Chondroitin synthase 1 is a key molecule in myeloma cell-osteoclast interactions

There is a symbiotic relationship between continued growth and proliferation of myeloma cells and the bone destructive process. It has been shown in animal models that blocking bone destruction can result in decreased myeloma tumor burden. Osteoclasts are bone destroying cells found in the bone marrow, and their significance in myeloma is supported by recent findings that osteoclasts alone can support sustained survival and proliferation of purified primary myeloma cells in ex vivo co-cultures. However, molecular mechanisms associated with interactions between myeloma cells and osteoclasts remain unclear. Here, we show that when myeloma plasma cells are co-cultured with osteoclasts, chondroitin synthase 1 (CHSY1) is the most significantly altered soluble, secreted protein present in the conditioned medium. RNA interference experiments with CHSY1 small interfering RNA (siRNA) reduced the amount of CHSY1 in the co-culture conditioned medium, and this was associated with a 6.25-fold increase in apoptotic myeloma cells over control co-cultures. CHSY1 contains a Fringe domain, and Fringe is well known for its regulation of Notch signaling via its DDD motif. And interestingly, Fringe domain in CHSY1 has this DDD motif. Shortly after co-culture with osteoclasts, we found that the Notch2 receptor was activated in myeloma cells but Notch1 was not. Activation of Notch2 was down-regulated by CHSY1 siRNA treatment. Modulating Notch signaling by CHSY1 via its DDD motif provides new insight into mechanisms of the interactions between myeloma cells and their bone marrow microenvironment. Targeting this interaction could shed light on treatment of myeloma, which is currently incurable.     

Galactose differentially modulates lunatic and manic fringe effects on Delta1-induced NOTCH signaling

NOTCH signaling induced by Delta1 (DLL1) and Jagged1 (JAG1) NOTCH ligands is modulated by the β3N-acetylglucosaminyl transferase Fringe. LFNG (Lunatic Fringe) and MFNG (Manic Fringe) transfer N-acetylglucosamine (GlcNAc) to O-fucose attached to EGF-like repeats of NOTCH receptors. In co-culture NOTCH signaling assays, LFNG generally enhances DLL1-induced, but inhibits JAG1-induced, NOTCH signaling. In mutant Chinese hamster ovary (CHO) cells that do not add galactose (Gal) to the GlcNAc transferred by Fringe, JAG1-induced NOTCH signaling is not inhibited by LFNG or MFNG. In mouse embryos lacking B4galt1, NOTCH signaling is subtly reduced during somitogenesis. Here we show that DLL1-induced NOTCH signaling in CHO cells was enhanced by LFNG, but this did not occur in either Lec8 or Lec20 CHO mutants lacking Gal on O-fucose glycans. Lec20 mutants corrected with a B4galt1 cDNA became responsive to LFNG. By contrast, MFNG promoted DLL1-induced NOTCH signaling better in the absence of Gal than in its presence. This effect was reversed in Lec8 cells corrected by expression of a UDP-Gal transporter cDNA. The MFNG effect was abolished by a DDD to DDA mutation that inactivates MFNG GlcNAc transferase activity. The binding of soluble NOTCH ligands and NOTCH1/EGF1-36 generally reflected changes in NOTCH signaling caused by LFNG and MFNG. Therefore, the presence of Gal on O-fucose glycans differentially affects DLL1-induced NOTCH signaling modulated by LFNG versus MFNG. Gal enhances the effect of LFNG but inhibits the effect of MFNG on DLL1-induced NOTCH signaling, with functional consequences for regulating the strength of NOTCH signaling.     

NOTCH2 mutations cause Alagille syndrome, a heterogeneous disorder of the notch signaling pathway

Alagille syndrome (AGS) is caused by mutations in the gene for the Notch signaling pathway ligand Jagged1 (JAG1), which are found in 94% of patients. To identify the cause of disease in patients without JAG1 mutations, we screened 11 JAG1 mutation-negative probands with AGS for alterations in the gene for the Notch2 receptor (NOTCH2). We found NOTCH2 mutations segregating in two families and identified five affected individuals. Renal manifestations, a minor feature in AGS, were present in all the affected individuals. This demonstrates that AGS is a heterogeneous disorder and implicates NOTCH2 mutations in human disease.     

