Lysosomal lipid peroxidation regulates tumor immunity

Lysosomal inhibition elicited by palmitoyl protein transferase 1 (PPT1) inhibitors such as DC661 can produce cell death, but the mechanism is not completely understood. Programmed cell death pathways (autophagy, apoptosis, necroptosis, ferroptosis, and pyroptosis) were not required to achieve the cytotoxic effect of DC661. Inhibition of cathepsins, or iron or calcium chelation, did not rescue DC661-induced cytotoxicity. PPT1 inhibition induced lysosomal lipid peroxidation (LLP), which led to lysosomal membrane permeabilization and cell death that could be reversed by the antioxidant N-acetylcysteine (NAC), but not by other lipid peroxidation antioxidants. The lysosomal cysteine transporter MFSD12, was required for intralysosomal transport of NAC and rescue of LLP. PPT1 inhibition produced cell-intrinsic immunogenicity with surface expression of calreticulin that could only be reversed with NAC. DC661-treated cells primed naïve T cells, and enhanced T cell-mediated toxicity. Mice vaccinated with DC661-treated cells, engendered adaptive immunity and tumor rejection in "immune hot" tumors but not in "immune cold" tumors. These findings demonstrate LLP drives lysosomal cell death, a unique immunogenic form of cell death, pointing the way to rational combinations of immunotherapy and lysosomal inhibition that can be tested in clinical trials.

Targeting UGCG Overcomes Resistance to Lysosomal Autophagy Inhibition

Lysosomal autophagy inhibition (LAI) with hydroxychloroquine or DC661 can enhance cancer therapy, but tumor regrowth is common. To elucidate LAI resistance, proteomics and immunoblotting demonstrated that LAI induced lipid metabolism enzymes in multiple cancer cell lines. Lipidomics showed that LAI increased cholesterol, sphingolipids, and glycosphingolipids. These changes were associated with striking levels of GM1+ membrane microdomains (GMM) in plasma membranes and lysosomes. Inhibition of cholesterol/sphingolipid metabolism proteins enhanced LAI cytotoxicity. Targeting UDP-glucose ceramide glucosyltransferase (UGCG) synergistically augmented LAI cytotoxicity. Although UGCG inhibition decreased LAI-induced GMM and augmented cell death, UGCG overexpression led to LAI resistance. Melanoma patients with high UGCG expression had significantly shorter disease-specific survival. The FDA-approved UGCG inhibitor eliglustat combined with LAI significantly inhibited tumor growth and improved survival in syngeneic tumors and a therapy-resistant patient-derived xenograft. These findings nominate UGCG as a new cancer target, and clinical trials testing UGCG inhibition in combination with LAI are warranted.

SIGNIFICANCE

We discovered UGCG-dependent lipid remodeling drives resistance to LAI. Targeting UGCG with a drug approved for a lysosomal storage disorder enhanced LAI antitumor activity without toxicity. LAI and UGCG inhibition could be tested clinically in multiple cancers. This article is highlighted in the In This Issue feature, p. 247.

Anticancer properties of bisaminoquinolines with modified linkers

We have previously reported the unique features of dimeric bisaminoquinolines as anticancer agents and have identified their cellular target as PPT1, a protein palmitoyl-thioesterase. We now report a systematic study on the role of the linker in these constructs, both with respect to the distance between the heterocycles, the linker hydrophobicity and the methylation status (primary vs. secondary vs. tertiary) of the central nitrogen atom on the observed biological activity.

Immature myeloid progenitors promote disease progression in a mouse model of Barrett's-like metaplasia

