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.

Control of mammary tumor differentiation by SKI-606 (bosutinib).

C-Src is infrequently mutated in human cancers but it mediates oncogenic signals of many activated growth factor receptors and thus remains a key target for cancer therapy. However, the broad function of Src in many cell types and processes requires evaluation of Src-targeted therapeutics within a normal developmental and immune-competent environment. In an effort to understand the appropriate clinical use of Src inhibitors, we tested an Src inhibitor, SKI-606 (bosutinib), in the MMTV-PyVmT transgenic mouse model of breast cancer.

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.

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.

Transcriptional repressor erf determines extraembryonic ectoderm differentiation.

Extraembryonic ectoderm differentiation and chorioallantoic attachment are fibroblast growth factor (FGF)- and transforming growth factor beta-regulated processes that are the first steps in the development of the placenta labyrinth and the establishment of the fetal-maternal circulation in the developing embryo. Only a small number of genes have been demonstrated to be important in trophoblast stem cell differentiation. Erf is a ubiquitously expressed Erk-regulated, ets domain transcriptional repressor expressed throughout embryonic development and adulthood.

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.

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

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.

Alu sequence involvement in transcriptional insulation of the keratin 18 gene in transgenic mice.

The human keratin 18 (K18) gene is expressed in a variety of adult simple epithelial tissues, including liver, intestine, lung, and kidney, but is not normally found in skin, muscle, heart, spleen, or most of the brain. Transgenic animals derived from the cloned K18 gene express the transgene in appropriate tissues at levels directly proportional to the copy number and independently of the sites of integration. We have investigated in transgenic mice the dependence of K18 gene expression on the distal 5' and 3' flanking sequences and upon the RNA polymerase III promoter of an Alu repetitive DNA transcription unit immediately upstream of the K18 promoter.

Transcriptional insulation of the human keratin 18 gene in transgenic mice.

Expression of the 10-kb human keratin 18 (K18) gene in transgenic mice results in efficient and appropriate tissue-specific expression in a variety of internal epithelial organs, including liver, lung, intestine, kidney, and the ependymal epithelium of brain, but not in spleen, heart, or skeletal muscle. Expression at the RNA level is directly proportional to the number of integrated K18 transgenes. These results indicate that the K18 gene is able to insulate itself both from the commonly observed cis-acting effects of the sites of integration and from the potential complications of duplicated copies of the gene arranged in head-to-tail fashion.

Posttranslational regulation of keratins: degradation of mouse and human keratins 18 and 8.

Human keratin 18 (K18) and keratin 8 (K8) and their mouse homologs, Endo B and Endo A, respectively, are expressed in adult mice primarily in a variety of simple epithelial cell types in which they are normally found in equal amounts within the intermediate filament cytoskeleton. Expression of K18 alone in mouse L cells or NIH 3T3 fibroblasts from either the gene or a cDNA expression vector results in K18 protein which is degraded relatively rapidly without the formation of filaments. A K8 cDNA containing all coding sequences was isolated and expressed in mouse fibroblasts either singly or in combination with K18.

Identification of the gene coding for the Endo B murine cytokeratin and its methylated, stable inactive state in mouse nonepithelial cells.

The Endo B type-I keratin intermediate filament protein is first expressed at the 4- to 8-cell stage of mouse development. In the adult, its expression is restricted to a variety of simple epithelial cell types. To investigate the mechanisms responsible for the restricted expression of Endo B, the gene coding for Endo B has been identified from among the five different Endo B genes found in the mouse genome by Southern hybridization analysis and cloning all or part of four of the genes.

Comparison of mouse and human keratin 18: a component of intermediate filaments expressed prior to implantation.

Keratin 18 is a type-I keratin that is found in a variety of simple epithelial tissues. In mice, the corresponding protein, called Endo B, is expressed at the 4- to 8-cell stage of mouse development and may be one of the first intermediate-filament proteins synthesized after fertilization. A cDNA clone for keratin 18, designated pK18, was isolated from a human placental cDNA library by hybridization with the mouse Endo-B probe.