The Rho-specific guanine nucleotide exchange factor Plekhg5 modulates cell polarity, adhesion, migration, and podosome organization in macrophages and osteoclasts

Abr, a Rho-regulating protein, modulates osteoclastogenesis by enhancing lamellipodia formation by interacting with poly(ADP-ribose) glycohydrolase

BACKGROUND

Osteoclasts are multinucleated bone-resorbing cells formed by the fusion of monocyte/macrophage lineage. During osteoclast differentiation, Rho GTPases are involved in various processes, including cell migration, adhesion, and polarity. However, the role of Rho-regulatory molecules in the regulation of osteoclast differentiation remains unclear. In this study, among these genes, we focused on active breakpoint cluster region-related (Abr) protein that is a multifunctional regulator of Rho GTPases.

METHODS AND RESULTS

We examined using knockdown and overexpression experiments in RANKL-stimulated RAW-D macrophages whether Abr regulates osteoclast differentiation and cell morphology. We observed an increase in Abr expression during osteoclast differentiation and identified expression of a variant of the Abr gene in osteoclasts. Knockdown of Abr suppressed osteoclast differentiation and resorption. Abr knockdown markedly inhibited the expression of osteoclast markers, such as Nfatc1, c-fos, Src, and Ctsk in osteoclasts. Conversely, overexpression of Abr enhanced the formation of multinucleated osteoclasts, bone resorption activity, and osteoclast marker gene expression. Moreover, Abr overexpression accelerated lamellipodia formation and induced the formation of well-developed actin in osteoclasts. Importantly, the Abr protein interacted with poly(ADP-ribose) glycohydrolase (PARG) and Rho GTPases, including RhoA, Rac1/2/3, and Cdc42 in osteoclasts.

CONCLUSIONS

Taken together, these results indicate that Abr modulates osteoclastogenesis by enhancing lamellipodia formation via its interaction with PARG.

Prostaglandins and calprotectin are genetically and functionally linked to the Inflammatory Bowel Diseases

Background

Genome wide association studies (GWAS) have identified and validated more than 200 genomic loci associated with the inflammatory bowel disease (IBD), although for most the causal gene remains unknown. Given the importance of myeloid cells in IBD pathogenesis, the current study aimed to uncover the role of genes within IBD genetic loci that are endogenously expressed in this cell lineage.

Methods

The open reading frames (ORF) of 42 genes from IBD-associated loci were expressed via lentiviral transfer in the THP-1 model of human monocytes and the impact of each of these on the cell’s transcriptome was analyzed using a RNA sequencing-based approach. We used a combination of genetic and pharmacologic approaches to validate our findings in the THP-1 line with further validation in human induced pluripotent stem cell (hiPSC)-derived-monocytes.

Results

This functional genomics screen provided evidence that genes in four IBD GWAS loci (PTGIR, ZBTB40, SLC39A11 and NFKB1) are involved in controlling S100A8 and S100A9 genes expression, which encode the two subunits of calprotectin (CP). We demonstrated that increasing PTGIR expression and/or stimulating PTGIR signaling resulted in increased CP expression in THP-1.

This was further validated in hiPSC-derived monocytes. Conversely, knocking-down PTGIR endogenous expression and/or inhibiting PTGIR signaling led to decreased CP expression. These analyses were extended to the known IBD gene PTGER4, whereby its specific agonist also led to increased CP expression. Furthermore, we demonstrated that the PTGIR and PTGER4 mediated control of CP expression was dependent on signaling via adenylate cyclase and STAT3. Finally, we demonstrated that LPS-mediated increases in CP expression could be potentiated by agonists of PTGIR and PTGER4, and diminished by their antagonists.

Conclusion

Our results support a causal role for the PTGIR, PTGER4, ZBTB40, SLC39A11 and NFKB1 genes in IBD, with all five genes regulating the expression of CP in myeloid cells, as well as potential roles for the prostacyclin/prostaglandin biogenesis and signaling pathways in IBD susceptibility and pathogenesis.

