TIA nuclear proteins regulate the alternate splicing of lysyl hydroxylase 2.

Synthesis of collagen, a major component of the extracellular matrix, is increased dramatically in fibrotic conditions such as scleroderma. This overaccumulation of collagen is associated with increased pyridinoline cross-links. These cross-links are derived by the action of the alternatively spliced long form of lysyl hydroxylase 2 (LH2), a collagen telopeptide LH. As LH2 (long) is reported to be overexpressed in scleroderma fibroblasts, the regulation of LH2 splicing suggests an important step in controlling fibrosis. Using an LH2 minigene, we have compared the regulation of the alternative splicing pattern of LH2, both endogenously and in the minigene, by the RNA-binding splicing proteins TIA-1 and TIAL1 (T-cell-restricted intracellular antigens). A decrease in the ratio of LH2 (long) to LH2 (short) was observed in fibroblasts from TIAL1 knockout mice, and in HEK293 cells knocked down for TIA-1 and TIAL1. As a corollary, overexpression of TIA-1/TIAL1 in HEK293 cells resulted in an increase in LH2 (long) minigene transcripts, accompanied by a decrease in LH2 (short). In scleroderma fibroblasts, a double TIA-1/TIAL1 knockdown reduced the ratio of LH2 (long) to LH2 (short) by over fivefold compared to controls. Identification of these TIA regulatory factors therefore suggests a tool to manipulate cellular LH2 levels in scleroderma so that potential intervention therapies may be identified.

An Ehlers-Danlos syndrome type VIA patient with cystic malformations of the meninges.

We have characterized a patient with the phenotype of Ehlers-Danlos syndrome type VIA (EDS VIA: kyphoscoliotic form), accompanied by the unique feature of cystic malformations of the meninges, to be homozygous for a large duplication of 8.9 kb in the lysyl hydroxylase 1 (LH1) gene that is the cause of severely decreased levels of LH activity in her skin fibroblasts. Electrophoresis of full length cDNA for LH1, prepared from the patient's fibroblasts and amplified by PCR, showed an abnormally large DNA fragment indicative of a duplication mutation; this mutation was confirmed in genomic DNA by PCR using duplication-specific primers and sequence analysis of the duplication junction. The homozygosity of this mutation was confirmed by analysis of DNA from the unaffected parents which showed them to be carriers of this duplication. This seven exon duplication is the most common mutation in the LH1 gene in patients with EDS VIA and occurs via a homologous recombination of Alu sequences in introns 9 and 16. Using the data from this study and other recent reports, we have updated the allele frequency for this mutation, based on 19 duplicated alleles out of a total of 104 genetically independent alleles from 53 EDS VIA families, to be 18.3%.

A novel mutation in the lysyl hydroxylase 1 gene causes decreased lysyl hydroxylase activity in an Ehlers-Danlos VIA patient.

The clinical diagnosis of a patient with the phenotype of Ehlers-Danlos syndrome type VI was confirmed biochemically by the severely diminished level of lysyl hydroxylase (LH) activity in the patient's skin fibroblasts. A novel homozygous mutation, a single base change of T(1360)-->G in exon 13 of the LH1 gene, predicted to result in W446G, was identified in the patient's full-length cDNA. This was confirmed in genomic DNA from both the patient and her parents, who were heterozygous for the mutation. This mutation was introduced into an LH1-pAcGP67 baculoviral construct and expressed, in parallel with normal LH1, in an insect cell system. The loss of LH activity in the mutated recombinant construct confirmed the pathogenicity of this mutation. Although not in the major catalytic site, this mutation occurs in a highly conserved region of the LH1 gene and may contribute to loss of activity by interfering with normal folding of the enzyme.

Tissue-specific expression and regulation of the alternatively-spliced forms of lysyl hydroxylase 2 (LH2) in human kidney cells and skin fibroblasts.

Lysyl hydroxylases 1, 2, and 3 catalyse the hydroxylation of specific lysines in collagen. A small percentage of these hydroxylysine residues are precursors for the cross-link formation essential for the tensile strength of collagen. Lysyl hydroxylase 2 (LH2) exists as two alternatively-spliced forms; the long transcript (the major ubiquitously-expressed form) includes a 63 bp exon (13A) that is spliced out in the short form (expressed, together with the long form, in human kidney, spleen, liver, and placenta). This study shows that this alternative splicing event can be regulated by both cell density and cycloheximide (CHX). Although only the long form of LH2 is detected in untreated confluent human skin fibroblasts, after 24 h treatment with CHX the short LH2 transcript is also expressed. In kidney cells, in which both LH2 transcripts are equally expressed, the long LH2 transcript is significantly decreased after 24 h CHX treatment, whereas expression of the short transcript is slightly increased. This suggests that, in kidney cells, the splicing mechanism for the inclusion of exon 13A in LH2 requires a newly-synthesized protein factor that is suppressed by CHX, whereas, in skin fibroblasts in which levels of LH2 (long) are unaffected, CHX appears to suppress a factor that inhibits exclusion of exon 13A, thereby promoting expression of LH2 (short). As these alternate transcripts of LH2 may have specificity for hydroxylation of lysines in either telopeptide or helical collagen domains, their relative expression determines the type of cross-links formed, thereby affecting collagen strength. Therefore, any perturbation of the regulation of LH2 splicing could influence the stability of the extracellular matrix and contribute to specific connective tissue disorders.