Protein serine/threonine phosphatase 2A activity is inhibited by cAMP in MA-10 cells.
ABSTRACT PP1 and PP2A are members of the protein serine/threonine phosphatases (PPs) family and their activities have been proposed as a requirement for hormone- and cAMP-regulated steroid synthesis. These findings raise the question whether the PPs activity is increased by hormonal action in steroidogenic systems. Thus, the aim of the study was to evaluate the action of cAMP on the activity of PP1 and PP2A in MA-10 Leydig cells. Our results demonstrate that 8Br-cAMP stimulation produces a transient inhibition of PP2A activity. In contrast, PP1 activity remains unchangeable. As reported in other steroidogenic cells, cAMP-induced steroidogenesis in MA-10 cells is reduced by Cantharidin (Can) and also by Calyculin A (CA), two chemically unrelated PP1/PP2A inhibitors (data not shown). Taking into account the inhibitory effect of cAMP treatment on PP2A activity, the latest findings result paradoxical. Therefore, we next evaluated the action of these compounds on total protein synthesis. Can 10(-5) M and CA 10(-7) M markedly reduced total protein synthesis (35 and 50% respectively) in MA-10 cells, measured by 35S-methonine incorporation. These results suggest that hormone-dependent steroidogenesis is working through inhibition of PP2A-dependent dephosphorylation and the effect of PP1/PP2A inhibitors on steroidogenesis may be due to a general inhibition of protein synthesis rather than to a specific action on StAR protein induction.
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ABSTRACT: Protein kinase A (PKA) plays a crucial role in tau hyperphosphorylation, an early event of Alzheimer disease (AD), and 17beta-estradiol replacement in aging women forestalls the onset of AD. However, the role of estradiol in PKA-induced tau hyperphosphorylation is not known. Here, we investigated the effect of 17beta-estradiol on cAMP/PKA activity and the PKA-induced tau hyperphosphorylation in HEK293 cells stably expressing tau441. We found that 17beta-estradiol effectively attenuated forskolin-induced overactivation of PKA and elevation of cAMP, and thus prevented tau from hyperphosphorylation. These data provide the first evidence that 17beta-estradiol can inhibit PKA overactivation and the PKA-induced tau hyperphosphorylation, implying a preventive role of 17beta-estradiol in AD-like tau pathology.Neurochemical Research 04/2008; 33(9):1811-20. · 2.13 Impact Factor
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ABSTRACT: In addition to their multilineage potential, mesenchymal stem cells (MSCs) also have a wide range of functionality. Not only can MSCs reconstruct a tissue, but they also have the ability to control or cure other cells and can reconstruct a coordinating function. The opportunity to control other cells depends on MSCs being able to secrete factors like cytokines and chemokines. Therefore, we focused on asking, Which factors can be secreted by human MSCs? To answer this question, we analyzed the secreting profile of in vitro-expanded MSCs by using cytokine arrays. The media concentrations of 44 of the 120 analyzed cytokines were significantly increased by MSCs. Conversely, concentrations of 40 cytokines given with the sera were significantly decreased. The data presented here provide an overview about a large range of factors that were secreted by MSCs under cell culture conditions. These data indicate that MSCs demonstrate all previously described functions in cellular interactions without an external stimulus. The MSCs secreted angiogenic, immunosuppressive, anti-apoptotic, and proliferation-stimulating factors.Stem Cells and Development 03/2008; 17(1):199-206. · 4.67 Impact Factor