Okadaic acid, phosphatase blocking

For in vitro studies there are a number of compounds available to block protein phosphatase activity. Phosphate buffers inactivate all of these enzymes. Several naturally occurring toxins are potent inhibitors of PPPs, e.g., okadaic acid or microcystin, and are frequently used tools. PPM and PTP family members are not affected by these toxins. Vanadate containing solutions are competitive inhibitors of PTPs, pervanadate is an irreversible inhibitor of PTPs. 

Elastin gene expression in rat lung fibroblasts was selectively inhibited by okadaic acid (Berk et al. 1996). In vitro, 5 nM had minimal effects (91 % control values) on elastin mRNA levels okadaic acid at 25 nm and 50 nm decreased elastin mRNA to 23 and 6 % of control levels, respectively. Inhibition of protein synthesis with cycloheximide did not block okadaic add-induced suppression of elastin mRNA levels. Okadaic acid had minimal effect of rat GTP-binding protein mRNA levels. Sodium orthovanadate, a tyrosine phosphatase inhibitor, induced minor decreases in elastin mRNA levels at micromolar concentration. Protein kinase C desensitisation by prolonged exposure to phorbol 12-myristate 13-acetate did not alter the effect of okadaic add on elestin mRNA levels. 

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