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Okadaic acid mimics multiple changes in early protein phosphorylation and gene expression induced by tumor necrosis
1Institute of Molecular and Cell Biology, National University of Singapore.
Abstract:
Okadaic acid, a phosphatase inhibitor from a marine organism, mimics tumor necrosis factor/interleukin-1 (TNF/IL-1) in inducing changes in early cellular protein phosphorylation. A total of approximately 116 proteins exhibit significant and concordant changes in phosphorylation or dephosphorylation within 15 min in human fibroblasts activated by either okadaic acid, TNF, or IL-1. The fidelity of this mimicry by okadaic acid extends to the phosphorylation of the 27 hsp complex, stathmin, eIF-4E, myosin light chain, nucleolin, epidermal growth factor receptor, and other cdc2-kinase substrates (c-abl, RB, and p53). The okadaic acid-induced pattern of protein phosphorylation is distinct from that observed in cells treated with phorbol 12-myristate 13-acetate or with ligands like epidermal growth factor, cyclic AMP agonists, bradykinin, or interferons. Like TNF, okadaic acid also induces the transcription of immediate early response genes like c-jun and Egr-1 as well as the interleukin-6 genes. The overall early effects of okadaic acid uniquely parallel those of TNF/IL-1 and not those of other cytokines or ligands. Regulation of protein phosphatase inhibition is discussed as a mechanism for TNF/IL-1 signal transduction.
Insights
Okadaic acid, a marine toxin, mimics tumor necrosis factor/interleukin-1 (TNF/IL-1) by altering protein phosphorylation in human cells. This finding suggests protein phosphatase inhibition as a key mechanism in TNF/IL-1 signaling pathways.
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- Tumor Necrosis Factor (TNF) and Interleukin-1 (IL-1) are key inflammatory cytokines.
- Cellular responses to these cytokines involve rapid protein phosphorylation changes.
- Okadaic acid is a potent inhibitor of protein phosphatases.
Purpose of the Study:
- To investigate whether Okadaic acid mimics the early cellular effects of TNF/IL-1.
- To identify specific proteins affected by Okadaic acid treatment.
- To explore the role of protein phosphatase inhibition in cytokine signaling.
Main Methods:
- Treatment of human fibroblasts with Okadaic acid, TNF, or IL-1.
- Analysis of protein phosphorylation changes using quantitative methods.
- Assessment of immediate early gene transcription.
Main Results:
- Okadaic acid induced concordant phosphorylation changes in approximately 116 proteins within 15 minutes.
- The phosphorylation patterns mimicked those induced by TNF/IL-1, including specific substrates like stathmin and cdc2-kinase targets.
- Okadaic acid also induced transcription of immediate early genes (c-jun, Egr-1) and interleukin-6 genes, similar to TNF.
- The phosphorylation profile differed from responses to phorbol esters or other growth factors/cytokines.
Conclusions:
- Okadaic acid effectively mimics the early cellular signaling events induced by TNF/IL-1.
- Protein phosphatase inhibition is a plausible mechanism underlying TNF/IL-1 signal transduction.
- Okadaic acid serves as a valuable tool for studying cytokine signaling pathways.