A novel gene, fad49, plays a crucial role in the immediate early stage of adipocyte differentiation via involvement in mitotic clonal expansion

Intercellular transfer of cancer cell invasiveness via endosome-mediated protease shedding

Overexpression of the transmembrane matrix metalloproteinase MT1-MMP/MMP14 promotes cancer cell invasion. Here we show that MT1-MMP-positive cancer cells turn MT1-MMP-negative cells invasive by transferring a soluble catalytic ectodomain of MT1-MMP. Surprisingly, this effect depends on the presence of TKS4 and TKS5 in the donor cell, adaptor proteins previously implicated in invadopodia formation. In endosomes of the donor cell, TKS4/5 promote ADAM-mediated cleavage of MT1-MMP by bridging the two proteases, and cleavage is stimulated by the low intraluminal pH of endosomes. The bridging depends on the PX domains of TKS4/5, which coincidently interact with the cytosolic tail of MT1-MMP and endosomal phosphatidylinositol 3-phosphate. MT1-MMP recruits TKS4/5 into multivesicular endosomes for their subsequent co-secretion in extracellular vesicles, together with the enzymatically active ectodomain. The shed ectodomain converts non-invasive recipient cells into an invasive phenotype. Thus, TKS4/5 promote intercellular transfer of cancer cell invasiveness by facilitating ADAM-mediated shedding of MT1-MMP in acidic endosomes.

Reorganization of the DNA replication landscape during adipogenesis is closely linked with adipogenic gene expression

The temporal order of DNA replication along the chromosomes is thought to reflect the transcriptional competence of the genome. During differentiation of mouse 3T3-L1 cells into adipocytes, cells undergo one or two rounds of cell division called mitotic clonal expansion (MCE). MCE is an essential step for adipogenesis; however, little is known about the regulation of DNA replication during this period. Here, we performed genome-wide mapping of replication timing (RT) in mouse 3T3-L1 cells before and during MCE, and identified a number of chromosomal regions shifting toward either earlier or later replication through two rounds of replication. These RT changes were confirmed in individual cells by single-cell DNA-replication sequencing. Coordinate changes between a shift toward earlier replication and transcriptional activation of adipogenesis-associated genes were observed. RT changes occurred before the full expression of these genes, indicating that RT reorganization might contribute to the mature adipocyte phenotype. To support this, cells undergoing two rounds of DNA replication during MCE had a higher potential to differentiate into lipid droplet-accumulating adipocytes, compared with cells undergoing a single round of DNA replication and non-replicating cells.

Inhibitory effect of ethanolic extract of Abeliophyllum distichum leaf on 3T3-L1 adipocyte differentiation

BACKGROUND/OBJECTIVES

Abeliophyllum distichum is a plant endemic to Korea, containing several beneficial natural compounds. This study investigated the effect of A. distichum leaf extract (ALE) on adipocyte differentiation.

MATERIALS/METHODS

The cytotoxic effect of ALE was analyzed using cell viability assay. 3T3-L1 preadipocytes were differentiated using induction media in the presence or absence of ALE. Lipid accumulation was confirmed using Oil Red O staining. The mRNA expression of adipogenic markers was measured using RT-PCR, and the protein expressions of mitogen-activated protein kinase (MAPK) and peroxisome proliferator-activated receptor gamma (PPARγ) were measured using western blot. Cell proliferation was measured by calculating the incorporation of Bromodeoxyuridine (BrdU) into DNA.

RESULTS

ALE reduced lipid accumulation in differentiated adipocytes, as indicated by Oil Red O staining and triglyceride assays. Treatment with ALE decreased the gene expression of adipogenic markers such as Pparγ, CCAAT/enhancer binding protein alpha (C/ebpα), lipoprotein lipase, adipocyte protein-2, acetyl-CoA carboxylase, and fatty acid synthase. Also, the protein expression of PPARγ was reduced by ALE. Treating the cells with ALE at different time points revealed that the inhibitory effect of ALE on adipogenesis is higher in the early period treatment than in the terminal period. Furthermore, ALE inhibited adipocyte differentiation by reducing the early phase of adipogenesis and mitotic clonal expansion. This was indicated by the lower number of cells in the Synthesis phase of the cell cycle (labeled using BrdU assay) and a decrease in the expression of early adipogenic transcription factors such as C/ebpβ and C/ebpδ. ALE suppressed the phosphorylation of MAPK, confirming that the effect of ALE was through the suppression of early phase of adipogenesis.

