Disease relevance of HAPLN1

• OBJECTIVE: To determine whether patients with osteoarthritis (OA) express cellular immunity to cartilage link protein (LP) and the G1 globular domain of proteoglycan (PG) aggrecan, and whether immunity to the G1 domain is influenced by the removal of keratan sulfate (KS) [1].
• It has been established that suppression of uPA expression and invasiveness by UTI is mediated through inhibition of protein kinase C-dependent signaling pathways and that human chondrosarcoma cell line HCS-2/8 expresses two types of UTI-BPs; a 40-kDa UTI-BP (UTI-BP(40)), which is identical to link protein (LP), and a 45-kDa UTI-BP (UTI-BP(45)) [2].
• Expression of the Myxococcus xanthus gene crtl is controlled by a light-inducible promoter [3].
• Aberrations of the long arm of chromosome 5 (5q) were studied in 79 clear cell renal carcinomas (clear cell RCC) by LOH (loss of heterozygosity) method, using microsatellite markers D5S107, CRTL1, LNS-CA, IL-9.RP1, CFS1R and GeneScan analysis software [4].
• This study used a cross-sectional comparison of endurance athletes (n=20; ATHL) exhibiting resting bradycardia and age-matched nonathletes (n=12; CRTL) to indirectly assess training effects on amplitude and timing characteristics of respiratory sinus arrhythmia (RSA) [5].
• Proliferation, motility, invasion, and soft-agar colony formation assays on mesothelioma cells overexpressing full-length HAPLN1 or its functional domains strongly supported the protumorigenic role of HAPLN1 and its SP-IgV domain [6].

High impact information on HAPLN1

• Detection of LP was by means of an antiserum directed against a peptide from the NH2-terminal half of LP [7].
• Polylysine could not inhibit the interaction of LP with HA [7].
• SOX9 induced CRTL1 expression effectively in human non-chondrocytic immortalized cell lines as well as in mesenchymal stem cell and adult dermal fibroblast [8].
• Cartilage link protein is a key component of the cartilage extracellular matrix [8].
• These findings suggest that the enhancer elements may mediate differential expression of CRTL1 during chondrocyte differentiation and maturation [8].

Biological context of HAPLN1

• Two cis-acting enhancer elements resided in the 5'-untranslated region of CRTL1 [8].
• Here, we investigated the regulation of CRTL1 by SOX9, a key regulator of cartilage matrix genes and chondrogenesis [8].
• Subsequent refinement of the physical map allows ordering of known polymorphic microsatellites and excludes CRTL1 as a likely candidate for the disorder [9].
• Refined genetic and physical localization of the Wagner disease (WGN1) locus and the genes CRTL1 and CSPG2 to a 2- to 2.5-cM region of chromosome 5q14.3 [9].
• Complete amino acid sequence of human cartilage link protein (CRTL1) deduced from cDNA clones and chromosomal assignment of the gene [10].

Anatomical context of HAPLN1

• METHODS: LP and the G1 globular domain of PG were isolated from human and/or bovine cartilage and used in proliferation assays with peripheral blood lymphocytes (PBL) from 42 patients with OA and 40 healthy control subjects [1].
• Our results suggest that LP is involved in the stabilization of extracellular matrices of a wide variety of non-cartilaginous tissues [11].
• Investigations on the interactions between LP and proteoglycans from skin and proventriculus demonstrate that LP can enhance the binding of proteoglycans from these tissues to HA [11].
• LP is localized in the extracellular matrix of the mesoderm along the entire digestive tract and in the dermis of the embryonic skin as revealed by immunofluorescence analysis [11].
• METHODS: Aggrecan and LP were prepared from fetal bovine epiphyseal cartilage, and PG aggregates were formed in the presence or absence of LP [12].

Associations of HAPLN1 with chemical compounds

• Link protein (LP) is an abundant protein of cartilage which stabilizes the interaction of aggrecan with hyaluronic acid (HA) [11].
• The concentration of LP was less than that of the G1-domain in all extracts of cartilage from individuals over 13 years, but this was particularly noticeable in the 1 M guanidinium chloride extracts, and it was surmised that a deficiency in LP produces unstable aggregates in situ [13].
• Degradation of HA, aggrecan and LP were assessed by gel filtration chromatography and polyacrylamide gel electrophoresis [12].
• The proteoglycan aggregate, including LP, is dissociated in the presence of chaotropes such as 4 M guanidine hydrochloride [14].
• The proteoglycan aggregate, including LP, is dissociated in the presence of chaotropes such as 4 M guanidine hydrochloride [15].

Regulatory relationships of HAPLN1

• RESULTS: Patients with RA (34%) and AS (71%) expressed a significantly higher prevalence of cellular immune responses to human LP compared with the healthy control group (13%) [16].

Other interactions of HAPLN1

• Within the critical region lie genes encoding two extracellular macromolecules, link protein (CRTL1) and versican (CSPG2), which are important in binding hyaluronan, a significant component of the mammalian vitreous gel, and which therefore represent excellent candidates for Wagner syndrome [9].
• Half the patients with RA responding to LP exhibited cellular immunity to both human and bovine protein [16].
• The distribution of cartilage proteoglycan core protein (aggrecan) and cartilage proteoglycan link protein was investigated by in situ hybridization during different stages of human skeletal development [17].
• We demonstrate, using RNase protection experiments, that the coding region of the LP mRNAs isolated from these tissues is identical to that present in cartilage [11].
• Histological and immunohistochemical analysis of the TGF-beta 1-treated PLA/alginate amalgam and PLA constructs showed development of a cartilaginous phenotype from day 7 to day 21 as demonstrated by colocalization of Alcian blue staining with collagen type II and cartilage proteoglycan link protein [18].

Analytical, diagnostic and therapeutic context of HAPLN1

• Furthermore, we show that the LP mRNAs are translated in non-cartilaginous tissues by the identification of LP polypeptides with monoclonal antibody 4B6/A5 in Western blots [11].
• Cartilage link protein of high purity was prepared and used in an enzyme linked immunosorbent assay (ELISA) [19].
• METHOD: Six dinucleotide STRs (D2S123, D5S107, CRTL1, D7S500, D11S1356, and TP53) were analyzed by touchdown (TD)-PCR followed by medium size non-denaturing polyacrylamide gel electrophoresis and silver staining [20].

References