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Cryptic exon activation by disruption of exon splice enhancer: novel mechanism causing 3-methylcrotonyl-CoA carboxylase deficiency


Stucki, M; Suormala, T; Fowler, B; Valle, D; Baumgartner, M R (2009). Cryptic exon activation by disruption of exon splice enhancer: novel mechanism causing 3-methylcrotonyl-CoA carboxylase deficiency. Journal of Biological Chemistry, 284(42):28953-28957.

Abstract

3-Methylcrotonyl-CoA carboxylase (MCC) deficiency is an autosomal recessive disorder of leucine catabolism. MCC is a heteromeric mitochondrial enzyme composed of biotin-containing alpha (MCCA) and smaller beta (MCCB) subunits encoded by MCCA and MCCB, respectively. We report studies of the c.1054G-->A mutation in exon 11 of MCCB detected in the homozygous state in a patient with MCC deficiency. Sequence analysis of MCCB cDNA revealed two overlapping transcripts, one containing the normal 73 bp of exon 11 including the missense mutation c.1054G-->A (p.G352R), the other with exon 11 replaced by a 64-bp sequence from intron 10 (cryptic exon 10a) that maintains the reading frame and is flanked by acceptable splice consensus sites. In expression studies, we show that both transcripts lack detectable MCC activity. Western blot analysis showed slightly reduced levels of MCCB using the transcript containing the missense mutation, whereas no MCCB was detected with the transcript containing the cryptic exon 10a. Analysis of the region harboring the mutation revealed that the c.1054G-->A mutation is located in an exon splice enhancer sequence. Using MCCB minigene constructs to transfect MCCB-deficient fibroblasts, we demonstrate that the reduction in utilization of exon 11 associated with the c.1054G-->A mutation is due to alteration of this exon splice enhancer. Further, we show that optimization of the weak splice donor site of exon 11 corrects the splicing defect. To our knowledge, this is the first demonstration of a point mutation disrupting an exon splice enhancer that causes exon skipping along with utilization of a cryptic exon.

3-Methylcrotonyl-CoA carboxylase (MCC) deficiency is an autosomal recessive disorder of leucine catabolism. MCC is a heteromeric mitochondrial enzyme composed of biotin-containing alpha (MCCA) and smaller beta (MCCB) subunits encoded by MCCA and MCCB, respectively. We report studies of the c.1054G-->A mutation in exon 11 of MCCB detected in the homozygous state in a patient with MCC deficiency. Sequence analysis of MCCB cDNA revealed two overlapping transcripts, one containing the normal 73 bp of exon 11 including the missense mutation c.1054G-->A (p.G352R), the other with exon 11 replaced by a 64-bp sequence from intron 10 (cryptic exon 10a) that maintains the reading frame and is flanked by acceptable splice consensus sites. In expression studies, we show that both transcripts lack detectable MCC activity. Western blot analysis showed slightly reduced levels of MCCB using the transcript containing the missense mutation, whereas no MCCB was detected with the transcript containing the cryptic exon 10a. Analysis of the region harboring the mutation revealed that the c.1054G-->A mutation is located in an exon splice enhancer sequence. Using MCCB minigene constructs to transfect MCCB-deficient fibroblasts, we demonstrate that the reduction in utilization of exon 11 associated with the c.1054G-->A mutation is due to alteration of this exon splice enhancer. Further, we show that optimization of the weak splice donor site of exon 11 corrects the splicing defect. To our knowledge, this is the first demonstration of a point mutation disrupting an exon splice enhancer that causes exon skipping along with utilization of a cryptic exon.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Center for Integrative Human Physiology
04 Faculty of Medicine > University Children's Hospital Zurich > Medical Clinic
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:16 October 2009
Deposited On:19 Oct 2009 15:36
Last Modified:05 Apr 2016 13:30
Publisher:American Society for Biochemistry and Molecular Biology
ISSN:0021-9258
Additional Information:This research was originally published in: Stucki, M; Suormala, T; Fowler, B; Valle, D; Baumgartner, M R (2009). Cryptic exon activation by disruption of exon splice enhancer: novel mechanism causing 3-methylcrotonyl-CoA carboxylase deficiency. Journal of Biological Chemistry, 284(42):28953-28957. © the American Society for Biochemistry and Molecular Biology
Publisher DOI:10.1074/jbc.M109.050674
PubMed ID:19706617
Permanent URL: http://doi.org/10.5167/uzh-23232

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