Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/5345
Breast epithelial morphogenesis is maintained by tissue specific stem cells. Recent studies indicate that some aggressive forms of breast cancer originate in these stem cells. Therefore, linking the molecular signals and mechanisms that control the fate decisions and branching morphogenesis in breast epithelial stem cells to cancer progression is important.
D492 is a breast epithelial cell line with stem cell properties. It was established by retroviral transduction of the E6 and E7 genes from human papilloma virus 16. When cultured in three dimensional (3D) assays the D492 cell line forms branching structures with an inner layer of luminal epithelial cells and an outer layer of myoepithelial cells clearly showing a bipotential phenotype, correct histoarchitecture and thus stem cell properties. We have recently localized the retroviral insert in the D492 stem cell line 95kb upstream of a gene coding for the protein tyrosine phosphatase 1B (PTP1B) at chromosome 20q13.1, a region that is frequently amplified in breast cancer.
In this work I have studied the role of PTP1B in the proliferation and survival of the D492 cell line as well as other epithelial cells. PTP1B protein expression in various cell lines and primary cells indicated that PTP1B is overexpressed in D492, possibly due to the retroviral insert. Treatment of the D492 cells with a specific PTP1B inhibitor induced apoptosis, but did not induce cell death in MCF-7, a breast cancer cell line which also has high PTP1B expression. My data further indicates that the cell death in D492 is primarily in dividing cells, possibly due to anoikis, i.e. programmed cell death when anchorage dependent cells detach from the surrounding matrix. I also provide evidence that PTP1B can activate Src, a well known oncogene which plays a role in anoikis. Interestingly, I also noticed a smaller form of the PTP1B protein when evaluating PTP1B expression in various cell lines. This smaller form is reported to be a more active subunit of PTP1B cleaved by Calpain2 protease. Pharmacological inhibition on Calpain in D492 resulted in cell death suggesting a role for calpain, possibly through PTP1B.
In summary my data suggest an important role of PTP1B for cell survival in D492 and helps to elucidate its role in signaling pathways. This thesis provides a foundation for further studies on PTP1B during breast morphogenesis and cancer.
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