Inactivation of Fam20B in Joint Cartilage Leads to Chondrosarcoma and Postnatal Ossification Defects

Whole-genome bisulfite sequencing identifies stage- and subtype-specific DNA methylation signatures in pancreatic cancer

In pancreatic ductal adenocarcinoma (PDAC), no recurrent metastasis-specific mutation has been found, suggesting that epigenetic mechanisms, such as DNA methylation, are the major contributors of late-stage disease progression. Here, we performed the first whole-genome bisulfite sequencing (WGBS) on mouse and human PDAC organoid models to identify stage-specific and molecular subtype-specific DNA methylation signatures. With this approach, we identified thousands of differentially methylated regions (DMRs) that can distinguish between the stages and molecular subtypes of PDAC. Stage-specific DMRs are associated with genes related to nervous system development and cell-cell adhesions, and are enriched in promoters and bivalent enhancers. Subtype-specific DMRs showed hypermethylation of GATA6 foregut endoderm transcriptional networks in the squamous subtype and hypermethylation of EMT transcriptional networks in the progenitor subtype. These results indicate that aberrant DNA methylation contributes to both PDAC progression and subtype differentiation, resulting in significant and reoccurring DNA methylation patterns with diagnostic and prognostic potential.

Deficiency of Fam20b-Catalyzed Glycosaminoglycan Chain Synthesis in Neural Crest Leads to Cleft Palate

Cleft palate is one of the most common birth defects. Previous studies revealed that multiple factors, including impaired intracellular or intercellular signals, and incoordination of oral organs led to cleft palate, but were little concerned about the contribution of the extracellular matrix (ECM) during palatogenesis. Proteoglycans (PGs) are one of the important macromolecules in the ECM. They exert biological functions through one or more glycosaminoglycan (GAG) chains attached to core proteins. The family with sequence similarity 20 member b (Fam20b) are newly identified kinase-phosphorylating xylose residues that promote the correct assembly of the tetrasaccharide linkage region by creating a premise for GAG chain elongation. In this study, we explored the function of GAG chains in palate development through Wnt1-Cre; Fam20b^f/f mice, which exhibited complete cleft palate, malformed tongue, and micrognathia. In contrast, Osr2-Cre; Fam20b^f/f mice, in which Fam20b was deleted only in palatal mesenchyme, showed no abnormality, suggesting that failed palatal elevation in Wnt1-Cre; Fam20b^f/f mice was secondary to micrognathia. In addition, the reduced GAG chains promoted the apoptosis of palatal cells, primarily resulting in reduced cell density and decreased palatal volume. The suppressed BMP signaling and reduced mineralization indicated an impaired osteogenesis of palatine, which could be rescued partially by constitutively active Bmpr1a. Together, our study highlighted the key role of GAG chains in palate morphogenesis.

Family with sequence similarity 20 member B regulates osteogenic differentiation of bone marrow mesenchymal stem cells on titanium surfaces

Successful bone regeneration on titanium (Ti) surfaces is a key process in dental implant treatment. Bone marrow mesenchymal stem cells (BMSCs) are fundamental cellular components of this process, and their early recruitment, proliferation, and differentiation into bone-forming osteoblasts are crucial. A proteoglycan (PG)-rich layer has been reported to exist between Ti surfaces and bones; however, the molecules that could potentially affect the formation of this layer remain unknown. Family with sequence similarity 20 member B (FAM20B) is a newly identified kinase that regulates the synthesis of glycosaminoglycans, an important component of the PG-rich layer. Because FAM20B is also closely associated with bone development, in this study, we examined the function of FAM20B in osteogenic differentiation of BMSCs on Ti surfaces. For this, BMSC cell lines with knocked down FAM20B (shBMSCs) were cultured on Ti surfaces. The results showed that the depletion of FAM20B reduced the formation of a PG-rich layer between the Ti surfaces and cells. The shBMSCs exhibited downregulated expression of osteogenic marker genes (ALP and OCN) and decreased mineral deposition. Moreover, shBMSCs reduced the molecular levels of p-ERK1/2, which plays an important role in MSC osteogenesis. The nuclear translocation of RUNX2, an important transcription factor for osteogenic differentiation, on the Ti surfaces is inhibited by the depletion of FAM20B in BMSCs. Moreover, the depletion of FAM20B reduced the transcriptional activity of RUNX2, which is important in regulating the expression of osteogenic genes. STATEMENT OF SIGNIFICANCE: Bone healing and regeneration on implanted titanium surfaces is a cell-material interaction. Such an interaction is enabled by bone marrow mesenchymal stem cells (BMSCs), and their early recruitment, proliferation, and differentiation into bone-forming osteoblasts are essential for bone healing and osseointegration. In this study, we found that the family with sequence similarity 20-B influenced the formation of a proteoglycan rich layer between BMSCs and the titanium surface and regulated the differentiation of BMSCs into bone-forming osteoblasts. We believe that our study contributes significantly to the further exploration of bone healing and osseointegration mechanisms on implanted titanium surfaces.

