PROBING THE EFFECT OF IKK ON FOXO3: A REGULATORY MECHANISM OF APOPTOSIS AND AUTOPHAGY IN CHEMORESISTANCE
Biological Sciences and Bioengineering, Ph.D. Dissertation, 2012
Prof. Dr. Hüveyda Başağa (Thesis supervisor), Assoc. Prof. Devrim Gözüaçık, Assoc. Prof. O.Uğur Sezerman, Prof. Dr. Canan Atılgan, Asst. Prof. Dilek Telci
Date &Time: July 26th, 2012 – 14:00
Place: FENS G029
Keywords: FOXO3, IKK, apoptosis, autophagy, breast cancer
Chemotherapeutic drugs in use are only 50% successful in breast cancer treatment due to the chemoresistance mechanisms of cancer cells. FOXO3, a tumor suppressor, is involved in the regulation of several cell death-related genes; however, the extent of FOXO3 regulation in chemoresistance is not fully understood.
In this study our aim was to characterize the potential crosstalk between FOXO3 and NFκB pathway with a special focus on IKK-FOXO3 interaction in chemoresistance mechanism. For this purpose, we characterized chemoresistant (MDA-MB-231) and chemosensitive (MCF-7) breast cancer cell lines by paclitaxel (20nM) or cisplatin (30μM) treatments. Administration of 30μM cisplatin induces FOXO3-dependent apoptosis in MCF-7 cells as indicated by RNA interference studies. Following the analysis of NFκB pathway elements by immunoblotting and overexpression studies, we identified the physical interaction between IKKβ and FOXO3 by co-immunoprecipitation. We investigated that IKKβ sequesters FOXO3 in the nucleus promoting chemoresistance in MDA-MB-231 cells. Additionally, imbalance between FOXO3 and IKKβ levels induces autophagy rather than apoptosis in FOXO3 overexpressing MDA-MB-231 cells. We have also studied the effect of p53 on FOXO3 and showed p53-dependent FOXO3 inhibition in colorectal cancer cells. This is the first study describing FOXO3 regulation by IKKβ in detail and showing that FOXO3/IKKβ ratio may influence the cellular decision of apoptosis or autophagy.
In view of the results obtained, NFκB pathway-FOXO3 crosstalk has been discussed and future studies have been proposed. In the light of recent data published, the interaction between FOXO3 and IKKβ is proposed as a target for therapeutic interventions.