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Dimethylsulfoxide, retinoic acid and 12-O-tetradecanoylphorbol-13-acetate induce a selective decrease in the
Abstract:
Studies have been carried out to analyze protein phosphorylation in membranes isolated from adriamycin resistant HL60 cells which have been grown for various time periods in the presence of dimethylsulfoxide (DMSO), retinoic acid (RA) or 12-O-tetradecanoylphorbol-13-acetate (TPA). The results show that membranes isolated from cells treated with these agents are defective in the phosphorylation of P150, a membrane phosphoprotein associated with drug resistance in HL60 cells. This response is highly selective since only a few membrane proteins show decreased phosphorylation levels under these conditions. Magnesium dependent protein kinase activity in membranes from cells treated with DMSO, RA or TPA is not altered relative to untreated membranes under conditions where there is a major decrease in P150 phosphorylation. Additional studies also show that treatment of resistant cells with TPA results in a major decrease in the in vivo phosphorylation of P150. These results thus demonstrate that agents capable of inducing differentiation in HL60 cells can selectively modulate the phosphorylation of P150. This system should be of value in clarifying mechanisms involved in the phosphorylation of this protein.
Insights
Dimethyl sulfoxide (DMSO), retinoic acid (RA), and TPA treatments reduce P150 phosphorylation in drug-resistant HL60 cells. This selective modulation of a key phosphoprotein suggests a mechanism for overcoming drug resistance.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Pharmacology
Background:
- Adriamycin resistance in HL60 cells is linked to specific membrane phosphoproteins.
- Understanding the regulation of these phosphoproteins is crucial for developing resistance-modulating therapies.
Purpose of the Study:
- To investigate the effect of differentiation-inducing agents on protein phosphorylation in adriamycin-resistant HL60 cells.
- To determine if P150 phosphorylation is altered by dimethyl sulfoxide (DMSO), retinoic acid (RA), or 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment.
Main Methods:
- Isolation of membranes from HL60 cells cultured with DMSO, RA, or TPA.
- Analysis of protein phosphorylation levels, focusing on the P150 phosphoprotein.
- Assay of magnesium-dependent protein kinase activity.
Main Results:
- Treatment with DMSO, RA, or TPA selectively decreased P150 phosphorylation in isolated membranes.
- This effect was specific, as other membrane proteins showed minimal changes in phosphorylation.
- In vivo studies confirmed a significant reduction in P150 phosphorylation upon TPA treatment.
- Magnesium-dependent protein kinase activity remained unchanged despite altered P150 phosphorylation.
Conclusions:
- Differentiation-inducing agents (DMSO, RA, TPA) selectively modulate P150 phosphorylation in drug-resistant HL60 cells.
- The findings suggest a mechanism by which these agents impact drug resistance.
- This system provides a valuable model for studying P150 phosphorylation mechanisms.