Loss of Fam20c causes defects in the acinar and duct structure of salivary glands in mice

Fam20c regulates the calpain proteolysis system through phosphorylating Calpasatatin to maintain cell homeostasis

BACKGROUND

The family with sequence similarity 20-member C (FAM20C) kinase, a Golgi casein kinase, which is responsible for phosphorylating the majority of the extracellular phosphoproteins within S-x-E/pS motifs, and is fundamentally associated with multiple biological processes to maintain cell proliferation, biomineralization, migration, adhesion, and phosphate homeostasis. In dissecting how FAM20C regulates downstream molecules and potential mechanisms, however, there are multiple target molecules of FAM20C, particularly many phenomena remain elusive, such as changes in cell-autonomous behaviors, incompatibility in genotypes and phenotypes, and others.

METHODS

Here, assay for transposase-accessible chromatin using sequencing (ATAC-seq), RNA sequencing (RNA-seq), proteomics, and phosphoproteomics were performed in Fam20c-dificient osteoblasts and to facilitate an integrated analysis and determine the impact of chromatin accessibility, genomic expression, protein alterations, signaling pathway, and post translational modifcations.

RESULTS

By combining ATAC-seq and RNA-seq, we identified TCF4 and Wnt signaling pathway as the key regulators in Fam20c-dificient cells. Further, we showed Calpastatin/Calpain proteolysis system as a novel target axis for FAM20C to regulate cell migration and F-actin cytoskeleton by integrated analysis of proteomics and phosphoproteomics. Furthermore, Calpastatin/Calpain proteolysis system could negatively regulate the Wnt signaling pathway.

CONCLUSION

These observations implied that Fam20c knockout osteoblasts would cause cell homeostatic imbalance, involving changes in multiple signaling pathways in the conduction system.

Mesenchymal-to-epithelial transition of osteoblasts induced by Fam20c knockout

BACKGROUND

Fam20c is intimately related to tissue development and diseases. At present, it has been reported that Fam20c regulates the mineralization of osteoblasts, but there are few reports on other effects.

OBJECTIVE

To study the effect of Fam20c on osteoblasts by knocking out the Fam20c gene.

METHODS

Fam20c knockout osteoblasts were constructed by transfecting mouse osteoblasts with lentivirus. The proliferation, migration and mineralization of Fam20c knockout cells were detected by CCK-8, scratch test and alizarin red staining assays. The subcellular structure was observed by transmission electron microscopy. RT-PCR was used to detect the differential expression of mesenchymal-to-epithelial transition (MET)-related marker genes and core transcription factors. The differential expression of MET-related proteins was detected by immunofluorescence or Western blot. Transcriptome analysis of Fam20c knockout osteoblasts was performed, and real-time PCR was used to verify transcriptome analysis related to MET.

RESULTS

The proliferation ability of osteoblasts was not significantly changed after Fam20c deletion, but the migration ability and mineralization ability were significantly weakened. There were tight junctions between Fam20c knockout cells. The expression of mesenchymal cell marker genes and core transcription factors was significantly decreased, and the expression of epithelial cell marker genes was significantly increased. The expression of mesenchymal cell marker proteins was significantly decreased, and the expression of epithelial cell marker proteins was significantly increased. Multiple signalling molecules and pathways involved in MET have changed.

CONCLUSIONS

Knockdown of Fam20c resulted in MET. Fam20c affects the transcription of key factors in osteoblast MET.

FAM20C Overview: Classic and Novel Targets, Pathogenic Variants and Raine Syndrome Phenotypes

