Lysyl oxidase (LOX) is an enzyme responsible for the cross-linking of collagen and elastin both in vitro and in vivo. The unique functions of the individual members of this multigene family have been difficult to ascertain because of highly conserved catalytic domains and overlapping tissue expression patterns. To address this problem of functional and structural redundancy and to determine the role of LOX in the development of tissue integrity, Lox gene expression was deleted by targeted mutagenesis in mice. Lox-targeted mice (LOX ؊/؊ ) died soon after parturition, exhibiting cardiovascular instability with ruptured arterial aneurysms and diaphragmatic rupture. Microscopic analysis of the aorta demonstrated fragmented elastic fiber architecture in homozygous mutant null mice. LOX activity, as assessed by desmosine (elastin cross-link) analysis, was reduced by ϳ60% in the aorta and lungs of homozygous mutant animals compared with wild type mice. Immature collagen cross-links were decreased but to a lesser degree than elastin cross-links in LOX ؊/؊ mice. Thus, lysyl oxidase appears critical during embryogenesis for structural stability of the aorta and diaphragm and connective tissue development.

GCRI gene function is required for high-level glycolytic gene expression in Saccharomyces cerevisiae.Recently, we suggested that the CTTCC sequence motif found in front of many genes encoding glycolytic enzymes lay at the core of the GCR1-binding site. Here we mapped the DNA-binding domain of GCR1 to the carboxy-terminal 154 amino acids of the polypeptide. DNase I protection studies showed that a hybrid MBP-GCR1 fusion protein protected a region of the upstream activating sequence of TPI (UASTpI), which harbored the CTTCC sequence motif, and suggested that the fusion protein might also interact with a region of the UAS that contained the related sequence CATCC. A series of in vivo G methylation protection experiments of the native TPI promoter were carried out with wild-type and gcrl deletion mutant strains. The G doublets that correspond to the C doublets in each site were protected in the wild-type strain but not in the gcrl mutant strain. These data demonstrate that the UAS of TPI contains two GCRl-binding sites which are occupied in vivo. Furthermore, adjacent RAPl/GRFI/TUF-and REB1/GRF2/QBP/Y-binding sites in UASTp, were occupied in the backgrounds of both strains. In addition, DNA band-shift assays were used to show that the MBP-GCR1 fusion protein was able to form nucleoprotein complexes with oligonucleotides that contained CTTCC sequence elements found in front of other glycolytic genes, namely, PGK, ENO], PYK, and ADHi, all of which are dependent on GCRI gene function for full expression. However, we were unable to detect specific interactions with CTTCC sequence

These studies were undertaken to determine how lysyl oxidase (LOX) and lysyl oxidase like-1 (LOXL) enzymes are targeted to their substrates in the extracellular matrix. Full-length LOX/LOXL and constructs containing just the pro-regions of each enzyme localized to elastic fibers when expressed in cultured cells. However, the LOXL catalytic domain without the pro-region was secreted into the medium but did not associate with matrix. Ligand blot and mammalian two-hybrid assays confirmed an interaction between tropoelastin and the pro-regions of both LOX and LOXL. Immunofluorescence studies localized both enzymes to elastin at the earliest stages of elastic fiber assembly. Our results showed that the proregions of LOX and LOXL play a significant role in directing the deposition of both enzymes onto elastic fibers by mediating interactions with tropoelastin. These findings confirmed that an important element of substrate recognition lies in the pro-domain region of the molecule and that the pro-form of the enzyme is what initially interacts with the matrix substrate. These results have raised the interesting possibility that sequence differences between the prodomain of LOX and LOXL account for some of the functional differences observed for the two enzymes.Production of a mature and functional elastic fiber is a complex process that is only partially understood. Monomers of elastin (tropoelastin) are cross-linked in the extracellular space by one or more members of the lysyl oxidase (LO) 3 gene family to form an elastin polymer, which is the functional form of the mature protein. Fibrillin-containing microfibrils are thought to play an important role in the assembly process by serving as a scaffold for aligning cross-linking domains within tropoelastin. Recently, several other proteins, such as members of the fibulin and emilin families, have been suggested to play a role in elastic fiber formation, although their exact function has not yet been determined (1).LOs are extracellular copper-requiring enzymes that catalyze the cross-linking of collagen and elastin through oxidative deamination of lysine or hydroxylysine side chains. The resultant allysine residues can then spontaneously condense with vicinal peptidyl aldehydes or with ⑀-amino groups of peptidyl lysines to generate covalent cross-linkages.There are five members of the LO family: lysyl oxidase (LOX) and lysyl oxidase-like 1-4 (LOXL 1-4) (reviewed in Ref.2). The C-terminal region of all of the LO family members contains the elements required for catalytic activity (the copper binding site, tyrosyl and lysyl residues that contribute to the carbonyl cofactor, and 10 cysteine residues), and the high sequence homology in this region suggests that all family members share a common enzymatic mechanism. The N-terminal regions, in contrast, show the greatest variability in size and sequence.The genes for LOX and LOXL have a similar exon structure consisting of seven exons, five of which (exons 2-6) are of similar size and encode proteins with 76% amino acid iden...

