Krüppel-like factor 4 is a radioprotective factor for the intestine following γ-radiation-induced gut injury in mice

A graded neonatal mouse model of necrotizing enterocolitis demonstrates that mild enterocolitis is sufficient to activate microglia and increase cerebral cytokine expression

Background

Necrotizing enterocolitis (NEC) is an inflammatory gastrointestinal process that afflicts approximately 10% of preterm infants born in the United States each year, with a mortality rate of 30%. NEC severity is graded using Bell's classification system, from stage I mild NEC to stage III severe NEC. Over half of NEC survivors present with neurodevelopmental impairment during adolescence, a long-term complication that is poorly understood but can occur even after mild NEC. Although multiple animal models exist, none allow the experimenter to control nor represent the gradient of symptom severities seen in NEC patients. We bridge this knowledge gap by developing a graded murine model of NEC and studying its relationship with neuroinflammation across a range of NEC severities.

Methods

Postnatal day 3 (P3) C57BL/6 mice were fed a formula containing different concentrations (0% control, 0.25%, 1%, 2%, and 3%) of dextran sodium sulfate (DSS). P3 mice were fed every 3 hours for 72-hours. We collected data on weight gain and behavior (activity, response, body color) during feeding. At the end of the experiment, we collected tissues (intestine, liver, plasma, brain) for immunohistochemistry, immunofluorescence, and cytokine and chemokine analysis.

Results

Throughout NEC induction, mice fed higher concentrations of DSS died sooner, lost weight faster, and became sick or lethargic earlier. Intestinal characteristics (dilation, color, friability) were worse in mice fed with higher DSS concentrations. Histology revealed small intestinal disarray among mice fed all DSS concentrations, while higher DSS concentrations resulted in reduced small intestinal cellular proliferation and increased hepatic and systemic inflammation. In the brain, IL-2, G-CSF, and CXCL1 concentrations increased with higher DSS concentrations. Although the number of neurons and microglia in the CA1 hippocampal region did not differ, microglial branching was significantly reduced in DSS-fed mice.

Conclusion

We characterize a novel graded model of NEC that recapitulates the full range of NEC severities. We show that mild NEC is sufficient to initiate neuroinflammation and microglia activation. This model will facilitate studies on the neurodevelopmental effects of NEC.

Enhanced infection efficiency and cytotoxicity mediated by vpx-containing lentivirus in chimeric antigen receptor macrophage (CAR-M)

Genetically modified macrophage infusion has been proven to be a novel treatment for cancer. One of the most important processes in macrophage-based therapy is the efficient transfer of genes. HIV-1-derived lentiviruses were widely used as delivery vectors in chimeric antigen receptor T and NK cell construction. While macrophages are relatively refractory to this lentiviral vector transduction as a result of the myeloid-specific restriction factor SAMHD1, which inhibited the virion cycle through exhausting the dNTPs pool and degradating RNAs. An efficient macrophage transduction strategy has been developed via packaging the HIV-2 accessory protein Vpx into the virion. Vpx counteracts SAMHD1 through CRL4 (DCAF1) E3 ubiquitin ligase mediated SAMHD1 degradation, yet the influence by the introduction of Vpx on macrophage has not been fully evaluated. Here, we constructed the chimeric lentiviral vector HIV-1-Vpx and systematically analyzed the infection efficiency of this vector in time-dependent manner. Our results showed that the simplified chimeric virus exhibited dramatically enhanced infection in human macrophages compared to normal lentivirus. Moreover, transcriptome sequencing was performed to evaluate the cellular status after chimeric virus infection. The sequencing results indicated that Vpx introduction promoted macrophage remodeling towards a proinflammatory phenotype, without affecting classic M1/M2 cell surface markers. Our results suggest that the Vpx-containing lentivirus could be used as an ideal tool for the generation of genetically engineered macrophages with high gene transfer efficiency and poised proinflammatory gene sets, especially for solid tumor treatment.

