PI3-kinase activates p38 MAPK independently of PKB/Akt during myogenic differentiation of H9c2 cardiac myoblasts

Abstract

Estrogens potentiate the differentiation of myeloid cells, but little is known about estrogen metabolism in such cells. In this abstract we show that release of estrone from estrone sulphate,catalysed by the enzyme steroid sulphtase, is a major source of estrone in HL60 promyelocytic cells. Estrone was not further metabolised to 17p-estradiol in vivo. Treatment of HL60 cells with retinoids or la,25-dihydroxyvitamin D3increased the expression of steroid sulphatase mRNA and enzyme activity. These changes were contemporaneous with the induction of CDllb, an early marker of myeloid differentiation. Use of RAR and RXR agonists and antagonists revealed that both classes of receptor can drive steroid sulphatase up-regulation. Steroid sulphatase activity fluctuates during the cell cycle, being highest around the GI/S phase boundary. HI60 cells express both classes of estrogen receptor (ERa and ERP). During differentiation of HL60 cells there is also increased conversion of 17P-estradiol to estrone by an oxidative 17phydroxysteroid dehydrogenase. These observations support the view that local estrone production may have a role in orchestrating haemopoietic cell differentiation.Detection and partial characterization of a metallothionein-Oo4 like protein in Dictyostelium discoideum. Dictyostelium discoideum grows as single amoebae engulfing bacteria and digesting them. When the food is exhausted the amoebae aggregate to form a multicellular organism which differentiates, actively moves and displays other activities which have made it a valuable experimental organism for the study of development. The continuous intake of bacteria must result in the buildup of metals but no reports have appeared describing its processing of metal ions. We have grown the organism on E. coli in the presence of 2mM ZnC12 , harvested the cells in the culmination stage of development, homogenized them and analyzed the supernatant. We detected and purified to near homogeneity a small, heat-stable protein whose molecular size is 3000-3500 by SDS-PAGE and gel filtration chromatography, is sensitive to trypsin and has a high Lowering the pH in ste s from 8.0 to 4.7 reduced and finally eliminated the A2' peak; the spectrum was not affected by calcium or cobalt ions but was decreased by cadmium. Based on these findings we suggest that this is a zinc metallothionein. The amount of the protein was highest during the aggregation stage which suggests that it plays a role during the development of the organism.The activation of PI)-kinase and p38 MAPK is required for myogenic differentiation. However, it has not been reported that there is crosstalk between these two kinases during this process. Therefore, in this study we attempted to investigate this possibility using H9c2 cardiac myoblasts. When these cells were induced to differentiate, both kinases were activated. Consistent with this result, LY294002 and SB203580, the inhibitors of these kinases, inhibited myogenic differentiation. Ly294002 suppressed p38 MAPK activity in a dose-dependent manner, but S...