title: A SMNDelta7 read-through product confers functionality to the SMNDelta7 protein.
abstract: Spinal muscular atrophy (SMA) affects about 1 in every 6000 children born and is the leading genetic cause of infant death. SMA is a recessive disorder caused by the mutation or deletion of Survival Motor Neuron-1 (SMN1). SMN2, a nearly identical copy gene, has the potential to encode the same protein as SMN1 and is retained in all SMA patients. The majority of SMN2-derived transcripts are alternatively spliced and therefore encode a truncated isoform lacking exon 7 (SMNDelta7), which is a defective protein because it is unstable, has a reduced ability to self-associate and is unable to efficiently function in SMN cellular activities. However, we have shown that the SMN C-terminus functions non-specifically, since heterologous sequences can compensate for the exon 7 sequence. Several classes of compounds identified in SMN-inducing high throughput screens have been proposed to function through a read-through mechanism; however, a functional analysis of the SMNDelta7 read-through product has not been performed. In this report, the SMNDelta7 read-through product is characterized and compared to the SMNDelta7 protein. In a series of in vitro and cell based assays, SMNDelta7 read-through product is shown to increase protein stability, promote neurite outgrowths in SMN deficient neurons, and significantly elevate SMN-dependent UsnRNP assembly in extracts from SMA patient fibroblasts. Collectively, these results demonstrate that SMNDelta7 read-through product is more active than the SMNDelta7 protein and suggest that SMA therapeutics that specifically induce SMNDelta7 read-through may provide an alternative platform for drug discovery.
authors.affiliation: Department of Veterinary Pathobiology, Life Sciences Center, Room 404, University of Missouri, Columbia, MO 65211, United States.
authors.forename: Virginia B
authors.initials: VB
authors.lastname: Mattis
authors.forename: Melissa
authors.initials: M
authors.lastname: Bowerman
authors.forename: Rashmi
authors.initials: R
authors.lastname: Kothary
authors.forename: Christian L
authors.initials: CL
authors.lastname: Lorson
mesh_terms: D000818:Animals; D017362:Cyclic AMP Response Element-Binding Protein / Q000502:physiology*; D006801:Humans; D009134:Muscular Atrophy, Spinal / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D016601:RNA-Binding Proteins / Q000502:physiology*; D055532:SMN Complex Proteins; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; C526471:SMN1 protein, human; C526477:SMN2 protein, human; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein