Calcium uptake and gp80 messenger RNA destabilization follows cAMP receptor down regulation in Dictyostelium discoideum

Abstract

The mechanism by which high concentrations of cAMP selectively destabilize the gp80 mRNA in Dictyostelium discoideum was investigated. This treatment which leads to down-regulation of the cAMP receptor was also found to cause an increase in calcium uptake. Given this observation, we sought a role for calcium as a second messenger in the degradation of the gp80 mRNA. Changes in the mRNA levels were examined after treating cells with compounds known to alter their intracellular Ca 2+ concentrations. This included the use of A23187, Ca 2+, 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate HCl (TMB-8), LiCl and 8-p-chlorophenylthioadenosine 3′,5′-cyclic monophosphate (ClPhS-Ado-3′:5′-P). The sum of the data suggest that it is the cAMP-induced influx of Ca 2+ acoss the plasma membrane, as opposed to a cAMP-mediated release of Ca 2+ from intracellular stores, that initiates gp80 mRNA degradation. Treatment of cells with Concanavalin A (ConA) to induce cAMP receptor down-regulation, also causes a reduction in gp80 mRNA levels and an increase in calcium uptake.