Krüppel-like Factor 10 as a Prognostic and Predictive Biomarker of Radiotherapy in Pancreatic Adenocarcinoma

The prognosis of pancreatic adenocarcinoma (PDAC) remains poor, with a 5-year survival rate of 12%. Although radiotherapy is effective for the locoregional control of PDAC, it does not have survival benefits compared with systemic chemotherapy. Most patients with localized PDAC develop distant metastasis shortly after diagnosis. Upfront chemotherapy has been suggested so that patients with localized PDAC with early distant metastasis do not have to undergo radical local therapy. Several potential tissue markers have been identified for selecting patients who may benefit from local radiotherapy, thereby prolonging their survival. This review summarizes these biomarkers including SMAD4, which is significantly associated with PDAC failure patterns and survival. In particular, Krüppel-like factor 10 (KLF10) is an early response transcription factor of transforming growth factor (TGF)-β. Unlike TGF-β in advanced cancers, KLF10 loss in two-thirds of patients with PDAC was associated with rapid distant metastasis and radioresistance; thus, KLF10 can serve as a predictive and therapeutic marker for PDAC. For patients with resectable PDAC, a combination of KLF10 and SMAD4 expression in tumor tissues may help select those who may benefit the most from additional radiotherapy. Future trials should consider upfront systemic therapy or include molecular biomarker-enriched patients without early distant metastasis.

Introducing novel key genes and transcription factors associated with rectal cancer response to chemoradiation through co-expression network analysis

Preoperative radiochemotherapy is a promising therapeutic method for locally advanced rectal cancer patients. However, the response of colorectal cancer (CRC) patients to preoperative radiotherapy varies widely. In this study, we aimed to identify novel biomarkers that could predict the response of colorectal tumors to treatment using a systems biology approach. We applied the Weighted Gene Co-Expression Network Analysis to construct co-expression networks and evaluated the correlation of these networks with radiation using the module-trait relationship. We then identified hub genes and related transcription factors in the selected co-expression module. Our analysis of seven constructed modules revealed that one module, which contained 113 nodes and 6066 edges, had the strongest correlation with radiation effects on CRC (correlation = 0.85; p-value = 6e-7). By analyzing the selected module with the CytoHubba plugin, we identified four hub genes, including ZEB2, JAM2, NDN, and PPAP2A. We also identified seven important transcription factors, including KLF4, SUZ12, TCF4, NANOG, POU5F1, SOX2, and SMARCA4, which may play essential roles in regulating the four hub genes. In summary, our findings suggest that ZEB2, JAM2, NDN, and PPAP2A, along with the seven transcription factors related to these hub genes, may be associated with the response of colorectal tumors to chemoradiotherapy.

Exposure to MoS2 nanosheets or bulk activated Kruppel-like factor 4 in 3D Caco-2 spheroids in vitro and mouse intestines in vivo

MoS₂ nanosheets (NSs) are novel 2D nanomaterials (NMs) being used in many important fields. Recently, we proposed the need to evaluate the influences of NMs on Kruppel-like factors (KLFs) even if these materials are relatively biocompatible. In this study, we investigated the influences of MoS₂ NSs or bulk on KLF4 signaling pathway in 3D Caco-2 spheroids in vitro and mouse intestines in vivo. Through the analysis of our previous RNA-sequencing data, we found that exposure to MoS₂ NSs or bulk activated KLF4 expression in 3D Caco-2 spheroids. Consistently, these materials also activated KLF4-related gene ontology (GO) terms and down-regulated a panel of KLF4-downstream genes. To verify these findings, we repeatedly exposed mice to MoS₂ NSs or bulk materials via intragastrical administration (1 mg/kg bodyweight, once a day, for 4 days). It was shown that oral exposure to these materials decreased bodyweight, leading to relatively higher organ coefficients. As expected, exposure to both types of materials increased Mo elements as well as other trace elements, such as Zn, Fe, and Mn in mouse intestines. The exposure also induced morphological changes of intestines, such as shortening of intestinal villi and decreased crypt depth, which may result in decreased intestinal lipid staining. Consistent with RNA-sequencing data, we found that material exposure increased KLF4 protein staining in mouse intestines and decreased two KLF4 downstream proteins, namely extracellular signal-regulated kinase (ERK) and serine/threonine kinase (AKT). We concluded that MoS₂ materials were capable to activate KLF4-signaling pathway in intestines both in vivo and in vitro.

