Research in the laboratory is focused on the molecular mechanisms that control cell proliferation and the formation of tumors. Our research is concentrated in three areas: (1) We have invested much effort in understanding the collaborative interactions between epithelial and mesenchymal cells that result in the formation of carcinomas. (2) We are also interested in how human cancer cells acquire the ability to invade and metastasize. (3) Finally, we are studying the molecular mechanisms of cellular senescence and its effects on cell proliferation in vitro and in vivo.
Epithelial-stromal interactions in human tumors. Our previous work indicated that the transformation of human cells is a complex, multi-step process that requires the deregulation of at least five distinct signaling pathways operating in these cells – those involving telomerase and telomere maintenance, the pRb (retinoblastoma protein) pathway, the p53 tumor suppressor pathway, the Ras mitogenic signaling pathway, and a poorly understood pathway that is governed by PP2A (protein phosphatase 2A). We have found that the deregulation of this pathway in a wide spectrum of normal human cells enables their transformation into tumorigenic cells. Additional work demonstrated that when human mammary epithelial cells are transformed into tumor cells, these cells must recruit stromal cells (e.g., fibroblasts, endothelial cells, macrophages) into their midst before they form carcinomas. We are currently investigating the mechanism(s) by which this recruitment occurs. In addition, we have determined that the stromal fibroblasts that are present in human mammary carcinomas are biologically abnormal and are in an activated state reminiscent of that of myofibroblasts. We have recently developed a method by which we can insert human mammary fibroblasts into a mouse mammary fat pad; subsequent implantation of normal human mammary epithelial cells into the humanized stroma results in normal human mammary gland morphogenesis and occasionally in the development of growths that are indistinguishable from ductal hyperplasias, in situ carcinomas, and invasive carcinomas. Together, this experimental system enables us to model all of the steps of human mammary gland morphogenesis and, it seems, carcinoma pathogenesis. Development of a method for culturing mammary epithelial stem cells affords us the means of generating genetically defined human breast carcinoma cells that generate growths virtually indistinguishable from those seen in patients in the clinic. In addition, we have uncovered a signaling pathway within epithelial cells that enable them to release angiogenic signals to the nearby stroma and are investigating how prolactin is able to act mitogenically on mammaryepithelial cells. [Akira Orimo, Christina Scheel, Matthew Saelzler, Tan Ince, Mai-Jing Liao, Samuel Godar, Sandra McAllister, Antoine Karnoub]
Invasion and metastasis.Having learned many of the requirements for creating primary human tumors, we would like to determine the nature of some of the genetic elements that lead to the formation of invasive and ultimately metastatic tumor cells. Using expression arrays, we have identified two transcription factors, Twist and Mesenchyme Forkhead (also known as FOXC2) , which appear to play key roles in programming many of the phenotypes of invasive cells. Embryology reveals the identity of a third factor, termed Goosecoid, which appears capable of programming the epithelial-mesenchymal transition both during early embryogenesis and during the invasive stages of certain carcinomas. A fourth factor, termed Slug, may contribute to the invasive phenotype of yet other tumors. Acting alone or in combination, these factors may be able to program many of the phenotypes associated with invasive and metastatic cells. In addition, we are examining the last stage of the invasion-metastasis cascade, in order to determine how disseminated cancer cells are able to adapt to a novel tissue environment and colonize this environment, yielding a macroscopic metastasis. [Jing Yang, Sendurai Mani, Kimberly Hartwell, Christina Scheel, Tamer Onder, Lynne Waldman, Richard Lee, Ittai Ben-Porath]
Cell Senescence. A widespread view is that cultured cells enter senescence after the telomeric DNA at the ends of their chromosomes shorten below a certain threshold. We have found that the overall length of telomeric DNA is not important for governing entrance into replicative senescence. Instead, the configuration of the single-strand DNA overhanging the ends of the chromosomes appears to be the critical determinant of senescence. This DNA is lost when cells enter into replicative senescence. Loss of this overhanging DNA appears to be caused, in turn, by physiologic stresses experienced by cells in culture. Contributing importantly to these stresses are those generated by reactive oxygen species and the oxidized nucleotides that they create. [Ittai Ben-Porath, Priya Rai]
Research in the Weinberg Lab is supported in part by the National Institutes of Health/National Cancer Institute, American Cancer Society, Novartis Pharma, MIT/Ludwig Fund for Cancer Research, Breast Cancer Research Foundation and the Ellison Medical Foundation.
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