Date

2014

Author

Alpsoy, Aktan

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Even though chemotherapy keeps its position as the most preferred and potent strategy of cancer treatment, resistance of tumor to the anti-neoplastic drug poses an obstacle for chemotherapy success. Multidrug resistance (MDR) is a phenomenon that is defined as the intrinsic or acquired resistance against structurally and functionally unrelated drugs. Acquisition of multidrug resistance can be through several distinct mechanisms such as increased drug efflux by ABC transporters, increased drug detoxification through phase I and II enzymes, altered death pathways and increased damage repair, making MDR a multifaceted problem that remodel many regulatory or metabolic circuits. MDR phenotype has also been linked to increased aggressiveness marked by mobility and invasiveness or vice versa. Protein kinase D2 (PKD2) is one of the isoforms in three-membered serine/threonine kinase family, PKD. PKD family members can possess redundant as well as specific roles on proliferation, survival, angiogenesis and motility, the events that are relevant to cancer. In glioblastoma, leukemia, colorectal, pancreas and breast cancer, tumor promoting and suppressing roles of PKD members have been shown. In particular, breast cancer, the most common cancer type in women, PKD2 and PKD3 appear to have oncogenic roles while PKD1 possesses tumor-suppressive functions. Specifically, PKD2 seems to be ubiquitous in many breast cancer types, while PKD1 and PKD3 are not. To this end, we aimed to characterize the ubiquitous member, PKD2, in a panel of breast cancer cell lines. We found that the expression of PKD2 does not differ between cell lines, whereas its basal level activity is higher in chemoresistant MCF7 derivatives compared to parental MCF7 cell line, implying that PKD2 may have role in drug resistance and associated phenotypes. Cell proliferation assay showed that PKD2 downregulation does not affect the drug resistance in MCF7/DOX cells. PKD2 knockdown also does not significantly change the expression of potential PKD targets that are implicated in MDR and apoptosis. MCF7/DOX cells are phenotypically different from parental cell line such that they have higher expression of epithelial to mesenchymal transition markers, higher mobility and invasive characteristics. Since PKD2 is also implicated in motility we checked whether PKD2 downregulation influences the migration of MCF7/DOX cells towards a chemoattractant. The migration assay showed that PKD2 downregulation suppresses the migration of MCF7/DOX cells. The data implied that under this experimental setup PKD2 did not alter the drug resistance whereas it changes the migration potential of doxorubicin resistant MCF7 cell line. Further research is needed to uncover the roles of other isoforms PKD1 and PKD3 as well as upstream regulators of PKD members in chemoresistance.

Subject Keywords

Cancer cells., Drug resistance., Protein kinases., Breast

URI

http://etd.lib.metu.edu.tr/upload/12617519/index.pdf
https://hdl.handle.net/11511/23694

Collections

Graduate School of Natural and Applied Sciences, Thesis