Klf4 protects thymus integrity during late pregnancy

Pregnancy causes abrupt thymic atrophy. This atrophy is characterized by a severe decrease in the number of all thymocyte subsets and qualitative (but not quantitative) changes in thymic epithelial cells (TECs). Pregnancy-related thymic involution is triggered by progesterone-induced functional changes affecting mainly cortical TECs (cTECs). Remarkably, this severe involution is rapidly corrected following parturition. We postulated that understanding the mechanisms of pregnancy-related thymic changes could provide novel insights into signaling pathways regulating TEC function. When we analyzed genes whose expression in TECs was modified during late pregnancy, we found a strong enrichment in genes bearing KLF4 transcription factor binding motifs. We, therefore, engineered a Psmb11-iCre : Klf4^lox/lox mouse model to study the impact of TEC-specific Klf4 deletion in steady-state conditions and during late pregnancy. Under steady-state conditions, Klf4 deletion had a minimal effect on TEC subsets and did not affect thymic architecture. However, pregnancy-induced thymic involution was much more pronounced in pregnant females lacking Klf4 expression in TECs. These mice displayed a substantial ablation of TECs with a more pronounced loss of thymocytes. Transcriptomic and phenotypic analyses of Klf4 ^-/- TECs revealed that Klf4 maintains cTEC numbers by supporting cell survival and preventing epithelial-to-mesenchymal plasticity during late pregnancy. We conclude that Klf4 is essential for preserving TEC's integrity and mitigating thymic involution during late pregnancy.

Upregulation of the microRNA rno-miR-146b-5p may be involved in the development of intestinal injury through inhibition of Kruppel-like factor 4 in intestinal sepsis

Regulatory mechanisms of microRNAs (miRNAs) in the development of intestinal sepsis are unclear. This study investigated the role of rno-miR-146b-5p in sepsis-induced intestinal injury. A rat sepsis model was created using the cecal ligation and puncture method. The expression profiles of miRNA and mRNA in sepsis rats were examined using miRNA and mRNA sequencing; rno-miR-146b was selected for further investigation. The mimics and inhibitors of rno-miR-146b-5p were transfected into IEC-6 cells and then with or without lipopolysaccharide (LPS) treatment, and the expressions of Kruppel-like factor 4 (Klf4) and Cyclin D2 (Ccnd2) were assessed by quantitative real-time transcriptase-polymerase chain reaction (qRT-PCR) and western blotting. Next, cell counting kit-8 assay was used to detect cell viability, and scratch wound healing assay was used to assess cell migration. In sepsis rat model, crypt cell proliferation was inhibited and crypt cell apoptosis was increased. Compared with the sham control, results of miRNA and mRNA sequencing showed that there were 17 miRNAs and 1617 mRNAs that were upregulated and 123 miRNAs and 1917 mRNAs that were downregulated in the sepsis model group. The network diagrams and qRT-PCR validation indicated that rno-miR-146b-5p may inhibit the expression of Klf4. By adjusting the expression of rno-miR-146b-5p in IEC-6 cells with or without LPS treatment, we found that increased expression of rno-miR-146b-5p inhibited cell proliferation and migration and inhibited the expression of Ccnd2. rno-miR-146b-5p may play a vital role in the development of sepsis intestinal injury through targeting Klf4 expression and affecting promoter activity of Ccnd2.

New insight into the significance of KLF4 PARylation in genome stability, carcinogenesis, and therapy

KLF4 plays a critical role in determining cell fate responding to various stresses or oncogenic signaling. Here, we demonstrated that KLF4 is tightly regulated by poly(ADP‐ribosyl)ation (PARylation). We revealed the subcellular compartmentation for KLF4 is orchestrated by PARP1‐mediated PARylation. We identified that PARylation of KLF4 is critical to govern KLF4 transcriptional activity through recruiting KLF4 from soluble nucleus to the chromatin. We mapped molecular motifs on KLF4 and PARP1 that facilitate their interaction and unveiled the pivotal role of the PBZ domain YYR motif (Y430, Y451 and R452) on KLF4 in enabling PARP1‐mediated PARylation of KLF4. Disruption of KLF4 PARylation results in failure in DNA damage response. Depletion of KLF4 by RNA interference or interference with PARP1 function by KLF4^YYR/AAA (a PARylation‐deficient mutant) significantly sensitizes breast cancer cells to PARP inhibitors. We further demonstrated the role of KLF4 in modulating homologous recombination through regulating BRCA1 transcription. Our work points to the synergism between KLF4 and PARP1 in tumorigenesis and cancer therapy, which provides a potential new therapeutic strategy for killing BRCA1‐proficient triple‐negative breast cancer cells.

