A Cell-Autonomous Molecular Cascade Initiated by AMP-Activated Protein Kinase Represses Steroidogenesis

Steroid hormones regulate essential physiological processes, and inadequate levels are associated with various pathological conditions. In testosterone-producing Leydig cells, steroidogenesis is strongly stimulated by luteinizing hormone (LH) via its receptor leading to increased cyclic AMP (cAMP) production and expression of the steroidogenic acute regulatory (STAR) protein, which is essential for the initiation of steroidogenesis. Steroidogenesis then passively decreases with the degradation of cAMP into AMP by phosphodiesterases. In this study, we show that AMP-activated protein kinase (AMPK) is activated following cAMP-to-AMP breakdown in MA-10 and MLTC-1 Leydig cells. Activated AMPK then actively inhibits cAMP-induced steroidogenesis by repressing the expression of key regulators of steroidogenesis, including Star and Nr4a1. Similar results were obtained in Y-1 adrenal cells and in the constitutively steroidogenic R2C cells. We have also determined that maximum AMPK activation following stimulation of steroidogenesis in MA-10 Leydig cells occurs when steroid hormone production has reached a plateau. Our data identify AMPK as a molecular rheostat that actively represses steroid hormone biosynthesis to preserve cellular energy homeostasis and prevent excess steroid production.     

Effect of seed pretreatments on phosphorus uptake by alfalfa

Summary A pot experiment was made to study the effect of two seed pretreatments on the phosphorus uptake by alfalfa in two different soils. The results showed that the dry weight of both the tops and the roots as well as the total P-uptake of alfalfa in both soils increased when the seeds were previously soaked in 0.5 mol/l KH₂PO₄ or 150 ppm indoleacetic acid for 6 hours when compared with the control. The increase was much higher with the seeds soaked in the former than in the later solution. Both soil and fertilizer phosphorus taken up by alfalfa increased by seed soaking in the above mentioned solutions and the increase was most pronounced in the fraction that derived from the soil.Professor of Soils, Professor of Plant Nutrition and a Lecturer in the Faculty of Agriculture, Ain Shams University, Cairo, respectively.