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BACKGROUND {\&} AIMS RNase H2 is a holoenzyme,composed of 3 subunits (ribonuclease H2 subunits A,B,and C),that cleaves RNA:DNA hybrids and removes mis-incorporated ribonucleotides from genomic DNA through ribonucleotide excision repair. Ribonucleotide incorporation by eukaryotic DNA polymerases occurs during every round of genome duplication and produces the most frequent type of naturally occurring DNA lesion. We investigated whether intestinal epithelial proliferation requires RNase H2 function and whether RNase H2 activity is disrupted during intestinal carcinogenesis. METHODS We generated mice with epithelial-specific deletion of ribonuclease H2 subunit B (H2b$\Delta$IEC) and mice that also had deletion of tumor-suppressor protein p53 (H2b/p53$\Delta$IEC); we compared phenotypes with those of littermate H2bfl/fl or H2b/p53fl/fl (control) mice at young and old ages. Intestinal tissues were collected and analyzed by histology. We isolated epithelial cells,generated intestinal organoids,and performed RNA sequence analyses. Mutation signatures of spontaneous tumors from H2b/p53$\Delta$IEC mice were characterized by exome sequencing. We collected colorectal tumor specimens from 467 patients,measured levels of ribonuclease H2 subunit B,and associated these with patient survival times and transcriptome data. RESULTS The H2b$\Delta$IEC mice had DNA damage to intestinal epithelial cells and proliferative exhaustion of the intestinal stem cell compartment compared with controls and H2b/p53$\Delta$IEC mice. However,H2b/p53$\Delta$IEC mice spontaneously developed small intestine and colon carcinomas. DNA from these tumors contained T{\textgreater}G base substitutions at GTG trinucleotides. Analyses of transcriptomes of human colorectal tumors associated lower levels of RNase H2 with shorter survival times. CONCLUSIONS In analyses of mice with disruption of the ribonuclease H2 subunit B gene and colorectal tumors from patients,we provide evidence that RNase H2 functions as a colorectal tumor suppressor. H2b/p53$\Delta$IEC mice can be used to study the roles of RNase H2 in tissue-specific carcinogenesis. View Publication

A coding variant of the inflammatory bowel disease (IBD) risk gene ATG16L1 has been associated with defective autophagy and deregulation of endoplasmic reticulum (ER) function. IL-22 is a barrier protective cytokine by inducing regeneration and antimicrobial responses in the intestinal mucosa. We show that ATG16L1 critically orchestrates IL-22 signaling in the intestinal epithelium. IL-22 stimulation physiologically leads to transient ER stress and subsequent activation of STING-dependent type I interferon (IFN-I) signaling,which is augmented in Atg16l1$\Delta$IEC intestinal organoids. IFN-I signals amplify epithelial TNF production downstream of IL-22 and contribute to necroptotic cell death. In vivo,IL-22 treatment in Atg16l1$\Delta$IEC and Atg16l1$\Delta$IEC/Xbp1$\Delta$IEC mice potentiates endogenous ileal inflammation and causes widespread necroptotic epithelial cell death. Therapeutic blockade of IFN-I signaling ameliorates IL-22-induced ileal inflammation in Atg16l1$\Delta$IEC mice. Our data demonstrate an unexpected role of ATG16L1 in coordinating the outcome of IL-22 signaling in the intestinal epithelium. View Publication