Recent Discoveries on the Involvement of Krüppel-Like Factor 4 in the Most Common Cancer Types

Krüppel-like factor 4 (KLF4) is a transcription factor highly conserved in evolution. It is particularly well known for its role in inducing pluripotent stem cells. In addition, KLF4 plays many roles in cancer. The results of most studies suggest that KLF4 is a tumor suppressor. However, the functioning of KLF4 is regulated at many levels. These include regulation of transcription, alternative splicing, miRNA, post-translational modifications, subcellular localization, protein stability and interactions with other molecules. Simple experiments aimed at assaying transcript levels or protein levels fail to address this complexity and thus may deliver misleading results. Tumor subtypes are also important; for example, in prostate cancer KLF4 is highly expressed in indolent tumors where it impedes tumor progression, while it is absent from aggressive prostate tumors. KLF4 is important in regulating response to many known drugs, and it also plays a role in tumor microenvironment. More and more information is available about upstream regulators, downstream targets and signaling pathways associated with the involvement of KLF4 in cancer. Furthermore, KLF4 performs critical function in the overall regulation of tissue homeostasis, cellular integrity, and progression towards malignancy. Here we summarize and analyze the latest findings concerning this fascinating transcription factor.

Interplay among p21Waf1/Cip1, MUSASHI-1 and Krüppel-like factor 4 in activation of Bmi1-CreER reserve intestinal stem cells after gamma radiation-induced injury

Gamma radiation is a commonly used adjuvant treatment for abdominally localized cancer. Since its therapeutic potential is limited due to gastrointestinal (GI) syndrome, elucidation of the regenerative response following radiation-induced gut injury is needed to develop a preventive treatment. Previously, we showed that Krüppel-like factor 4 (KLF4) activates certain quiescent intestinal stem cells (ISCs) marked by Bmi1-Cre^ER to give rise to regenerating crypts following γ irradiation. In the current study, we showed that γ radiation-induced expression of p21^Waf1/Cip1 in Bmi1-Cre^ER cells is likely mitigated by MUSASHI-1 (MSI1) acting as a negative regulator of p21^Waf1/Cip1 mRNA translation, which promotes exit of the Bmi1-Cre^ER cells from a quiescent state. Additionally, Bmi1-specific Klf4 deletion resulted in decreased numbers of MSI1⁺ cells in regenerating crypts compared to those of control mice. We showed that KLF4 binds to the Msi1 promoter and activates its expression in vitro. Since MSI1 has been shown to be crucial for crypt regeneration, this finding elucidates a pro-proliferative role of KLF4 during the postirradiation regenerative response. Taken together, our data suggest that the interplay among p21^Waf1/Cip1, MSI1 and KLF4 regulates Bmi1-Cre^ER cell survival, exit from quiescence and regenerative potential upon γ radiation-induced injury.

Genome-wide association study identifies genetic susceptibility loci and pathways of radiation-induced acute oral mucositis

Background

Radiation-induced oral mucositis (OM) is one of the most common acute complications for head and neck cancer. Severe OM is associated with radiation treatment breaks, which harms successful tumor management. Radiogenomics studies have indicated that genetic variants are associated with adverse effects of radiotherapy.

Methods

A large-scale genome-wide scan was performed in 1467 nasopharyngeal carcinoma patients, including 753 treated with 2D-CRT from Genetic Architecture of the Radiotherapy Toxicity and Prognosis (GARTP) cohort and 714 treated with IMRT (192 from the GARTP and 522 newly recruited). Subgroup analysis by radiotherapy technique was further performed in the top associations. We also performed physical and regulatory mapping of the risk loci and gene set enrichment analysis of the candidate target genes.

Results

We identified 50 associated genomic loci and 64 genes via positional mapping, expression quantitative trait locus (eQTL) mapping, chromatin interaction mapping and gene-based analysis, and 36 of these loci were replicated in subgroup analysis. Interestingly, one of the top loci located in TNKS, a gene relevant to radiation toxicity, was associated with increased OM risk with OR = 3.72 of the lead SNP rs117157809 (95% CI 2.10–6.57; P = 6.33 × 10⁻⁶). Gene set analyses showed that the 64 candidate target genes were enriched in the biological processes of regulating telomere capping and maintenance and telomerase activity (Top P = 7.73 × 10⁻⁷).

Conclusions

These results enhance the biological understanding of radiotherapy toxicity. The association signals enriched in telomere function regulation implicate the potential underlying mechanism and warrant further functional investigation and potential individual radiotherapy applications.

