CACP, encoding a secreted proteoglycan, is mutated in camptodactyly-arthropathy-coxa vara-pericarditis syndrome.

Altered growth and function of synoviocytes, the intimal cells which line joint cavities and tendon sheaths, occur in a number of skeletal diseases. Hyperplasia of synoviocytes is found in both rheumatoid arthritis and osteoarthritis, despite differences in the underlying aetiologies of the two disorders. We have studied the autosomal recessive disorder camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP; MIM 208250) to identify biological pathways that lead to synoviocyte hyperplasia, the principal pathological feature of this syndrome. Using a positional-candidate approach, we identified mutations in a gene (CACP) encoding a secreted proteoglycan as the cause of CACP. The CACP protein, which has previously been identified as both 'megakaryocyte stimulating factor precursor' and 'superficial zone protein', contains domains that have homology to somatomedin B, heparin-binding proteins, mucins and haemopexins. In addition to expression in joint synovium and cartilage, CACP is expressed in non-skeletal tissues including liver and pericardium. The similarity of CACP sequence to that of other protein families and the expression of CACP in non-skeletal tissues suggest it may have diverse biological activities.     

A humanized model for multiple sclerosis using HLA-DR2 and a human T-cell receptor

Multiple sclerosis (MS) is a complex chronic neurologic disease with a suspected autoimmune pathogenesis. Although there is evidence that the development of MS is determined by both environmental influences and genes, these factors are largely undefined, except for major histocompatibility (MHC) genes. Linkage analyses and association studies have shown that susceptibility to MS is associated with genes in the human histocompatibility leukocyte antigens (HLA) class II region, but the contribution of these genes to MS disease development less compared with their contribution to disorders such as insulin-dependent diabetes mellitus. Due to the strong linkage disequilibrium in the MHC class II region, it has not been possible to determine which gene(s) is responsible for the genetic predisposition. In transgenic mice, we have expressed three human components involved in T-cell recognition of an MS-relevant autoantigen presented by the HLA-DR2 molecule: DRA*0101/DRB1*1501 (HLA-DR2), an MHC class II candidate MS susceptibility genes found in individuals of European descent; a T-cell receptor (TCR) from an MS-patient-derived T-cell clone specific for the HLA-DR2 bound immunodominant myelin basic protein (MBP) 4102 peptide; and the human CD4 coreceptor. The amino acid sequence of the MBP 84-102 peptide is the same in both human and mouse MBP. Following administration of the MBP peptide, together with adjuvant and pertussis toxin, transgenic mice developed focal CNS inflammation and demyelination that led to clinical manifestations and disease courses resembling those seen in MS. Spontaneous disease was observed in 4% of mice. When DR2 and TCR double-transgenic mice were backcrossed twice to Rag2 (for recombination-activating gene 2)-deficient mice, the incidence of spontaneous disease increased, demonstrating that T cells specific for the HLA-DR2 bound MBP peptide are sufficient and necessary for development of disease. Our study provides evidence that HLA-DR2 can mediate both induced and spontaneous disease resembling MS by presenting an MBP self-peptide to T cells.     

Spastin, a new AAA protein, is altered in the most frequent form of autosomal dominant spastic paraplegia

Autosomal dominant hereditary spastic paraplegia (AD-HSP) is a genetically heterogeneous neurodegenerative disorder characterized by progressive spasticity of the lower limbs. Among the four loci causing AD-HSP identified so far, the SPG4 locus at chromosome 2p2-1p22 has been shown to account for 40-50% of all AD-HSP families. Using a positional cloning strategy based on obtaining sequence of the entire SPG4 interval, we identified a candidate gene encoding a new member of the AAA protein family, which we named spastin. Sequence analysis of this gene in seven SPG4-linked pedigrees revealed several DNA modifications, including missense, nonsense and splice-site mutations. Both SPG4 and its mouse orthologue were shown to be expressed early and ubiquitously in fetal and adult tissues. The sequence homologies and putative subcellular localization of spastin suggest that this ATPase is involved in the assembly or function of nuclear protein complexes.     

Cytotoxic T-cell immunity to virus-infected non-haematopoietic cells requires presentation of exogenous antigen

Cytotoxic T lymphocytes (CTLs) are thought to detect viral infections by monitoring the surface of all cells for the presence of viral peptides bound to major histocompatibility complex (MHC) class I molecules. In most cells, peptides presented by MHC class I molecules are derived exclusively from proteins synthesized by the antigen-bearing cells. Macrophages and dendritic cells also have an alternative MHC class I pathway that can present peptides derived from extracellular antigens; however, the physiological role of this process is unclear. Here we show that virally infected non-haematopoietic cells are unable to stimulate primary CTL-mediated immunity directly. Instead, bone-marrow-derived cells are required as antigen-presenting cells (APCs) to initiate anti-viral CTL responses. In these APCs, the alternative (exogenous) MHC class I pathway is the obligatory mechanism for the initiation of CTL responses to viruses that infect only non-haematopoietic cells.     

Chaperone-like activity of the AAA domain of the yeast Yme1 AAA protease

The AAA domain, a conserved Walker-type ATPase module, is a feature of members of the AAA family of proteins, which are involved in many cellular processes, including vesicular transport, organelle biogenesis, microtubule rearrangement and protein degradation. The function of the AAA domain, however, has not been explained. Membrane-anchored AAA proteases of prokaryotic and eukaryotic cells comprise a subfamily of AAA proteins that have metal-dependent peptidase activity and mediate the degradation of non-assembled membrane proteins. Inactivation of an orthologue of this protease family in humans causes neurodegeneration in hereditary spastic paraplegia. Here we investigate the AAA domain of the yeast protein Yme1, a subunit of the iota-AAA protease located in the inner membrane of mitochondria. We show that Yme1 senses the folding state of solvent-exposed domains and specifically degrades unfolded membrane proteins. Substrate recognition and binding are mediated by the amino-terminal region of the AAA domain. The purified AAA domain of Yme1 binds unfolded polypeptides and suppresses their aggregation. Our results indicate that the AAA domain of Ymel has a chaperone-like activity and suggest that the AAA domains of other AAA proteins may have a similar function.     

Electrical conduction through DNA molecules

The question of whether DNA is able to transport electrons has attracted much interest, particularly as this ability may play a role as a repair mechanism after radiation damage to the DNA helix. Experiments addressing DNA conductivity have involved a large number of DNA strands doped with intercalated donor and acceptor molecules, and the conductivity has been assessed from electron transfer rates as a function of the distance between the donor and acceptor sites. But the experimental results remain contradictory, as do theoretical predictions. Here we report direct measurements of electrical current as a function of the potential applied across a few DNA molecules associated into single ropes at least 600 nm long, which indicate efficient conduction through the ropes. We find that the resistivity values derived from these measurements are comparable to those of conducting polymers, and indicate that DNA transports electrical current as efficiently as a good semiconductor. This property, and the fact that DNA molecules of specific composition ranging in length from just a few nucleotides to chains several tens of micrometres long can be routinely prepared, makes DNA ideally suited for the construction of mesoscopic electronic devices.