Protein phosphatase inhibitors enhance the expression of an alpha-amylase gene, alpha Amy3, in cultured rice cells.

A rice (Oryza sativa L.) gene for alpha-amylase, alpha Amy3, was strongly and rapidly induced by treatment of suspension-cultured cells with okadaic acid (OA), a potent and specific inhibitor of protein serine/threonine phosphatases 1 and 2A. The massive accumulation of alpha Amy3 mRNA in response to OA treatment was due to the stimulation of gene transcription and a partial stabilization of this mRNA. This induction of alpha Amy3 message by OA occurred even though cellular protein synthesis was inhibited. Simultaneous treatment of cultured cells with OA and anisomycin synergistically induced alpha Amy3 expression. In addition, the inhibition of protein synthesis stabilized OA-induced alpha Amy3 mRNA. In the presence of protein kinase inhibitors H7, W7, and H8, alpha Amy3 mRNA accumulation induced by OA was unaffected. These results indicate that OA-dependent alpha Amy3 induction is regulated transcriptionally by a signal transduction pathway involving protein phosphorylation, but independent of both protein kinase C and Ca2+/calmodulin- or Ca(2+)-dependent protein kinases. Furthermore, an AMP-activated protein kinase may be required for this induction of alpha Amy3 expression.