β-Arrestin1-mediated decrease in endoplasmic reticulum stress impairs intestinal stem cell proliferation following radiation

Gastrointestinal toxicity limits the clinical application of abdominal and pelvic radiotherapy and currently has no effective treatment. Intestinal leucine-rich-repeat-containing GPCR 5 (Lgr5)-positive stem cell depletion and loss of proliferative ability due to radiation may be the primary factors causing intestinal injury following radiation. Here, we report the critical role of β-arrestin1 (βarr1) in radiation-induced intestinal injury. Intestinal βarr1 was highly expressed in radiation enteritis and in a radiation model. βarr1 knockout (KO) or knockdown mice exhibited increased proliferation in intestinal Lgr5+ stem cell, crypt reproduction, and survival following radiation. Unexpectedly, the beneficial effects of βarr1 deficiency on intestinal stem cells in response to radiation were compromised when the endoplasmic reticulum stress-related protein kinase RNA-like ER kinase (PERK)/eukaryotic initiation factor-2α (eIF2α) pathway was inhibited, and this result was further supported in vitro. Furthermore, we found that βarr1 knockdown with small interfering RNA significantly enhanced intestinal Lgr5⁺ stem cell proliferation after radiation via directly targeting PERK. βarr1 offers a promising target for mitigating radiation-induced intestinal injury.-Liu, Z., Jiang, J., He, Q., Liu, Z., Yang, Z., Xu, J., Huang, Z., Wu, B. β-Arrestin1-mediated decrease in endoplasmic reticulum stress impairs intestinal stem cell proliferation following radiation.

A novel small-molecule antagonizes PRMT5-mediated KLF4 methylation for targeted therapy

Background

Triple negative breast cancers (TNBCs) have a poor prognosis and are not amenable to endocrine- or HER2-targeted therapies. The malignant and invasive feature of TNBCs is correlated with its high cancer stem cell population. Recent results from us and others have unveiled an oncogenic role for the PRMT5-KLF4 axis in regulating tumor progression by orchestrating the stemness in mammary tumor cell as well as genome stability. Methylation of KLF4 by PRMT5 leads to KLF4 stabilization, resulting in promoting mitogenesis.

Methods

We have developed a small molecule inhibitor, WX2–43, that specifically intercepts the interaction between PRMT5 and KLF4, thereby enhancing KLF4 degradation.

Findings

Results from our characterization demonstrate that WX2–43 binds to the region between amino acids L400-M500 on PRMT5. Degradation of KLF4 down-regulates KLF4-mediated genes transcription. We have characterized the potent effect for WX2–43 in inhibiting PRMT5-KLF4 binding that, in turns, suppresses tumor progression and induces tumor cell death in both TNBC cultured-cell and animal models.

Interpretation

WX2–43-mediated inhibition of KLF4 methylation by PRMT5 could be a potential strategy for anti-TNBC treatment.

Fund

This work was supported, in whole or in part, by National Institutes of Health grants CA202963 and CA202948 (Wan), R21HL109654 (Xie), P30DA035778 (Xie and Bahar) and P41GM103712 (Bahar).

The Role of Intestinal Stem Cells in Epithelial Regeneration Following Radiation-Induced Gut Injury

Purpose of Review

Intestinal epithelial cells show remarkable plasticity in regenerating the epithelium following radiation injury. In this review, we explore the regenerative capacity and mechanisms of various populations of intestinal stem cells (ISCs) in response to ionizing radiation.

Recent Findings

Ionizing radiation targets mitotic cells that include “active” ISCs and progenitor cells. Lineage-tracing experiments showed that several different cell types identified by a single or combination of markers are capable of regenerating the epithelium, confirming that ISCs exhibit a high degree of plasticity. However, the identities of the contributing cells marked by various markers require further validation.

Summary

Following radiation injury, quiescent and/or radioresistant cells become active stem cells to regenerate the epithelium. Looking forward, understanding the mechanisms by which ISCs govern tissue regeneration is crucial to determine therapeutic approaches to promote intestinal epithelial regeneration following injury.

SP and KLF Transcription Factors in Digestive Physiology and Diseases

Specificity proteins (SPs) and Krüppel-like factors (KLFs) belong to the family of transcription factors that contain conserved zinc finger domains involved in binding to target DNA sequences. Many of these proteins are expressed in different tissues and have distinct tissue-specific activities and functions. Studies have shown that SPs and KLFs regulate not only physiological processes such as growth, development, differentiation, proliferation, and embryogenesis, but pathogenesis of many diseases, including cancer and inflammatory disorders. Consistently, these proteins have been shown to regulate normal functions and pathobiology in the digestive system. We review recent findings on the tissue- and organ-specific functions of SPs and KLFs in the digestive system including the oral cavity, esophagus, stomach, small and large intestines, pancreas, and liver. We provide a list of agents under development to target these proteins.