CONCLUSIONS

Altogether, the results of the present study revealed that ALE inhibits lipid accumulation and may be a potential agent for managing obesity.

Characterization of the Intramolecular Interactions and Regulatory Mechanisms of the Scaffold Protein Tks4

The scaffold protein Tks4 is a member of the p47^phox-related organizer superfamily. It plays a key role in cell motility by being essential for the formation of podosomes and invadopodia. In addition, Tks4 is involved in the epidermal growth factor (EGF) signaling pathway, in which EGF induces the translocation of Tks4 from the cytoplasm to the plasma membrane. The evolutionarily-related protein p47^phox and Tks4 share many similarities in their N-terminal region: a phosphoinositide-binding PX domain is followed by two SH3 domains (so called “tandem SH3”) and a proline-rich region (PRR). In p47^phox, the PRR is followed by a relatively short, disordered C-terminal tail region containing multiple phosphorylation sites. These play a key role in the regulation of the protein. In Tks4, the PRR is followed by a third and a fourth SH3 domain connected by a long (~420 residues) unstructured region. In p47^phox, the tandem SH3 domain binds the PRR while the first SH3 domain interacts with the PX domain, thereby preventing its binding to the membrane. Based on the conserved structural features of p47^phox and Tks4 and the fact that an intramolecular interaction between the third SH3 and the PX domains of Tks4 has already been reported, we hypothesized that Tks4 is similarly regulated by autoinhibition. In this study, we showed, via fluorescence-based titrations, MST, ITC, and SAXS measurements, that the tandem SH3 domain of Tks4 binds the PRR and that the PX domain interacts with the third SH3 domain. We also investigated a phosphomimicking Thr-to-Glu point mutation in the PRR as a possible regulator of intramolecular interactions. Phosphatidylinositol-3-phosphate (PtdIns(3)P) was identified as the main binding partner of the PX domain via lipid-binding assays. In truncated Tks4 fragments, the presence of the tandem SH3, together with the PRR, reduced PtdIns(3)P binding, while the presence of the third SH3 domain led to complete inhibition.

Advances in Understanding TKS4 and TKS5: Molecular Scaffolds Regulating Cellular Processes from Podosome and Invadopodium Formation to Differentiation and Tissue Homeostasis

Scaffold proteins are typically thought of as multi-domain "bridging molecules." They serve as crucial regulators of key signaling events by simultaneously binding multiple participants involved in specific signaling pathways. In the case of epidermal growth factor (EGF)-epidermal growth factor receptor (EGFR) binding, the activated EGFR contacts cytosolic SRC tyrosine-kinase, which then becomes activated. This process leads to the phosphorylation of SRC-substrates, including the tyrosine kinase substrates (TKS) scaffold proteins. The TKS proteins serve as a platform for the recruitment of key players in EGFR signal transduction, promoting cell spreading and migration. The TKS4 and the TKS5 scaffold proteins are tyrosine kinase substrates with four or five SH3 domains, respectively. Their structural features allow them to recruit and bind a variety of signaling proteins and to anchor them to the cytoplasmic surface of the cell membrane. Until recently, TKS4 and TKS5 had been recognized for their involvement in cellular motility, reactive oxygen species-dependent processes, and embryonic development, among others. However, a number of novel functions have been discovered for these molecules in recent years. In this review, we attempt to cover the diverse nature of the TKS molecules by discussing their structure, regulation by SRC kinase, relevant signaling pathways, and interaction partners, as well as their involvement in cellular processes, including migration, invasion, differentiation, and adipose tissue and bone homeostasis. We also describe related pathologies and the established mouse models.

