Barrett's Esophagus: Emerging Knowledge and Management Strategies

The incidence of esophageal adenocarcinoma (EAC) has increased exponentially in the last 3 decades. Barrett's esophagus (BE) is the only known precursor of EAC. Patients with BE have a greater than 40 folds higher risk of EAC compared with the general population. Recent years have witnessed a revolution in the clinical and molecular research related to BE. However, several aspects of this condition remain controversial. Data regarding the true prevalence of BE have varied widely. Recent studies have suggested a lower incidence of EAC in nondysplastic BE (NDBE) than previously reported. There is paucity of prospective data showing a survival benefit of screening or surveillance for BE. Furthermore, the ever-increasing emphasis on healthcare cost containment has called for reexamination of the screening and surveillance strategies for BE. There is a need for identification of reliable clinical predictors or molecular biomarkers to risk-stratify patients who might benefit the most from screening or surveillance for BE. Finally, new therapies have emerged for the management of dysplastic BE. In this paper, we highlight the key areas of controversy and uncertainty surrounding BE. The paper discusses, in detail, the current literature about the molecular pathogenesis, biomarkers, histopathological diagnosis, and management strategies for BE

p120-Catenin Down-Regulation and Epidermal Growth Factor Receptor Overexpression Results in a Transformed Epithelium That Mimics Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is an aggressive malignancy with a poor prognosis due to its highly invasive and metastatic potential. The molecular pathogenesis underlying the invasive mechanism of ESCC is not well known because of the lack of existing models to study this disease. p120-Catenin (p120ctn) and the epidermal growth factor receptor (EGFR) have each been implicated in several cancers, including ESCC. p120ctn is down-regulated in 60% of ESCC tumors, whereas EGFR is the most commonly overexpressed oncogene in ESCC. For these reasons, we investigated the cooperation between p120ctn and EGFR and its effect on ESCC invasion. We show that p120ctn down-regulation is commonly associated with EGFR overexpression. By using a three-dimensional culture system, we demonstrate that the inverse relationship between p120ctn and EGFR has biological implications. Specifically, p120ctn down-regulation coupled with EGFR overexpression in human esophageal keratinocytes (EPC1-PE) was required to promote invasion. Morphological comparison of EPC1-PE cells grown in three-dimensional culture and human ESCC revealed identical features, including significantly increased cellularity, nuclear grade, and proliferation. Molecular characteristics were measured by keratin expression patterns, which were nearly identical between EPC1-PE cells in three-dimensional culture and ESCC samples. Altogether, our analyses have demonstrated that p120ctn down-regulation and EGFR overexpression are able to mimic human ESCC in a relevant three-dimensional culture model

Cdx1 and c-Myc Foster the Initiation of Transdifferentiation of the Normal Esophageal Squamous Epithelium toward Barrett's Esophagus

Barrett's esophagus is a premalignant condition whereby the normal stratified squamous esophageal epithelium undergoes a transdifferentiation program resulting in a simple columnar epithelium reminiscent of the small intestine. These changes are typically associated with the stratified squamous epithelium chronically exposed to acid and bile salts as a result of gastroesophageal reflux disease (GERD). Despite this well-defined epidemiologic association between acid reflux and Barrett's esophagus, the genetic changes that induce this transdifferentiation process in esophageal keratinocytes have remained undefined.To begin to identify the genetic changes responsible for transdifferentiaiton in Barrett's esophagus, we performed a microarray analysis of normal esophageal, Barrett's esophagus and small intestinal biopsy specimens to identify candidate signaling pathways and transcription factors that may be involved. Through this screen we identified the Cdx1 homeodomain transcription factor and the c-myc pathway as possible candidates. Cdx1 and c-myc were then tested for their ability to induce transdifferentiation in immortalized human esophageal keratinocytes using organotypic culturing methods. Analyses of these cultures reveal that c-myc and cdx1 cooperate to induce mucin production and changes in keratin expression that are observed in the epithelium of Barrett's esophagus.These data demonstrate the ability of Cdx1 and c-myc to initiate the earliest stages of transdifferentiation of esophageal keratinocytes toward a cell fate characteristic of Barrett's esophagus

Isoform-specific requirement for Akt1 in the developmental regulation of cellular metabolism during lactation

SummaryThe metabolic demands and synthetic capacity of the lactating mammary gland exceed that of any other tissue, thereby providing a useful paradigm for understanding the developmental regulation of cellular metabolism. By evaluating mice bearing targeted deletions in Akt1 or Akt2, we demonstrate that Akt1 is specifically required for lactating mice to synthesize sufficient quantities of milk to support their offspring. Whereas cellular proliferation, differentiation, and apoptosis are unaffected, loss of Akt1 disrupts the coordinate regulation of metabolic pathways that normally occurs at the onset of lactation. This results in a failure to upregulate glucose uptake, Glut1 surface localization, lipid synthesis, and multiple lipogenic enzymes, as well as a failure to downregulate lipid catabolic enzymes. These findings demonstrate that Akt1 is required in an isoform-specific manner for orchestrating many of the developmental changes in cellular metabolism that occur at the onset of lactation and establish a role for Akt1 in glucose metabolism

SOX2 is an amplified lineage-survival oncogene in lung and esophageal squamous cell carcinomas

Lineage survival oncogenes are activated by somatic DNA alterations in cancers arising from the cell lineages in which these genes play a role in normal development.1,2 Here we show that a peak of genomic amplification on chromosome 3q26.33, found in squamous cell carcinomas (SCCs) of the lung and esophagus, contains the transcription factor gene SOX2—which is mutated in hereditary human esophageal malformations3 and necessary for normal esophageal squamous development4, promotes differentiation and proliferation of basal tracheal cells5 and co-operates in induction of pluripotent stem cells.6,7,8 SOX2 expression is required for proliferation and anchorage-independent growth of lung and esophageal cell lines, as shown by RNA interference experiments. Furthermore, ectopic expression of SOX2 cooperated with FOXE1 or FGFR2 to transform immortalized tracheobronchial epithelial cells. SOX2-driven tumors show expression of markers of both squamous differentiation and pluripotency. These observations identify SOX2 as a novel lineage survival oncogene in lung and esophageal SCC

