Marie-Pier Tetreault

Krüppel-like factors in cancer

Krüppel-like factors (KLFs) are a family of DNA-binding transcriptional regulators with diverse and essential functions in a multitude of cellular processes, including proliferation, differentiation, migration, inflammation and pluripotency. In this Review, we discuss the roles and regulation of the 17 known KLFs in various cancer-relevant processes. Importantly, the functions of KLFs are context dependent, with some KLFs having different roles in normal cells and cancer, during cancer development and progression and in different cancer types. We also identify key questions for the field that are likely to lead to important new translational research and discoveries in cancer biology.

Krüppel-like Factor 5 Controls Keratinocyte Migration via the Integrin-linked Kinase

Migration of epithelial cells is critical for normal homeostasis in gut and skin, but the factors regulating this process are not completely understood. The zinc finger transcription factor Klf5 (IKLF; BTEB2) is highly expressed in proliferating cells of esophagus, skin, and other organs. We hypothesized that Klf5 regulates keratinocyte migration via the integrin-linked kinase (ILK), which, like Klf5, is localized to basal keratinocytes. We stably transduced mouse primary esophageal keratinocytes to overexpress Klf5 or small interfering RNA against Klf5. Klf5 overexpression in keratinocytes increased migration and correlated directly with ILK expression and activation. ILK expression restored migratory capacity in keratinocytes with suppression of Klf5, whereas ILK small interfering RNA blocked the increased migration resulting from Klf5 overexpression. By chromatin immunoprecipitation, electromobility shift assay, and luciferase reporter assays, we confirmed that ILK was a direct target for Klf5. In addition, Klf5 induced the activation of the ILK targets Cdc42 and myosin light chain, which are critical for cell migration and motility but not Rac1, AKT, or GSK3β. Overall, these results demonstrate that Klf5 is a key regulator of cell migration via ILK and provide new insight into the regulation of epithelial cell migration.

Esophageal Squamous Cell Dysplasia and Delayed Differentiation With Deletion of Krüppel-Like Factor 4 in Murine Esophagus

BACKGROUND & AIMS Krüppel-like factor 4 (Klf; previously known a gut-enriched Krüppel-like factor) is a DNA-binding transcriptional regulator highly expressed in skin and gastrointestinal epithelia, specifically in regions of cellular differentiation. Homozygous null mice for Klf4 die shortly after birth from skin defects, precluding their analysis at later stages. The aim of this study was to analyze the function of Klf4 in keratinocyte biology and epithelial homeostasis in the adult by focusing on the squamous lined esophagus. METHODS By using the ED-L2 promoter of Epstein-Barr virus to drive Cre, we obtained tissue-specific ablation of Klf4 in the squamous epithelia of the tongue, esophagus, and forestomach. RESULTS Mice with loss of Klf4 in esophageal epithelia survived to adulthood, bypassing the early lethality. Tissue-specific Klf4 knockout mice had increased basal cell proliferation and a delay in cellular maturation; these mice developed epithelial hypertrophy and subsequent dysplasia by 6 months of age. Moreover, loss of Klf4 in vivo was associated with increased expression of the pro-proliferative Klf5, and Klf4 down-regulated Klf5 both transcriptionally and posttranscriptionally. By using gene expression profiling, we also showed decreased expression of critical late-stage differentiation factors and identified alterations of several genes important in cellular differentiation. CONCLUSIONS Klf4 is essential for squamous epithelial differentiation in vivo and interacts with Klf5 to maintain normal epithelial homeostasis.

Differential Secreted Proteome Approach in Murine Model for Candidate Biomarker Discovery in Colon Cancer

The complexity and heterogeneity of the plasma proteome have presented significant challenges in the identification of protein changes associated with tumor development. We used cell culture as a model system and identified differentially expressed, secreted proteins which may constitute serological biomarkers. A stable isotope labeling by amino acids in cell culture (SILAC) approach was used to label the entire secreted proteomes of the CT26 murine colon cancer cell line and normal young adult mouse colon (YAMC) cell line, thereby creating a stable isotope labeled proteome (SILAP) standard. This SILAP standard was added to unlabeled murine CT26 colon cancer cell or normal murine YAMC colon epithelial cell secreted proteome samples. A multidimensional approach combining isoelectric focusing (IEF), strong cation exchange (SCX) followed by reversed phase liquid chromatography was used for extensive protein and peptide separation. A total of 614 and 929 proteins were identified from the YAMC and CT26 cell lines, with 418 proteins common to both cell lines. Twenty highly abundant differentially expressed proteins from these groups were selected for liquid chromatography-multiple reaction monitoring/mass spectrometry (LC-MRM/MS) analysis in sera. Differential secretion into the serum was observed for several proteins when Apc(min) mice were compared with control mice. These findings were then confirmed by Western blot analysis.

