Oncogenic KRASG12D Reprograms Lipid Metabolism by Upregulating SLC25A1 to Drive Pancreatic Tumorigenesis

Pancreatic cancer is a highly lethal disease with obesity as one of the risk factors. Oncogenic KRAS mutations are prevalent in pancreatic cancer and can rewire lipid metabolism by altering fatty acid (FA) uptake, FA oxidation (FAO), and lipogenesis. Identification of the underlying mechanisms could lead to improved therapeutic strategies for treating KRAS-mutant pancreatic cancer. Here, we observed that KRASG12D upregulated the expression of SLC25A1, a citrate transporter that is a key metabolic switch to mediate FAO, fatty acid synthesis, glycolysis, and gluconeogenesis. In genetically engineered mouse models and human pancreatic cancer cells, KRASG12D induced SLC25A1 upregulation via GLI1, which directly stimulated SLC25A1 transcription by binding its promoter. The enhanced expression of SLC25A1 increased levels of cytosolic citrate, FAs, and key enzymes in lipid metabolism. In addition, a high-fat diet (HFD) further stimulated the KRASG12D-GLI1-SLC25A1 axis and the associated increase in citrate and FAs. Pharmacologic inhibition of SLC25A1 and upstream GLI1 significantly suppressed pancreatic tumorigenesis in KrasG12D/+ mice on a HFD. These results reveal a KRASG12D-GLI1-SLC25A1 regulatory axis, with SLC25A1 as an important node that regulates lipid metabolism during pancreatic tumorigenesis, thus indicating an intervention strategy for oncogenic KRAS-driven pancreatic cancer.

SIGNIFICANCE

Upregulation of SLC25A1 induced by KRASG12D-GLI1 signaling rewires lipid metabolism and is exacerbated by HFD to drive the development of pancreatic cancer, representing a targetable metabolic axis to suppress pancreatic tumorigenesis.

Identifying Fibrogenic Cells Following Salivary Gland Obstructive Injury

Fibrosis results from excess extracellular matrix accumulation, which alters normal tissue architecture and impedes function. In the salivary gland, fibrosis can be induced by irradiation treatment for cancer therapy, Sjögren's Disease, and other causes; however, it is unclear which stromal cells and signals participate in injury responses and disease progression. As hedgehog signaling has been implicated in fibrosis of the salivary gland and other organs, we examined contributions of the hedgehog effector, Gli1, to fibrotic responses in salivary glands. To experimentally induce a fibrotic response in female murine submandibular salivary glands, we performed ductal ligation surgery. We detected a progressive fibrotic response where both extracellular matrix accumulation and actively remodeled collagen trended upwards at 7 days and significantly increased at 14 days post- ligation. Macrophages, which participate in extracellular matrix remodeling, Gli1 + and PDGFRα + stromal cells, which may deposit extracellular matrix, both increased with injury. Using single-cell RNA-sequencing, we found that a majority of Gli1 + cells at embryonic day 16 also express Pdgfra and/or Pdgfrb. However, in adult mice, only a small subset of Gli1 + cells express PDGFRα and/or PDGFRβ at the protein level. Using lineage-tracing mice, we found that Gli1-derived cells expand with ductal ligation injury. Although some of the Gli1 lineage-traced tdTomato + cells expressed vimentin and PDGFRβ following injury, there was no increase in the classic myofibroblast marker, smooth muscle alpha-actin. Additionally, there was little change in extracellular matrix area, remodeled collagen area, PDGFRα, PDGFRβ, endothelial cells, neurons, or macrophages in Gli1 null salivary glands following injury when compared with controls, suggesting that Gli1 signaling and Gli1 + cells have only a minor contribution to mechanical injury-induced fibrotic changes in the salivary gland. We used scRNA-seq to examine cell populations that expand with ligation and/or showed increased expression of matrisome genes. Pdgfra + /Pdgfrb + stromal cell subpopulations both expanded in response to ligation, showed increased expression and a greater diversity of matrisome genes expressed, consistent with these cells being fibrogenic. Defining the signaling pathways driving fibrotic responses in stromal cell sub-types could reveal future therapeutic targets.

