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Loss of mouse fibroblast cell response to phorbol esters restored by microinjected protein kinase C
Abstract:
The phorbol esters in addition to being among the most potent mouse skin tumour promoters profoundly affect many different biological systems. It is postulated that they act through activation of protein kinase C, but substantial heterogeneity in their pharmacological and binding behaviour in some systems has caused concern about whether this is their only target. Evidence linking protein kinase C activation with biological responses to the phorbol esters includes similarity in structure-activity relations for binding and response; in vitro phosphorylation of specific proteins by protein kinase C at the same sites at which phorbol ester treatment induces phosphorylation in intact cells; and correlation in certain cell types between down regulation of protein kinase C on chronic phorbol ester treatment and loss of cellular responsiveness to the phorbol ester. Here we report that microinjection of purified protein kinase C into Swiss 3T3 fibroblasts pretreated with the phorbol ester phorbol 12,13-dibutyrate (PDBu) restores the mitogenic response of the cells to PDBu, directly establishing the involvement of protein kinase C in this response.
Insights
Phorbol esters, potent tumor promoters, activate protein kinase C (PKC). This study demonstrates that restoring PKC in cells treated with phorbol 12,13-dibutyrate (PDBu) re-establishes their mitogenic response to PDBu.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Phorbol esters are potent mouse skin tumor promoters with diverse biological effects.
- Their primary proposed mechanism involves activating protein kinase C (PKC).
- However, varied pharmacological and binding behaviors raise questions about PKC being the sole target.
Purpose of the Study:
- To directly establish the role of protein kinase C (PKC) in mediating the biological responses to phorbol esters.
- To investigate the direct link between PKC activation and cellular mitogenesis induced by phorbol esters.
Main Methods:
- Microinjection of purified protein kinase C (PKC) into Swiss 3T3 fibroblasts.
- Pretreatment of cells with the phorbol ester phorbol 12,13-dibutyrate (PDBu).
- Assessment of the restoration of the mitogenic response to PDBu.
Main Results:
- Microinjection of purified PKC into PDBu-pretreated Swiss 3T3 fibroblasts restored the mitogenic response.
- This direct restoration provides compelling evidence for PKC's involvement.
Conclusions:
- Protein kinase C (PKC) is directly involved in mediating the mitogenic response to phorbol esters.
- The findings support the hypothesis that PKC activation is the key mechanism for phorbol ester-induced cellular responses.