FoxO3 increases miR-34a to cause palmitate-induced cholangiocyte lipoapoptosis

Nonalcoholic steatohepatitis (NASH) patients have elevated plasma saturated free fatty acid levels. These toxic fatty acids can induce liver cell death and our recent results demonstrated that the biliary epithelium may be susceptible to lipotoxicity. Here, we explored the molecular mechanisms of cholangiocyte lipoapoptosis in cell culture and in an animal model of NASH. Treatment of cholangiocytes with palmitate (PA) showed increased caspase 3/7 activity and increased levels of cleaved poly (ADP-ribose) polymerase and cleaved caspase 3, demonstrating cholangiocyte lipoapoptosis. Interestingly, treatment with PA significantly increased the levels of microRNA miR-34a, a pro-apoptotic microRNA known to be elevated in NASH. PA induction of miR-34a was abolished in cholangiocytes transduced with forkhead family of transcription factor class O (FoxO)3 shRNA, demonstrating that FoxO3 activation is upstream of miR-34a and suggesting that FoxO3 is a novel transcriptional regulator of miR-34a. Further, anti-miR-34a protected cholangiocytes from PA-induced lipoapoptosis. Direct and indirect targets of miR-34a, such as SIRT1, receptor tyrosine kinase (MET), Kruppel-like factor 4, fibroblast growth factor receptor (FGFR)1, and FGFR4, were all decreased in PA-treated cholangiocytes. SIRT1 and MET were partially rescued by a miR-34a antagonist. Cholangiocyte apoptosis and miR-34a were dramatically increased in the liver of mice with early histologic features of NASH. Our study provides evidence for the pro-apoptotic role of miR-34a in PA-induced cholangiocyte lipoapoptosis in culture and in the liver.

Krüppel-like factor 4 (KLF4): What we currently know

Krüppel-like factor 4 (KLF4) is an evolutionarily conserved zinc finger-containing transcription factor that regulates diverse cellular processes such as cell growth, proliferation, and differentiation. Since its discovery in 1996, KLF4 has been gaining a lot of attention, particularly after it was shown in 2006 as one of four factors involved in the induction of pluripotent stem cells (iPSCs). Here we review the current knowledge about the different functions and roles of KLF4 in various tissue and organ systems.

The role of gene mutations and gene products in intestinal tissue reactions from ionising radiation

The response of the intestine to (low linear-energy-transfer) ionising radiation is reviewed regarding the cellular basis to the reactions, the regenerative processes which restore the tissue, and external agents which aid its recovery. In the steady-state, it is generally considered that the crypt cell lineages in both small and large intestine are maintained by a small number of stem cells, but there are differences for example in the composition of their niche residence and in the numbers of transit cell generations. Various cell surface markers are now available to indentify particular lineage cell types. Radiation doses up to 1Gy cause apoptotic stem-cell death in particular locations, at higher doses to >6Gy Lgr5⁺ stem cells are required for normal intestinal recovery, and at >8Gy some crypts are sterilised and the probability of animal death from intestinal injury increases with higher doses. Mutations in repair genes, tumour suppressor genes, and survival genes cause various degrees of stem cell and clonogenic cell radiosensitisation. Recent evidence is suggesting much plasticity in the crypt cell lineage, potentially contributing to flexibility in the hierarchical lineage, clonogen number variations and the sensitisation differences. Knockout mice for many different genes have been used to detect their role in both steady state and in irradiated conditions, expected to lead to further insight to the damage and restorative processes. Many different external agents have been used to ameliorate intestinal reactions, including prostaglandins, interleukins, angiogenic and epithelial growth factors, other cytokines, and intraluminal factors.