GLI1+ cells are a source of repair-supportive mesenchymal cells (RSMCs) during airway epithelial regeneration

Repair-supportive mesenchymal cells (RSMCs) have been recently reported in the context of naphthalene (NA)-induced airway injury and regeneration. These cells transiently express smooth muscle actin (Acta2) and are enriched with platelet-derived growth factor receptor alpha (Pdgfra) and fibroblast growth factor 10 (Fgf10) expression. Genetic deletion of Ctnnb1 (gene coding for beta catenin) or Fgf10 in these cells using the Acta2-Cre-ERT2 driver line after injury (defined as NA-Tam condition; Tam refers to tamoxifen) led to impaired repair of the airway epithelium. In this study, we demonstrate that RSMCs are mostly captured using the Acta2-Cre-ERT2 driver when labeling occurs after (NA-Tam condition) rather than before injury (Tam-NA condition), and that their expansion occurs mostly between days 3 and 7 following NA treatment. Previous studies have shown that lineage-traced peribronchial GLI1+ cells are transiently amplified after NA injury. Here, we report that Gli1 expression is enriched in RSMCs. Using lineage tracing with Gli1^Cre−ERT2 mice combined with genetic inactivation of Fgf10, we show that GLI1+ cells with Fgf10 deletion fail to amplify around the injured airways, thus resulting in impaired airway epithelial repair. Interestingly, Fgf10 expression is not upregulated in GLI1+ cells following NA treatment, suggesting that epithelial repair is mostly due to the increased number of Fgf10-expressing GLI1+ cells. Co-culture of SCGB1A1+ cells with GLI1+ cells isolated from non-injured or injured lungs showed that GLI1+ cells from these two conditions are similarly capable of supporting bronchiolar organoid (or bronchiolosphere) formation. Single-cell RNA sequencing on sorted lineage-labeled cells showed that the RSMC signature resembles that of alveolar fibroblasts. Altogether, our study provides strong evidence for the involvement of mesenchymal progenitors in airway epithelial regeneration and highlights the critical role played by Fgf10-expressing GLI1+ cells in this context.

Horizontal transfer of the stemness-related markers EZH2 and GLI1 by neuroblastoma-derived extracellular vesicles in stromal cells

Neuroblastoma (NB) is the most common extracranial pediatric solid cancer originating from undifferentiated neural crest cells. NB cells express EZH2 and GLI1 genes that are known to maintain the undifferentiated phenotype of cancer stem cells (CSC) in NB. Recent studies suggest that tumor-derived extracellular vesicles (EVs) can regulate the transformation of surrounding cells into CSC by transferring tumor-specific molecules they contain. However, the horizontal transfer of EVs molecules in NB remains largely unknown. We report the analysis of NB-derived EVs in bioengineered models of NB that are based on a collagen 1/hyaluronic acid scaffold designed to mimic the native tumor niche. Using these models, we observed an enrichment of GLI1 and EZH2 mRNAs in NB-derived EVs. As a consequence of the uptake of NB-derived EVs, the host cells increased the expression levels of GLI1 and EZH2. These results suggest the alteration of the expression profile of stromal cells through an EV-based mechanism, and point the GLI1 and EZH2 mRNAs in the EV cargo as diagnostic biomarkers in NB.

