Epithelial X-Box Binding Protein 1 Coordinates Tumor Protein p53-Driven DNA Damage Responses and Suppression of Intestinal Carcinogenesis

BACKGROUND & AIMS

Throughout life, the intestinal epithelium undergoes constant self-renewal from intestinal stem cells. Together with genotoxic stressors and failing DNA repair, this self-renewal causes susceptibility toward malignant transformation. X-box binding protein 1 (XBP1) is a stress sensor involved in the unfolded protein response (UPR). We hypothesized that XBP1 acts as a signaling hub to regulate epithelial DNA damage responses.

METHODS

Data from The Cancer Genome Atlas were analyzed for association of XBP1 with colorectal cancer (CRC) survival and molecular interactions between XBP1 and p53 pathway activity. The role of XBP1 in orchestrating p53-driven DNA damage response was tested in vitro in mouse models of chronic intestinal epithelial cell (IEC) DNA damage (Xbp1/H2bfl/fl, Xbp1ΔIEC, H2bΔIEC, H2b/Xbp1ΔIEC) and via orthotopic tumor organoid transplantation. Transcriptome analysis of intestinal organoids was performed to identify molecular targets of Xbp1-mediated DNA damage response.

RESULTS

In The Cancer Genome Atlas data set of CRC, low XBP1 expression was significantly associated with poor overall survival and reduced p53 pathway activity. In vivo, H2b/Xbp1ΔIEC mice developed spontaneous intestinal carcinomas. Orthotopic tumor organoid transplantation revealed a metastatic potential of H2b/Xbp1ΔIEC-derived tumors. RNA sequencing of intestinal organoids (H2b/Xbp1fl/fl, H2bΔIEC, H2b/Xbp1ΔIEC, and H2b/p53ΔIEC) identified a transcriptional program downstream of p53, in which XBP1 directs DNA-damage-inducible transcript 4-like (Ddit4l) expression. DDIT4L inhibits mechanistic target of rapamycin-mediated phosphorylation of 4E-binding protein 1. Pharmacologic mechanistic target of rapamycin inhibition suppressed epithelial hyperproliferation via 4E-binding protein 1.

CONCLUSIONS

Our data suggest a crucial role for XBP1 in coordinating epithelial DNA damage responses and stem cell function via a p53-DDIT4L-dependent feedback mechanism.

Microbial regulation of hexokinase 2 links mitochondrial metabolism and cell death in colitis

Hexokinases (HK) catalyze the first step of glycolysis limiting its pace. HK2 is highly expressed in gut epithelium, contributes to immune responses, and is upregulated during inflammation. We examined the microbial regulation of HK2 and its impact on inflammation using mice lacking HK2 in intestinal epithelial cells (Hk2ΔIEC). Hk2ΔIEC mice were less susceptible to acute colitis. Analyzing the epithelial transcriptome from Hk2ΔIEC mice during colitis and using HK2-deficient intestinal organoids and Caco-2 cells revealed reduced mitochondrial respiration and epithelial cell death in the absence of HK2. The microbiota strongly regulated HK2 expression and activity. The microbially derived short-chain fatty acid (SCFA) butyrate repressed HK2 expression via histone deacetylase 8 (HDAC8) and reduced mitochondrial respiration in wild-type but not in HK2-deficient Caco-2 cells. Butyrate supplementation protected wild-type but not Hk2ΔIEC mice from colitis. Our findings define a mechanism how butyrate promotes intestinal homeostasis and suggest targeted HK2-inhibition as therapeutic avenue for inflammation.

Longitudinal Multi-omics Analyses Identify Responses of Megakaryocytes, Erythroid Cells, and Plasmablasts as Hallmarks of Severe COVID-19

Temporal resolution of cellular features associated with a severe COVID-19 disease trajectory is needed for understanding skewed immune responses and defining predictors of outcome. Here, we performed a longitudinal multi-omics study using a two-center cohort of 14 patients. We analyzed the bulk transcriptome, bulk DNA methylome, and single-cell transcriptome (>358,000 cells, including BCR profiles) of peripheral blood samples harvested from up to 5 time points. Validation was performed in two independent cohorts of COVID-19 patients. Severe COVID-19 was characterized by an increase of proliferating, metabolically hyperactive plasmablasts. Coinciding with critical illness, we also identified an expansion of interferon-activated circulating megakaryocytes and increased erythropoiesis with features of hypoxic signaling. Megakaryocyte- and erythroid-cell-derived co-expression modules were predictive of fatal disease outcome. The study demonstrates broad cellular effects of SARS-CoV-2 infection beyond adaptive immune cells and provides an entry point toward developing biomarkers and targeted treatments of patients with COVID-19.

