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Inhibition of protein kinase C and proto-oncogene expression by crocetin in NIH/3T3 cells
1Institute of Biochemistry, Chung Shan Medical and Dental College, Taichung, Taiwan, Republic of China.
Abstract:
Crocetin, a carotenoid isolated from the seeds of Gardenia jasminoides, was found to be a potent inhibitor of tumor promotion induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse skin. When mouse fibroblast NIH/3T3 cells were treated with TPA alone, protein kinase C (PKC) translocated from the cytosolic fraction to the particulate fraction. Pretreatment with 60 and 120 microM crocetin for 15 min inhibited the TPA-induced PKC activity in the particulate fraction by 50% and 66%, respectively, but did not affect the level of PKC protein. Crocetin also reduced the level of TPA-stimulated phosphorylation of cellular proteins. Cells pretreated with crocetin (120 microM) had 55% less PKC [3H]phorbol dibutyrate-binding capacity. Suppression of TPA (100 ng/mL)-induced c-jun and c-fos gene expression was also observed in the mouse fibroblast cells pretreated with crocetin (30, 60, and 120 microM). Our results provided a basis for understanding the inhibitory effect of crocetin on TPA-mediated tumor promotion.
Insights
Crocetin, a compound from Gardenia jasminoides, effectively inhibits tumor promotion by blocking protein kinase C (PKC) activity and reducing gene expression. This natural carotenoid shows promise in cancer research by interfering with key cellular signaling pathways.
Area of Science:
- Pharmacology
- Carotenoid Chemistry
- Molecular Biology
Background:
- Tumor promotion involves complex cellular signaling pathways.
- 12-O-tetradecanoylphorbol-13-acetate (TPA) is a known tumor promoter.
- Protein Kinase C (PKC) plays a crucial role in TPA-induced signaling.
Purpose of the Study:
- To investigate the inhibitory effects of crocetin on TPA-induced tumor promotion.
- To elucidate the molecular mechanisms underlying crocetin's anti-tumor promoting activity.
Main Methods:
- Experiments were conducted using mouse fibroblast NIH/3T3 cells.
- Assessed TPA-induced translocation and activity of Protein Kinase C (PKC).
- Measured TPA-stimulated protein phosphorylation, PKC binding capacity, and gene expression (c-jun, c-fos).
Main Results:
- Crocetin significantly inhibited TPA-induced PKC activity and translocation without affecting PKC protein levels.
- Crocetin reduced TPA-stimulated cellular protein phosphorylation and PKC binding capacity.
- Pretreatment with crocetin suppressed the expression of TPA-induced c-jun and c-fos genes.
Conclusions:
- Crocetin acts as a potent inhibitor of TPA-mediated tumor promotion.
- The mechanism involves the suppression of PKC activation and downstream signaling pathways.
- Crocetin demonstrates potential as a chemopreventive agent against skin carcinogenesis.