FAM20C is a gene coding for a protein kinase that targets S-X-E/pS motifs on different phosphoproteins belonging to diverse tissues. Pathogenic variants of FAM20C are responsible for Raine syndrome (RS), initially described as a lethal and congenital osteosclerotic dysplasia characterized by generalized atherosclerosis with periosteal bone formation, characteristic facial dysmorphisms and intracerebral calcifications. The aim of this review is to give an overview of targets and variants of FAM20C as well as RS aspects. We performed a wide phenotypic review focusing on clinical aspects and differences between all lethal (LRS) and non-lethal (NLRS) reported cases, besides the FAM20C pathogenic variant description for each. As new targets of FAM20C kinase have been identified, we reviewed FAM20C targets and their functions in bone and other tissues, with emphasis on novel targets not previously considered. We found the classic lethal and milder non-lethal phenotypes. The milder phenotype is defined by a large spectrum ranging from osteonecrosis to osteosclerosis with additional congenital defects or intellectual disability in some cases. We discuss our current understanding of FAM20C deficiency, its mechanism in RS through classic FAM20C targets in bone tissue and its potential biological relevance through novel targets in non-bone tissues.

From biomineralization to tumorogenesis-the expanding insight of the physiological and pathological roles of Fam20C

Fam20C is a Golgi kinase phosphorylating the majority of the secreted proteins. In this decade, the function of Fam20C has been largely disclosed in the loss-of function models. How the influence of the overexpressed Fam20C on cells or organs, and whether Fam20C was associated with tumorogensis still remain unknown. In the latest article in Bioscience Reports, a group from The Second Affiliated Hospital of Harbin Medical University established a correlation between the elevated Fam20C expression and the poor prognosis of multiple cancers (Biosci. Rep. (2021), 41(1) BSR20201920). In addition, they also proposed the potential mechanisms how the increased Fam20C expression played a detrimental role in tumor progression by suggesting that the up-regulated Fam20C level affected the infiltration of immune cells and the capability of cancer metastasis. To give an overview of the expanding knowledge of Fam20C involved in the physiological and pathological events, we first reviewed the history of Fam20C study in this commentary, then, evaluated the correlation of the elevated Fam20C expression to the prognosis of multiple cancers, and finally, interpreted the perspectives that the Fam20C gain-of-function model was also critical for cancer therapy.

Cell signaling regulation in salivary gland development

The mammalian salivary gland develops as a highly branched structure designed to produce and secrete saliva. This review focuses on research conducted on mammalian salivary gland development, particularly on the differentiation of acinar, ductal, and myoepithelial cells. We discuss recent studies that provide conceptual advances in the understanding of the molecular mechanisms of salivary gland development. In addition, we describe the organogenesis of submandibular glands (SMGs), model systems used for the study of SMG development, and the key signaling pathways as well as cellular processes involved in salivary gland development. The findings from the recent studies elucidating the identity of stem/progenitor cells in the SMGs, and the process by which they are directed along a series of cell fate decisions to form functional glands, are also discussed. Advances in genetic tools and tissue engineering strategies will significantly increase our knowledge about the mechanisms by which signaling pathways and cells establish tissue architecture and function during salivary gland development, which may also be conserved in the growth and development of other organ systems. An increased knowledge of organ development mechanisms will have profound implications in the design of therapies for the regrowth or repair of injured tissues. In addition, understanding how the processes of cell survival, expansion, specification, movement, and communication with neighboring cells are regulated under physiological and pathological conditions is critical to the development of future treatments.

Regulation of bone morphogenetic protein 4 on epithelial tissue

Epithelial tissues provide tissue barriers and specialize in organs and glands. When epithelial homeostasis is physiologically or pathologically stimulated, epithelial cells produce mesenchymal cells through the epithelial-mesenchymal transition, forming new tissues, promoting the cure of diseases or leading to illness. A variety of cytokines are involved in the regulation of epithelial cell differentiation. Bone morphogenetic proteins (BMPs), especially the bone morphogenetic protein 4 (BMP4) has a variety of biological functions and plays a prominent role in the regulation of epithelial cell differentiation. BMP4 is an important regulatory factor of a series of life activities in vertebrates, which is also related to cell proliferation, differentiation and mobility, it also has relation with tumor development. This paper mainly reviews the mechanism of BMP4's regulation on epithelial tissues, as well as its effect on the growth, differentiation, benign lesions and malignant lesions of epithelial tissues, and expounds the function of BMP4 in epithelial tissues, to provide theoretical support for the research on reducing epithelial diseases.