0.5‑Gy X‑ray irradiation induces reorganization of cytoskeleton and differentiation of osteoblasts

Osteoblasts are sensitive to ionizing radiation. The small GTPase RhoA and its effector Rho‑associated protein kinase (ROCK) are critical to several cellular functions, including cytoskeleton reorganization, cell survival, and cell differentiation. However, whether the RhoA/ROCK signaling pathway is involved in the regulation of osteoblast cytoskeleton reorganization and differentiation induced by low‑dose X‑ray irradiation remains to be determined. The aim of the present study was to investigate the role of the RhoA/ROCK signaling pathway in mediating differentiation of osteoblasts and reorganization of the cytoskeleton under low‑dose X‑ray irradiation. Osteoblasts were pretreated with the ROCK kinase‑specific inhibitor (Y‑27632) before exposure to low‑dose X‑ray irradiation. The changes of F‑actin in MC3T3 cells were observed at different time points following X‑ray irradiation. Cell Counting Kit‑8 assay, alkaline phosphatase activity, Alizarin red staining and western blotting were used to detect the proliferation and differentiation of osteoblasts after 0.5‑Gy X‑ray irradiation. In the present study, low‑dose X‑ray irradiation promoted the expression of genes associated with the cytoskeleton reorganization. Indeed, the results showed that, 0.5‑Gy X‑ray irradiation can induce reorganization of cytoskeleton and promote differentiation of osteoblasts through the RhoA/ROCK signaling pathway. Additionally, inhibiting ROCK activity blocked low‑dose X‑ray irradiation‑induced LIMK2 phosphorylation, stress fiber formation and cell differentiation. Thus, these results demonstrated the excitatory effects of low‑dose X‑ray irradiation on MC3T3‑E1 cells, including reorganization of the cytoskeleton and differentiation of osteoblasts.

HIV-1 uses dynamic podosomes for entry into macrophages

Macrophages are one of the major targets of Human Immunodeficiency virus 1 (HIV-1) and play crucial roles in viral dissemination and persistence during AIDS progression. Here, we reveal the dynamic podosome-mediated entry of HIV-1 into macrophages. Inhibition of podosomes prevented HIV-1 entry into macrophages, while stimulation of podosome formation promoted viral entry. Single-virus tracking revealed the temporal and spatial mechanism of the dynamic podosome-mediated viral entry process. The core and ring structures of podosomes played complex roles in viral entry. The HIV coreceptor, CCR5, was recruited to form specific clusters at the podosome ring, where it participated in viral entry. The podosome facilitated HIV-1 entry with a rotation mode triggered by dynamic actin. Our discovery of this novel HIV-1 entry route into macrophages, mediated by podosomes critical for cell migration and tissue infiltration, provides a new view of HIV infection and pathogenesis, which may assist in the development of new antiviral strategies.IMPORTANCEMacrophages are motile leukocytes and play critical roles in HIV-1 infection and AIDS progression. Podosomes, as small dynamic adhesion microdomains driven by the dynamic actin cytoskeleton, are mainly involved in cell migration of macrophages. Herein, we found that HIV-1 uses dynamic podosomes to facilitate its entry into macrophages. Single-virus imaging coupled with drug assays revealed the mechanism underlying the podosome-mediated route of HIV-1 entry into macrophages, including the dynamic relationship between the viral particles and the podosome core and ring structures, the CCR5 coreceptor. The dynamic podosome-mediated entry of HIV-1 into macrophages will be very significant for HIV-1 pathogenesis, especially for viral dissemination via macrophage migration and tissue infiltration. Thus, we report a novel HIV-1 entry route into macrophages mediated by podosomes, which extends our understanding of HIV infection and pathogenesis.

NF-κB promotes osteoclast differentiation by overexpressing MITF via down regulating microRNA-1276 expression

BACKGROUND

Nuclear factor-kappa B (NF-κB) is an important nuclear transcription factor in cells, involving in a series of processes such as cell proliferation, apoptosis, and differentiation. In this study, we explored the specific mechanism of NF-κB on the differentiation of osteoclasts.

METHODS

MicroRNAs (miRNAs) expression microarray data GSE105027 related to osteoarthritis was obtained to screen out the differentially expressed miRNA. Phorbol-12-myristate-13-acetate (PMA) was used to induce THP-1 cells to differentiate into macrophages, followed by induction to osteoclasts using macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL). ELISA and RT-qPCR were conducted to examine IL-6 and IL-1β expression. The binding of NF-κB to the miR-1276 promoter region was demonstrated by ChIP assay, and targeting relationship between miR-1276 and MITF was verified by dual luciferase reporter assay. KK, iKBα, NF-kB, p-IKK, p-iKBα, p-NF-kB expression was analyzed by western blot. NF-κB and miR-1276 expression in osteoclasts was examined later. After gain- and less-of-function study, the effects on osteoclast differentiation were detected by TRAP-positive osteoclasts, TRAP activity, TRAP-5b content, F-Actin expression, as well as osteoclast differentiation marker genes expression.

RESULTS

NF-κB was activated in osteoclasts, and down-regulation of NF-κB inhibited osteoclast differentiation. Next, miR-1276 was downregulated in osteoclasts after differentiation from monocytes. Meanwhile, NF-κB decreased the expression of miR-1276 by binding to the miR-1276 promoter, thereby elevating MITF expression, thereby promoting osteoclast differentiation.

