Ets2 regulates colonic stem cells and sensitivity to tumorigenesis.

Ets2 has both tumor repressive and supportive functions for different types of cancer. We have investigated the role of Ets2 within intestinal epithelial cells in postnatal mouse colon development and tumorigenesis. Conditional inactivation of Ets2 within intestinal epithelial cells results in over representation of Ets2-deficient colon crypts within young and adult animals. This preferential representation is associated with an increased number of proliferative cells within the stem cell region and an increased rate of crypt fission in young mice that result in larger patches of Ets2-deficient crypts. These effects are consistent with a selective advantage of Ets2-deficient intestinal stem cells in colonizing colonic crypts and driving crypt fission. Ets2-deficient colon crypts have an increased mucosal thickness, an increased number of goblet cells, and an increased density. Mice with Ets2-deficient intestinal cells develop more colon tumors in response to treatment with azoxymethane and dextran sulfate sodium. The selective population of colon crypts, the altered differentiation state and increased sensitivity to carcinogen-induced tumors all indicate that Ets2 deficiency alters colon stem cell number or behavior. Ets2-dependent, epithelial cell-autonomous repression of intestinal tumors may contribute to protection from colon cancer of persons with increased dosage of chromosome 21.

Contrasting expression of keratins in mouse and human embryonic stem cells.

RNA expression data reveals that human embryonic stem (hES) cells differ from mouse ES (mES) cells in the expression of RNAs for keratin intermediate filament proteins. These differences were confirmed at the cellular and protein level and may reflect a fundamental difference in the epithelial nature of embryonic stem cells derived from mouse and human blastocysts. Mouse ES cells express very low levels of the simple epithelial keratins K8, K18 and K19. By contrast hES cells express moderate levels of the RNAs for these intermediate filament proteins as do mouse stem cells derived from the mouse epiblast. Expression of K8 and K18 RNAs are correlated with increased c-Jun RNA expression in both mouse and human ES cell cultures. However, decreasing K8 and K18 expression associated with differentiation to neuronal progenitor cells is correlated with increasing expression of the Snai2 (Slug) transcriptional repression and not decreased Jun expression. Increasing K7 expression is correlated with increased CDX2 and decreased Oct4 RNA expression associated with the formation of trophoblast derivatives by hES cells. Our study supports the view that hES cells are more similar to mouse epiblast cells than mouse ES cells and is consistent with the epithelial nature of hES cells. Keratin intermediate filament expression in hES cells may modulate sensitivity to death receptor mediated apoptosis and stress.

Ets2 is required for trophoblast stem cell self-renewal.

The Ets2 transcription factor is essential for the development of the mouse placenta and for generating signals for embryonic mesoderm and axis formation. Using a conditional targeted Ets2 allele, we show that Ets2 is essential for trophoblast stem (TS) cells self-renewal. Inactivation of Ets2 results in TS cell slower growth, increased expression of a subset of differentiation-associated genes and decreased expression of several genes implicated in TS self-renewal. Among the direct TS targets of Ets2 is Cdx2, a key master regulator of TS cell state. Thus Ets2 contributes to the regulation of multiple genes important for maintaining the undifferentiated state of TS cells and as candidate signals for embryonic development.

Differential sensitivity of mouse epithelial tissues to the polyomavirus middle T oncogene.

To determine how different epithelial cell types respond to the same oncogenic stimulation, we have used a modified human keratin 18 gene to conditionally express the polyomavirus middle T antigen (PyMT) oncogene in simple epithelial tissues of transgenic mice. Activation of PyMT expression by transgenic Cre recombinase in mammary epithelial cells resulted in carcinomas in all bitransgenic females. PyMT expression induced by K18-driven Cre in internal epithelial organs resulted in pancreatic acinar metaplasia and ductal dysplasia with remarkable desmoplastic stromal responses in all 25 bitransgenic mice. Hepatoma formation with altered lipid metabolism and gastric adenocarcinoma occurred in 96 and 54% of these mice, respectively. Elevated PyMT RNA expression also correlated with intraepithelial neoplasia in the prostate. Activated Erk2 was found in mammary tumors, pancreatic tissues, and affected livers. Hes1 RNA, a target of Notch signaling that has been implicated downstream of Ras pathway activation, was elevated in pancreatic and liver lesions. The variety of responses of different epithelia to PyMT demonstrates the importance of the differentiated state in interpreting oncogenic signals.

Expression of conditional cre recombinase in epithelial tissues of transgenic mice.

SUMMARY: Keratin 18 (K18) expression is a defining characteristic of internal epithelial cells of mammals. Here, we used the K18 gene and an internal ribosome entry site (IRES) to express green fluorescent protein, human placental alkaline phosphatase, and a modified Cre recombinase in an epithelial specific pattern in transgenic mice. The K18-driven alkaline phosphatase was expressed in liver, kidney, uterine endometrium, and other internal epithelia. The enzymatic activity of the Cre recombinase-mutant estrogen receptor fusion protein was dependent on tamoxifen administration and resulted in a mosaic pattern in internal epithelia, including bladder, uterus, liver, and kidney. This conditional Cre activity in internal epithelial organs should be valuable for strategies utilizing Cre for activation of gene expression. This study demonstrates that the tissue-specific, position-independent transcriptional activity of the K18 gene is not compromised by the use of an IRES element for the expression of a second protein from a bicistronic mRNA.