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Phorbol ester impairs melanotropin receptor function and stimulates growth of cultured M2R melanoma cells
J E Gerst1, M Benezra, A Schimmer
1Department of Hormone Research, Weizmann Institute of Science, Rehovot, Israel.
Abstract:
We have examined the effects of a biologically active tumor promoting phorbol ester (phorbol 12-myristate, 13-acetate (PMA] which activates protein kinase C (PKC) on melanotropin receptor function and cell growth in the M2R mouse melanoma cell clone. Treatment of M2R cells with PMA resulted in a significant loss of beta-MSH binding. The effect was both time- and concentration-dependent. The inhibition of beta-MSH binding resulted from a decrease (greater than 85%) in active membranal receptors available on the external cell surface and not from either enhanced internalization or change in the binding affinity. Agonist-stimulated cyclic AMP accumulation was profoundly increased in a non-selective manner following short-term incubation (3 h) with PMA. This effect was completely reversed during long-term (72-96 h) incubation with the tumor promoting agent. Long-term culturing of M2R cells with PMA resulted in enhanced (+50%) proliferation of the melanoma cells. This enhancement was blocked by the addition of agents which stimulate the production of cAMP. Hence, phorbol esters are powerful growth promoters in transformed melanocytes and our findings indicate that the effects of melanotropins are selectively impaired during the process of growth promotion.
Insights
Phorbol ester (phorbol 12-myristate, 13-acetate, PMA) treatment impairs melanotropin receptor function and enhances melanoma cell growth. This tumor promoter affects receptor binding and cell proliferation, with effects reversed by cAMP-stimulating agents.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Melanotropin receptors play a role in melanocyte function.
- Tumor promoters like phorbol esters can influence cell signaling and growth.
- Protein kinase C (PKC) activation is a key pathway affected by phorbol esters.
Purpose of the Study:
- To investigate the impact of phorbol ester (PMA) on melanotropin receptor function in M2R mouse melanoma cells.
- To determine the effect of PMA on melanoma cell growth and proliferation.
- To elucidate the relationship between PMA-induced signaling, receptor function, and cell growth.
Main Methods:
- Treatment of M2R mouse melanoma cells with phorbol 12-myristate, 13-acetate (PMA).
- Measurement of beta-melanocyte-stimulating hormone (beta-MSH) binding to cell surface receptors.
- Assay of agonist-stimulated cyclic AMP (cAMP) accumulation.
- Assessment of melanoma cell proliferation rates.
Main Results:
- PMA treatment significantly reduced beta-MSH binding, primarily by decreasing surface receptors, in a time- and concentration-dependent manner.
- Short-term PMA incubation increased cAMP accumulation, which was reversed by long-term incubation.
- Long-term PMA exposure enhanced M2R cell proliferation by 50%, an effect blocked by cAMP-stimulating agents.
Conclusions:
- Phorbol esters are potent growth promoters for transformed melanocytes.
- PMA impairs melanotropin receptor function during tumor cell growth promotion.
- The findings suggest a complex interplay between PKC signaling, receptor modulation, and uncontrolled cell proliferation in melanoma.