Defects in microvillus crosslinking sensitize to colitis and inflammatory bowel disease

Intestinal epithelial cells are covered by the brush border, which consists of densely packed microvilli. The Intermicrovillar Adhesion Complex (IMAC) links the microvilli and is required for proper brush border organization. Whether microvillus crosslinking is involved in the intestinal barrier function or colitis is currently unknown. We investigate the role of microvillus crosslinking in colitis in mice with deletion of the IMAC component CDHR5. Electron microscopy shows pronounced brush border defects in CDHR5-deficient mice. The defects result in severe mucosal damage after exposure to the colitis-inducing agent DSS. DSS increases the permeability of the mucus layer and brings bacteria in direct contact with the disorganized brush border of CDHR5-deficient mice. This correlates with bacterial invasion into the epithelial cell layer which precedes epithelial apoptosis and inflammation. Single-cell RNA sequencing data of patients with ulcerative colitis reveals downregulation of CDHR5 in enterocytes of diseased areas. Our results provide experimental evidence that a combination of microvillus crosslinking defects with increased permeability of the mucus layer sensitizes to inflammatory bowel disease.

Correction: Dependency on the TYK2/STAT1/MCL1 axis in anaplastic large cell lymphoma

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

IDO1+ Paneth cells promote immune escape of colorectal cancer

Tumors have evolved mechanisms to escape anti-tumor immunosurveillance. They limit humoral and cellular immune activities in the stroma and render tumors resistant to immunotherapy. Sensitizing tumor cells to immune attack is an important strategy to revert immunosuppression. However, the underlying mechanisms of immune escape are still poorly understood. Here we discover Indoleamine-2,3-dioxygenase-1 (IDO1)⁺ Paneth cells in the stem cell niche of intestinal crypts and tumors, which promoted immune escape of colorectal cancer (CRC). Ido1 expression in Paneth cells was strictly Stat1 dependent. Loss of IDO1⁺ Paneth cells in murine intestinal adenomas with tumor cell-specific Stat1 deletion had profound effects on the intratumoral immune cell composition. Patient samples and TCGA expression data suggested corresponding cells in human colorectal tumors. Thus, our data uncovered an immune escape mechanism of CRC and identify IDO1⁺ Paneth cells as a target for immunotherapy.

Pflügler, Svinka et al. identify a subset of Paneth cells in mouse intestinal crypts and tumors, which express the immune checkpoint molecule Ido1 in a Stat1-dependent manner and promote tumor growth. Gene expression data from human colorectal cancer (CRC) suggest that a similar population is present in human cancer and opens the door for further studies of immune escape mechanisms in CRC.

Myeloid Cells Restrict MCMV and Drive Stress-Induced Extramedullary Hematopoiesis through STAT1

Cytomegalovirus (CMV) has a high prevalence worldwide, is often fatal for immunocompromised patients, and causes bone marrow suppression. Deficiency of signal transducer and activator of transcription 1 (STAT1) results in severely impaired antiviral immunity. We have used cell-type restricted deletion of Stat1 to determine the importance of myeloid cell activity for the defense against murine CMV (MCMV). We show that myeloid STAT1 limits MCMV burden and infection-associated pathology in the spleen but does not affect ultimate clearance of infection. Unexpectedly, we found an essential role of myeloid STAT1 in the induction of extramedullary hematopoiesis (EMH). The EMH-promoting function of STAT1 was not restricted to MCMV infection but was also observed during CpG oligodeoxynucleotide-induced sterile inflammation. Collectively, we provide genetic evidence that signaling through STAT1 in myeloid cells is required to restrict MCMV at early time points post-infection and to induce compensatory hematopoiesis in the spleen.