Klf4 Overexpression Activates Epithelial Cytokines and Inflammation-Mediated Esophageal Squamous Cell Cancer in Mice

BACKGROUND & AIMS Esophageal squamous cell cancer accounts for more than 90% of cases of esophageal cancers. Its pathogenesis involves chronic epithelial irritation, although the factors involved in the inflammatory process and the mechanisms of carcinogenesis are unknown. We sought to develop a mouse model of this cancer. METHODS We used the ED-L2 promoter of Epstein-Barr virus to overexpress the transcriptional regulator Krüppel-like factor 4 (Klf4) in esophageal epithelia of mice; we used mouse primary esophageal keratinocytes to examine the mechanisms by which KLF4 induces cytokine production. RESULTS KLF4 was an epithelial-specific mediator of inflammation; we developed a new mouse model of esophageal squamous dysplasia and inflammation-mediated squamous cell cancer. KLF4 activated a number of proinflammatory cytokines, including TNF-α, CXCL5, G-CSF and IL-1α, within keratinocytes in an NF-κB-dependent manner. KLF4 was not detected in proliferating or cancer cells, indicating a non-cell autonomous effect of KLF4 on proliferation and carcinogenesis. CONCLUSIONS KLF4 has distinct functions in carcinogenesis; upregulation of Klf4 specifically in esophageal epithelial cells induces inflammation. This mouse model might be used to determine the molecular mechanisms of esophageal squamous cell cancer and inflammation-mediated carcinogenesis.

Loss of transcription factor KLF5 in the context of p53 ablation drives invasive progression of human squamous cell cancer

Squamous cell cancers account for more than half of all human cancers, and esophageal cancer is the sixth leading cause of cancer death worldwide. The majority of esophageal squamous cell carcinomas have identifiable p53 mutations, yet the same p53 mutations are found at comparable frequencies in precancerous dysplasia, indicating that transformation requires additional somatic changes yet to be defined. Here, we show that the zinc finger transcription factor Krüppel-like factor 5 (KLF5) transactivates NOTCH1 in the context of p53 mutation or loss. KLF5 loss limited NOTCH1 activity and was sufficient on its own to transform primary human keratinocytes harboring mutant p53, leading to the formation of invasive tumors. Restoration of NOTCH1 blocked transformation of KLF5-deficient and p53-mutant keratinocytes. Although human dysplastic epithelia accumulated KLF5, KLF5 expression was lost concurrently with NOTCH1 in squamous cell cancers. Taken together, these results define KLF5 loss as a critical event in squamous cell transformation and invasion. Our findings suggest that KLF5 may be a useful diagnostic and therapeutic target in esophageal squamous carcinomas and possibly more generally in other cancers associated with p53 loss of function.

Epidermal growth factor receptor‐dependent PI3K‐activation promotes restitution of wounded human gastric epithelial monolayers

Restitution is a crucial event during the healing of superficial injury of the gastric mucosa involving epithelial cell sheet movement into the damaged area. We demonstrated that growth factors promote the restitution of human gastric epithelial cells. However, the intracellular signaling pathways that transmit extracellular cues as well as regulate basal and growth factor‐stimulated gastric epithelial cell migration are still unclear. Herein, confluent human gastric epithelial cell monolayers (HGE‐17) or primary cultures of gastric epithelial cells were wounded with a razor blade and the migration response was analyzed in presence or absence of TGFα or of pharmacological inhibitors of signaling proteins. Kinase activation profile analysis and phase‐contrast microscopy were also performed in parallel. We report that ERK1/2 and Akt activities are rapidly stimulated following wounding of HGE‐17 cells. Treatment of confluent HGE‐17 cells or primary cultures of gastric epithelial cells with the phosphatidylinositol 3‐kinase inhibitor LY294002, but not the MEK1 inhibitor, PD98059, significantly inhibits basal and TGFα‐induced migration following wounding. Conversely, treatment of wounded HGE‐17 cells with phosphatidylinositol(3,4,5)‐triphosphate is sufficient to stimulate basal cell migration by 235%. In addition, pp60c‐src kinase activity and tyrosine phosphorylation of epidermal growth factor receptors (EGFR) are also rapidly enhanced after wounding and pharmacological inhibition of both these activities strongly attenuates basal and TGFα‐induced migration as well as Akt phosphorylation levels. In conclusion, the present results indicate that EGFR‐dependent PI3K activation promotes restitution of wounded human gastric epithelial monolayers. J. Cell. Physiol. 214: 545–557, 2008.