Combined inhibition of JAK2-STAT3 and SMO-GLI1/tGLI1 pathways suppresses breast cancer stem cells, tumor growth, and metastasis

Triple-negative breast cancer (TNBC) and HER2-positive breast cancer are particularly aggressive and associated with unfavorable prognosis. TNBC lacks effective treatments. HER2-positive tumors have treatment options but often acquire resistance to HER2-targeted therapy after initial response. To address these challenges, we determined whether novel combinations of JAK2-STAT3 and SMO-GLI1/tGLI1 inhibitors synergistically target TNBC and HER2 breast cancer since these two pathways are concurrently activated in both tumor types and enriched in metastatic tumors. Herein, we show that novel combinations of JAK2 inhibitors (ruxolitinib and pacritinib) with SMO inhibitors (vismodegib and sonidegib) synergistically inhibited in vitro growth of TNBC and HER2-positive trastuzumab-resistant BT474-TtzmR cells. Synergy was also observed against breast cancer stem cells. To determine if the combination is efficacious in inhibiting metastasis, we treated mice with intracardially inoculated TNBC cells and found the combination to inhibit lung and liver metastases, and prolong host survival without toxicity. The combination inhibited orthotopic growth, VEGF-A expression, and tumor vasculature of both TNBC and HER2-positive trastuzumab-refractory breast cancer. Lung metastasis of orthotopic BT474-TtzmR xenografts was suppressed by the combination. Together, our results indicated that dual targeting of JAK2 and SMO resulted in synergistic suppression of breast cancer growth and metastasis, thereby supporting future clinical testing.

GLI1 expression in pancreatic ductal adenocarcinoma correlates the clinical significance and prognosis: A meta-analysis

BACKGROUND

Glioma-associated oncogene homolog 1(GLI1) expression correlates with the clinical significance and prognosis of several cancers. However, the evaluation of the role GLI1 expression plays in pancreatic ductal adenocarcinoma (PDAC) clinicopathological features and outcomes still lacks.

OBJECTIVE

The present study systemic reviewed the association of GLI1 expression and clinical significance as well as patients survival in PDAC.

METHODS

We systematically searched the database of The Cochrane Library, PubMed, Embase, CNKI, Weipu data, and Wanfang data according to the inclusion and exclusion criteria. (The search ended on January 1, 2019; no language restrictions). The Newcastle-Ottawa Scale (NOS) scale was implemented to assess the quality of the literature and the Review Manager 5.3 Software was used to conduct a meta-analysis. Finally, 9 studies, a total of 1058 patients, have been included.

RESULTS

GLI1 is more likely expressed in PDAC tissue rather than para-carcinoma tissue (OR = 2.86, 95%CI = 1.87-4.36, P < .00001). GLI1 expression is associated with the TNM stage (OR = 3.11, 95%CI = 2.01-4.79, P < .00001), perineural invasion (OR = 2.50, 95%CI = 1.28-4.91, P = .008), and lymphatic metastasis (OR = 2.73, 95%CI = 1.71-4.36, P < .0001). But the association with differentiation (OR = 1.20, 95%CI = 0.74-1.96, P = .46) and tumor size (OR = 2.41, 95%CI = 0.97-6.00, P = .06) was not significant. GLI1 expression is related to the worse overall survival in PDACs (HR = 1.68, 95%CI = 1.40-2.02, P < .00001).

CONCLUSION

Positive GLI1 expression promotes the progression and metastasis of PDACs and plays an important role in the clinical significance and the patients survival.

Expression analysis of Shh signaling members in early stages of chick lung development

Lung organogenesis is guided by epithelial-mesenchymal interactions that coordinate cellular events responsible for the formation of the respiratory system. Several signaling pathways have been implicated in this process; among them, sonic hedgehog (Shh) signaling has emerged as a crucial regulator of branching morphogenesis in the mammalian lung. Canonical Shh signaling requires the presence of patched (Ptch) and smoothened (Smo) transmembrane receptors in order to induce the activation of glioblastoma (Gli) zinc finger transcription factors that are the true effectors of the pathway. Signal transduction is finely regulated by Ptch1, Gli, and Hhip (hedgehog-interacting protein). The present work characterizes, for the first time, the expression pattern of shh, ptch1, smo, gli1, and hhip in early stages of the embryonic chick lung. In situ hybridization studies revealed that these genes are expressed in the same cellular compartments as their mammalian counterparts, although their proximo-distal distribution is slightly changed. Moreover, the molecular interactions between fibroblast growth factor (FGF) and Shh signaling pathway were assessed, in vitro, by grafting beads soaked in SU5402 (an FGF receptor inhibitor). In the chick lung, Shh signaling seems to have some features that are species specific since shh is not a downstream target of FGF signaling. Nonetheless and despite the observed differences, these findings suggest a role for Shh signaling in the epithelial-mesenchymal interactions that control chick lung morphogenesis.

