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Tamoxifen stimulates phospholipase D activity by an estrogen receptor-independent mechanism
1Hormel Institute, University of Minnesota, Austin 55912.
Abstract:
The effects of tamoxifen (TAM), a widely used agent in the treatment of breast cancer, were examined on phospholipase D (PLD)-mediated phospholipid hydrolysis. In drug-sensitive MCF-7 human breast carcinoma cells TAM, similar to several well-established activators of PLD, had no effect on phospholipid hydrolysis. In an estrogen receptor-deficient multidrug-resistant subline of MCF-7 cells, TAM preferentially stimulated the hydrolysis of phosphatidylethanolamine; two-fold stimulation required 2.5 or 5 microM TAM in the absence or presence of serum, respectively. In NIH 3T3 fibroblasts significant (4- to 4.8-fold) stimulation of phosphatidylethanolamine and phosphatidylcholine hydrolysis in the presence of serum required 10 microM TAM. These data establish that TAM can stimulate PLD activity by an estrogen receptor-independent mechanism.
Insights
Tamoxifen (TAM) stimulates phospholipase D (PLD) activity in certain breast cancer cells and fibroblasts through an estrogen receptor-independent pathway. This finding reveals a novel mechanism of TAM action beyond its known hormonal effects.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Tamoxifen (TAM) is a crucial drug for breast cancer treatment.
- Phospholipase D (PLD) plays a role in cellular signaling and phospholipid metabolism.
- The mechanism of TAM action, particularly its non-hormonal effects, requires further investigation.
Purpose of the Study:
- To investigate the effects of tamoxifen (TAM) on phospholipase D (PLD)-mediated phospholipid hydrolysis.
- To determine if TAM-induced PLD activity is dependent on estrogen receptors.
Main Methods:
- Assessing PLD activity in drug-sensitive MCF-7 cells, estrogen receptor-deficient multidrug-resistant MCF-7 sublines, and NIH 3T3 fibroblasts.
- Measuring phospholipid hydrolysis, specifically phosphatidylethanolamine and phosphatidylcholine, following TAM treatment.
- Quantifying TAM concentrations and serum presence to determine dose-dependent effects on PLD stimulation.
Main Results:
- Tamoxifen (TAM) did not affect phospholipid hydrolysis in drug-sensitive MCF-7 cells.
- TAM preferentially stimulated phosphatidylethanolamine hydrolysis in estrogen receptor-deficient MCF-7 cells.
- TAM significantly stimulated phosphatidylethanolamine and phosphatidylcholine hydrolysis in NIH 3T3 fibroblasts in a dose-dependent manner.
Conclusions:
- Tamoxifen (TAM) can stimulate phospholipase D (PLD) activity.
- This stimulation occurs via an estrogen receptor-independent mechanism.
- TAM exhibits non-hormonal effects on cellular phospholipid metabolism.