STRAP inhibits transforming growth factor-Beta (TGF-Beta) signaling and enhances tumorigenicity. The aim of our current research project was to identify novel TGF-Beta independent functions of STRAP. STRAP acts as a scaffold for the assembly of multi-protein complexes and our study has uncovered two novel but independent functions of STRAP.
In the first part, we report, for the first time, that deletion of STRAP from Mouse Embryonic Fibroblasts (MEFs) results in a loss of mesenchymal morphology. These cells lose their spindle shape and exhibit cobloid epithelial morphology. Loss of STRAP leads to upregulation of WT1 that subsequently upregulates E-cadherin leading to the formation of adherens junctions, and sequesters Beta-catenin to the cell membrane and downregulation of the mesenchymal markers like LEF1. Finally, stable expression of STRAP in these cells results in a loss of WT1 and E-cadherin expressions, and a reversal from epithelial to the mesenchymal morphology.
In the second part, we validated that STRAP binds with GSK3-Beta, an enzyme that plays multiple roles in a cell, including insulin and Wnt signaling. In a completely novel finding, we observed that STRAP, GSK3-Beta and Axin form a ternary complex. We also, for the first time show that intracellular fragment of Notch3 (ICN3) binds with GSK3-Beta, suggesting that Notch3 may be a novel substrate of GSK3-Beta.
We show that STRAP binds ICN3 in a proteasomal inhibition-dependent manner. Further studies revealed that STRAP binds ICN3 through the same ankyrin repeat region. In-vivo ubiquitination studies indicate that STRAP is able to reduce ubiquitination of ICN3, raising a possibility that STRAP may stabilize ICN3 leading to a longer half life in the cells. STRAP and Notch3 are both known to be upregulated in lung cancers and we observed that STRAP and ICN3 are co-overexpressed in 59 % of lung cancers in a tissue microarray study. STRAP shows oncogenic activity and our results from the two independent studies provide additional insights into how STRAP may behave as an oncogene using diverse mechanisms.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-06042010-154014 |
| Date | 04 June 2010 |
| Creators | Kashikar, Nilesh Digvijay |
| Contributors | Dr. Utpal P. Davé, Dr. Anna L. Means, Dr. Sarki A. Abdulkadir, Dr. Pran K. Datta, Dr. Robert J. Matusik |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-06042010-154014/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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