Inhibition of hedgehog signaling ameliorates hepatic inflammation in mice with nonalcoholic fatty liver disease

Hedgehog (Hh) signaling plays a critical role in liver development, regeneration, injury repair, and carcinogenesis. Activation of Hh signaling has been observed in patients with nonalcoholic fatty liver diseases (NAFLD); however, the pathobiological function and regulatory mechanism of hepatic Hh signaling in the pathogenesis of NAFLD remain to be further defined. This study was designed to examine the effect and mechanism of hepatic Hh signaling in high-fat diet-induced NAFLD by using pharmacological Smoothened (Smo) inhibitors (GDC-0449 and LED225) and liver-specific Smo knockout mice. Administration of Smo inhibitors to high-fat diet-fed wild-type mice significantly reduced the numbers of activated macrophages and decreased the expression of proinflammatory cytokines (tumor necrosis factor-α, interleukin-1β, monocyte chemoattractant protein 1, and interleukin-6) as assessed by F4/80 immunohistochemistry and quantitative reverse-transcription polymerase chain reaction, respectively. The Smo inhibitors were noted to have variable effects on hepatic fat accumulation. Liver-specific deletion of Smo also reduced macrophage activation and inhibited proinflammatory cytokine expression, while it did not significantly alter fat accumulation in the liver. Mechanistically, we found that activation of glioma-associated oncogene 1 by Hh signaling in primary hepatocytes increased the production of osteopontin, which subsequently enhanced the macrophage-mediated proinflammatory response through paracrine signaling.

CONCLUSION

Hepatocyte Hh signaling can promote liver inflammation through osteopontin-mediated macrophage activation; this mechanism importantly contributes to the progression of NAFLD.

Back to the drawing board: Re-thinking the role of GLI1 in pancreatic carcinogenesis

Aberrant activation of the transcription factor GLI1, a central effector of the Hedgehog (HH) pathway, is associated with several malignancies, including pancreatic ductal adenocarcinoma (PDAC), one of most deadly human cancers. GLI1 has been described as an oncogene in PDAC, making it a promising target for drug therapy. Surprisingly, clinical trials targeting HH/GLI1 axis in advanced PDAC were unsuccessful, leaving investigators questioning the mechanism behind these failures. Recent evidence suggests the loss of GLI1 in the later stages of PDAC may actually accelerate disease. This indicates GLI1 may play a dual role in PDAC, acting as an oncogene in the early stages of disease and a tumor-suppressor in the late stages.

Gli1 contributes to cellular resistance to cisplatin through altered cellular accumulation of the drug

Cellular resistance to platinum anticancer compounds is governed by no less than two molecular processes; DNA repair and cellular accumulation of drug. Gli1 is an upstream regulator of nucleotide excision repair, effecting this process through c-jun. We, therefore, investigated whether Gli1 plays a role in cellular accumulation of cisplatin. Using a Gli1-specific shRNA, we explored the role of Gli1 in the cellular accumulation and efflux of cisplatin, in cisplatin-resistant A2780-CP70 human ovarian cancer cells. When Gli1 is inhibited, cellular uptake of cisplatin was approximately 33% of the level of uptake under control conditions. When Gli1 is inhibited, cellular efflux of cisplatin was completely abrogated, over a 12-h period of observation. We assayed nuclear lysates from these cells, for the ability to bind the DNA sequence that is the Gli-binding site (GBS) in the 5'UTR for each of five known cisplatin transmembrane transporters. Four of these transporters are active in cisplatin uptake; and, one is active in cisplatin efflux. In each case, nuclear lysate from A2780-CP70 cells binds the GBS of the respective cisplatin transport gene. We conclude that Gli1 plays a strong role in total cellular accumulation of cisplatin in these cells; and, that the combined effects on cellular accumulation of drug and on DNA repair may indicate a role for Gli1 in protecting cellular DNA from lethal types of DNA damage.