Regulation of secretory pathway kinase or kinase-like proteins in human cancers

Secretory pathway kinase or kinase-like proteins (SPKKPs) are effective in the lumen of the endoplasmic reticulum (ER), Golgi apparatus (GA), and extracellular space. These proteins are involved in secretory signaling pathways and are distinctive from typical protein kinases. Various reports have shown that SPKKPs regulate the tumorigenesis and progression of human cancer via the phosphorylation of various substrates, which is essential in physiological and pathological processes. Emerging evidence has revealed that the expression of SPKKPs in human cancers is regulated by multiple factors. This review summarizes the current understanding of the contribution of SPKKPs in tumorigenesis and the progression of immunity. With the epidemic trend of immunotherapy, targeting SPKKPs may be a novel approach to anticancer therapy. This study briefly discusses the recent advances regarding SPKKPs.

An Overview of in vivo Functions of Chondroitin Sulfate and Dermatan Sulfate Revealed by Their Deficient Mice

Chondroitin sulfate (CS), dermatan sulfate (DS) and heparan sulfate (HS) are covalently attached to specific core proteins to form proteoglycans in their biosynthetic pathways. They are constructed through the stepwise addition of respective monosaccharides by various glycosyltransferases and maturated by epimerases as well as sulfotransferases. Structural diversities of CS/DS and HS are essential for their various biological activities including cell signaling, cell proliferation, tissue morphogenesis, and interactions with a variety of growth factors as well as cytokines. Studies using mice deficient in enzymes responsible for the biosynthesis of the CS/DS and HS chains of proteoglycans have demonstrated their essential functions. Chondroitin synthase 1-deficient mice are viable, but exhibit chondrodysplasia, progression of the bifurcation of digits, delayed endochondral ossification, and reduced bone density. DS-epimerase 1-deficient mice show thicker collagen fibrils in the dermis and hypodermis, and spina bifida. These observations suggest that CS/DS are essential for skeletal development as well as the assembly of collagen fibrils in the skin, and that their respective knockout mice can be utilized as models for human genetic disorders with mutations in chondroitin synthase 1 and DS-epimerase 1. This review provides a comprehensive overview of mice deficient in CS/DS biosyntheses.

Altered Expression of Aggrecan, FAM20B, B3GALT6, and EXTL2 in Patients with Osteoarthritis and Kashin-Beck Disease

OBJECTIVE

The objective of this study was to investigate the expression of enzymes involved in synthesis and modification of chondroitin sulfate (CS) in knee cartilage tissue of patients with osteoarthritis (OA) and Kashin-Beck disease (KBD).

METHODS

The knee articular cartilage samples were obtained from 18 age- and gender-matched donors with 6 each in KBD, OA, and control groups. Hematoxylin and eosin (HE) staining, toluidine blue (TB) staining, and immunohistochemical (IHC) staining were performed to estimate the expression level and localization of aggrecan, along with FAM20B, GalT-II, and EXTL2, which are associated with CS synthesis and modification. Rank-based analyses of variance test was used for the multiple comparisons of discrepancy in the positive staining rate among the 3 groups.

RESULTS

In HE and TB staining results, damaged morphology, decreased chondrocyte numbers and proteoglycans were observed in OA and KBD groups compared with the control group. In line with these trends, the positive staining rates of aggrecan were lower in KBD and OA groups than in the control group. Meanwhile, the positive staining rates of CS chain modifying enzymes FAM20B, GalT-II, and EXTL2 decreased in OA and KBD groups.