Enhanced endothelial motility and multicellular sprouting is mediated by the scaffold protein TKS4

Endothelial cell motility has fundamental role in vasculogenesis and angiogenesis during developmental or pathological processes. Tks4 is a scaffold protein known to organize the cytoskeleton of lamellipodia and podosomes, and thus modulating cell motility and invasion. In particular, Tks4 is required for the localization and activity of membrane type 1-matrix metalloproteinase, a key factor for extracellular matrix (ECM) cleavage during cell migration. While its role in transformed cells is well established, little is known about the function of Tks4 under physiological conditions. In this study we examined the impact of Tks4 gene silencing on the functional activity of primary human umbilical vein endothelial cells (HUVEC) and used time-lapse videomicrosopy and quantitative image analysis to characterize cell motility phenotypes in culture. We demonstrate that the absence of Tks4 in endothelial cells leads to impaired ECM cleavage and decreased motility within a 3-dimensional ECM environment. Furthermore, absence of Tks4 also decreases the ability of HUVEC cells to form multicellular sprouts, a key requirement for angiogenesis. To establish the involvement of Tks4 in vascular development in vivo, we show that loss of Tks4 leads sparser vasculature in the fetal chorion in the Tks4-deficient ‘nee’ mouse strain.

Analysis of Tks4 Knockout Mice Suggests a Role for Tks4 in Adipose Tissue Homeostasis in the Context of Beigeing

Obesity and adipocyte malfunction are related to and arise as consequences of disturbances in signaling pathways. Tyrosine kinase substrate with four Src homology 3 domains (Tks4) is a scaffold protein that establishes a platform for signaling cascade molecules during podosome formation and epidermal growth factor receptor (EGFR) signaling. Several lines of evidence have also suggested that Tks4 has a role in adipocyte biology; however, its roles in the various types of adipocytes at the cellular level and in transcriptional regulation have not been studied. Therefore, we hypothesized that Tks4 functions as an organizing molecule in signaling networks that regulate adipocyte homeostasis. Our aims were to study the white and brown adipose depots of Tks4 knockout (KO) mice using immunohistology and western blotting and to analyze gene expression changes regulated by the white, brown, and beige adipocyte-related transcription factors via a PCR array. Based on morphological differences in the Tks4-KO adipocytes and increased uncoupling protein 1 (UCP1) expression in the white adipose tissue (WAT) of Tks4-KO mice, we concluded that the beigeing process was more robust in the WAT of Tks4-KO mice compared to the wild-type animals. Furthermore, in the Tks4-KO WAT, the expression profile of peroxisome proliferator-activated receptor gamma (PPARγ)-regulated adipogenesis-related genes was shifted in favor of the appearance of beige-like cells. These results suggest that Tks4 and its downstream signaling partners are novel regulators of adipocyte functions and PPARγ-directed white to beige adipose tissue conversion.

Significance of the Tks4 scaffold protein in bone tissue homeostasis

The main driver of osteoporosis is an imbalance between bone resorption and formation. The pathogenesis of osteoporosis has also been connected to genetic alterations in key osteogenic factors and dysfunction of bone marrow mesenchymal stem/stromal cells (BM-MSCs). Tks4 (encoded by the Sh3pxd2b gene) is a scaffold protein involved in podosome organization. Homozygous mutational inactivation of Sh3pxd2b causes Frank-ter Haar syndrome (FTHS), a genetic disease that affects bone tissue as well as eye, ear, and heart functions. To date, the role of Tks4 in adult bone homeostasis has not been investigated. Therefore, the aim of this study was to analyze the facial and femoral bone phenotypes of Sh3pxd2b knock-out (KO) mice using micro-CT methods. In addition to the analysis of the Sh3pxd2b-KO mice, the bone microstructure of an FTHS patient was also examined. Macro-examination of skulls from Tks4-deficient mice revealed craniofacial malformations that were very similar to symptoms of the FTHS patient. The femurs of the Sh3pxd2b-KO mice had alterations in the trabecular system and showed signs of osteoporosis, and, similarly, the FTHS patient also showed increased trabecular separation/porosity. The expression levels of the Runx2 and osteocalcin bone formation markers were reduced in the bone and bone marrow of the Sh3pxd2b-KO femurs, respectively. Our recent study demonstrated that Sh3pxd2b-KO BM-MSCs have a reduced ability to differentiate into osteoblast lineage cells; therefore, we concluded that the Tks4 scaffold protein is important for osteoblast formation, and that it likely plays a role in bone cell homeostasis.

