRT,

hypoxanthine phosphoribosyltransferase