The SR Protein SC35 Is Responsible for Aberrant Splicing of the E1α Pyruvate Dehydrogenase mRNA in a Case of Mental Retardation with Lactic Acidosis

Abstract

Pyruvate dehydrogenase (PDH) complex deficiency is a major cause of lactic acidosis and Leigh's encephalomyelopathies in infancy and childhood, resulting in early death in the majority of patients. Most of the molecular defects have been localized in the coding regions of the E1α PDH gene. Recently, we identified a novel mutation of the E1α PDH gene in a patient with an encephalopathy and lactic acidosis. This mutation, located downstream of exon 7, activates a cryptic splice donor and leads to the retention of intronic sequences. Here, we demonstrate that the mutation results in an increased binding of the SR protein SC35. Consistently, ectopic overexpression of this splicing factor enhanced the use of the cryptic splice site, whereas small interfering RNA-mediated reduction of the SC35 protein levels in primary fibroblasts from the patient resulted in the almost complete disappearance of the aberrantly spliced E1α PDH mRNA. Our findings open the exciting prospect for a novel therapy of an inherited disease by altering the level of a specific splicing factor.

ACKNOWLEDGMENTS

We thank J. Stévenin for providing us with ASF/SF2 and SC35 purified proteins and antibodies.

This work was supported by the GIS-Institut des maladies rares, by the Contrat de recherche clinique CRC 03-004 to M.B., and by a grant from the Association pour la Recherche sur le Cancer to J.S. This work was also supported in part by contract QLG2-CT-1999-00660 from the European Union. M.G. was supported by a graduate fellowship from the Ministère Délégué à la Recherche et aux Technologies. M.M. was supported by a grant from the Fédération des maladies orphelines FMO-AFRG.