Cyclopamine did not affect mouse oocyte maturation in vitro but decreased early embryonic development

Hedgehog (Hh) pathway has been studied in various animal body life procedures and is suggested to be important for the development of multiple organs. The genes involved in the Hh signaling pathway were expressed in the ovary of mice, pigs and cattle. However, the function of Hh signaling pathway on oocyte maturation and early embryonic development is still controversial. We detected the effect of sonic hedgehog (Shh) and cyclopamine on the in vitro maturation of mouse oocytes and embryo development. The results showed that the presence of Shh or cyclopamine resulted in similar oocyte maturation to control groups. Shh did not improve early embryonic development. However, the supplement of cyclopamine depressed early embryo development. The mRNA of shh, ptch1, smo and gli1 were less detected in the denuded oocytes. The expression levels of ptch1 ascended from the uncleaved zygote to blastocyst stage. Smo or gli1 were expressed on a higher level at the two-cell or four-cell stage in early embryonic development separately. Therefore, Shh did not affect mouse oocyte maturation and early embryo development, but cyclopamine led to inhibited development of mouse early embryo. The effects of Hh signaling on the oocyte maturation and early embryo development might be species-specific.

Adrenocortical stem and progenitor cells: implications for adrenocortical carcinoma

The continuous centripetal repopulation of the adrenal cortex is consistent with a population of cells endowed with the stem/progenitor cell properties of self-renewal and pluripotency. The adrenocortical capsule and underlying undifferentiated cortical cells are emerging as critical components of the stem/progenitor cell niche. Recent genetic analysis has identified various signaling pathways including Sonic Hedgehog (Shh) and Wnt as crucial mediators of adrenocortical lineage and organ homeostasis. Shh expression is restricted to the peripheral cortical cells that express a paucity of steroidogenic genes but give rise to the underlying differentiated cells of the cortex. Wnt/β-catenin signaling maintains the undifferentiated state and adrenal fate of adrenocortical stem/progenitor cells, in part through induction of its target genes Dax1 and inhibin-α, respectively. The pathogenesis of ACC, a rare yet highly aggressive cancer with an extremely poor prognosis, is slowly emerging from studies of the stem/progenitor cells of the adrenal cortex coupled with the genetics of familial syndromes in which ACC occurs. The frequent observation of constitutive activation of Wnt signaling due to loss-of-function mutations in the tumor suppressor gene APC or gain-of-function mutation in β-catenin in both adenomas and carcinomas, suggests perhaps that the Wnt pathway serves an early or initiating insult in the oncogenic process. Loss of p53 might be predicted to cooperate with additional genetic insults such as IGF2 as both are the most common genetic abnormalities in malignant versus benign adrenocortical neoplasms. It is unclear whether other factors such as Pod1 and Pref1, which are implicated in stem/progenitor cell biology in the adrenal and/or other organs, are also implicated in the etiology of adrenocortical carcinoma. The rarity and heterogeneous presentation of ACC makes it difficult to identify the cellular origin and the molecular progression to cancer. A more complete understanding of adrenocortical stem/progenitor cell biology will invariably aid in characterization of the molecular details of ACC tumorigenesis and may offer new options for therapeutic intervention.

