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
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Article info
Publication history
Published online: February 06, 2012
Accepted:
November 1,
2011
Received in revised form:
October 15,
2011
Received:
March 3,
2011
Identification
Copyright
© 2011 Japanese Society for Investigative Dermatology. Published by Elsevier Inc. All rights reserved.