Temtamy preaxial brachydactyly syndrome is caused by loss-of-function mutations in chondroitin synthase 1, a potential target of BMP signaling

Altered Bone Morphogenetic Protein (BMP) signaling leads to multiple developmental defects, including brachydactyly and deafness. Here we identify chondroitin synthase 1 (CHSY1) as a potential mediator of BMP effects. We show that loss of human CHSY1 function causes autosomal-recessive Temtamy preaxial brachydactyly syndrome (TPBS), mainly characterized by limb malformations, short stature, and hearing loss. After mapping the TPBS locus to chromosome 15q26-qterm, we identified causative mutations in five consanguineous TPBS families. In zebrafish, antisense-mediated chsy1 knockdown causes defects in multiple developmental processes, some of which are likely to also be causative in the etiology of TPBS. In the inner ears of zebrafish larvae, chsy1 is expressed similarly to the BMP inhibitor dan and in a complementary fashion to bmp2b. Furthermore, unrestricted Bmp2b signaling or loss of Dan activity leads to reduced chsy1 expression and, during epithelial morphogenesis, defects similar to those that occur upon Chsy1 inactivation, indicating that Bmp signaling affects inner-ear development by repressing chsy1. In addition, we obtained strikingly similar zebrafish phenotypes after chsy1 overexpression, which might explain why, in humans, brachydactyly can be caused by mutations leading either to loss or to gain of BMP signaling.     

Chondroitin sulfate synthase 1 (Chsy1) is required for bone development and digit patterning

Joint and skeletal development is highly regulated by extracellular matrix (ECM) proteoglycans, of which chondroitin sulfate proteoglycans (CSPGs) are a major class. Despite the requirement of joint CSPGs for skeletal flexibility and structure, relatively little is understood regarding their role in establishing joint positioning or in modulating signaling and cell behavior during joint formation. Chondroitin sulfate synthase 1 (Chsy1) is one of a family of enzymes that catalyze the extension of chondroitin and dermatan sulfate glycosaminoglycans. Recently, human syndromic brachydactylies have been described to have loss-of-function mutations at the CHSY1 locus. In concordance with these observations, we demonstrate that mice lacking Chsy1, though viable, display chondrodysplasia and decreased bone density. Notably, Chsy1(-/-) mice show a profound limb patterning defect in which orthogonally shifted ectopic joints form in the distal digits. Associated with the digit-patterning defect is a shift in cell orientation and an imbalance in chondroitin sulfation. Our results place Chsy1 as an essential regulator of joint patterning and provide a mouse model of human brachydactylies caused by mutations in CHSY1.     

Oncogene APOL1 promotes proliferation and inhibits apoptosis via activating NOTCH1 signaling pathway in pancreatic cancer

APOL1 encodes a secreted high-density lipoprotein, which has been considered as an aberrantly expressed gene in multiple cancers. Nevertheless, the role of APOL1 in the regulatory mechanisms of pancreatic cancer remains unknown and should be explored. We identified APOL1 was abnormally elevated in human pancreatic cancer tissues compared with that in adjacent tissues and was associated with poor prognosis. The effects of APOL1 in PC cell proliferation, cell cycle, and apoptosis was verified via functional in vitro and in vivo experiments. The results showed that knockdown of APOL1 significantly inhibited the proliferation and promoted apoptosis of pancreatic cancer. In addition, we identified APOL1 could be a regulator of NOTCH1 signaling pathway using bioinformatics tools, qRT-PCR, dual-luciferase reporter assay, and western blotting. In summary, APOL1 could function as an oncogene to promote proliferation and inhibit apoptosis through activating NOTCH1 signaling pathway expression in pancreatic cancer; therefore, it may act as a novel therapeutic target for pancreatic cancer.Subject terms: Oncogenes, Protein-protein interaction networks     