Dependency on the TYK2/STAT1/MCL1 axis in anaplastic large cell lymphoma

TYK2 is a member of the JAK family of tyrosine kinases that is involved in chromosomal translocation-induced fusion proteins found in anaplastic large cell lymphomas (ALCL) that lack rearrangements activating the anaplastic lymphoma kinase (ALK). Here we demonstrate that TYK2 is highly expressed in all cases of human ALCL, and that in a mouse model of NPM-ALK-induced lymphoma, genetic disruption of Tyk2 delays the onset of tumors and prolongs survival of the mice. Lymphomas in this model lacking Tyk2 have reduced STAT1 and STAT3 phosphorylation and reduced expression of Mcl1, a pro-survival member of the BCL2 family. These findings in mice are mirrored in human ALCL cell lines, in which TYK2 is activated by autocrine production of IL-10 and IL-22 and by interaction with specific receptors expressed by the cells. Activated TYK2 leads to STAT1 and STAT3 phosphorylation, activated expression of MCL1 and aberrant ALCL cell survival. Moreover, TYK2 inhibitors are able to induce apoptosis in ALCL cells, regardless of the presence or absence of an ALK-fusion. Thus, TYK2 is a dependency that is required for ALCL cell survival through activation of MCL1 expression. TYK2 represents an attractive drug target due to its essential enzymatic domain, and TYK2-specific inhibitors show promise as novel targeted inhibitors for ALCL.

STAT1 is a sex-specific tumor suppressor in colitis-associated colorectal cancer

The interferon‐inducible transcription factor STAT1 is a tumor suppressor in various malignancies. We investigated sex‐specific STAT1 functions in colitis and colitis‐associated colorectal cancer (CRC) using mice with specific STAT1 deletion in intestinal epithelial cells (STAT1^∆IEC). Male but not female STAT1^∆IEC mice were more resistant to DSS‐induced colitis than sex‐matched STAT1^flox/flox controls and displayed reduced intraepithelial infiltration of CD8⁺ TCRαβ⁺ granzyme B⁺ T cells. Moreover, DSS treatment failed to induce expression of T‐cell‐attracting chemokines in intestinal epithelial cells of male but not of female STAT1^∆IEC mice. Application of the AOM‐DSS protocol for induction of colitis‐associated CRC resulted in increased intestinal tumor load in male but not in female STAT1^∆IEC mice. A sex‐specific stratification of human CRC patients corroborated the data obtained in mice and revealed that reduced tumor cell‐intrinsic nuclear STAT1 protein expression is a poor prognostic factor in men but not in women. These data demonstrate that epithelial STAT1 is a male‐specific tumor suppressor in CRC of mice and humans.

Epidermal growth factor signaling protects from cholestatic liver injury and fibrosis

We have demonstrated that the signal transducer and activator of transcription 3 (STAT3) protects from cholestatic liver injury. Specific ablation of STAT3 in hepatocytes and cholangiocytes (STAT3∆hc) aggravated liver damage and fibrosis in the Mdr2-/- (multidrug resistance 2) mouse model for cholestatic disease. Upregulation of bile acid biosynthesis genes and downregulation of epidermal growth factor receptor (EGFR) expression were observed in STAT3∆hc Mdr2-/- mice but the functional consequences of these processes in cholestatic liver injury remained unclear. Here, we show normal canalicular architecture and bile flow but increased amounts of bile acids in the bile of STAT3∆hc Mdr2-/- mice. Moreover, STAT3-deficient hepatocytes displayed increased sensitivity to bile acid-induced apoptosis in vitro. Since EGFR signaling has been reported to protect hepatocytes from bile acid-induced apoptosis, we generated mice with hepatocyte/cholangiocyte-specific ablation of EGFR (EGFR∆hc) and crossed them to Mdr2-/- mice. Importantly, deletion of EGFR phenocopied deletion of STAT3 and led to aggravated liver damage, liver fibrosis, and hyperproliferation of K19+ cholangiocytes. Our data demonstrate hepatoprotective functions of the STAT3-EGFR signaling axis in cholestatic liver disease.

KEY MESSAGE

STAT3 is a negative regulator of bile acid biosynthesis. STAT3 protects from bile acid-induced apoptosis and regulates EGFR expression. EGFR signaling protects from cholestatic liver injury and fibrosis.