Sonic hedgehog signaling confers ventral telencephalic progenitors with distinct cortical interneuron fates

Interneurons in the cerebral cortex regulate cortical functions through the actions of distinct subgroups that express parvalbumin, somatostatin, or calretinin. The genesis of the first two subgroups requires the expression of NKX2.1, which is maintained by SHH signaling during neurogenesis. In this paper, we report that mosaic elimination in the medial ganglionic eminence (MGE) of Smo, a key effector of SHH signaling, reveals that MGE progenitors retain a remarkable degree of plasticity during the neurogenic period. SHH signaling prevents the upregulation of GSX2 and conversion of some MGE progenitors to a caudal ganglionic eminence-like, bipolar calretinin-expressing cell fate that is promoted by GSX2. In addition, a higher level of SHH signaling promotes the generation of the somatostatin-expressing interneuron at the expense of parvalbumin-expressing subgroup. These results indicate that cortical interneuron diversity, a major determinant of cortical function, is critically influenced by differential levels of SHH signaling within the ventral telencephalon.

Bone marrow stromal cells increase oligodendrogenesis after stroke

Oligodendrocytes are sensitive to ischemic damage. The Sonic hedgehog (Shh) pathway is critical in oligodendrogenesis; Gli1 is the principal effector of Shh signaling. We investigated oligodendrogenesis and Shh/Gli1 pathway activation after bone marrow stromal cell (BMSC) treatment of stroke in rats. Rats were subjected to the middle cerebral artery occlusion (MCAo). BMSCs have been shown to promote functional recovery post stroke. A therapeutic dose of BMSC (3 x 10(6) cells) treatment was initiated 1 day after MCAo. Immunohistochemistry was carried out to measure the oligodendrocyte progenitor cells, oligodendrocytes, myelin, and expressions of Shh and Gli1 at 14 days after MCAo. Gene expression of Shh and Gli1 was tested at 2 days after MCAo. An in vitro study was used to investigate the effects of BMSC on a premature oligodendrocyte cell line (N20.1 cells). BMSC treatment significantly increased O4(+) oligodendrocytes, MBP(+) area, and bromodeoxyuridine (BrdU)(+), NG2(+), BrdU(+)-NG2(+) cells, and mRNA and protein expressions of Shh and Gli1 in the ipsilateral brain of the MCAo rats than that in phosphate buffered saline (PBS)-treated rats. BMSCs promoted N20.1 cell proliferation and Gli1 mRNA expression, and these effects were abolished by the Shh pathway inhibitor cyclopamine. These data indicate that the BMSC treatment stimulates oligodendrogenesis by activation of the Shh/Gli1 pathway post stroke.

Gli1, downregulated in colorectal cancers, inhibits proliferation of colon cancer cells involving Wnt signalling activation

BACKGROUND

Early events in the progression of 90% of sporadic colorectal cancers depend on constitutive activation of Wnt signalling. Recent data also indicate a close association between the Hedgehog (Hh) and Wnt pathways in colonic epithelial cell differentiation.

AIMS

To investigate whether expression of Gli1, a transactivator of Hh signalling, can suppress Wnt signalling and inhibit proliferation of human colorectal cancer cells.

METHODS

Gli1 and nuclear beta-catenin expression were examined in a series of 40 human colorectal cancers by immunohistochemistry. We quantified Gli1 and nuclear beta-catenin staining as markers of Hh and Wnt pathway activation, respectively. Two human colon cancer cell lines, SW480 and HCT116, with mutations in APC and beta-catenin, respectively, were used. The effects of Gli1 overexpression on Wnt transcriptional activity, beta-catenin subcellular distribution, and proliferation in these cells were analysed.

RESULTS

Nuclear accumulation of beta-catenin and the Gli1 staining level were inversely associated in the 40 human colorectal cancers. Wnt transcriptional activity was reduced in Gli1 transfected cells. These effects were observed even in Gli1 transfected cells cotransfected with mutated beta-catenin. Furthermore, nuclear accumulation of beta-catenin was diminished compared with that in empty vector transfected cells, and downregulated transcription of c-Myc was observed in Gli1 transfected cells. Proliferation of Gli1 transfected cells was also significantly suppressed compared with that in empty vector transfected cells.

CONCLUSIONS

Our data suggest that Gli1 plays an inhibitory role in the development of colorectal cancer involving Wnt signalling, even in cases with the stabilising mutation of beta-catenin.