Hedgehog signaling inhibitor GANT61 induces endoplasmic reticulum stress-mediated protective autophagy in hepatic stellate cells

IRE1α inhibits osteogenic differentiation of mouse embryonic fibroblasts by limiting Shh signaling

OBJECTIVES

This study aimed to investigate the effect of endoplasmic reticulum (ER) stress sensor inositol-requiring enzyme 1α (IRE1α) on the sonic hedgehog N-terminus (N-Shh)-enhanced-osteogenic differentiation process in mouse embryonic fibroblasts (MEFs).

MATERIALS AND METHODS

Osteogenesis of MEFs was observed by alkaline phosphatase (ALP) staining, alizarin red staining, and Von Kossa staining assays. Activation of unfolded protein response and Shh signaling were examined using real-time quantitative PCR and western blot assays. IRE1α-deficient MEFs were used to explore the effect of IRE1α on N-Shh-driven osteogenesis.

RESULTS

N-Shh increased ALP activity, matrix mineralization, and the expression of Alp and Col-I in MEFs under osteogenic conditions; notably, this was reversed when combined with the ER stress activator Tm treatment. Interestingly, the administration of N-Shh decreased the expression of IRE1α. Abrogation of IRE1α increased the expression of Shh pathway factors in osteogenesis-induced MEFs, contributing to the osteogenic effect of N-Shh. Moreover, IRE1α-deficient MEFs exhibited elevated levels of osteogenic markers.

CONCLUSIONS

Our findings suggest that the IRE1α-mediated unfolded protein response may alleviate the ossification of MEFs by attenuating Shh signaling. Our research has identified a strategy to inhibit excessive ossification, which may have clinical significance in preventing temporomandibular joint bony ankylosis.

Inhibition of Hedgehog signaling ameliorates foam cell formation by promoting autophagy in early atherosclerosis

Macrophages are the origin of most foam cells in the early stage of atherosclerotic plaques. However, the mechanism involved in the formation of macrophage-derived foam cell formation remains unclear. Here, we revealed that the hedgehog (Hh) signaling is critical in autophagy-lysosome pathway regulation and macrophage-derived foam cell formation. Inhibition of Hh signaling by vismodegib ameliorated lipid deposition and oxidative stress level in atherosclerotic plaques in high-fat diet-fed apoE-/- mice. For mechanistic study, how the Hh signaling modulate the process of foam cell formation were accessed afterward. Unexpectedly, we found that suppression of Hh signaling in apoE-/- mice had no significant impact on circulating cholesterol levels, indicating that Hh pathway modulate the procession of atherosclerotic plaque not through a traditional lipid-lowing mechanism. Instead, vismodegib was found to accelerate autophagosomes maturation as well as cholesterol efflux in macrophage-derived foam cell and in turn improve foam cell formation, while autophagy inhibitors (LY294002 or CQ) administration significantly attenuated vismodegib-induced cholesterol efflux and reversed the effect on foam cell formation. Therefore, our result demonstrated that inhibition of the Hh signaling pathway increases cholesterol efflux and ameliorates macrophage-derived foam cell formation by promoting autophagy in vitro. Our data thus suggested a novel therapeutic target of atherosclerosis and indicated the potential of vismodegib to treat atherosclerosis.

GANT61/BI-847325 combination: a new hope in lung cancer treatment

Despite the huge efforts employed to implement novel chemotherapeutic paradigms for lung cancer, the disease still remains a major concern worldwide. Targeting molecular pathways as Hedgehog (Hh) and Mitogen-activated protein kinase (MAPK) represent a new hope in lung cancer treatment. This work was undertaken to evaluate the antitumor effects of GANT61 (5 μM), BI-847325(30 μM), and GANT61 (5 μM)/BI-847325(30 μM) combination on A549 adenocarcinoma lung cancer cell line. The growth inhibition 50 (GI50) for both drugs was performed using MTT. The protein levels of Caspase-3, Bcl-2-associated X protein (Bax), Myeloid cell leukemia sequence 1 (MCL-1), cyclin D1, vascular endothelial growth factor (VEGF), extracellular signal-regulated kinases (ERK), p-Akt, and phosphohistone H3 (pHH3) were measured using ELISA. Glioma-associated oncogene homolog 1(Gli1) gene expression was assessed by quantitative real-time PCR. The GI50 for GANT61 and BI-8473255 were 5 µM and 30 µM, respectively. Caspase-3 and Bax protein levels were significantly elevated while MCL-1, cyclin D1, VEGF, ERK 1/2, p-Akt, and pHH3 levels were significantly reduced by both drugs and their combination relative to the control group. Gli1 gene expression was down-regulated in all groups relative to the control group. GANT61, BI-847325 and their combination inhibited proliferation and angiogenesis but activated the apoptotic pathway. Both drugs conferred a profound negative impact on the crosstalk between each of Hh and MAPK pathways and Phosphoinositide 3 -kinases (PI3K)/Akt/Mammalian target of Rapamycin (mTOR). To the best of our knowledge, the antitumor effects of BI-847325/GANT61 combination have not been tested before. Further in-vitro and in-vivo studies are warranted to support the findings.