CONCLUSION

In summary, NF-κB promoted osteoclast differentiation through downregulating miR-1276 to upregulate MITF.

FANCA D1359Y mutation in a patient with gastric polyposis and cancer susceptibility: A case report and review of literature

Gastric polyposis is a rare disease. Not all polyps progress to cancer. Monoallelic mutation in Fanconi anemia (FA) genes, unlike biallelic gene mutations that causes typical FA phenotype, can increase risks of cancers in a sporadic manner. Aberrations in the FA pathway were reported in all molecular subtypes of gastric cancer. We studied a patient with synchronous gastric cancer from gastric polyposis by conducting a 13-year long-term follow up. Via pathway-driven massive parallel genomic sequencing, a germline mutation at FANCA D1359Y was identified. We identified several recurrent mutations in DNA methylation (TET1, V873I), the β-catenin pathway (CTNNB1, S45F) and RHO signaling pathway (PLEKHG5, R203C) by comparing the genetic events between benign and malignant gastric polyps. Furthermore, we revealed gastric polyposis susceptible genes and genetic events promoting malignant transformation using pathway-driven targeted gene sequencing.

Non-canonical Wnt signals regulate cytoskeletal remodeling in osteoclasts

Osteoclasts are multinucleated cells responsible for bone resorption. Osteoclasts adhere to the bone surface through integrins and polarize to form actin rings, which are formed by the assembly of podosomes. The area contained within actin rings (also called sealing zones) has an acidic pH, which causes dissolution of bone minerals including hydroxyapatite and the degradation of matrix proteins including type I collagen by the protease cathepsin K. Osteoclasts resorb bone matrices while moving on bone surfaces. Osteoclasts change their cell shapes and exhibit three modes for bone resorption: motile resorbing mode for digging trenches, static resorbing mode for digging pits, and motile non-resorbing mode. Therefore, the actin cytoskeleton is actively remodeled in osteoclasts. Recent studies have revealed that many molecules, such as Rac, Cdc42, Rho, and small GTPase regulators and effectors, are involved in actin cytoskeletal remodeling during the formation of actin rings and resorption cavities on bone slices. In this review, we introduce how these molecules and non-canonical Wnt signaling regulate the bone-resorbing activity of osteoclasts.

Inhibition of RhoA and mTORC2/Rictor by Fingolimod (FTY720) induces p21-activated kinase 1, PAK-1 and amplifies podosomes in mouse peritoneal macrophages

Macrophage functions in the immune response depend on their ability to infiltrate tissues and organs. The penetration between and within the tissues requires degradation of extracellular matrix (ECM), a function performed by the specialized, endopeptidase- and actin filament- rich organelles located at the ventral surface of macrophage, called the podosomes. Podosome formation requires local inhibition of small GTPase RhoA activity, and depends on Rac 1/Rho guanine nucleotide exchange factor 7, β-PIX and its binding partner the p21-activated kinase (PAK-1). The activity of RhoA and Rac 1 is in turn regulated by mTOR/mTORC2 pathway. Here we showed that a fungus metabolite Fingolimod (FTY720, Gilenya), which is clinically approved for the treatment of multiple sclerosis, down-regulates Rictor, which is a signature molecule of mTORC2 and dictates its substrate (actin cytoskeleton) specificity, down-regulates RhoA, up-regulates PAK-1, and causes amplification of podosomes in mouse peritoneal macrophages.

Actin binding LIM 1 (abLIM1) negatively controls osteoclastogenesis by regulating cell migration and fusion

Actin binding LIM 1 (abLIM1) is a cytoskeletal actin-binding protein that has been implicated in interactions between actin filaments and cytoplasmic targets. Previous biochemical and cytochemical studies have shown that abLIM1 interacts and co-localizes with F-actin in the retina and muscle. However, whether abLIM1 regulates osteoclast differentiation has not yet been elucidated. In this study, we examined the role of abLIM1 in osteoclast differentiation and function. We found that abLIM1 expression was upregulated during receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclast differentiation, and that a novel transcript of abLIM1 was exclusively expressed in osteoclasts. Overexpression of abLIM1 in the murine monocytic cell line, RAW-D suppressed osteoclast differentiation and decreased expression of several osteoclast-marker genes. By contrast, small interfering RNA-induced knockdown of abLIM1 enhanced the formation of multinucleated osteoclasts and markedly increased the expression of the osteoclast-marker genes. Mechanistically, abLIM1 regulated the localization of tubulin, migration, and fusion in osteoclasts. Thus, these results indicate that abLIM1 negatively controls osteoclast differentiation by regulating cell migration and fusion mediated via actin formation.