Krüppel-like Factor 4 Modulates Development of BMI1(+) Intestinal Stem Cell-Derived Lineage Following γ-Radiation-Induced Gut Injury in Mice

In response to ionizing radiation-induced injury, the normally quiescent intestinal stem cells marked by BMI1 participate in the regenerative response. Previously, we established a protective role for Krüppel-like factor 4 (KLF4) in the intestinal epithelium where it reduces senescence, apoptosis, and crypt atrophy following γ-radiation-induced gut injury. We also described a pro-proliferative function for KLF4 during the regenerative phase post irradiation. In the current study, using a mouse model in which Klf4 is deleted from quiescent BMI1⁺ intestinal stem cells, we observed increased proliferation from the BMI1⁺ lineage during homeostasis. In contrast, following irradiation, Bmi1-specific Klf4 deletion leads to decreased expansion of the BMI1⁺ lineage due to a combination of reduced proliferation and increased apoptosis. Our results support a critical role for KLF4 in modulating BMI1⁺ intestinal stem cell fate in both homeostasis and the regenerative response to radiation injury.

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KLF4 is expressed in a subpopulation of quiescent BMI1⁺ intestinal stem cells (ISCs)

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KLF4 restricts BMI1⁺ ISC proliferation at homeostasis

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KLF4 promotes expansion of the BMI1⁺ lineage during radiation-induced regeneration

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KLF4 exerts context-dependent activity in modulating BMI1⁺ ISC fate

Kruppel-like Pluripotency Factors as Modulators of Cancer Cell Therapeutic Responses

Tumor cells inherit from their normal precursors an extensive stress response machinery that is critical for survival in response to challenges including oxidative stress, wounding, and shear stress. Kruppel-like transcription factors, including KLF4 and KLF5, are rarely affected by genetic alteration during tumorigenesis, but compose key components of the stress response machinery in normal and tumor cells and interact with critical survival pathways, including RAS, p53, survivin, and the BCL2 family of cell death regulators. Within tumor cells, KLF4 and KLF5 play key roles in tumor cell fate, regulating cell proliferation, cell survival, and the tumor-initiating properties of cancer stem-like cells. These factors can be preferentially expressed in embryonic stem cells or cancer stem-like cells. Indeed, specific KLFs represent key components of a cross-regulating pluripotency network in embryonic stem cells and induce pluripotency when coexpressed in adult cells with other Yamanaka factors. Suggesting analogies between this pluripotency network and the cancer cell adaptive reprogramming that occurs in response to targeted therapy, recent studies link KLF4 and KLF5 to adaptive prosurvival signaling responses induced by HER2-targeted therapy. We review literature supporting KLFs as shared mechanisms in stress adaptation and cellular reprogramming and address the therapeutic implications. Cancer Res; 76(7); 1677-82. ©2016 AACR.

KLF4 Is Essential for Induction of Cellular Identity Change and Acinar-to-Ductal Reprogramming during Early Pancreatic Carcinogenesis

Understanding the molecular mechanisms of tumor initiation has significant impact on early cancer detection and intervention. To define the role of KLF4 in pancreatic ductal adenocarcinoma (PDA) initiation, we used molecular biological analyses and mouse models of klf4 gain- and loss-of-function and mutant Kras. KLF4 is upregulated in and required for acinar-to-ductal metaplasia. Klf4 ablation drastically attenuates the formation of pancreatic intraepithelial neoplasia induced by mutant Kras(G12D), whereas upregulation of KLF4 does the opposite. Mutant KRAS and cellular injuries induce KLF4 expression, and ectopic expression of KLF4 in acinar cells reduces acinar lineage- and induces ductal lineage-related marker expression. These results demonstrate that KLF4 induces ductal identity in PanIN initiation and may be a potential target for prevention of PDA initiation.

Novel regenerative peptide TP508 mitigates radiation-induced gastrointestinal damage by activating stem cells and preserving crypt integrity

In recent years, increasing threats of radiation exposure and nuclear disasters have become a significant concern for the United States and countries worldwide. Exposure to high doses of radiation triggers a number of potentially lethal effects. Among the most severe is the gastrointestinal (GI) toxicity syndrome caused by the destruction of the intestinal barrier, resulting in bacterial translocation, systemic bacteremia, sepsis, and death. The lack of effective radioprotective agents capable of mitigating radiation-induced damage has prompted a search for novel countermeasures that can mitigate the effects of radiation post exposure, accelerate tissue repair in radiation-exposed individuals, and prevent mortality. We report that a single injection of regenerative peptide TP508 (rusalatide acetate, Chrysalin) 24 h after lethal radiation exposure (9 Gy, LD100/15) appears to significantly increase survival and delay mortality by mitigating radiation-induced intestinal and colonic toxicity. TP508 treatment post exposure prevents the disintegration of GI crypts, stimulates the expression of adherens junction protein E-cadherin, activates crypt cell proliferation, and decreases apoptosis. TP508 post-exposure treatment also upregulates the expression of DCLK1 and LGR5 markers of stem cells that have been shown to be responsible for maintaining and regenerating intestinal crypts. Thus, TP508 appears to mitigate the effects of GI toxicity by activating radioresistant stem cells and increasing the stemness potential of crypts to maintain and restore intestinal integrity. These results suggest that TP508 may be an effective emergency nuclear countermeasure that could be delivered within 24 h post exposure to increase survival and delay mortality, giving victims time to reach clinical sites for advanced medical treatment.