Cdx2, an intestine specific transcription factor, is expressed in Barrett's esophagus (BE). We sought to determine if esophageal Cdx2 expression would accelerate the onset of metaplasia in the L2-IL-1β transgenic mouse model for Barrett's-like metaplasia. The K14-Cdx2::L2-IL-1β double transgenic mice had half as many metaplastic nodules as control L2-IL-1β mice. This effect was not due to a reduction in esophageal IL-1β mRNA levels nor diminished systemic inflammation. The diminished metaplasia was due to an increase in apoptosis in the K14-Cdx2::L2-IL-1β mice. Fluorescence activated cell sorting of immune cells infiltrating the metaplasia identified a population of CD11b+Gr-1+ cells that are significantly reduced in K14-Cdx2::L2-IL-1β mice. These cells have features of immature granulocytes and have immune-suppressing capacity. We demonstrate that the apoptosis in K14-Cdx2::L2-IL-1β mice is CD8+ T cell dependent, which CD11b+Gr-1+ cells are known to inhibit. Lastly, we show that key regulators of CD11b+Gr-1+ cell development, IL-17 and S100A9, are significantly diminished in the esophagus of K14-Cdx2::L2-IL-1β double transgenic mice. We conclude that metaplasia development in this mouse model for Barrett's-like metaplasia requires suppression of CD8+ cell dependent apoptosis, likely mediated by immune-suppressing CD11b+Gr-1+ immature myeloid cells.

Culturing adult stem cells from mouse small intestinal crypts

In recent years, the study of primary cells in culture has evolved from an extraphysiological, two-dimensional platform to novel, three-dimensional platforms in which the addition of matrix components and/or supporting cells provide an ex vivo niche. Such studies have provided the basis on which to study more advanced physiological processes in detail, including multilayered, long-term cultures, epithelial-stromal interactions, and stem cell behaviors that more closely recapitulate normal morphology than two-dimensional culture. Various techniques for three-dimensional organotypic culture and crypt culture of primary cells from mouse and human small intestine and colon have been described. These methods have allowed for the study of specific stem cell characteristics, including survival, self-renewal, and long-term growth in culture, as well as the ability to propagate all the appropriate progenitor and postmitotic lineages. These assays have become a widely accepted functional measure of "stemness" and, in combination with lineage-tracing experiments in various genetically engineered mouse models, have been critical in the identification of specific markers of intestinal stem cells. In this protocol we draw upon recently described methods for the isolation and culture of mouse small intestinal enterospheres/enteroids from isolated crypts and/or single cells. Cultures of murine colon epithelium, as well as human small intestine and colon, require additional growth factors not discussed here. The description provided here represents current knowledge, and it is possible, if not likely, that modifications in the future will emerge.

Cdx2 levels modulate intestinal epithelium maturity and Paneth cell development

BACKGROUND & AIMS

Caudal-related homeobox protein 2 (Cdx2) is an intestine-specific transcription factor that is important for intestinal development and intestine-specific gene expression. Cdx2 regulates intestinal cell-cell adhesion, proliferation, and the transcriptional activities of Wnt and β-catenin in cell culture systems. We generated transgenic mice that overexpress Cdx2 in the small intestinal and colonic epithelium to investigate the role of Cdx2 in differentiation and function of the intestinal epithelium.

METHODS

We established 4 different lines of villin-Cdx2 transgenic mice. Intestines were collected from infant, 3-month old, and wild-type mice. Genes of interest and cell lineage markers were examined by polymerase chain reaction and immunohistochemistry.

RESULTS

Villin-Cdx2 transgenic mice had complex phenotypes that were associated with transgene expression levels. The 2 lines that had the greatest levels of transgene expression had significant, preweaning failure to grow and death; these were the result of early epithelial maturation and alterations in nutrient digestion and absorption. Fat malabsorption was a prominent feature. Other effects associated with the transgene expression included loss of Paneth cell markers, increases in goblet cells, and migration of proliferating, EphB2-expressing cells to the crypt base. Loss of Paneth cell markers was associated with reduced nuclear localization of β-catenin but not homeotic posteriorization of the epithelium by Cdx2.

CONCLUSIONS

Overexpression of Cdx2 in the small intestine is associated with reduced post-natal growth, early epithelial maturation, alterations in crypt base organization, and changes in Paneth and goblet cell lineages. Cdx2 is a critical regulator not only of intestine-specific genes, but also processes that determine epithelial maturity and function.

