Constitutive lysosomal targeting and degradation of bovine endothelin-converting enzyme-1a mediated by novel signals in its alternatively spliced cytoplasmic tail.

Endothelin-converting enzyme-1 (ECE-1) is a type II membrane protein that catalyzes the proteolytic activation of big endothelin-1 to endothelin-1 (ET-1). The subcellular distribution of ECE-1, and hence the exact site of physiological activation of big ET-1, remains controversial. Here, we demonstrate with several complementary methods that the two alternatively spliced bovine ECE-1 isoforms, ECE-1a and ECE-1b, differing only in the first 30 amino acids of their N-terminal cytoplasmic tails, exhibit strikingly distinct intracellular sorting patterns. Bovine ECE-1a, which is responsible for the intracellular cleavage of big ET-1 in endothelial cells, is constitutively recruited into the lysosome, where it is rapidly degraded. In contrast, bovine ECE-1b, the isoform found in cultured smooth muscle cells, is transported to the plasma membrane by a default pathway and functions as an ectoenzyme. Mutational analyses reveal that the N-terminal tip of the cytoplasmic domain of bovine ECE-1a contains novel proline-containing signals that mediate constitutive lysosomal targeting. Analyses of chimeric ECE-1/transferrin receptors demonstrate that the cytoplasmic tail of bovine ECE-1a is sufficient for the lysosomal delivery and rapid degradation. Our results suggest that the distinct intracellular targeting of bovine ECE-1 isoforms may provide new insights into functional aspect of the endothelin system and that the cell permeability of ECE inhibitor compounds should be carefully considered during their pharmacological development.

Deletion of twenty seven nucleotides within exon 11 of the band 3 gene identified in ovalocytosis in Lombok Island, Indonesia.

This study reports the molecular characterization of ovalocytosis in Lombok Island, Indonesia. The analysis of genomic DNA by polymerase chain reaction shows that all 21 ovalocytotic individuals have two amplified products of different size from a region encompassing exon 11 of the band 3 gene. The sequence of the larger product matched perfectly with that of normal individuals. In the sequence of the smaller product, 27 nucleotides within exon 11 were deleted. The heterozygous presence of the deletion identified in other parts of Southeast Asia was confirmed in patients with ovalocytosis in an isolated island of eastern Indonesia.

Japanese cases of type 1 thanatophoric dysplasia exclusively carry a C to T transition at nucleotide 742 of the fibroblast growth factor receptor 3 gene.

Type I thanatophoric dysplasia (TD) is typically a lethal neonatal dwarfism, but a limited number of cases of type I TD cases survive more than one year, suggesting genetic heterogeneity. In this study, we analyzed the fibroblast growth factor receptor 3 (FGFR3) gene in 5 Japanese cases of type I TD with clinical symptoms ranging from lethal to long-survival. In every case, nucleotide sequence analysis of cDNA revealed a C to T transition at nucleotide 742 (C742T) in one allele of the FGFR3 gene, suggesting that type I TD is a rather homogeneous genetic condition, irrespective of clinical course. No association was found between C742T and C882T, although both nucleotides changes were from CpG dinucleotide in a near location.

Induction of exon skipping of the dystrophin transcript in lymphoblastoid cells by transfecting an antisense oligodeoxynucleotide complementary to an exon recognition sequence.

In this paper we first report that exon skipping from the dystrophin gene transcript could be induced in living cells by an antisense oligodeoxynucleotide (ODN) complementary to an exon recognition sequence (ERS). Incubation of lymphoblastoid cells with an antisense ODN against the purine-rich region of dystrophin exon 19 resulted in skipping of the exon from the dystrophin transcript. Skipping of exon 19 started to appear after 6 hours of incubation, and complete skipping was observed after 24 hours of incubation. None of the other 78 dystrophin exons were skipped, and exon 19 skipping could be induced by the sense ODN or by an antisense ODN corresponding to another ERS. These results showed that antisense ODN against ERS can induce exon skipping even in living cells and ERS is functioning as an essential cis-element for proper splicing in dystrophin pre-mRNA.

A case of Becker muscular dystrophy resulting from the skipping of four contiguous exons (71-74) of the dystrophin gene during mRNA maturation.

The mutations in one-third of both Duchenne and Becker muscular dystrophy patients remain unknown because they do not involve gross rearrangements of the dystrophin gene. Here we report the first example of multiple exon skipping during the splicing of dystrophin mRNA precursor encoded by an apparently normal dystrophin gene. A 9-year-old Japanese boy exhibiting excessive fatigue and high serum creatine kinase activity was examined for dystrophinopathy. An immunohistochemical study of muscle tissue biopsy disclosed faint and discontinuous staining of the N-terminal and rod domains of dystrophin but no staining at all of the C-terminal domain of dystrophin. The dystrophin transcript from muscle tissue was analyzed by the reverse transcriptase polymerase chain reaction. An amplified product encompassing exons 67-79 of dystrophin cDNA was found to be smaller than that of the wild-type product. Sequence analysis of this fragment showed that the 3' end of exon 70 was directly connected to the 5' end of exon 75 and, thus, that exons 71-74 were completely absent. As a result, a truncated dystrophin protein lacking 110 amino acids from the C-terminal domain should result from translation of this truncated mRNA, and the patient was diagnosed as having Becker muscular dystrophy at the molecular level. Genomic DNA was analyzed to identify the cause of the disappearance of these exons. Every exon-encompassing region could be amplified from genomic DNA, indicating that the dystrophin gene is intact. Furthermore, sequencing of these amplified products did not disclose any particular nucleotide change that could be responsible for the multiple exon skipping observed. Considering that exons 71-74 are spliced out alternatively in some tissue-specific isoforms, to suppose that the alternative splicing machinery is present in the muscle tissue of the index case and that it is activated by an undetermined mechanism is reasonable. These results illustrate a novel genetic anomaly that results in dystrophinopathy.

A novel mutation substituting tryptophan with arginine in the carboxyl-terminal, non-collagenous domain of collagen X in a case of Schmid metaphyseal chondrodysplasia.

A novel nucleotide change in the collagen X gene was identified in a Japanese family with Schmid metaphyseal chondrodysplasia (SMCD). The T to C change at nucleotide 1951 resulted in replacement of tryptophan by arginine at residue 651 (W651R). This missense mutation is considered to be responsible for SMCD because 1, the same mutation was not be identified in the collagen X gene from normal individuals; 2, the mutation segregated with the SMCD phenotype in the index family; 3, the substituted amino acid is highly conserved in type X collagens, and 4, the mutation causes a marked change in the hydrophobicity profile of the surrounding region in the NC1 domain. This novel mutation (W651) seems to have the same impact on bone development as W651X mutation.