The Golgi 'casein kinase' Fam20C is a genuine 'phosvitin kinase' and phosphorylates polyserine stretches devoid of the canonical consensus

Gene expression profiles of Chinese medaka (Oryzias sinensis) primary hepatocytes in response to estrone (E1), 17β-estradiol (E2) and estriol (E3)

The natural estrogens, including estrone (E1), 17β-estradiol (E2), and estriol (E3), are frequently detected in aquatic environment at relatively high levels. The most commonly used biomarkers for estrogens are mainly expressed in the liver of fish. Analyses of the global gene profiling in fish liver cells under estrogens treatment will provide precise toxicogenomic information of the natural estrogens which is still not well known. In this study, we developed methods for isolation and culture of primary hepatocytes from liver tissue of male Chinese medaka (Oryzias sinensis), and analyzed the global gene expression profiling in the primary hepatocytes treated with E1 (1, 10, and 100 nmol/L), E2 (0.01, 0.1, 1, 10, and 100 nmol/L), and E3 (1, 10, and 100 nmol/L) using RNA-seq. It was found that 175, 248, and 218 genes were differentially expressed in the E1, E2, and E3 groups, respectively. These differentially expressed genes (DEGs) were mainly enriched in Gene Ontology (GO) terms of "response to estradiol", "response to estrogen", and "lipid transport". Of the DEGs, vitellogenin genes, including vtg1, vtg2, and vtg3, were the mostly up-regulated and followed by zona pellucida genes which include zp2.3, zp2l1 and zp3a.2. In addition, genes of slc41a1, zp2.1, esr1, pkd1l1, fam20ca, best3, etc. were also obviously up-regulated by the estrogens in concentration-dependent patterns. RT-qPCR was used to validate the results of RNA-seq and found that vtg2 should be the best biomarker gene for estrogen study, which could well response to natural estrogens and weak estrogenic chemical, propyl 4-hydroxybenzoate.

Toxicogenomic signatures of estrogen-related modes of action in the zebrafish embryo

Endocrine disruptors represent a diverse array of chemicals known to interfere with the endocrine systems of both human and environmental organisms, adversely affecting reproduction, development, and behavior, thus raising significant health and ecological concerns. Traditional regulatory tests for endocrine activity typically involve juvenile or adult fish, which is both time-consuming and resource-intensive and necessitates substantial animal use. This study adopts a transcriptomic approach to identify toxicogenomic signatures associated with the disruption of estrogen signaling in zebrafish (Danio rerio) embryos. Utilizing a modified zebrafish embryo toxicity test based on Organisation for Economic Co-operation and Development test guideline 236, the embryos were exposed to two sublethal concentrations of estradiol, bisphenol A, and fulvestrant. Despite no significant effects on survival or hatching rate observed in treated groups compared with the controls, our study effectively pinpointed several genes, including vtg1, cyp19a1b, fam20cl, sult1st2, pck1, agxtb, hsd17b12a, ptgs2a, and ccn1, as linked to a disruption of estrogen signaling. These genes emerge as promising biomarker candidates for identifying and distinguishing estrogen-related modes of action. Additionally, this approach not only supports the detection of potential endocrine disruptors but also opens up possibilities for prioritizing substances for higher tier endocrine testing, which could substantially reduce animal testing in the future.

Discovery of a novel Fam20C inhibitor for treatment of triple-negative breast cancer

Sequence similarity 20 family member C (Fam20C), a Golgi casein kinase, has a gradually elucidated mechanism in triple-negative breast cancer (TNBC) and is considered a possible target for therapeutic intervention. In this study, we combined virtual screening and chemical synthesis methods to obtain a new small-molecule Fam20C inhibitor, compound 5k, which possesses desirable kinase inhibitory activity against Fam20C and significant anti-proliferative activity against MDA-MB-231 and BT-549 cells. Subsequently, cellular thermal shift assay (CETSA), molecular docking, and molecular dynamics (MD) simulations revealed that compound 5k binds to Fam20C. Moreover, compound 5k showed favorable antitumor efficacy in TNBC cells and xenograft models by promoting apoptosis and inhibiting migration. Mechanistically, compound 5k can inhibit the proliferation, promote apoptosis, and inhibit migration of TNBC cells by targeting Fam20C, thereby inhibiting the deterioration of TNBC and preventing its progression. Taken together, these results suggest that compound 5k can be utilized as a novel Fam20C inhibitor, laying a foundation for the discovery of more small-molecule drugs for the treatment of TNBC in the future.