FAD104, a regulator of adipogenesis, is a novel suppressor of TGF-β-mediated EMT in cervical cancer cells

Epithelial-to-mesenchymal transition (EMT) is a biological process in which epithelial cells translate into a mesenchymal phenotype with invasive capacities, contributing to tumour progression, metastasis, and the acquisition of chemotherapy resistance. To identify new therapeutic targets for cancers, it is important to clarify the molecular mechanism of induction of EMT. We have previously reported that fad104, a positive regulator of adipocyte differentiation, suppressed the invasion and metastasis of melanoma and breast cancer cells. In this study, we showed that FAD104 functions as a novel suppressor of transforming growth factor-β (TGF-β)–mediated EMT in cervical cancer cells. Expression of FAD104 is upregulated during TGF-β–mediated EMT in human cervical cancer HeLa cells. Reduction of fad104 expression enhanced TGF-β–mediated EMT and migration in HeLa cells. Conversely, overexpression of FAD104 suppressed TGF-β–induced EMT. In addition, we showed that FAD104 negatively regulated phosphorylation of Smad2 and Smad3 but positively regulated phosphorylation of Smad1/5/8 via treatment with TGF-β. These findings demonstrate that FAD104 is a novel suppressor of TGF-β signalling and represses TGF-β–mediated EMT in cervical cancer cells.

The scaffold protein Tks4 is required for the differentiation of mesenchymal stromal cells (MSCs) into adipogenic and osteogenic lineages

The commitment steps of mesenchymal stromal cells (MSCs) to adipogenic and other lineages have been widely studied but not fully understood. Therefore, it is critical to understand which molecules contribute to the conversion of stem cells into differentiated cells. The scaffold protein Tks4 plays a role in podosome formation, EGFR signaling and ROS production. Dysfunction of Tks4 causes a hereditary disease called Frank-ter Haar syndrome with a variety of defects concerning certain mesenchymal tissues (bone, fat and cartilage) throughout embryogenic and postnatal development. In this study, we aimed to analyze how the mutation of Tks4 affects the differentiation potential of multipotent bone marrow MSCs (BM-MSCs). We generated a Tks4 knock-out mouse strain on C57Bl/6 background, and characterized BM-MSCs isolated from wild type and Tks4^-/- mice to evaluate their differentiation. Tks4^-/- BM-MSCs had reduced ability to differentiate into osteogenic and adipogenic lineages compared to wild type. Studying the expression profile of a panel of lipid-regulated genes during adipogenic induction revealed that the expression of adipogenic transcription factors, genes responsible for lipid droplet formation, sterol and fatty acid metabolism was delayed or reduced in Tks4^-/- BM-MSCs. Taken together, these results establish a novel function for Tks4 in the regulation of MSC differentiation.

FAD104, a Regulator of Adipogenesis and Osteogenesis, Interacts with the C-Terminal Region of STAT3 and Represses Malignant Transformation of Melanoma Cells

Anchorage-independent growth is one of the defining characteristics of cancer cells. Many oncogenes and tumor suppressor genes are involved in regulating this type of growth. Factor for adipocyte differentiation 104 gene (fad104) is a regulator of adipogenesis and osteogenesis. Previously, we reported that fad104 suppressed metastasis as well as invasion of melanoma cells. However, it is unclear whether fad104 is involved in malignant transformation, which is associated with metastasis. In this study, we revealed that fad104 negatively regulated the colony forming activity of melanoma cells. The presence of the N-terminal region of FAD104 was required for the regulation of malignant transformation of melanoma cells. In addition, the deletion mutant of FAD104 that contained the N-terminal region and transmembrane domain interacted with signal transducer and activator of transcription 3 (STAT3) and suppressed STAT3 activity. However, the deletion mutant of FAD104 lacking the N-terminal region did not influence the interaction with STAT3 or suppress the STAT3 activity. Moreover, FAD104 interacted with the C-terminal region of STAT3. In summary, we demonstrated that fad104 suppressed anchorage-independent growth of melanoma cells, and that the N-terminal region of FAD104 is essential for inhibiting malignant transformation and STAT3 activity.

[Molecular Mechanisms of Early-stage Adipocyte Differentiation and Multi-functional Roles of Newly Isolated Adipogenic Factors]