CONCLUSIONS

In conclusion, it was demonstrated that altered expression of CS chain modifying enzymes in OA and KBD groups influenced the synthesis procession of CS and could contribute to the damage of cartilage. Further investigation of these enzymes can provide new theoretical and experimental targets for OA and KBD pathogenesis studies.

Comparative genomics provides insights into the aquatic adaptations of mammals

Divergent lineages can respond to common environmental factors through convergent processes involving shared genomic components or pathways, but the molecular mechanisms are poorly understood. Here, we provide genomic resources and insights into the evolution of mammalian lineages adapting to aquatic life. Our data suggest convergent evolution, for example, in association with thermoregulation through genes associated with a surface heat barrier (NFIA) and internal heat exchange (SEMA3E). Combined with the support of previous reports showing that the UCP1 locus has been lost in many marine mammals independently, our results suggest that the thermostatic strategy of marine mammals shifted from enhancing heat production to limiting heat loss.

The ancestors of marine mammals once roamed the land and independently committed to an aquatic lifestyle. These macroevolutionary transitions have intrigued scientists for centuries. Here, we generated high-quality genome assemblies of 17 marine mammals (11 cetaceans and six pinnipeds), including eight assemblies at the chromosome level. Incorporating previously published data, we reconstructed the marine mammal phylogeny and population histories and identified numerous idiosyncratic and convergent genomic variations that possibly contributed to the transition from land to water in marine mammal lineages. Genes associated with the formation of blubber (NFIA), vascular development (SEMA3E), and heat production by brown adipose tissue (UCP1) had unique changes that may contribute to marine mammal thermoregulation. We also observed many lineage-specific changes in the marine mammals, including genes associated with deep diving and navigation. Our study advances understanding of the timing, pattern, and molecular changes associated with the evolution of mammalian lineages adapting to aquatic life.

Chondrodysplasias With Multiple Dislocations Caused by Defects in Glycosaminoglycan Synthesis

Chondrodysplasias with multiple dislocations form a group of severe disorders characterized by joint laxity and multiple dislocations, severe short stature of pre- and post-natal onset, hand anomalies, and/or vertebral anomalies. The majority of chondrodysplasias with multiple dislocations have been associated with mutations in genes encoding glycosyltransferases, sulfotransferases, and transporters implicated in the synthesis or sulfation of glycosaminoglycans, long and unbranched polysaccharides composed of repeated disaccharide bond to protein core of proteoglycan. Glycosaminoglycan biosynthesis is a tightly regulated process that occurs mainly in the Golgi and that requires the coordinated action of numerous enzymes and transporters as well as an adequate Golgi environment. Any disturbances of this chain of reactions will lead to the incapacity of a cell to construct correct glycanic chains. This review focuses on genetic and glycobiological studies of chondrodysplasias with multiple dislocations associated with glycosaminoglycan biosynthesis defects and related animal models. Strong comprehension of the molecular mechanisms leading to those disorders, mostly through extensive phenotypic analyses of in vitro and/or in vivo models, is essential for the development of novel biomarkers for clinical screenings and innovative therapeutics for these diseases.

The ABCs of the atypical Fam20 secretory pathway kinases

The study of extracellular phosphorylation was initiated in late 19th century when the secreted milk protein, casein, and egg-yolk protein, phosvitin, were shown to be phosphorylated. However, it took more than a century to identify Fam20C, which phosphorylates both casein and phosvitin under physiological conditions. This kinase, along with its family members Fam20A and Fam20B, defined a new family with altered amino acid sequences highly atypical from the canonical 540 kinases comprising the kinome. Fam20B is a glycan kinase that phosphorylates xylose residues and triggers peptidoglycan biosynthesis, a role conserved from sponges to human. The protein kinase, Fam20C, conserved from nematodes to humans, phosphorylates well over 100 substrates in the secretory pathway with overall functions postulated to encompass endoplasmic reticulum homeostasis, nutrition, cardiac function, coagulation, and biomineralization. The preferred phosphorylation motif of Fam20C is SxE/pS, and structural studies revealed that related member Fam20A allosterically activates Fam20C by forming a heterodimeric/tetrameric complex. Fam20A, a pseudokinase, is observed only in vertebrates. Loss-of-function genetic alterations in the Fam20 family lead to human diseases such as amelogenesis imperfecta, nephrocalcinosis, lethal and nonlethal forms of Raine syndrome with major skeletal defects, and altered phosphate homeostasis. Together, these three members of the Fam20 family modulate a diverse network of secretory pathway components playing crucial roles in health and disease. The overarching theme of this review is to highlight the progress that has been made in the emerging field of extracellular phosphorylation and the key roles secretory pathway kinases play in an ever-expanding number of cellular processes.