Regulation of anti-apoptotic signaling by Kruppel-like factors 4 and 5 mediates lapatinib resistance in breast cancer

The Kruppel-like transcription factors (KLFs) 4 and 5 (KLF4/5) are coexpressed in mouse embryonic stem cells, where they function redundantly to maintain pluripotency. In mammary carcinoma, KLF4/5 can each impact the malignant phenotype, but potential linkages to drug resistance remain unclear. In primary human breast cancers, we observed a positive correlation between KLF4/5 transcript abundance, particularly in the human epidermal growth factor receptor 2 (HER2)-enriched subtype. Furthermore, KLF4/5 protein was rapidly upregulated in human breast cancer cells following treatment with the HER2/epidermal growth factor receptor inhibitor, lapatinib. In addition, we observed a positive correlation between these factors in the primary tumors of genetically engineered mouse models (GEMMs). In particular, the levels of both factors were enriched in the basal-like tumors of the C3(1) TAg (SV40 large T antigen transgenic mice under control of the C3(1)/prostatein promoter) GEMM. Using tumor cells derived from this model as well as human breast cancer cells, suppression of KLF4 and/or KLF5 sensitized HER2-overexpressing cells to lapatinib. Indicating cooperativity, greater effects were observed when both genes were depleted. KLF4/5-deficient cells had reduced basal mRNA and protein levels of the anti-apoptotic factors myeloid cell leukemia 1 (MCL1) and B-cell lymphoma-extra large (BCL-XL). Moreover, MCL1 was upregulated by lapatinib in a KLF4/5-dependent manner, and enforced expression of MCL1 in KLF4/5-deficient cells restored drug resistance. In addition, combined suppression of KLF4/5 in cultured tumor cells additively inhibited anchorage-independent growth, resistance to anoikis and tumor formation in immunocompromised mice. Consistent with their cooperative role in drug resistance and other malignant properties, KLF4/5 levels selectively stratified human HER2-enriched breast cancer by distant metastasis-free survival. These results identify KLF4 and KLF5 as cooperating protumorigenic factors and critical participants in resistance to lapatinib, furthering the rationale for combining anti-MCL1/BCL-XL inhibitors with conventional HER2-targeted therapies.

Role of Krüppel-like factor 5 in the maintenance of the stem cell niche in the intestinal crypt

The intestinal epithelium is a tissue that undergoes continuous self-renewal initiated at the bottom of the crypts, which harbor the intestinal stem cell (ISC) pool. The ISC pool is sub-divided into crypt base columnar (CBC) cells at the crypt bottom and label retention cells (LRC) at position +4 from the crypt bottom. CBC cells are marked by Leucine-rich repeat-containing G-protein coupled receptor (Lgr5) while LRC cells are identified by several markers including Bmi1, mTert, Hopx, Lrig1, and Sox9. Krüppel-like factors (KLFs) belong to a family of transcription factors that exert important physiological function in various tissues. In the intestine, KLF4 is predominantly expressed in the terminally differentiated, non-proliferating cells lining the villus. Its deletion in the adult mouse intestine results in perturbed homeostasis. In contrast, KLF5 is expressed in actively proliferating cells of the intestinal crypt, including CBC cells and transit amplifying (TA) cells. We recently investigated the effect of Klf5 deletion specifically from the Lgr5-expressing CBC cells in adult mouse intestine using an inducible Cre recombinase system. Shortly (3-5 days) after Cre induction, proliferation of both CBC and TA cells ceased, which was accompanied by an increase in apoptosis in the crypt. Beginning at two weeks following Cre induction, both Klf5 expression and proliferation re-appeared but without the re-emergence of Lgr5-positive CBC cells, which were eventually depleted by four months following induction. These findings indicate that KLF5 plays an important role in regulating proliferation and survival of CBC stem cells in the intestine.