Pioglitazone mediates apoptosis in Caki cells via downregulating c-FLIP(L) expression and reducing Bcl-2 protein stability

Ji Hoon Jang; Tae-Jin Lee; Eon-Gi Sung; In-Hwan Song; Joo-Young Kim

doi:10.3892/ol.2021.13004

Pioglitazone mediates apoptosis in Caki cells via downregulating c-FLIP_(L) expression and reducing Bcl-2 protein stability

Oncol Lett. 2021 Oct;22(4):743. doi: 10.3892/ol.2021.13004. Epub 2021 Aug 20.

Authors

Ji Hoon Jang¹, Tae-Jin Lee¹, Eon-Gi Sung¹, In-Hwan Song¹, Joo-Young Kim¹

Affiliation

¹ Department of Anatomy, College of Medicine, Yeungnam University, Daegu 42415, Republic of Korea.

Abstract

Pioglitazone is an anti-diabetic agent used in the treatment of type 2 diabetes, which belongs to the thiazolidinediones (TZDs) group. TZDs target peroxisome proliferator-activated receptor γ (PPARγ), which functions as a transcription factor of the nuclear hormone receptor. Pioglitazone has antitumor effects in several cancer types and could be a tool for drug therapy in various cancer treatments. Nevertheless, the molecular basis for pioglitazone-induced anticancer effects in renal cancer (RC) has not yet been elucidated. Thus, the aim of the present study was to investigate the detailed signaling pathway underlying pioglitazone-induced apoptosis in Caki cells derived from human clear cell renal cell carcinoma. As a result, it was demonstrated by flow cytometry analysis and Annexin V-propidium iodide staining that pioglitazone treatment induced apoptotic cell death in a dose-dependent manner in Caki cells. The protein expression levels of cellular FLICE (FADD-like IL-1β-converting enzyme)-inhibitory protein (c-FLIP)_(L) and Bcl-2, which were determined by western blotting, decreased after pioglitazone treatment in Caki cells. Flow cytometry and western blot analyses demonstrated that pioglitazone-mediated apoptosis was blocked following pretreatment with the pan-caspase inhibitor, z-VAD-fmk, indicating that pioglitazone-induced apoptosis was mediated via a caspase-dependent signaling pathway. However, the reactive oxygen species (ROS) scavenger, N-acetylcysteine (NAC), did not affect pioglitazone-mediated apoptosis and degradation of c-FLIP_(L) and Bcl-2 protein. Of note, it was found by western blot analysis that Bcl-2 protein expression was downregulated by the decreased protein stability of Bcl-2 in pioglitazone-treated Caki cells. In conclusion, these findings indicated that pioglitazone-induced apoptosis is regulated through caspase-mediated degradation of FLIP_(L) and reduction of Bcl-2 protein stability, suggesting that pioglitazone is a feasible apoptotic agent that could be used in the treatment of human RC.

Keywords: B cell lymphoma 2; apoptosis; cellular FADD-like IL-1β-converting enzyme-inhibitory protein; pioglitazone; renal cancer.

Grants and funding

The present study was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (grant no. 2020R1I1A1A01068857).