Liquid-phase ASEM imaging of cellular and structural details in cartilage and bone formed during endochondral ossification: Keap1-deficient osteomalacia

Chondrogenesis and angiogenesis drive endochondral ossification. Using the atmospheric scanning electron microscopy (ASEM) without decalcification and dehydration, we directly imaged angiogenesis-driven ossification at different developmental stages shortly after aldehyde fixation, using aqueous radical scavenger glucose solution to preserve water-rich structures. An embryonic day 15.5 mouse femur was fixed and stained with phosphotungstic acid (PTA), and blood vessel penetration into the hypertrophic chondrocyte zone was visualised. We observed a novel envelope between the perichondrium and proliferating chondrocytes, which was lined with spindle-shaped cells that could be borderline chondrocytes. At postnatal day (P)1, trabecular and cortical bone mineralisation was imaged without staining. Additional PTA staining visualised surrounding soft tissues; filamentous connections between osteoblast-like cells and osteocytes in cortical bone were interpreted as the osteocytic lacunar-canalicular system. By P10, resorption pits had formed on the tibial trabecular bone surface. The applicability of ASEM for pathological analysis was addressed using knockout mice of Keap1, an oxidative-stress sensor. In Keap1-/- femurs, we observed impaired calcification and angiogenesis of epiphyseal cartilage, suggesting impaired bone development. Overall, the quick ASEM method we developed revealed mineralisation and new structures in wet bone tissue at EM resolution and can be used to study mineralisation-associated phenomena of any hydrated tissue.

Inactivation of FAM20B causes cell fate changes in annulus fibrosus of mouse intervertebral disc and disc defects via the alterations of TGF-β and MAPK signaling pathways

Intervertebral disc (IVD) disorder is often caused by the defect of annulus fibrosus (AF), especially that of the outer AF. Studies about the mechanisms governing the development of the outer AF are needed for a better understanding of pathogenesis of IVD defects. Glycosaminoglycans (GAGs) are essential components of extracellular matrix (ECM) in AF. FAM20B is a newly identified xylose kinase that catalyzes the biosynthesis of GAGs. In this study, we created Fam20B conditional knockout (cKO) mice in which FAM20B was inactivated in type I collagen-expressing cells, the main type of cells in the outer AF of IVD. The cKO mice showed severe spine deformity and remarkable IVD defects associated with AF malformation. The AF of cKO mice had a lower level of chondroitin sulfate and heparan sulfate, and the outer AF cells lost their normal fibroblast-like morphology and acquired chondrocyte phenotypes, expressing a higher level of Sox 9 and type II collagen along with a reduced level of type I collagen. The level of phospho-Smad 2 and phospho-Smad 3, and that of scleraxis, a downstream target molecule of canonical TGF-β signaling pathway were significantly lower in the AF of cKO mice. The AF in cKO mice also manifested altered levels in the molecules associated with the activations of MAPK pathway; the changes included the increase of phospho-P38 and phospho-ERK and a decrease of phospho-JNK. These results indicate that FAM20B plays an essential role in the development of AF by regulating the TGF-β signaling and MAPK signaling pathways.