OBJECTIVE Exposure to lethal doses of radiation has severe effects on normal tissues. Exposed individuals experience a plethora of symptoms in different organ systems including the gastrointestinal (GI) tract,summarized as Acute Radiation Syndrome (ARS). There are currently no approved drugs for mitigating GI-ARS. A recent high-throughput screen performed at the UCLA Center for Medical Countermeasures against Radiation identified compounds containing sulfonylpiperazine groups with radiation mitigation properties to the hematopoietic system and the gut. Among these 1-[(4-Nitrophenyl)sulfonyl]-4-phenylpiperazine (Compound {\#}5) efficiently mitigated gastrointestinal ARS. However,the mechanism of action and target cells of this drug is still unknown. In this study we examined if Compound {\#}5 affects gut-associated lymphoid tissue (GALT) with its subepithelial domes called Peyer's patches. METHODS C3H mice were irradiated with 0 or 12 Gy total body irradiation (TBI). A single dose of Compound {\#}5 or solvent was administered subcutaneously 24 h later. 48 h after irradiation the mice were sacrificed,and the guts examined for changes in the number of visible Peyer's patches. In some experiments the mice received 4 daily injections of treatment and were sacrificed 96 h after TBI. For immune histochemistry gut tissues were fixed in formalin and embedded in paraffin blocks. Sections were stained with H{\&}E,anti-Ki67 or a TUNEL assay to assess the number of regenerating crypts,mitotic and apoptotic indices. Cells isolated from Peyer's patches were subjected to immune profiling using flow cytometry. RESULTS Compound {\#}5 significantly increased the number of visible Peyer's patches when compared to its control in non-irradiated and irradiated mice. Additionally,assessment of total cells per Peyer's patch isolated from these mice demonstrated an overall increase in the total number of Peyer's patch cells per mouse in Compound {\#}5-treated mice. In non-irradiated animals the number of CD11bhigh in Peyer's patches increased significantly. These Compound {\#}5-driven increases did not coincide with a decrease in apoptosis or an increase in proliferation in the germinal centers inside Peyer's patches 24 h after drug treatment. A single dose of Compound {\#}5 significantly increased the number of CD45+ cells after 12 Gy TBI. Importantly,96 h after 12 Gy TBI Compound {\#}5 induced a significant rise in the number of visible Peyer's patches and the number of Peyer's patch-associated regenerating crypts. CONCLUSION In summary,our study provides evidence that Compound {\#}5 leads to an influx of immune cells into GALT,thereby supporting crypt regeneration preferentially in the proximity of Peyer's patches. View Publication

Targeting of cancer stem cells (CSC) is expected to be a paradigm-shifting approach for the treatment of cancers. Cell surface proteoglycans bearing sulfated glycosaminoglycan (GAG) chains are known to play a critical role in the regulation of stem cell fate. Here,we show for the first time that G2.2,a sulfated nonsaccharide GAG mimetic (NSGM) of heparin hexasaccharide,selectively inhibits colonic CSCs in vivo G2.2-reduced CSCs (CD133+/CXCR4+,Dual hi) induced HT-29 and HCT 116 colon xenografts' growth in a dose-dependent fashion. G2.2 also significantly delayed the growth of colon xenograft further enriched in CSCs following oxaliplatin and 5-fluorouracil treatment compared with vehicle-treated xenograft controls. In fact,G2.2 robustly inhibited CSCs' abundance (measured by levels of CSC markers,e.g.,CD133,DCMLK1,LGR5,and LRIG1) and self-renewal (quaternary spheroids) in colon cancer xenografts. Intriguingly,G2.2 selectively induced apoptosis in the Dual hi CSCs in vivo eluding to its CSC targeting effects. More importantly,G2.2 displayed none to minimal toxicity as observed through morphologic and biochemical studies of vital organ functions,blood coagulation profile,and ex vivo analyses of normal intestinal (and bone marrow) progenitor cell growth. Through extensive in vitro,in vivo,and ex vivo mechanistic studies,we showed that G2.2's inhibition of CSC self-renewal was mediated through activation of p38$\alpha$,uncovering important signaling that can be targeted to deplete CSCs selectively while minimizing host toxicity. Hence,G2.2 represents a first-in-class (NSGM) anticancer agent to reduce colorectal CSCs. View Publication

The role of negative checkpoint regulators (NCRs) in human health and disease cannot be overstated. V-domain Ig-containing Suppressor of T-cell Activation (VISTA) is an Ig superfamily protein predominantly expressed within the hematopoietic compartment and has been studied for its role in the negative regulation of T cell responses. The findings presented in this study show that,unlike all other NCRs,VISTA deficiency dramatically impacts on macrophage cytokine and chemokine production,as well as the chemotactic response of VISTA-deficient macrophages. A select group of inflammatory chemokines,including CCL2,CCL3,CCL4,and CCL5,was strikingly elevated in culture supernatants from VISTA KO macrophages. VISTA deficiency also altered chemokine receptor recycling and profoundly disrupted myeloid chemotaxis. The impact of VISTA deficiency on chemotaxis in vivo was apparent with the reduced ability of both KO macrophages and MDSCs to migrate to the tumor microenvironment. This is the first demonstration of an NCR impacting on myeloid mediator production and chemotaxis,and will guide the use of anti-VISTA therapeutics to manipulate the chemotaxis of inflammatory macrophages or immunosuppressive MDSCs in inflammatory diseases and cancer. View Publication