Obesity is a major risk factor for diabetes, hypertension, hyperlipidemia, and arteriosclerosis. Although the middle and late stages of adipocyte differentiation are well characterized, the earliest step in the differentiation process has remained largely unknown. We isolated 102 genes expressed at the beginning of the differentiation of a mouse preadipocyte cell line, 3T3-L1 cells. Because approximately half of these genes were unknown, we named them factor for adipocyte differentiation (fad) genes. I first show how these genes regulate the early stage of adipocyte differentiation. We next generated fad104-deficient mice, and demonstrated that fad104-deficient mice died due to cyanosis-associated lung dysplasia with atelectasis. We also found that fad104 positively regulated adipocyte differentiation and negatively regulated osteoblast differentiation. We then demonstrated that fad24-knockdown inhibited mitotic clonal expansion (MCE) and that FAD24 contributed to the regulation of DNA replication by recruiting histone acetyltransferase binding to ORC1 (HBO1) to DNA replication origins. In vitro culture experiments revealed that fad24-null embryos developed normally to the morula stage, but acquired growth defects in subsequent stages. These results strongly suggest that fad24 is essential for pre-implantation in embryonic development, particularly for progression to the blastocyst stage. These findings together indicate that both fad104 and fad24 contribute not only to adipogenesis but also to other physiological events. The multi-functional roles of these genes are discussed.

Accumulation of the PX domain mutant Frank-ter Haar syndrome protein Tks4 in aggresomes

Background

Cells deploy quality control mechanisms to remove damaged or misfolded proteins. Recently, we have reported that a mutation (R43W) in the Frank-ter Haar syndrome protein Tks4 resulted in aberrant intracellular localization.

Results

Here we demonstrate that the accumulation of Tks4^R43W depends on the intact microtubule network. Detergent-insoluble Tks4 mutant colocalizes with the centrosome and its aggregate is encaged by the intermediate filament protein vimentin. Both the microtubule inhibitor nocodazole and the histone deacetylase inhibitor Trichostatin A inhibit markedly the aggresome formation in cells expressing Tks4^R43W. Finally, pretreatment of cells with the proteasome inhibitor MG132 markedly increases the level of aggresomes formed by Tks4^R43W. Furthermore, two additional mutant Tks4 proteins (Tks4^1–48 or Tks4^1–341) have been investigated. Whereas the shorter Tks4 mutant, Tks4^1–48, shows no expression at all, the longer Tks4 truncation mutant accumulates in the nuclei of the cells.

Conclusions

Our results suggest that misfolded Frank-ter Haar syndrome protein Tks4^R43W is transported via the microtubule system to the aggresomes. Lack of expression of Tks4^1–48 or aberrant intracellular expressions of Tks4^R43W and Tks4^1–341 strongly suggest that these mutations result in dysfunctional proteins which are not capable of operating properly, leading to the development of FTHS.

Fad104, a positive regulator of adipocyte differentiation, suppresses invasion and metastasis of melanoma cells by inhibition of STAT3 activity

Metastasis is the main cause of death in patients with cancer, and understanding the mechanisms of metastatic processes is essential for the development of cancer therapy. Although the role of several cell adhesion, migration or proliferation molecules in metastasis is established, a novel target for cancer therapy remains to be discovered. Previously, we reported that fad104 (factor for adipocyte differentiation 104), a regulatory factor of adipogenesis, regulates cell adhesion and migration. In this report, we clarify the role of fad104 in the invasion and metastasis of cancer cells. The expression level of fad104 in highly metastatic melanoma A375SM cells was lower than that in poorly metastatic melanoma A375C6 cells. Reduction of fad104 expression enhanced the migration and invasion of melanoma cells, while over-expression of FAD104 inhibited migration and invasion. In addition, melanoma cells stably expressing FAD104 showed a reduction in formation of lung colonization compared with control cells. FAD104 interacted with STAT3 and down-regulated the phosphorylation level of STAT3 in melanoma cells. These findings together demonstrate that fad104 suppressed the invasion and metastasis of melanoma cells by inhibiting activation of the STAT3 signaling pathway. These findings will aid a comprehensive description of the mechanism that controls the invasion and metastasis of cancer cells.

Expression, purification and preliminary crystallographic studies of the C-terminal SH3 domain of human Tks4

The Src homology 3 (SH3) domain is a small, noncatalytic domain with a conserved sequence of about 60 amino-acid residues that interacts with proline-rich peptides to form a protein complex. In this study, the C-terminal SH3 domain of human Tks4 (residues 853-911) was expressed, purified and crystallized. X-ray diffraction data were collected to 2.3 Å resolution. The crystal belonged to the trigonal space group P3121 (or P3221), with unit-cell parameters a = b = 83.87, c = 108.44 Å, α = β = 90, γ = 120°. Calculating the self-rotation and the native Patterson function did not lead to the detection of any noncrystallographic translational symmetry. Six, seven or eight protein molecules are likely to be present in the asymmetric unit, resulting in a Matthews coefficient and approximate solvent content of 2.71 Å(3) Da(-1) and 55%, 2.32 Å(3) Da(-1) and 47%, and 2.03 Å(3) Da(-1) and 39%, respectively. To solve the crystal structure of the C-terminal SH3 domain of human Tks4, the isomorphous replacement method is presently being utilized.

