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Crosstalk between epidermal growth factor receptor and P-glycoprotein in actinomycin D-resistant Chinese hamster lung
M B Meyers1, P Yu, J Mendelsohn
1Laboratory of Cellular and Biochemical Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021.
Abstract:
Multidrug-resistant cells can manifest an increase in epidermal growth factor (EGF) receptor number along with increased P-glycoprotein (Pgp) synthesis. An interrelationship of the two membrane proteins in actinomycin D-resistant Chinese hamster lung cells (DC-3F/AD X) in terms of the effect of EGF on Pgp phosphorylation was investigated. EGF was not a mitogen for the resistant cells, nor was it mitogenic for DC-3F, the parental drug-sensitive line. Brief treatment of DC-3F/AD X cells with EGF resulted in a 30-50% decrease in the level of Pgp phosphorylation, and treatment of the cells with okadaic acid, a specific inhibitor of protein phosphatases-1 and -2A (PP1 and 2A), increased Pgp phosphorylation. Okadaic acid also increased phosphorylation of Pgp in plasma membranes isolated from DC-3F/AD X cells by 30-40%. Protein phosphatase activity in extracts of cells grown in EGF-containing medium was greater by 30% than that of cells grown in standard medium, and okadaic acid inhibited the increases. The results suggested that EGF activated PP1 and PP2A in DC-3F/AD X cells and that Pgp was a substrate for the phosphatases. The properties of Pgp may be modulated by the signalling system transduced by ligand-activated EGF receptor.
Insights
Epidermal growth factor (EGF) signaling activates protein phosphatases, decreasing P-glycoprotein (Pgp) phosphorylation in multidrug-resistant cells. This suggests EGF receptor pathways modulate Pgp activity in drug resistance.
Area of Science:
- Cell Biology
- Molecular Pharmacology
- Cancer Research
Background:
- Multidrug resistance (MDR) in cancer cells is often associated with increased epidermal growth factor (EGF) receptor expression and P-glycoprotein (Pgp) synthesis.
- The functional relationship between EGF receptor signaling and Pgp activity in MDR cells remains incompletely understood.
Purpose of the Study:
- To investigate the interrelationship between EGF receptor signaling and P-glycoprotein (Pgp) phosphorylation in actinomycin D-resistant Chinese hamster lung cells (DC-3F/AD X).
- To determine if EGF influences Pgp phosphorylation status and to explore the role of protein phosphatases in this process.
Main Methods:
- Treatment of DC-3F/AD X cells with EGF and okadaic acid (a protein phosphatase inhibitor).
- Measurement of Pgp phosphorylation levels in whole cells and isolated plasma membranes.
- Assay of protein phosphatase activity in cell extracts.
Main Results:
- EGF treatment led to a 30-50% decrease in Pgp phosphorylation in resistant cells.
- Okadaic acid treatment increased Pgp phosphorylation by 30-40% in both whole cells and isolated membranes.
- Protein phosphatase activity was 30% higher in cells grown with EGF, and this increase was inhibited by okadaic acid.
Conclusions:
- EGF activates protein phosphatases 1 and 2A (PP1 and PP2A) in DC-3F/AD X cells.
- Pgp is a substrate for these activated phosphatases, indicating EGF receptor signaling modulates Pgp phosphorylation.
- These findings suggest that the EGF receptor signaling pathway can influence Pgp properties, potentially impacting multidrug resistance mechanisms.