Abstract
The M2 isoform of pyruvate kinase M2 (PKM2) has been shown to be up-regulated in human skin cancers. To test whether PKM2 may be a target for chemoprevention, shikonin, a natural product from the root of Lithospermum erythrorhizon and a specific inhibitor of PKM2, was used in a chemically-induced mouse skin carcinogenesis study. The results revealed that shikonin treatment suppressed skin tumor formation. Morphological examinations and immunohistochemical staining of the skin epidermal tissues suggested that shikonin inhibited cell proliferation without inducing apoptosis. Although shikonin alone suppressed PKM2 activity, it did not suppress tumor promoter-induced PKM2 activation in the skin epidermal tissues at the end of the skin carcinogenesis study. To reveal the potential chemopreventive mechanism of shikonin, an antibody microarray analysis was performed, and the results showed that the transcription factor ATF2 and its downstream target Cdk4 were up-regulated by chemical carcinogen treatment; whereas these up-regulations were suppressed by shikonin. In a promotable skin cell model, the nuclear levels of ATF2 were increased during tumor promotion, whereas this increase was inhibited by shikonin. Furthermore, knockdown of ATF2 decreased the expression levels of Cdk4 and Fra-1 (a key subunit of the activator protein 1. In summary, these results suggest that shikonin, rather than inhibiting PKM2 in vivo, suppresses the ATF2 pathway in skin carcinogenesis.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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9,10-Dimethyl-1,2-benzanthracene
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Activating Transcription Factor 2 / antagonists & inhibitors*
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Activating Transcription Factor 2 / genetics
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Activating Transcription Factor 2 / metabolism
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Animals
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Antineoplastic Agents, Phytogenic / pharmacology*
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Apoptosis / drug effects
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Carcinogens
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Carrier Proteins / genetics
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Carrier Proteins / metabolism
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Cell Line
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Cell Proliferation / drug effects
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Cell Transformation, Neoplastic / drug effects*
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Cell Transformation, Neoplastic / genetics
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Cell Transformation, Neoplastic / metabolism
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Cell Transformation, Neoplastic / pathology
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Cyclin-Dependent Kinase 4 / genetics
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Cyclin-Dependent Kinase 4 / metabolism
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Epidermis / drug effects
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Epidermis / metabolism
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Epidermis / pathology
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Epithelial Cells / drug effects
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Epithelial Cells / metabolism
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Epithelial Cells / pathology
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Female
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Gene Expression Regulation, Neoplastic*
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Humans
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Membrane Proteins / genetics
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Membrane Proteins / metabolism
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Mice
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Mice, Inbred DBA
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Naphthoquinones / pharmacology*
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Proto-Oncogene Proteins c-fos / genetics
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Proto-Oncogene Proteins c-fos / metabolism
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Pyridines
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Signal Transduction
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Skin Neoplasms / chemically induced
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Skin Neoplasms / drug therapy*
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Skin Neoplasms / genetics
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Skin Neoplasms / pathology
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Thyroid Hormone-Binding Proteins
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Thyroid Hormones / genetics
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Thyroid Hormones / metabolism
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Transcriptional Activation
Substances
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Activating Transcription Factor 2
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Antineoplastic Agents, Phytogenic
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Atf2 protein, mouse
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Carcinogens
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Carrier Proteins
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Membrane Proteins
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Naphthoquinones
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Proto-Oncogene Proteins c-fos
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Pyridines
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Thyroid Hormones
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fos-related antigen 1
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tris(2-pyridylmethyl)amine
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shikonin
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9,10-Dimethyl-1,2-benzanthracene
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Cdk4 protein, mouse
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Cyclin-Dependent Kinase 4