FAD104, a regulatory factor of adipogenesis, acts as a novel regulator of calvarial bone formation

Osteogenesis is a complex process that is orchestrated by several growth factors, extracellular cues, signaling molecules, and transcriptional factors. Understanding the mechanisms of bone formation is pivotal for clarifying the pathogenesis of bone diseases. Previously, we reported that fad104 (factor for adipocyte differentiation 104), a novel positive regulator of adipocyte differentiation, negatively regulated the differentiation of mouse embryonic fibroblasts into osteocytes. However, the physiological role of fad104 in bone formation has not been elucidated. Here, we clarified the role of fad104 in bone formation in vivo and in vitro. fad104 disruption caused craniosynostosis-like premature ossification of the calvarial bone. Furthermore, analyses using primary calvarial cells revealed that fad104 negatively regulated differentiation and BMP/Smad signaling pathway. FAD104 interacted with Smad1/5/8. The N-terminal region of FAD104, which contains a proline-rich motif, was capable of binding to Smad1/5/8. We demonstrated that down-regulation of Smad1/5/8 phosphorylation by FAD104 is dependent on the N-terminal region of FAD104 and that fad104 functions as a novel negative regulator of BMP/Smad signaling and is required for proper development for calvarial bone. These findings will aid a comprehensive description of the mechanism that controls normal and premature calvarial ossification.

EGF regulates tyrosine phosphorylation and membrane-translocation of the scaffold protein Tks5

Background

Tks5/FISH is a scaffold protein comprising of five SH3 domains and one PX domain. Tks5 is a substrate of the tyrosine kinase Src and is required for the organization of podosomes/invadopodia implicated in invasion of tumor cells. Recent data have suggested that a close homologue of Tks5, Tks4, is implicated in the EGF signaling.

Results

Here, we report that Tks5 is a component of the EGF signaling pathway. In EGF-treated cells, Tks5 is tyrosine phosphorylated within minutes and the level of phosphorylation is sustained for at least 2 hours. Using specific kinase inhibitors, we demonstrate that tyrosine phosphorylation of Tks5 is catalyzed by Src tyrosine kinase. We show that treatment of cells with EGF results in plasma membrane translocation of Tks5. In addition, treatment of cells with LY294002, an inhibitor of PI 3-kinase, or mutation of the PX domain reduces tyrosine phosphorylation and membrane translocation of Tks5.

Conclusions

Our results identify Tks5 as a novel component of the EGF signaling pathway.

Frank-ter Haar syndrome protein Tks4 regulates epidermal growth factor-dependent cell migration

Mutations in the SH3PXD2B gene coding for the Tks4 protein are responsible for the autosomal recessive Frank-ter Haar syndrome. Tks4, a substrate of Src tyrosine kinase, is implicated in the regulation of podosome formation. Here, we report a novel role for Tks4 in the EGF signaling pathway. In EGF-treated cells, Tks4 is tyrosine-phosphorylated and associated with the activated EGF receptor. This association is not direct but requires the presence of Src tyrosine kinase. In addition, treatment of cells with LY294002, an inhibitor of PI 3-kinase, or mutations of the PX domain reduces tyrosine phosphorylation and membrane translocation of Tks4. Furthermore, a PX domain mutant (R43W) Tks4 carrying a reported point mutation in a Frank-ter Haar syndrome patient showed aberrant intracellular expression and reduced phosphoinositide binding. Finally, silencing of Tks4 was shown to markedly inhibit HeLa cell migration in a Boyden chamber assay in response to EGF or serum. Our results therefore reveal a new function for Tks4 in the regulation of growth factor-dependent cell migration.