•

SARS-CoV2 infection elicits dynamic changes of circulating cells in the blood

•

Severe COVID-19 is characterized by increased metabolically active plasmablasts

•

Elevation of IFN-activated megakaryocytes and erythroid cells in severe COVID-19

•

Cell-type-specific expression signatures are associated with a fatal COVID-19 outcome

Remarks on the relation between fractional moments and fractional derivatives of characteristic functions

We consider fractional derivatives of characteristic functions. We use these fractional derivatives for the formulation of new conditions for the existence of non-integer moments. We also compare the known conditions for the existence of moments of arbitrary random variables with our new conditions. As a consequence many conditions can be written in a unified terminology.

Communication between plants: induced resistance in wild tobacco plants following clipping of neighboring sagebrush

The possibility of communication between plants was proposed nearly 20 years ago, although previous demonstrations have suffered from methodological problems and have not been widely accepted. Here we report the first rigorous, experimental evidence demonstrating that undamaged plants respond to cues released by neighbors to induce higher levels of resistance against herbivores in nature. Sagebrush plants that were clipped in the field released a pulse of an epimer of methyl jasmonate that has been shown to be a volatile signal capable of inducing resistance in wild tobacco. Wild tobacco plants with clipped sagebrush neighbors had increased levels of the putative defensive oxidative enzyme, polyphenol oxidase, relative to control tobacco plants with unclipped sagebrush neighbors. Tobacco plants near clipped sagebrush experienced greatly reduced levels of leaf damage by grasshoppers and cutworms during three field seasons compared to unclipped controls. This result was not caused by an altered light regime experienced by tobacco near clipped neighbors. Barriers to soil contact between tobacco and sagebrush did not reduce the difference in leaf damage although barriers that blocked air contact negated the effect.

Fast track to the trichome: induction of N-acyl nornicotines precedes nicotine induction in Nicotiana repanda

Nicotiana repanda Wildenow ex Lehmann acylates nornicotine in its trichomes to produce N-acyl-nornicotine (NacNN) alkaloids which are dramatically more toxic than nicotine is to the nicotine-adapted herbivore, Manduca sexta. These NacNNs, like nicotine, were induced by methyl jasmonate (MeJA) and wounding, but the 2-fold increase in NacNN pools was much faster (within 6 h) than the MeJA-induced increase in nornicotine pools (24 h to 4 d), its parent substrate. When 15NO(-)3 pulse-chase experiments with intact and induced plants were used to follow the incorporation of 15N into alkaloids in different plant parts over the plant's lifetime, it was found that the root nicotine pool was most rapidly labeled, followed by the shoot nornicotine and NacNN pools. After 3 d, 3.12% of 15N acquired was in nicotine (0.93%), nornicotine (0.32%) and NacNNs (1.73%) while only 0.14% was in anabasine. Once NacNNs are externalized to the leaf surface, they are not readily re-distributed within the plant and are lost with senescing leaves. The wound- and MeJA-induced N-acylation of nornicotine is independent of induced changes in nornicotine pools and the rapidity of the response suggests its importance in defense against herbivores.

Cost-effective selection of fire fighter recruits

To discriminate suitable fire fighters from recurring large groups of applicants, an objective test battery was developed which screened applicants on the basis of physical, psychomotor, and mental abilities. The physical and psychomotor selection procedures first involved fundamental tests of general aerobic endurance, upper body strength, and anaerobic endurance. Successful candidates progressed to more specific tests. Measurements were made of height, weight, hamstring flexibility, balance, strength, upper body flexibility, hand-eye coordination, and the ability to negotiate a fire fighting simulation course. Results of these tests were weighted, allocating 25% to physical tests, 20% to psychomotor tests, and 39% to the simulation course. These scores were then combined with scores of several knowledge tests weighted to be 16% of the whole. This provided a computer-generated ability profile of the top applicants which was considered at their interview before a final selection board of fire service officers. Selected candidates were then required to pass a medical examination. Pearson correlation coefficient analysis of 1984 test results demonstrated general independence of the tests (R = -0.34 to R = 0.52), with the exception of bilateral grip strength (R = 0.77). The first four trials of the selection procedure screened 3,172 applicants, 16.4% of whom were finally selected for interview. City officials estimated that based on a comparison of new and previously used selection procedures, cost savings of +92,500 were being achieved by 1984.