Growth hormone resistance exacerbates cholestasis-induced murine liver fibrosis

Growth hormone (GH) resistance has been associated with liver cirrhosis in humans but its contribution to the disease remains controversial. In order to elucidate whether GH resistance plays a causal role in the establishment and development of liver fibrosis, or rather represents a major consequence thereof, we challenged mice lacking the GH receptor gene (Ghr(-/-), a model for GH resistance) by crossing them with Mdr2 knockout mice (Mdr2(-/-)), a mouse model of inflammatory cholestasis and liver fibrosis. Ghr(-/-);Mdr2(-/-) mice showed elevated serum markers associated with liver damage and cholestasis, extensive bile duct proliferation, and increased collagen deposition relative to Mdr2(-/-) mice, thus suggesting a more severe liver fibrosis phenotype. Additionally, Ghr(-/-);Mdr2(-/-) mice had a pronounced down-regulation of hepatoprotective genes Hnf6, Egfr, and Igf-1, and significantly increased levels of reactive oxygen species (ROS) and apoptosis in hepatocytes, compared to control mice. Moreover, single knockout mice (Ghr(-/-)) fed with a diet containing 1% cholic acid displayed an increase in hepatocyte ROS production, hepatocyte apoptosis, and bile infarcts compared to their wild-type littermates, indicating that loss of Ghr renders hepatocytes more susceptible to toxic bile acid accumulation. Surprisingly, and despite their severe fibrotic phenotype, Ghr(-/-);Mdr2(-/-) mice displayed a significant decrease in tumor incidence compared to Mdr2(-/-) mice, indicating that loss of Ghr signaling may slow the progression from fibrosis/cirrhosis to cancer in the liver.

CONCLUSION

GH resistance dramatically exacerbates liver fibrosis in a mouse model of inflammatory cholestasis, therefore suggesting that GH resistance plays a causal role in the disease and provides a novel target for the development of liver fibrosis treatments.

Myeloid STAT3 promotes formation of colitis-associated colorectal cancer in mice

Myeloid cells lacking STAT3 promote antitumor responses of NK and T cells but it is unknown if this crosstalk affects development of autochthonous tumors. We deleted STAT3 in murine myeloid cells (STAT3^Δm) and examined the effect on the development of autochthonous colorectal cancers (CRCs). Formation of Azoxymethane/Dextransulfate (AOM/DSS)-induced CRCs was strongly suppressed in STAT3^Δm mice. Gene expression profiling showed strong activation of T cells in the stroma of STAT3^Δm CRCs. Moreover, STAT3^Δm host mice were better able to control the growth of transplanted MC38 colorectal tumor cells which are known to be killed in a T cell-dependent manner. These data suggest that myeloid cells lacking STAT3 control formation of CRCs mainly via cross activation of T cells. Interestingly, the few CRCs that formed in STAT3^Δm mice displayed enhanced stromalization but appeared normal in size indicating that they have acquired ways to escape enhanced tumor surveillance. We found that CRCs in STAT3^Δm mice consistently activate STAT3 signaling which is implicated in immune evasion and might be a target to prevent tumor relapse.

Induction of colorectal cancer in mice and histomorphometric evaluation of tumors

Colorectal cancer (CRC) originates from the epithelial cells lining the colon or rectum of the gastrointestinal tract and represents the third most common form of cancer worldwide. CRC is frequently associated with Colitis Ulcerosa or Crohn's Disease demonstrating the tumor-promoting role of inflammation. Colorectal tumor cells establish heterotypic interactions with inflammatory cells and cancer-associated fibroblasts in the tumor stroma that support tumor angiogenesis and are essential for tumor progression. Therefore, establishment of suitable mouse models mimicking the inflammatory etiology of CRC is important. Here we describe methods to induce CRC in mice, to quantify tumor parameters (multiplicity, tumor load, mean tumor size), and to analyze the cellular composition of the CRC tumor stroma.

