9-cis-retinoic acided mediated endothelial transdifferentiation in breast cancer cells
Thesis (Ph.D.)--Georgetown University, 2008.; Includes bibliographical references.; Text (Electronic thesis) in PDF format. Retinoic acid is a vitamin A derivative that has growth inhibitory and differentiating effects. For these reasons, it was thought that retinoic acid could function as a chemopreventative and a chemotherapeutic agent. However, clinical trials have shown mixed results - it is beneficial to some patients and harmful to others. We studied the effects of 9-cis-retinoic acid on breast cancer in vitro. In this work I show that retinoic acid treatment of SKBR-3 cells has growth inhibitory and differentiating effects; however, instead of differentiating into epithelial cells, retinoic acid treated SKBR-3 cells differentiate into endothelial-like cells. These results may explain the failure of retinoic acid treatment in clinical trials in a subset of the population. Previous data in the laboratory indicates that SOX9 and ER81 expression are necessary but not sufficient for inducing the expression of VE-cadherin. The use of two pan-kinase inhibitors, Genistein and SD705702, demonstrates that VE-cadherin expression is dependent on kinase activity; however, the active kinase is not a receptor tyrosine kinase since retinoic acid treatment results in the loss of tyrosine kinase activity. The TGF-beta-R1 kinase inhibitor, SB431542, has the ability to inhibit VE-cadherin expression.; Retinoic acid also induces profound morphological changes in SKBR-3 cells, reminiscent of vasculogenic mimicry, an alternative form of tumor vascularization. When retinoic acid treated SKBR-3 cells are grown on Matrigel, they form endothelial like networks with hollowed out balls resulting from cell fusion. VE-cadherin siRNA and SB431542 treatment result in the loss of cell fusion, but not network formation in retinoic acid treated cells. On the other hand, COUP-TFII siRNA does not affect cell fusion, but inhibits network formation.; Functionally, retinoic acid treated SKBR-3 cells are able to interact with HUVECs in Matrigel. Untreated SKBR-3 cells grow on top of established HUVEC networks. On the other hand, retinoic acid treated SKBR-3 cells fuse together and form the nodal points into which HUVEC networks grow into and out of. This arrangement might allow a channel lined by tumor cells to conduct nutrients deep into the tumor.; In conclusion, VE-cadherin expression in retinoic acid treated SKBR-3 cells is mediated by 3 necessary but not sufficient factors - SOX9, ER81, and a TGF-beta pathway. The cell fusion portion of vasculogenic mimicry is mediated by VE-cadherin, while network formation is mediated by COUP-TFII. Given the poor prognosis associated with vasculogenic mimicry, it is important to understand the mechanism of vitamin A induced endothelial transdifferentiation to help tailor a patient's treatment.
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