A novel gene (FAM20B encoding glycosaminoglycan xylosylkinase) for neonatal short limb dysplasia resembling Desbuquois dysplasia

Desbuquois dysplasia (DBQD) is an autosomal recessive heterogeneous disorder characterized by joint laxity and skeletal changes, including a distinctive monkey-wrench appearance of the femora, advanced carpal ossification, and abnormal patterning of the preaxial digits. Two genes for DBQD (CANT1 encoding calcium-activated nucleotidase-1 and XYLT1 encoding xylosyltransferase-1) have been reported. We propose a novel gene for neonatal short limb dysplasia resembling DBQD, based on the phenotype and genotype of two affected siblings. The affected boy and girl died in early infancy and shortly after birth, respectively. The clinical hallmarks included mid-face hypoplasia, thoracic hypoplasia with respiratory failure, very short stature (approximately -7 SD of birth length) with mesomelic shortening of the limbs, and multiple dislocations of the large joints. Radiological examinations showed prominent lesser trochanter, flared metaphyses of the long bones, and joint dislocations. The affected boy had preaxial digital hypoplasia, and the affected girl showed overlapping and syndactyly of the preaxial digits. Molecular analyses of the girl showed compound heterozygous variants in FAM20B (NM_014864: c.174_178delTACCT p.T59Afs*19/c.1038delG p.N347Mfs*4). FAM20B encodes glycosaminoglycan xylosylkinase, which acts downstream of xylosyltransferase-1. Given the fact that FAM20B deficiency causes skeletal phenotypes in mice and zebrafish, these variants are highly probable to be pathogenic.

Thinking outside of the cell: Secreted protein kinases in bacteria, parasites, and mammals

Previous decades have seen an explosion in our understanding of protein kinase function in human health and disease. Hundreds of unique kinase structures have been solved, allowing us to create generalized rules for catalysis, assign roles of communities within the catalytic core, and develop specific drugs for targeting various pathways. Although our understanding of intracellular kinases has developed at a fast rate, our exploration into extracellular kinases has just begun. In this review, we will cover the secreted protein kinase families found in humans, bacteria, and parasites. © 2019 IUBMB Life, 71(6):749-759, 2019.

Inactivation of Fam20b in the neural crest-derived mesenchyme of mouse causes multiple craniofacial defects

The glycosaminoglycan (GAG) chains attached to the core proteins of proteoglycans exert multiple roles, such as enriching signal molecules and regulating the binding of ligands to the corresponding receptors. A newly identified kinase - family with sequence similarity 20 member B (FAM20B) - is essential for the formation of GAG chains. The FAM20B protein phosphorylates the initial xylose on the side chain of a serine residue in the protein. Although the GAG chains of proteoglycans are believed to be indispensable during craniofacial development, there are few reports on their exact functions in craniofacial organogenesis. In this study, by mating Wnt1-cre mice with Fam20b-floxed mice (Fam20bflox/flox), we created Wnt1-Cre;Fam20bflox/flox mice in which Fam20b is ablated in the neural crest-derived mesenchyme. The Wnt1-Cre;Fam20bflox/flox mice died immediately after birth because of complete cleft palates. In addition to cleft palate, Wnt1-Cre;Fam20bflox/flox mice also manifested tongue elevation, micrognathia, microcephaly, suture widening, and reduced mineralization in the calvaria, facial bones, and temporomandibular joint. These findings indicate that the proteoglycans formed through the catalysis of FAM20B are essential for the morphogenesis and mineralization of the craniofacial complex.

Structure and evolution of the Fam20 kinases

The Fam20 proteins are novel kinases that phosphorylate secreted proteins and proteoglycans. Fam20C phosphorylates hundreds of secreted proteins and is activated by the pseudokinase Fam20A. Fam20B phosphorylates a xylose residue to regulate proteoglycan synthesis. Despite these wide-ranging and important functions, the molecular and structural basis for the regulation and substrate specificity of these kinases are unknown. Here we report molecular characterizations of all three Fam20 kinases, and show that Fam20C is activated by the formation of an evolutionarily conserved homodimer or heterodimer with Fam20A. Fam20B has a unique active site for recognizing Galβ1-4Xylβ1, the initiator disaccharide within the tetrasaccharide linker region of proteoglycans. We further show that in animals the monomeric Fam20B preceded the appearance of the dimeric Fam20C, and the dimerization trait of Fam20C emerged concomitantly with a change in substrate specificity. Our results provide comprehensive structural, biochemical, and evolutionary insights into the function of the Fam20 kinases.