Analysis of JAG1 gene variant in Chinese patients with Alagille syndrome

Alagille syndrome (AGS) is an autosomal dominant disorder characterized by bile duct paucity. It can be caused by variations in the JAG1 gene encoding a protein of Notch ligand and by variations in the NOTCH2 gene encoding a Notch receptor. In this study we identified 15 different JAG1 gene variations in 17 Chinese patients, nine of which were novel alterations including c.766G > T, c.819delC, c.826delT, c.3099_3100delCA, c.1323_1326delCTGG, c.1771_1775delGTGCGinsT, c.1868delG, c. 2791_2792insA and c.866delG. These alterations were located in the extracellular domain of JAG1, in particular in the DSL and EGF-like repeat domain. All the specific variations in five inheritance cases investigated were de novo. Furthermore, no sequence variation of NOTCH2 was detected in JAG1 alteration negative patients.     

Inhibition of Notch signaling enhances transdifferentiation of the esophageal squamous epithelium towards a Barrett's-like metaplasia via KLF4

Barrett's esophagus (BE) is defined as an incomplete intestinal metaplasia characterized generally by the presence of columnar and goblet cells in the formerly stratified squamous epithelium of the esophagus. BE is known as a precursor for esophageal adenocarcinoma. Currently, the cell of origin for human BE has yet to be clearly identified. Therefore, we investigated the role of Notch signaling in the initiation of BE metaplasia. Affymetrix gene expression microarray revealed that BE samples express decreased levels of Notch receptors (NOTCH2 and NOTCH3) and one of the the ligands (JAG1). Furthermore, BE tissue microarray showed decreased expression of NOTCH1 and its downstream target HES1. Therefore, Notch signaling was inhibited in human esophageal epithelial cells by expression of dominant-negative-Mastermind-like (dnMAML), in concert with MYC and CDX1 overexpression. Cell transdifferentiation was then assessed by 3D organotypic culture and evaluation of BE-lineage specific gene expression. Notch inhibition promoted transdifferentiation of esophageal epithelial cells toward columnar-like cells as demonstrated by increased expression of columnar keratins (K8, K18, K19, K20) and glandular mucins (MUC2, MUC3B, MUC5B, MUC17) and decreased expression of squamous keratins (K5, K13, K14). In 3D culture, elongated cells were observed in the basal layer of the epithelium with Notch inhibition. Furthermore, we observed increased expression of KLF4, a potential driver of the changes observed by Notch inhibition. Interestingly, knockdown of KLF4 reversed the effects of Notch inhibition on BE-like metaplasia. Overall, Notch signaling inhibition promotes transdifferentiation of esophageal cells toward BE-like metaplasia in part via upregulation of KLF4. These results support a novel mechanism through which esophageal epithelial transdifferentiation promotes the evolution of BE.     

Smad proteins differentially regulate transforming growth factor-β-mediated induction of chondroitin sulfate proteoglycans

Traumatic injury to the CNS results in increased expression and deposition of chondroitin sulfate proteoglycans (CSPGs) that are inhibitory to axonal regeneration. Transforming growth factor-β (TGF-β) has been implicated as a major mediator of these changes, but the mechanisms through which TGF-β regulates CSPG expression are not known. Using lentiviral expressed Smad-specific ShRNA we show that TGF-β induction of CSPG expression in astrocytes is Smad-dependent. However, we find a differential dependence of the synthetic machinery on Smad2 and/or Smad3. TGF-β induction of neurocan and xylosyl transferase 1 required both Smad2 and Smad3, whereas induction of phosphacan and chondroitin synthase 1 required Smad2 but not Smad3. Smad3 knockdown selectively reduced induction of chondroitin-4-sulfotransferase 1 and the amount of 4-sulfated CSPGs secreted by astrocytes. Additionally, Smad3 knockdown in astrocytes was more efficacious in promoting neurite outgrowth of neurons cultured on the TGF-β-treated astrocytes. Our data implicate TGF-β Smad3-mediated induction of 4-sulfation as a critical determinant of the permissiveness of astrocyte secreted CSPGs for axonal growth.     

