ABSTRACT
Sorafenib induces apoptosis and enhances Tumour Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL)-induced cell killing of tumoural cells. We have investigated the effects of the multikinase inhibitor Sorafenib alone or in combination with TRAIL and agonistic Fas antibodies on endometrial carcinoma cells. We have also focused on the search of the differential molecular mechanisms by which Sorafenib induces cell death and the ones involved in sensitisation to TRAIL. In the present study, we show that Sorafenib induces apoptosis of both endometrial cancer cell lines and human primary cultures and sensitises these cells to TRAIL and agonistic Fas antibodies (aFas)-induced apoptosis. However, Raf/MEK/ERK inhibition by Sorafenib was not responsible for Sorafenib cell death or TRAIL sensitisation of endometrial cancer cells. Sorafenib treatment correlated with a downregulation of both FLICE-Inhibitory Protein (FLIP) and myeloid cell leukaemia-1 (Mcl-1), caused by a proteasomal degradation of both proteins. We evaluated the contribution of FLIP and Mcl-1 downregulation in apoptosis triggered by Sorafenib alone or Sorafenib plus TRAIL. Interestingly, cell death caused by Sorafenib was mediated by downregulation of Mcl-1, but not by FLIP. In contrast, we found that Sorafenib sensitisation of endometrial carcinoma cells to TRAIL- and Fas-induced apoptosis was dependent on FLIP but not on Mcl-1 downregulation. Altogether, we discern the dual mechanisms by which Sorafenib causes cell death from those involved in death receptor sensitisation.
Subject(s)
Adenocarcinoma/pathology , Antineoplastic Agents/pharmacology , Apoptosis/drug effects , Benzenesulfonates/pharmacology , Endometrial Neoplasms/pathology , Pyridines/pharmacology , TNF-Related Apoptosis-Inducing Ligand/pharmacology , Adenocarcinoma/metabolism , Antineoplastic Combined Chemotherapy Protocols/pharmacology , CASP8 and FADD-Like Apoptosis Regulating Protein/metabolism , Dose-Response Relationship, Drug , Drug Screening Assays, Antitumor/methods , Endometrial Neoplasms/metabolism , Female , Humans , MAP Kinase Signaling System/drug effects , Myeloid Cell Leukemia Sequence 1 Protein , Neoplasm Proteins/metabolism , Niacinamide/analogs & derivatives , Phenylurea Compounds , Protein Kinase Inhibitors/pharmacology , Proto-Oncogene Proteins c-bcl-2/metabolism , Sorafenib , Tumor Cells, Cultured , fas Receptor/immunologyABSTRACT
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has emerged as a promising antineoplastic agent because of its ability to selectively kill tumoral cells. However, some cancer cells are resistant to TRAIL-induced apoptosis. We have previously demonstrated that in endometrial carcinoma cells such resistance is caused by elevated FLICE-inhibitory protein (FLIP) levels. The present study focuses on the mechanisms by which FLIP could be modulated to sensitize endometrial carcinoma cells to TRAIL-induced apoptosis. We find that inhibition of casein kinase (CK2) sensitizes endometrial carcinoma cells to TRAIL- and Fas-induced apoptosis. CK2 inhibition correlates with a reduction of FLIP protein, suggesting that CK2 regulates resistance to TRAIL and Fas by controlling FLIP levels. FLIP downregulation correlates with a reduction of mRNA and is prevented by addition of the MG-132, suggesting that CK2 inhibition results in a proteasome-mediated degradation of FLIP. Consistently, forced expression of FLIP restores resistance to TRAIL and Fas. Moreover, knockdown of either FADD or caspase-8 abrogates apoptosis triggered by inhibition of CK2, indicating that CK2 sensitization requires formation of functional DISC. Finally, because of the possible role of both TRAIL and CK2 in cancer therapy, we demonstrate that CK2 inhibition sensitizes primary endometrial carcinoma explants to TRAIL apoptosis. In conclusion, we demonstrate that CK2 regulates endometrial carcinoma cell sensitivity to TRAIL and Fas by regulating FLIP levels.