Intestinal metaplasia with a high salt diet induces epithelial proliferation and alters cell composition in the gastric mucosa of mice

Intestinal metaplasia of the gastric mucosa is an important component in the pathway to adenocarcinoma. The mechanisms that induce the progression from intestinal metaplasia to cancer have not been elucidated. High dietary salt has been known as one of the risk factors for gastric cancer development in humans. Therefore, we investigated the role of high salt diet on gastric epithelial cell proliferation and differentiation, using our mouse model that ectopically expressed Cdx2 homeodomain transcription factor and induced an intestinal metaplastic phenotype in the gastric epithelia. Sixty Cdx2 transgenic and sixty age-matched wild-type littermates were studied. Fifty-percent Cdx2 transgenic and wild type mice were administered a high-salt diet and the other fifty-percent was fed a standard diet starting at 12 weeks after birth. At 10, 20 and 40 weeks after initiation of the diets, histopathological changes were determined by Hemotoxylin and Eosin, alcian blue, and periodic acid-Schiff (PAS) staining. Cell types and cell kinetics were assessed by immunohistochemistry. At 52 weeks, significant alterations in pathology were observed in the Cdx2 transgenic mice fed a high-salt diet, including elongation of gastric pits, reduction of the glandular zone in the gastric corpus, and deepening of glands in the antrum. In the Cdx2 transgenic mice fed a high salt diet, the parietal and chief cells were significantly decreased in the gastric corpus. A significant increase in cell proliferation and apoptosis in the corpus and antrum were observed in Cdx2 transgenic mice fed a high-salt diet as compared to wild-type littermates. Taken together, these data implicate that intestinal metaplasia in concert with a high-salt diet induces epithelial proliferation, apoptosis, and alters cellular types in the gastric mucosa of mice. Alteration in the composition of the gastric epithelium may play a role in influencing the microenvironment to engender susceptibility to carcinogens.

Massive hepatic apoptosis associated with TGF-beta1 activation after Fas ligand treatment of IGF binding protein-1-deficient mice

Acute liver failure caused by viral hepatitis or toxic damage involves both apoptotic and necrotic pathways. IGF binding protein-1 (IGFBP-1), a hepatocyte-derived secreted protein, is required for normal liver regeneration. To determine whether IGFBP-1 could prevent liver injury that entails direct stimulation of hepatocyte apoptosis, IGFBP-1(-/-) mice, IGFBP-1(+/+) mice, and mice pretreated with Ab's against IGFBP-1 were treated with a normally sublethal dose of Fas agonist. IGFBP-1 deficiency was associated with massive hepatocyte apoptosis and caspase activation within 3 hours of Fas agonist treatment, which could be corrected by pretreatment with IGFBP-1. IGFBP-1-deficient livers had enhanced signaling via the integrin receptor at early times (0.5 to 1 hour) after Fas agonist treatment accompanied by elevated activated matrix metalloproteinase-9 (MMP-9), a known target of fibronectin signaling and activator of TGF-beta. Within 3 hours of Fas agonist treatment, elevated expression of active TGF-beta1, a hepatocyte apoptogen, was observed in IGFBP-1-deficient livers that correlated with the appearance of the apoptotic process. Both MMP-9 and TGF-beta1 expression were suppressed by IGFBP-1 treatment, supporting their role in the apoptotic process. IGFBP-1(-/-) mice also displayed increased injury in a toxic hepatic injury model caused by CCl(4). These findings indicate that IGFBP-1 functions as a critical hepatic survival factor in the liver by reducing the level of proapoptotic signals.

Impaired hepatocyte DNA synthetic response posthepatectomy in insulin-like growth factor binding protein 1-deficient mice with defects in C/EBP beta and mitogen-activated protein kinase/extracellular signal-regulated kinase regulation