Discovery, characterization and functional analysis of the serine /threonine kinase Krct

Breast cancer is the most frequently diagnosed malignancy among women in the United States. Despite our advances in the ability to diagnose breast cancer at earlier stages, more women will die of breast cancer than any other type of cancer except lung cancer. Based on these findings, the Breast Cancer Progress Review Group from the National Cancer Institute set a goal of increasing our knowledge of the normal biological processes of the mammary gland. By understanding better the normal signaling events of the mammary gland researchers will better understand the abnormalities of the same signaling pathways found in breast cancer. This thesis addresses the role of a novel kinase in normal mammary development. We identified the novel serine/threonine kinase called Krct, Kinase Related to C erevisiae and Thaliana , in a screen designed to detect kinases expressed in the mammary gland. Homology database searches reveals that Krct belongs to a unique family of serine/threonine protein kinases that is conserved among all eukaryotes. Expression analysis demonstrates that Krct is ubiquitously expressed both in human and murine tissues. These data suggest that Krct is likely to be involved in an evolutionarily conserved biologic function. To identify Krct\u27s function we deleted its putative orthologue, YPL236c, in S. cerevisiae. Targeted disruption of YPL236c revealed that it is not an essential gene since deletion of the gene did not result in lethality. Phenotype screening did not reveal any growth defects under cellular stresses and mutant yeast were able to mate and sporulate normally. Therefore, we were not able to infer a function for Krct from targeted deletion of a putative orthologue. Given Krct\u27s function as a kinase and lack of any apparent regulatory domain, we hypothesized Krct would have binding partners that regulate its activity and substrate specificity. We therefore performed a yeast two-hybrid assay to identify Krct-interacting proteins. Our screen identified DRG1, Development Regulated G-protein 1, as an interacting protein. Confirmation of this interaction was demonstrated by GST-pulldown assays but co-immunoprecipitation assays were unable to verify this interaction. This raises some doubt about the relevance of the Krct-DRG1 interaction in vivo. We also generated a tetracycline-inducible mouse model that overexpresses Krct to determine whether perturbing Krct signaling in the mammary gland results in developmental defects. Examination of mammary glands in Krct-overexpressing mice reveals that even modest overexpression of Krct results in abnormal endbud formation during puberty whereas Krct expression during pregnancy or lactation has no apparent effect. These supernumery endbuds resemble normal endbuds with respect to their proliferation and apoptotic rates and cellular compartmentalization. Additionally, thickening of the periductal stroma surrounding these endbuds is seen that sometimes encompasses the endbud. These data suggest that Krct may play a role in stromal-epithelial signaling that occurs during ductal morphogenesis in the mammary gland

Discovery, characterization and functional analysis of the serine /threonine kinase Krct

Breast cancer is the most frequently diagnosed malignancy among women in the United States. Despite our advances in the ability to diagnose breast cancer at earlier stages, more women will die of breast cancer than any other type of cancer except lung cancer. Based on these findings, the Breast Cancer Progress Review Group from the National Cancer Institute set a goal of increasing our knowledge of the normal biological processes of the mammary gland. By understanding better the normal signaling events of the mammary gland researchers will better understand the abnormalities of the same signaling pathways found in breast cancer. This thesis addresses the role of a novel kinase in normal mammary development. We identified the novel serine/threonine kinase called Krct, Kinase Related to C erevisiae and Thaliana , in a screen designed to detect kinases expressed in the mammary gland. Homology database searches reveals that Krct belongs to a unique family of serine/threonine protein kinases that is conserved among all eukaryotes. Expression analysis demonstrates that Krct is ubiquitously expressed both in human and murine tissues. These data suggest that Krct is likely to be involved in an evolutionarily conserved biologic function. To identify Krct\u27s function we deleted its putative orthologue, YPL236c, in S. cerevisiae. Targeted disruption of YPL236c revealed that it is not an essential gene since deletion of the gene did not result in lethality. Phenotype screening did not reveal any growth defects under cellular stresses and mutant yeast were able to mate and sporulate normally. Therefore, we were not able to infer a function for Krct from targeted deletion of a putative orthologue. Given Krct\u27s function as a kinase and lack of any apparent regulatory domain, we hypothesized Krct would have binding partners that regulate its activity and substrate specificity. We therefore performed a yeast two-hybrid assay to identify Krct-interacting proteins. Our screen identified DRG1, Development Regulated G-protein 1, as an interacting protein. Confirmation of this interaction was demonstrated by GST-pulldown assays but co-immunoprecipitation assays were unable to verify this interaction. This raises some doubt about the relevance of the Krct-DRG1 interaction in vivo. We also generated a tetracycline-inducible mouse model that overexpresses Krct to determine whether perturbing Krct signaling in the mammary gland results in developmental defects. Examination of mammary glands in Krct-overexpressing mice reveals that even modest overexpression of Krct results in abnormal endbud formation during puberty whereas Krct expression during pregnancy or lactation has no apparent effect. These supernumery endbuds resemble normal endbuds with respect to their proliferation and apoptotic rates and cellular compartmentalization. Additionally, thickening of the periductal stroma surrounding these endbuds is seen that sometimes encompasses the endbud. These data suggest that Krct may play a role in stromal-epithelial signaling that occurs during ductal morphogenesis in the mammary gland