Indispensable role of factor for adipocyte differentiation 104 (fad104) in lung maturation

Factor for adipocyte differentiation 104 (fad104) is a regulator of adipogenesis and osteogenesis. Our previous study showed that fad104-deficient mice died immediately after birth, suggesting fad104 to be essential for neonatal survival. However, the cause of this rapid death is unclear. Here, we demonstrate the role of fad104 in neonatal survival. Phenotypic and morphological analyses showed that fad104-deficient mice died due to cyanosis-associated lung dysplasia including atelectasis. Furthermore, immunohistochemistry revealed that FAD104 was strongly expressed in ATII cells in the developing lung. Most importantly, the ATII cells in lungs were immature, and impaired the expression of surfactant-associated proteins. Collectively, these results indicate that fad104 has an indispensable role in lung maturation, especially the maturation and differentiation of ATII cells.

The homolog of the five SH3-domain protein (HOFI/SH3PXD2B) regulates lamellipodia formation and cell spreading

Motility of normal and transformed cells within and across tissues requires specialized subcellular structures, e.g. membrane ruffles, lamellipodia and podosomes, which are generated by dynamic rearrangements of the actin cytoskeleton. Because the formation of these sub-cellular structures is complex and relatively poorly understood, we evaluated the role of the adapter protein SH3PXD2B [HOFI, fad49, Tks4], which plays a role in the development of the eye, skeleton and adipose tissue. Surprisingly, we find that SH3PXD2B is requisite for the development of EGF-induced membrane ruffles and lamellipodia, as well as for efficient cellular attachment and spreading of HeLa cells. Furthermore, SH3PXD2B is present in a complex with the non-receptor protein tyrosine kinase Src, phosphorylated by Src, which is consistent with SH3PXD2B accumulating in Src-induced podosomes. Furthermore, SH3PXD2B closely follows the subcellular relocalization of cortactin to Src-induced podosomes, EGF-induced membrane ruffles and lamellipodia. Because SH3PXD2B also forms a complex with the C-terminal region of cortactin, we propose that SH3PXD2B is a scaffold protein that plays a key role in regulating the actin cytoskeleton via Src and cortactin.

Podosomal proteins as causes of human syndromes: a role in craniofacial development?

Podosomes and invadopodia are actin-rich protrusions of the plasma membrane important for matrix degradation and cell migration. Most of the information in this field has been obtained in cancer cells, where the presence of invadopodia has been related to increased invasiveness and metastatic potential. The importance of the related podosome structure in other pathological or physiological processes that require cell invasion is relatively unexplored. Recent evidence indicates that essential components of podosomes are responsible for several human syndromes, some of which are characterized by serious developmental defects involving the craniofacial area, skeleton and heart, and very poor prognosis. Here we will review them and discuss the possible role of podosomes as a player in correct embryo development.

Anterior segment dysgenesis and early-onset glaucoma in nee mice with mutation of Sh3pxd2b

PURPOSE

Mutations in SH3PXD2B cause Frank-Ter Haar syndrome, a rare condition characterized by congenital glaucoma, as well as craniofacial, skeletal, and cardiac anomalies. The nee strain of mice carries a spontaneously arising mutation in Sh3pxd2b. The purpose of this study was to test whether nee mice develop glaucoma.

METHODS

Eyes of nee mutants and strain-matched controls were comparatively analyzed at multiple ages by slit lamp examination, intraocular pressure recording, and histologic analysis. Cross sections of the optic nerve were analyzed to confirm glaucomatous progression.

RESULTS

Slit lamp examination showed that, from an early age, nee mice uniformly exhibited severe iridocorneal adhesions around the entire circumference of the eye. Presumably as a consequence of aqueous humor outflow blockage, they rapidly developed multiple indices of glaucoma. By 3 to 4 months of age, they exhibited high intraocular pressure (30.8 ± 12.5 mm Hg; mean ± SD), corneal opacity, and enlarged anterior chambers. Although histologic analyses at P17 did not reveal any indices of damage, similar analysis at 3 to 4 months of age revealed a course of progressive retinal ganglion cell loss, optic nerve head excavation, and axon loss.

CONCLUSIONS

Eyes of nee mice exhibit anterior segment dysgenesis and early-onset glaucoma. Because SH3PXD2B is predicted to be a podosome adaptor protein, these findings implicate podosomes in normal development of the iridocorneal angle and the genes influencing podosomes as candidates in glaucoma. Because of the early-onset, high-penetrance glaucoma, nee mice offer many potential advantages as a new mouse model of the disease.