Advances in glioma-associated oncogene (GLI) inhibitors for cancer therapy

The Hedgehog/Glioma-associated oncogene homolog (HH/GLI) signaling pathway regulates self-renewal of rare and highly malignant cancer stem cells, which have been shown to account for the initiation and maintenance of tumor growth as well as for drug resistance, metastatic spread and relapse. As an important component of the Hh signaling pathway, glioma-associated oncogene (GLI) acts as a key signal transmission hub for various signaling pathways in many tumors. Here, we review direct and indirect inhibitors of GLI; summarize the abundant active structurally diverse natural GLI inhibitors; and discuss how to better develop and utilize GLI inhibitors to solve the problem of drug resistance in tumors of interest. In summary, GLI inhibitors will be promising candidates for various cancer treatments.

Hepatic stellate cell activation by TGFβ induces hedgehog signaling and endoplasmic reticulum stress simultaneously

Activation of hepatic stellates (HSCs) is known as the major cause of initiation and progression of liver fibrosis. A wide array of events occurs during HSC activation including induction of hedgehog (Hh) signaling and endoplasmic reticulum (ER) stress. Targeting HSC activation may provide promising insights into liver fibrosis treatment. In this regard, establishing in vitro models which can mimic the molecular pathways of interest is very important. We aimed to activate HSC in which Hh signaling and ER stress are stimulated simultaneously. We used 5 ng/ml TGFβ to activate LX-2 cells, HSC cell line. Gene expression analysis using qRT-PCR, immunostaining and immunoblotting were performed to show HSC activation associated markers. Furthermore, the migration capacity of the TGFβ treated cells is evaluated. The results demonstrated that major fibrogenic markers including collagen1a, lysyl oxidase, and tissue inhibitor of matrix metalloproteinase 1 genes are up-regulated significantly. In addition, our immunofluorescence and immunoblotting results showed that protein levels of GLI-2 and XBP1, were enhanced. Moreover, we found that TGFβ treatment reduced the migration of LX-2 cells. Our results are compatible with high throughput data analysis with respect to differentially expressed genes of activated HSC compared to the quiescent ones. Moreover, our findings suggest that quercetin can reduce fibrogenic markers of activated HSCs as well as osteopontin expression, a target gene of hedgehog signaling.

Therapeutic potential of targeting regulatory mechanisms of hepatic stellate cell activation in liver fibrosis

Hepatic fibrosis is a manifestation of different etiologies of liver disease with the involvement of multiple mediators in complex network interactions. Activated hepatic stellate cells (aHSCs) are the central driver of hepatic fibrosis, given their potential to induce connective tissue formation and extracellular matrix (ECM) protein accumulation. Therefore, identifying the cellular and molecular pathways involved in the activation of HSCs is crucial in gaining mechanistic and therapeutic perspectives to more effectively target the disease. In addition to a comprehensive summary of our current understanding of the role of HSCs in liver fibrosis, we also discuss here the proposed therapeutic strategies based on targeting HSCs.

