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

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.

• Authors: Shi-Wei Huang, Chia-Che Chang, Chi-Chen Lin, Jaw-Ji Tsai, Yi-Ju Chen, Chun-Ying Wu, Kuang-Ting Liu, Jeng-Jer Shieh
• Journal: Journal of dermatological science (J Dermatol Sci) Vol. 65 Issue 3 Pg. 170-8 (Mar 2012) ISSN: 1873-569X [Electronic] Netherlands
• PMID: 22305615 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2011 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.

Chemical References

• Aminoquinolines
• Biomarkers, Tumor
• Myeloid Cell Leukemia Sequence 1 Protein
• Proto-Oncogene Proteins c-bcl-2
• RNA, Messenger
• bcl-X Protein
• Imiquimod

Topics

• Aminoquinolines (pharmacology)
• Apoptosis (drug effects)
• Autophagy (drug effects)
• Biomarkers, Tumor (metabolism)
• Carcinoma, Basal Cell (metabolism, pathology)
• Cell Line, Tumor
• Down-Regulation (drug effects)
• Humans
• Imiquimod
• Myeloid Cell Leukemia Sequence 1 Protein
• Proto-Oncogene Proteins c-bcl-2 (metabolism)
• RNA, Messenger (metabolism)
• Skin Neoplasms (metabolism, pathology)
• Up-Regulation (drug effects)
• bcl-X Protein (metabolism)