Effects of sesamin on the biosynthesis of chondroitin sulfate proteoglycans in human articular chondrocytes in primary culture

Osteoarthritis (OA) is a degenerative joint disease that progressively causes a loss of joint functions and the impaired quality of life. The most significant event in OA is a high degree of degradation of articular cartilage accompanied by the loss of chondroitin sulfate-proteoglycans (CS-PGs). Recently, the chondroprotective effects of sesamin, the naturally occurring substance found in sesame seeds, have been proved in a rat model of papain-induced osteoarthritis. We hypothesized that sesamin may be associated with possible promotion of the biosynthesis of CS-PGs in human articular chondrocytes. The aim of the study was to investigate the effects of sesamin on the major CS-PG biosynthesis in primary human chondrocyte. The effects of sesamin on the gene expression of the PG core and the CS biosynthetic enzymes as well as on the secretion of glycosaminoglycans (GAGs) in monolayer and pellet culture systems of articular chondrocytes. Sesamin significantly increased the GAGs content both in culture medium and pellet matrix. Real-time-quantitative PCR showed that sesamin promoted the expression of the genes encoding the core protein (ACAN) of the major CS-PG aggrecan and the biosynthetic enzymes (XYLT1, XYLT2, CHSY1 and CHPF) required for the synthesis of CS-GAG side chains. Safranin-O staining of sesamin treated chondrocyte pellet section confirmed the high degree of GAG accumulation. These results were correlated with an increased level of secreted GAGs in the media of cultured articular chondrocytes in both culture systems. Thus, sesamin would provide a potential therapeutic strategy for treating OA patients.     

NOTCH3 Is Induced in Cancer-Associated Fibroblasts and Promotes Angiogenesis in Oral Squamous Cell Carcinoma

Recent studies have shown that Notch signaling is involved in many types of cancers, including oral squamous cell carcinomas (OSCCs). However, the role of Notch signaling in the tumor microenvironment is not yet fully understood. In this study, we investigated the roles of NOTCH3 signaling in cancer associated fibroblasts (CAFs) in OSCCs. Immunohistochemical study of 93 human tongue OSCC cases indicated that about one third of OSCCs showed NOTCH3 expression in CAFs, and that this expression significantly correlated with tumor-size. In vitro study showed that OSCC cell lines, especially HO1-N-1 cells stimulated NOTCH3 expression in normal human dermal fibroblasts (NHDFs) through direct cell-to-cell contact. Immunohistochemical and morphometric analysis using human OSCC samples demonstrated that NOTCH3 expression in CAFs significantly correlated with micro-vessel density in cancer stroma. In vitro angiogenesis assays involving co-culture of NHDFs with HO1-N-1 and human umbilical endothelial cells (HUVECs), and NOTCH3 knockdown in NHDFs using siRNA, demonstrated that HO1-N-1 cells significantly promoted tube formation dependent on NOTCH3-expression in NHDFs. Moreover, NOTCH3 expression in CAFs was related to poor prognosis of the OSCC patients. This work provides a new insight into the role of Notch signaling in CAFs associated with tumor angiogenesis and the possibility of NOTCH3-targeted molecular therapy in OSCCs.     

MiR‐199b‐5p inhibits osteogenic differentiation in ligamentum flavum cells by targeting JAG1 and modulating the Notch signalling pathway

Ossification of the ligamentum flavum (OLF) is a pathology almost only reported in East Asian countries. The leading cause of OLF is thoracic spinal canal stenosis and myelopathy. In this study, the role of miR‐199b‐5p and jagged 1 (JAG1) in primary ligamentum flavum cell osteogenesis was examined. MiR‐199b‐5p was found to be down‐regulated during osteogenic differentiation in ligamentum flavum cells, while miR‐199b‐5p overexpression inhibited osteogenic differentiation. In addition, JAG1 was found to be up‐regulated during osteogenic differentiation in ligamentum flavum cells, while JAG1 knockdown via RNA interference caused an inhibition of Notch signalling and osteogenic differentiation. Moreover, target prediction analysis and dual luciferase reporter assays supported the notion that JAG1 was a direct target of miR‐199b‐5p, with miR‐199b‐5p found to down‐regulate both JAG1 and Notch. Further, JAG1 knockdown was demonstrated to block the effect of miR‐199b‐5p inhibition. These findings imply that miR‐199b‐5p performs an inhibitory role in osteogenic differentiation in ligamentum flavum cells by potentially targeting JAG1 and influencing the Notch signalling pathway.     