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 Overexpression Predicts Poor Outcomes and is a Diagnostic Biomarker in Lower-Grade Glioma

Glioma is a relatively low aggressive brain tumor. Although the median survival time of patients for lower-grade glioma (LGG) was longer than that of patients for glioblastoma, the overall survival was still short. Therefore, it is urgent to find out more effective molecular prognostic markers. The role of the Fam20 kinase family in different tumors was an emerging research field. However, the biological function of Fam20C and its prognostic value in brain tumors have rarely been reported. This study aimed to evaluate the value of Fam20C as a potential prognostic marker for LGG. A total of 761 LGG samples (our cohort, TCGA and CGGA) were included to investigate the expression and role of Fam20C in LGG. We found that Fam20C was drastically overexpressed in LGG and was positively associated with its clinical progression. Kaplan-Meier analysis and a Cox regression model were employed to evaluate its prognostic value, and Fam20C was found as an independent risk factor in LGG patients. Gene set enrichment analysis also revealed the potential signaling pathways associated with Fam20C gene expression in LGG; these pathways were mainly enriched in extracellular matrix receptor interactions, cell adhesion, cell apoptosis, NOTCH signaling, cell cycle, etc. In summary, our findings provide insights for understanding the potential role of Fam20C and its application as a new prognostic biomarker for LGG.

Effect of high phosphate diet on the formation of dentin in Fam20c-deficient mice

FAM20C (family with sequence similarity 20-member C), a kinase that phosphorylates secretory proteins, plays essential roles in various biological processes. In humans, mutations in FAM20C gene cause Raine syndrome, an autosomal recessive hereditary disease manifesting a broad spectrum of developmental defects including skeletal and craniofacial deformities. Our previous studies revealed that inactivation of Fam20c in mice led to hypophosphatemic rickets and that high phosphate (hPi) diet significantly improved the development of the skeleton in Fam20c-deficient mice. In this study, we evaluated the effects of hPi diet on the formation of dentin in Fam20c-deficient mice, using plain x-ray radiography, micro-computed tomography (µCT), histology, and immunohistochemistry. Plain x-ray radiography and µCT analyses showed that the hPi diet improved the dentin volume fraction and dentin mineral density of the Fam20c-deficient mice. Histology analyses further demonstrated that the hPi diet dramatically improved the integrity of the mandibular first molars and prevented pulp infection and dental abscesses in Fam20c-deficient mice. Our results support that the hPi diet significantly increased the formation and mineralization of dentin in Fam20c-deficient mice, implying that hypophosphatemia is a significant contributor to the dentin defects in Fam20c-deficient subjects.

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.

Enzymatic characterization of three human RNA adenosine methyltransferases reveals diverse substrate affinities and reaction optima

RNA methylations of varied RNA species (mRNA, tRNA, rRNA, non-coding RNA) generate a range of modified nucleotides, including N6-methyladenosine. Here we study the enzymology of three human RNA methyltransferases that methylate the adenosine amino group in diverse contexts, when it is: the first transcribed nucleotide after the mRNA cap (PCIF1), at position 1832 of 18S rRNA (MettL5-Trm112 complex), and within a hairpin in the 3′ UTR of the S-adenosyl-l-methionine synthetase (MettL16). Among these three enzymes, the catalytic efficiency ranges from PCIF1, with the fastest turnover rate of >230 h⁻¹ μM⁻¹ on mRNA cap analog, down to MettL16, which has the lowest rate of ∼3 h⁻¹ μM⁻¹ acting on an RNA hairpin. Both PCIF1 and MettL5 have a binding affinity (K_m) of ∼1 μM or less for both substrates of SAM and RNA, whereas MettL16 has significantly lower binding affinities for both (K_m >0.4 mM for SAM and ∼10 μM for RNA). The three enzymes are active over a wide pH range (∼5.4–9.4) and have different preferences for ionic strength. Sodium chloride at 200 mM markedly diminished methylation activity of MettL5-Trm112 complex, whereas MettL16 had higher activity in the range of 200 to 500 mM NaCl. Zinc ion inhibited activities of all three enzymes. Together, these results illustrate the diversity of RNA adenosine methyltransferases in their enzymatic mechanisms and substrate specificities and underline the need for assay optimization in their study.

