Mcl-1 determines the imiquimod-induced apoptosis but not imiquimod-induced autophagy in skin cancer cells

Huang, Shi-Wei; Chang, Chia-Che; Lin, Chi-Chen; Tsai, Jaw-Ji; Chen, Yi-Ju; Wu, Chun-Ying; Liu, Kuang-Ting; Shieh, Jeng-Jer

doi:10.1016/j.jdermsci.2011.11.001

« Previous Next »Journal of Dermatological Science
Volume 65, Issue 3 , Pages 170-178, March 2012

Mcl-1 determines the imiquimod-induced apoptosis but not imiquimod-induced autophagy in skin cancer cells

Shi-Wei Huang
- Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan
Chia-Che Chang
- Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan
Chi-Chen Lin
- Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan
- Department of Education and Research, Taichung Veterans General Hospital, Taichung, Taiwan
Jaw-Ji Tsai
- Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan
- Department of Education and Research, Taichung Veterans General Hospital, Taichung, Taiwan
Yi-Ju Chen
- Department of Dermatology, Taichung Veterans General Hospital, Taichung, Taiwan
Chun-Ying Wu
- Division of Gastroenterology and Hepatology, Taichung Veterans General Hospital, Taichung, Taiwan
Kuang-Ting Liu
- Department of Pathology & Laboratory Medicine, Taoyuan Armed Forces General Hospital, Taoyuan, Taiwan
Jeng-Jer Shieh
- Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan
- Department of Education and Research, Taichung Veterans General Hospital, Taichung, Taiwan
- Corresponding author at: Institute of Biomedical Sciences, College of Life Science, National Chung Hsing University, No. 250, Kuo Kuang Rd., Taichung 402, Taiwan. Tel.: +886 4 23592525x4052; fax: +886 4 23592705.

Received 3 March 2011; received in revised form 15 October 2011; accepted 1 November 2011. published online 06 February 2012.

Abstract

Background

Imiquimod had been shown to induce apoptosis and autophagy in several skin cancer cells, especially basal cell carcinoma (BCC) cells.

Objective

We evaluate the molecular mechanisms of imiquimod-induced apoptosis and autophagy in skin cancer cell lines.

Methods

The Mcl-1, Bcl-2 and Bcl-xL proteins were determined by immunoblotting. The Mcl-1 mRNA level was examined by RT-PCR and real-time PCR. The mechanisms of imiquimod-induced decrease in Mcl-1 protein were evaluated by addition of cycloheximide, MG132 proteasome inhibitor or pan-caspase inhibitor. The phosphorylation of eIF4E, 4E-BP1 and eEF2 in imiquimod treated cells were examined by immunoblotting. The imiquimod-induced apoptosis and autophagy were evaluated in Mcl-1-overexpressing cells by XTT test, mitochondrial membrane potential measurement, DNA content assay, LC3 immunoblotting, EGFP-LC3 puncta formation and quantification of acidic vesicular organelle with acridine orange staining.

Results

The decrease in the Mcl-1 protein level was faster and stronger than the decrease in Bcl-2 and Bcl-xL in imiquimod-treated skin cancer cells. The imiquimod-induced decrease in Mcl-1 protein was not caused by blocked transcription or the promotion of degradation but was associated with inactivation of translation factors in BCC cells. The Mcl-1-overexpressing BCC cells were more resistant to intrinsic cellular apoptosis than control BCC cells during imiquimod treatment. Mcl-1 overexpression in BCC cells resulted in the basal activation of autophagy but did not modulate imiquimod-induced autophagy or rescue imiquimod-induced autophagic cell death in BCC cells.

Conclusions

Imiquimod may rapidly downregulate Mcl-1 protein levels by inhibiting translation in skin cancer cells. Mcl-1 may act to protect against apoptosis but not autophagy and autophagic cell death during imiquimod treatment in skin cancer cells.

Keywords: Imiquimod, Mcl-1, Skin cancer cells, Basal cell carcinoma, Apoptosis, Autophagy