Notch signaling in human development and disease

Mutations in Notch signaling pathway members cause developmental phenotypes that affect the liver, skeleton, heart, eye, face, kidney, and vasculature. Notch associated disorders include the autosomal dominant, multi-system, Alagille syndrome caused by mutations in both a ligand (Jagged1 (JAG1)) and receptor (NOTCH2) and autosomal recessive spondylocostal dysostosis, caused by mutations in a ligand (Delta-like-3 (DLL3)), as well as several other members of the Notch signaling pathway. Mutations in NOTCH2 have also recently been connected to Hajdu-Cheney syndrome, a dominant disorder causing focal bone destruction, osteoporosis, craniofacial morphology and renal cysts. Mutations in the NOTCH1 receptor are associated with several types of cardiac disease and mutations in NOTCH3 cause the dominant adult onset disorder CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), a vascular disorder with onset in the 4th or 5th decades. Studies of these human disorders and their inheritance patterns and types of mutations reveal insights into the mechanisms of Notch signaling.     

Neoplastic transformation by truncated alleles of human NOTCH1/TAN1 and NOTCH2.

The Notch genes of Drosophila melanogaster and vertebrates encode transmembrane receptors that help determine cell fate during development. Although ligands for Notch proteins have been identified, the signaling cascade downstream of the receptors remains poorly understood. In human acute lymphoblastic T-cell leukemia, a chromosomal translocation damages the NOTCH1 gene. The damage apparently gives rise to a constitutively activated version of NOTCH protein. Here we show that a truncated version of NOTCH1 protein resembling that found in the leukemic cells can transform rat kidney cells in vitro. The transformation required cooperation with the E1A oncogene of adenovirus. The transforming version of NOTCH protein was located in the nucleus. In contrast, neither wild-type NOTCH protein nor a form of the truncated protein permanently anchored to the plasma membrane produced transformation in vitro. We conclude that constitutive activation of NOTCH similar to that found in human leukemia can contribute to neoplastic transformation. Transformation may require that the NOTCH protein be translocated to the nucleus. These results sustain a current view of how Notch transduces a signal from the surface of the cell to the nucleus.     

KSHV Manipulates Notch Signaling by DLL4 and JAG1 to Alter Cell Cycle Genes in Lymphatic Endothelia

Increased expression of Notch signaling pathway components is observed in Kaposi sarcoma (KS) but the mechanism underlying the manipulation of the canonical Notch pathway by the causative agent of KS, Kaposi sarcoma herpesvirus (KSHV), has not been fully elucidated. Here, we describe the mechanism through which KSHV directly modulates the expression of the Notch ligands JAG1 and DLL4 in lymphatic endothelial cells. Expression of KSHV-encoded vFLIP induces JAG1 through an NFκB-dependent mechanism, while vGPCR upregulates DLL4 through a mechanism dependent on ERK. Both vFLIP and vGPCR instigate functional Notch signalling through NOTCH4. Gene expression profiling showed that JAG1- or DLL4-stimulated signaling results in the suppression of genes associated with the cell cycle in adjacent lymphatic endothelial cells, indicating a role for Notch signaling in inducing cellular quiescence in these cells. Upregulation of JAG1 and DLL4 by KSHV could therefore alter the expression of cell cycle components in neighbouring uninfected cells during latent and lytic phases of viral infection, influencing cellular quiescence and plasticity. In addition, differences in signaling potency between these ligands suggest a possible complementary role for JAG1 and DLL4 in the context of KS.