Fad104, a positive regulator of adipogenesis, negatively regulates osteoblast differentiation

Fad104 (factor for adipocyte differentiation 104) is a novel gene expressed temporarily in the early stages of adipocyte differentiation. Previously, we showed that fad104 promotes adipocyte differentiation in mouse 3T3-L1 cells and mouse embryonic fibroblasts (MEFs). Furthermore, we reported that implanted wild-type MEFs could develop into adipocytes, whereas fad104-deficient MEFs could not. Interestingly, bone-like tissues were only observed in the implants derived from fad104-deficient MEFs. This result implies that fad104 is involved in osteoblast differentiation. However, the functions of fad104 during osteogenesis are unknown. In this paper, we show that fad104 negatively regulates osteoblast differentiation. During the differentiation process, the level of fad104 expression decreased. Deletion of fad104 facilitated osteoblast differentiation in MEFs, and elevated the level of runx2, a master regulator of osteoblast differentiation. Disruption of fad104 suppressed BMP-2-mediated adipocyte differentiation in MEFs. In conclusion, we demonstrate that fad104 reciprocally regulates differentiation of adipocytes and osteoblast; functions as a positive regulator in adipocyte differentiation and as a negative regulator in osteoblast differentiation.

The podosomal-adaptor protein SH3PXD2B is essential for normal postnatal development

Podosome-type adhesions are actin-based membrane protrusions involved in cell-matrix adhesion and extracellular matrix degradation. Despite growing knowledge of many proteins associated with podosome-type adhesions, much remains unknown concerning the function of podosomal proteins at the level of the whole animal. In this study, the spontaneous mouse mutant nee was used to identify a component of podosome-type adhesions that is essential for normal postnatal growth and development. Mice homozygous for the nee allele exhibited runted growth, craniofacial and skeletal abnormalities, ocular anterior segment dysgenesis, and hearing impairment. Adults also exhibited infertility and a form of lipodystrophy. Using genetic mapping and DNA sequencing, the cause of nee phenotypes was identified as a 1-bp deletion within the Sh3pxd2b gene on mouse Chromosome 11. Whereas the wild-type Sh3pxd2b gene is predicted to encode a protein with one PX domain and four SH3 domains, the nee mutation is predicted to cause a frameshift and a protein truncation altering a portion of the third SH3 domain and deleting all of the fourth SH3 domain. The SH3PXD2B protein is believed to be an important component of podosomes likely to mediate protein-protein interactions with membrane-spanning metalloproteinases. Testing this directly, SH3PXD2B localized to podosomes in constitutively active Src-transfected fibroblasts and through its last SH3 domain associated with a transmembrane member of a disintegrin and metalloproteinase family of proteins, ADAM15. These results identify SH3PXD2B as a podosomal-adaptor protein required for postnatal growth and development, particularly within physiologic contexts involving extracellular matrix regulation.

The role of C/EBPdelta in the early stages of adipogenesis

Adipocyte differentiation is a complex process triggered and facilitated by transcription factors such as peroxisome proliferator-activated receptor gamma (PPARgamma) and CCAAT/enhancer-binding protein (C/EBP) alpha. Most about the cascade underlying the differentiation process, especially events in the early stages, remain to be elucidated. Early on in adipocyte differentiation, the C/EBPbeta and C/EBPdelta genes are rapidly induced to express and later activate PPARgamma and C/EBPalpha expression. C/EBPbeta also plays a crucial role in mitotic clonal expansion (MCE), the approximately two rounds of mitosis which occurs soon after preadipocytes are stimulated by differentiation inducers and a necessary step for adipocyte differentiation. However, the effect of C/EBPdelta, another member of the C/EBP family, on MCE remains unclear. In the present study, we investigated the role of C/EBPdelta in the early stages of adipogenesis. A remarkable induction of C/EBPdelta gene expression after the initiation of differentiation was observed not in proliferating preadipocytes, but in growth-arrested, differentiable cells. RNAi-mediated knockdown of C/EBPdelta dramatically suppressed cell growth after differentiation was induced, and inhibited conversion into lipid-laden adipocytes. Furthermore, silencing of C/EBPdelta impaired the expression of factor for adipocyte differentiation (fad) 49, which is up-regulated and plays a crucial role early in adipogenesis. Taken together, these findings show that C/EBPdelta is involved in MCE and gene expression in the early stages of adipocyte differentiation.