Functions and regulation of the serine/threonine protein kinase CK1 family: moving beyond promiscuity

Regarded as constitutively active enzymes, known to participate in many, diverse biological processes, the intracellular regulation bestowed on the CK1 family of serine/threonine protein kinases is critically important, yet poorly understood. Here, we provide an overview of the known CK1-dependent cellular functions and review the emerging roles of CK1-regulating proteins in these processes. We go on to discuss the advances, limitations and pitfalls that CK1 researchers encounter when attempting to define relationships between CK1 isoforms and their substrates, and the challenges associated with ascertaining the correct physiological CK1 isoform for the substrate of interest. With increasing interest in CK1 isoforms as therapeutic targets, methods of selectively inhibiting CK1 isoform-specific processes is warranted, yet challenging to achieve given their participation in such a vast plethora of signalling pathways. Here, we discuss how one might shut down CK1-specific processes, without impacting other aspects of CK1 biology.

Discovery of a novel small-molecule inhibitor of Fam20C that induces apoptosis and inhibits migration in triple negative breast cancer

The family with sequence similarity 20, member C (Fam20C), a Golgi casein kinase, has been recently regarded as a potential therapeutic target for the treatment of triple negative breast cancer (TNBC). Lacking enzyme activity center has been becoming an obstacle to the development of small-molecule inhibitors of Fam20C. Herein, we combined in silico high-throughput screening with chemical synthesis methods to obtain a new small-molecule Fam20C inhibitor 3r, which exhibited desired anti-proliferative activities against MDA-MB-231 cells and also inhibited migration. Subsequently, the enzymatic assay, molecular docking, and molecular dynamics (MD) simulations were carried out for validating that 3r could bind to Fam20C. In addition, 3r was found to induce apoptosis via the mitochondrial pathway in MDA-MB-231 cells as well as to inhibit cell migration. Moreover, we demonstrated that 3r inhibited tumor growth in vivo and thereby having a good therapeutic potential on TNBC. Taken together, these results suggest that 3r may be a novel Fam20C inhibitor with anti-proliferative and apoptosis-inducing activities, which would shed light on discovering more small-molecule drugs for the future TNBC therapy.

Phosphoproteomic analysis of duck egg white and insight into the biological functions of identified phosphoproteins

Phosphorylation of proteins is one of the most important and pleiotropic modifications. It plays a vital role in controlling protein functions. However, the phosphoproteome of duck egg white (DEW) has not been studied yet. To investigate the role of phosphorylation on DEW proteins, a detailed phosphoproteome analysis of DEW was performed using an immobilized metal affinity chromatography enrichment strategy. A total of 92 phosphosites representing 36 phosphoproteins were identified. [S-x-E] and [T-x-E] were found to be the most overrepresented motifs in DEW. The identified phosphoproteins in DEW were mainly involved in the binding, transport activity, biological regulation, and metabolic processes. Gene ontology analysis was used to elucidate the biological functions of DEW phosphoproteins and compare them with those of chicken egg white (CEW), which showed the differences mostly involved molecular functions and biological processes. PRACTICAL APPLICATIONS: These findings provide fundamental insight into the biological functions of identified phosphoproteins of DEW to better understand the roles of phosphorylated DEW proteins for food industries and human health. Phosphoproteomic study of DEW would be valuable for the food and nutrition industry to exploit the potential of this avian proteins in the processing of health benefit products.

FAM20C-Mediated Phosphorylation of MEPE and Its Acidic Serine- and Aspartate-Rich Motif

Matrix extracellular phosphoglycoprotein (MEPE) is expressed in bone and teeth where it has multiple functions. The C-terminus of MEPE contains a mineral-binding, acidic serine- and aspartate-rich motif (ASARM) that is also present in other noncollagenous proteins of mineralized tissues. MEPE-derived ASARM peptides function in phosphate homeostasis and direct inhibition of bone mineralization in a phosphorylation-dependent manner. MEPE is phosphorylated by family with sequence similarity 20, member C (FAM20C), which is the main kinase phosphorylating secreted phosphoprotein. Although the functional importance of protein phosphorylation status in mineralization processes has now been well-established for secreted bone and tooth proteins (particularly for osteopontin), the phosphorylation pattern of MEPE has not been previously determined. Here we provide evidence for a very high phosphorylation level of this protein, reporting on the localization of 31 phosphoresidues in human MEPE after coexpression with FAM20C in HEK293T cells. This includes the finding that all serine residues located in the canonical target sequence of FAM20C (Ser-x-Glu) were phosphorylated, thus establishing the major target sites for this kinase. We also show that MEPE has numerous other phosphorylation sites, these not being positioned in the canonical phosphorylation sequence. Of note, and underscoring a possible important function in mineralization biology, all nine serine residues in the ASARM were phosphorylated, even though only two of these were positioned in the Ser-x-Glu sequence. The presence of many phosphorylated amino acids in MEPE, and particularly their high density in the ASARM motif, provides an important basis for the understanding of structural and functional interdependencies in mineralization and phosphate homeostasis. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

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.