MLN4924 inhibits hedgehog signaling pathway and activates autophagy to alleviate mouse laser-induced choroidal neovascularization lesion

Neovascular age-related macular degeneration (nAMD), featured as choroidal neovascularization (CNV), can cause blindness in the elderly population. MLN4924, a highly selective small-molecule inhibitor of NEDD8 (neuronal precursor cell-expressed developmentally down-regulated protein 8)-activating enzyme (NAE), inhibits the proliferation, angiogenesis and inflammation of multiple cancers via up-regulating hedgehog pathway-regulated autophagy. MLN4924 intraperitoneal injection mitigated the leakage, area and volume of mouse laser-induced CNV lesion. Additionally, compared to CNV 7 d group, MLN4924 treated mouse retina-retinal pigment epithelium (RPE)-choroid complex showed decreased expression of hedgehog pathway-associated molecules patched 1 (PTCH1), smoothened (SMO), GLI family zinc finger 1 (GLI1) and GLI family zinc finger 2 (GLI2) with increased expression of autophagy-associated molecules sequestosome 1 (p62) and LC microtubule-associated protein 1 light chain 3 (LC3). Meanwhile, human choroidal endothelial cells (HCECs) exposed to hypoxia condition also showed decreased expression of hedgehog pathway-associated molecules and increased expression of autophagy-associated molecules. Compared to hypoxia + MLN4924 group, SMO agonist SAG up-regulated hedgehog pathway and down-regulated autophagy, whereas autophagy inhibitor PIK-III inhibited autophagy with no effect on hedgehog pathway, indicating that MLN4924 facilitated autophagy of HCECs via hindering hedgehog pathway under hypoxia condition. Finally, MLN4924 inhibited proliferation, migration and tube formation of HCECs via boosting hedgehog pathway-regulated autophagy. In summary, MLN4924 relieved the formation of mouse laser-induced CNV lesion might via up-regulating hedgehog pathway-regulated autophagy. The results provide a potential interfering strategy for nAMD targeting the autophagy of choroidal endothelial cells.

Gant61 ameliorates CCl4-induced liver fibrosis by inhibition of Hedgehog signaling activity

As an intercellular signaling molecule, Hedgehog (Hh) plays a critical role in liver fibrosis/regeneration. Transcription effectors Gli1 and Gli2 are key components of the Hh signaling pathway. However, whether inhibition of Gli1/2 activity can affect liver fibrogenesis is largely unknown. In the present study, we investigated the effect of Gant61 (a Gli1/2 transcription factor inhibitor) on liver fibrosis and its possible mechanism. Wild-type and Shh-EGFP-Cre male mice were exposed to CCl₄, and then treated with or without Gant61 for four weeks. The level of liver injury/fibrosis and expression levels of mRNA and protein related to the Hh ligand/pathway were assessed. In our study, CCl₄ treatment induced liver injury/fibrosis and promoted activation of hepatic stellate cells (HSCs). In addition, CCl₄ induced the expression of Shh ligands in and around the fibrotic lesion, accompanied by induction of mRNA and protein expression of Hh components (Smo, Gli1 and Gli2). However, administration of Gant61 decreased liver fibrosis by reduction in HSC number, down-regulation of mRNA and protein expression of Hh components (Smo, Gli1 and Gli2), and cell-cycle arrest of HSCs. Our data highlight the importance of the Shh pathway for the development of liver fibrosis, and also suggest Glis as potential therapeutic targets for the treatment of liver fibrosis.

Hedgehog Signaling Pathway and Autophagy in Cancer

Hedgehog (Hh) pathway controls complex developmental processes in vertebrates. Abnormal activation of Hh pathway is responsible for tumorigenesis and maintenance of multiple cancers, and thus addressing this represents promising therapeutic opportunities. In recent years, two Hh inhibitors have been approved for basal cell carcinoma (BCC) treatment and show extraordinary clinical outcomes. Meanwhile, a series of novel agents are being developed for the treatment of several cancers, including lung cancer, leukemia, and pancreatic cancer. Unfortunately, Hh inhibition fails to show satisfactory benefits in these cancer types compared with the success stories in BCC, highlighting the need for better understanding of Hh signaling in cancer. Autophagy, a conserved biological process for cellular component elimination, plays critical roles in the initiation, progression, and drug resistance of cancer, and therefore, implied potential to be targeted. Recent evidence demonstrated that Hh signaling interplays with autophagy in multiple cancers. Importantly, modulating this crosstalk exhibited noteworthy capability to sensitize primary and drug-resistant cancer cells to Hh inhibitors, representing an emerging opportunity to reboot the efficacy of Hh inhibition in those insensitive tumors, and to tackle drug resistance challenges. This review will highlight recent advances of Hh pathway and autophagy in cancers, and focus on their crosstalk and the implied therapeutic opportunities.