WNT10A promotes an invasive and self-renewing phenotype in esophageal squamous cell carcinoma

Esophageal cells overexpressing epidermal growth factor receptor (EGFR) and TP53 mutation can invade into the extracellular matrix when grown in 3D-organotypic cultures (OTC) and mimic early invasion in esophageal squamous cell carcinoma (ESCC). We have performed laser capture microdissection with RNA microarray analysis on the invasive and non-invasive tumor cells of p53(R175H)-overexpressing OTC samples to determine candidate genes facilitating tumor invasion. WNT10A was found to be >4-fold upregulated in the invasive front. Since WNT10A is also prominently upregulated during placode promotion in hair follicle development, a process that requires epithelial cells to thicken and elongate, in order to allow downward growth, we hypothesized that WNT10A may be important in mediating a similar mechanism of tumor cell invasion in ESCC. We have found that WNT10A expression is significantly upregulated in human ESCC, when compared with normal adjacent tissue. Furthermore, high WNT10A expression levels correlate with poor survival. Interestingly, we observe that WNT10A is expressed early in embryogenesis, but is reduced dramatically postnatally. We demonstrate that overexpression of WNT10a promotes migration and invasion, and proliferation of transformed esophageal cells. Lastly, we show that WNT10A overexpression induces a greater CD44(High)/CD24(Low) population, which are putative markers of cancer stem cells, and increases self-renewal capability. Taken together, we propose that WNT10A acts as an oncofetal factor that is highly expressed and may promote proper development of the esophagus. During tumorigenesis, it is aberrantly overexpressed in order to promote ESCC migration and invasion, and may be linked to self-renewal of a subset of ESCC cells.

Specific signaling cascades involved in cell spreading during healing of micro-wounded gastric epithelial monolayers.

Mechanisms that specifically modulate cell spreading and/or cell migration following epithelial wounding are poorly understood. Using micro‐wounded human gastric epithelial monolayers, we show herein that EGF and TGFα maximally increase spreading of epithelial sheets under a cell proliferation‐independent mechanism. Treatment of confluent HGE‐17 cells with the phosphatidylinositol 3‐kinase inhibitor, LY294002, and the epidermal growth factor receptor inhibitor, PD153035, strongly reduced basal and TGFα‐stimulated cell spreading. While pharmacological inhibition of pp60src‐kinase activity also attenuated basal epithelial spreading, addition of the mTOR/p70S6K inhibitor rapamycin or a specific siRNA targeting ILK sequence did not affect the kinetic rates of wound closure. Epithelial wound healing was initiated by actin purse‐string contraction followed by lamellae formation. Conversely, disruption of actin and tubulin stability with cytochalasin D and nocodazole, respectively, inhibited epithelial sheet spreading. Finally, antibodies directed against the α3 integrin subunit, but not against the α6 or α2 subunits, attenuated epithelial sheet spreading as well as lamellae formation. In conclusion, the current investigation establishes that EGF/TGFα and the α3β1 integrin, pp60c‐src, EGFR and PI3K pathways are mainly associated with the cell spreading of the restitution process during healing of human gastric epithelial wounds. J. Cell. Biochem. 105: 1240–1249, 2008.

Krüppel-like factor 5 protects against murine colitis and activates JAK-STAT signaling in vivo.

Inflammatory bowel disease (IBD), which is characterized by chronic or recurring inflammation of the gastrointestinal tract, affects 1.4 million persons in the United States alone. KLF5, a Krüppel-like factor (KLF) family member, is expressed within the epithelia of the gastrointestinal tract and has been implicated in rapid cell proliferation, migration, and remodeling in a number of tissues. Given these functions, we hypothesized that constitutive Klf5 expression would protect against the development of colitis in vivo. To examine the role of KLF5 in vivo, we used the Villin promoter to target Klf5 to the entire horizontal axis of the small intestine and colon. Villin-Klf5 transgenic mice were born at normal Mendelian ratios and appeared grossly normal to at least 1 year of age. Surprisingly, there were no significant changes in cell proliferation or in the differentiation of any of the intestinal lineages within the duodenum, jejunum, ileum, and colon of Villin-Klf5 mice, compared to littermate controls. However, when Villin-Klf5 mice were treated with dextran sodium sulfate (DSS) to induce colitis, they developed less colonic injury and significantly reduced disease activity scores than littermate controls. The mechanism for this decreased injury may come via JAK-STAT signaling, the activation of which was increased in colonic mucosa of DSS treated Villin-Klf5 mice compared to controls. Thus, KLF5 and its downstream mediators may provide therapeutic targets and disease markers for IBD or other diseases characterized by injury and disruption of intestinal epithelia.