After a two-thirds hepatectomy, normally quiescent liver cells are stimulated to reenter the cell cycle and proliferate to restore the original liver mass. One of the most rapidly and highly induced genes and proteins in regenerating liver is insulin-like growth factor binding protein 1 (IGFBP-1), a secreted protein that may modulate the activities of insulin-like growth factors (IGFs) or signal via IGF-independent mechanisms. To assess the functional role of IGFBP-1 in liver regeneration, mice with a targeted disruption of the IGFBP-1 gene were generated. Although IGFBP-1(-/-) mice demonstrated normal development, they had abnormal liver regeneration after partial hepatectomy, characterized by liver necrosis and reduced and delayed hepatocyte DNA synthesis. The abnormal regenerative response was associated with blunted activation of mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) and a reduced induction of C/EBP beta protein expression posthepatectomy. Like cell cycle abnormalities observed in hepatectomized C/EBP beta(-/-) mice, cyclin A and cyclin B1 expression was delayed and reduced in IGFBP-1(-/-) livers, whereas cyclin D1 expression was normal. Treatment of IGFBP-1(-/-) mice with a preoperative dose of IGFBP-1 induced MAPK/ERK activation and C/EBP beta expression, suggesting that IGFBP-1 may support liver regeneration at least in part via its effect on MAPK/ERK and C/EBP beta activities. These findings are the first demonstration of the involvement of IGFBP-1 in the regulation of in vivo mitogenic signaling pathways.

Massive hepatic apoptosis associated with TGF-beta1 activation after Fas ligand treatment of IGF binding protein-1-deficient mice

Acute liver failure caused by viral hepatitis or toxic damage involves both apoptotic and necrotic pathways. IGF binding protein-1 (IGFBP-1), a hepatocyte-derived secreted protein, is required for normal liver regeneration. To determine whether IGFBP-1 could prevent liver injury that entails direct stimulation of hepatocyte apoptosis, IGFBP-1(-/-) mice, IGFBP-1(+/+) mice, and mice pretreated with Ab's against IGFBP-1 were treated with a normally sublethal dose of Fas agonist. IGFBP-1 deficiency was associated with massive hepatocyte apoptosis and caspase activation within 3 hours of Fas agonist treatment, which could be corrected by pretreatment with IGFBP-1. IGFBP-1-deficient livers had enhanced signaling via the integrin receptor at early times (0.5 to 1 hour) after Fas agonist treatment accompanied by elevated activated matrix metalloproteinase-9 (MMP-9), a known target of fibronectin signaling and activator of TGF-beta. Within 3 hours of Fas agonist treatment, elevated expression of active TGF-beta1, a hepatocyte apoptogen, was observed in IGFBP-1-deficient livers that correlated with the appearance of the apoptotic process. Both MMP-9 and TGF-beta1 expression were suppressed by IGFBP-1 treatment, supporting their role in the apoptotic process. IGFBP-1(-/-) mice also displayed increased injury in a toxic hepatic injury model caused by CCl(4). These findings indicate that IGFBP-1 functions as a critical hepatic survival factor in the liver by reducing the level of proapoptotic signals.

Up-regulated transcriptional repressors SnoN and Ski bind Smad proteins to antagonize transforming growth factor-beta signals during liver regeneration

Transforming growth factor-beta (TGF-beta) functions as an antiproliferative factor for hepatocytes. However, for unexplained reasons, hepatocytes become resistant to TGF-beta signals and can proliferate despite the presence of TGF-beta during liver regeneration. TGF-beta is up-regulated during liver regeneration, although it is not known whether it is active or latent. TGF-beta activity may be examined by assessing Smad activation, a downstream signaling pathway. Smad pathway activation during liver regeneration induced by partial hepatectomy or CC4 injury was examined by assessing the levels of phospho-Smad2 and Smad2-Smad4 complexes. We found that Smad proteins were slightly activated in quiescent liver, but that their activation was further enhanced in regenerating liver. Interestingly, TGF-beta/Smad pathway inhibitors (SnoN and Ski) were up-regulated during regeneration, and notably, SnoN was induced mainly in hepatocytes. SnoN and Ski are transcriptional repressors that may render some cells resistant to TGF-beta via binding Smad proteins. Complexes between SnoN, Ski, and the activated Smad proteins were detected from 2 to 120 h during the major proliferative phase in regenerating liver. Inhibitory complexes decreased after liver mass restitution (5-15 days), suggesting that persistently activated Smad proteins might participate in returning the liver to a quiescent state. Our data show that active TGF-beta/Smad signals are present during regeneration and suggest that SnoN/Ski induction might explain hepatocyte resistance to TGF-beta during the proliferative phase.