Abstract 5349: The role of growth hormone receptor in liver fibrosis and cancer

Liver fibrosis is defined as the pathological excessive deposition of extracellular matrix proteins which contributes to a disruption of normal liver architecture. Fibrosis can progress to cirrhosis, which can eventually result in hepatocellular carcinoma. Over the past decades our understanding of the cellular and molecular mechanisms of liver fibrosis has advanced greatly. Activated hepatic stellate cells, myofibroblasts of bone marrow origin and portal fibroblasts have all been identified as major contributors to fibrosis. Recently, growth hormone resistance and low serum levels of IGF-1 have also been associated with liver cirrhosis in humans, indicating a role for growth hormone receptor, which itself controls various cellular functions including the transcription of IGF-1 through Stat 5 signaling. Furthermore, supplementation of recombinant IGF-1 in cirrhotic animal models was shown to reduce disease severity. In order to elucidate whether the GHR plays an active role in the establishment of fibrotic liver diseases or rather represents a major consequence of this illness, we crossed mice lacking the Ghr/bp gene (Ghr -/-) with Mdr2 knockout mice (Mdr2-/-), a mouse model of inflammatory cholestasis and liver fibrosis. Our results show that Ghr-/-;Mdr2-/- mice display deregulated bile acid homeostasis and increased serum markers associated with inflammation and fibrosis. Bile duct proliferation and extensive collagen deposition were also observed in Ghr-/-;Mdr2-/- relative to Mdr2-/- mice. Additionally, compared to control mice a pronounced down regulation of the hepato-protective genes Hnf6, Egfr and Igf-1 was seen in Ghr-/-;Mdr2-/- animals, which also displayed significantly increased apoptosis. Moreover, single knockout mice (Ghr-/-) developed bile infacts when fed with 1% cholic acid compared to their wildtype littermates, indicating that loss of GHR renders hepatocytes more susceptible to toxic bile acid accumulation. Surprisingly and despite their severe fibrotic phenotype Ghr -/-; Mdr2 -/- mice showed a significant decrease in tumor incidence compared to Mdr2 -/- mice, indicating that loss of GHR signaling may slow the progression from fibrosis/cirrhosis to cancer in the liver.

Our findings suggest that loss of GHR signaling results in increased liver injury in the Mdr2 -/- mouse model of inflammatory cholestasis and liver fibrosis, signifying the possible therapeutic value of this pathway in the development of liver fibrosis treatments.

Citation Format: Patricia Stiedl, Leander Blaas, Viktoria Stanek, Jasmin Svinka, Robert Mc Mahon, Gernot Zollner, Thierry Claudel, Mathias Mueller, Wolfgang Mikulits, Harald Esterbauer, Robert Eferl, Johannes Haybaeck, Michael Trauner, Emilio Casanova. The role of growth hormone receptor in liver fibrosis and cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5349. doi:10.1158/1538-7445.AM2014-5349

STAT3 in hepatocellular carcinoma: new perspectives

Chronic liver damage and inflammation are strong promoters of hepatocellular carcinoma (HCC) formation. HCC cells communicate with inflammatory and stromal cells via cytokine/chemokine signals. These heterotypic interactions inhibit immunologic anticancer activities and promote protumorigenic activities, such as angiogenesis or invasiveness. STAT3 mediates several reciprocal interactions between liver cancer cells and stromal cells and modulates preconditions of tumor formation such as chronic inflammation. Therefore, activation of STAT3 is considered as a tumor-promoting event in HCC formation. However, the oncogenic role of STAT3 in cancers has been challenged by several reports that suggest a tumor-suppressive activity. Here we discuss tumor-promoting and tumor-suppressive effects of cytokine-activated STAT3 in HCC.

A mouse model to identify cooperating signaling pathways in cancer

We here establish a mouse cancer model called Multi-Hit that allows for the evaluation of oncogene cooperativities in tumor development. The model is based on the stochastic expression of oncogene combinations ('hits') that are mediated by Cre in a given tissue. Cells with cooperating hits are positively selected and give rise to tumors. We used this approach to evaluate the requirement of Ras downstream effector pathways in tumorigenesis.