Pseudoexfoliation (PEX) syndrome is a generalized disease of the extracellular matrix and the most common identifiable cause of open-angle glaucoma. Two single nucleotide polymorphisms in the lysyl oxidase-like 1 (LOXL1) gene (rs1048661 and rs3825942) have been recently identified as strong genetic risk factors for both PEX syndrome and PEX glaucoma. Here we investigated the expression and localization of LOXL1, LOXL2, and lysyl oxidase (LOX) in tissues of PEX syndrome/glaucoma patients and controls in correlation with their individual single nucleotide polymorphism genotypes and stages of disease. LOXL1 ocular expression was reduced by ϳ20% per risk allele of rs1048661, whereas risk alleles of rs3825942, which were highly overrepresented in PEX cases, did not affect LOXL1 expression levels. Irrespective of the individual genotype, LOXL1 expression was significantly increased in early PEX stages but was decreased in advanced stages both with and without glaucoma compared with controls, whereas LOX and LOXL2 showed no differences between groups. LOXL1 was also found to be a major component of fibrillar PEX aggregates in both intraand extraocular locations and to co-localize with various elastic fiber components. These findings provide evidence for LOXL1 involvement in the initial stages of abnormal fibrogenesis in PEX tissues. Alterations of LOXL1 activation, processing, and/or substrate specificity may contribute to the abnormal aggregation of elastic fiber components into characteristic PEX fibrils.

Dosage compensation of X-linked genes in male and female mammals is accomplished by random inactivation of one X chromosome in each female somatic cell. As a result, a transcriptionally active allele and a transcriptionally inactive allele of most X-linked genes reside within each female nucleus. To examine the mechanism responsible for maintaining this unique system of differential gene expression, we have analyzed the differential binding of regulatory proteins to the 5' region of the human hypoxanthine phosphoribosyltransferase (HPRT) gene on the active and inactive X chromosomes. Studies of DNA-protein interactions associated with the transcriptionally active and inactive HPRT alleles were carried out in intact cultured cells by in vivo footprinting by using ligation-mediated polymerase chain reaction and dimethyl sulfate. Analysis of the active allele demonstrates at least six footprinted regions, whereas no footprints were detected on the inactive allele.Of the footprints on the active allele, at least four occur over canonical GC boxes or Spl consensus binding sites, one is associated with a potential AP-2 binding site, and another is associated with a DNA sequence not previously reported to interact with a sequence-specific DNA-binding factor. While no footprints were observed for the HPRT gene on the inactive X chromosome, reactivation of the inactive allele with 5-azacytidine treatment restored the in vivo footprint pattern found on the active allele. Results of these experiments, in coijunction with recent studies on the X-linked human PGK-1 gene, bear implications for models of X chromosome inactivation.The random inactivation of a single X chromosome during normal mammalian female embryogenesis results in a unique system of differential gene expression in which a transcriptionally active X chromosome and transcriptionally inactive X chromosome occupy the same nucleus. The inactivation of genes on one X chromosome in female somatic cells compensates for the dosage imbalance of X-linked genes between the sexes (8, 9). The molecular mechanisms responsible for initiating, spreading, and maintaining X chromosome inactivation are unknown. However, DNA-protein interactions (8, 28), chromatin structure (20,34,36), DNA replication (7, 47), and DNA methylation (19,24,25,31,38,55,57) have all been postulated to be involved. Though X inactivation is a chromosome-wide phenomenon and process, some degree of regulation at the level of individual X-linked genes must also be involved, as indicated by the ability to independently reactivate individual genes on the inactive X chromosome by 5-azacytidine (5-azaC) (12,13,31,49,50).The differential expression of genes on the active and inactive X chromosomes is manifested by a difference in nuclease sensitivity of chromatin from the active and inactive alleles of the X-linked hypoxanthine-guanine phosphoribosyltransferase (HiPRT) and phosphoglycerate kinase (PGK-1) genes (12,23,39,40,54,56). Furthermore, the presence of DNase I hypersensitive sites in the 5' region of * ...