Epidermal growth factor regulates glucose metabolism through lactate dehydrogenase A messenger ribonucleic acid expression in cultured porcine Sertoli cells

In a previous work, we reported that lactate dehydrogenase A4 (LDH A4) acti vity is a key step in the stimulatory effect of epidermal growth factor (EG F) on lactate production in cultured Sertoli cells. Here, we further invest igated the regulatory mechanisms involved in EGF action on LDH A mRNA expre ssion. Steady-state levels of LDH A mRNA analyzed by Northern blot hybridiz ation were induced to 2.9-fold in response to a 36-h incubation with EGF (E D50 = 4 ng/ml, 0.63 x 10(-9) M). Whether EGF-induced increases of LDH A mRN A levels are the result of increased transcription and/or altered mRNA stab ility was investigated. The decay curves for the 1.5-kilobase LDH A mRNA tr anscript in Sertoli cells were not different in the absence or presence of EGF, suggesting that EGF did not affect LDH A mRNA stability. Inhibitors of protein synthesis (cycloheximide) and RNA synthesis (actinomycin D, and 5, 6-dichloro-1-beta-ribofuranosyl benzimidazole) completely abrogated the EGF -induced LDH A mRNA expression, indicating that EGF increased LDH A mRNA le vels through a transcriptional mechanism, which probably involves protein s ynthesis. Finally, the partial inhibitory effect of a protein kinase C (PKC ) inhibitor, bisindolylmaleimide, on EGF-stimulated LDH A mRNA supports a p artial involvement of PKC in the action of the growth factor. Since EGF is produced in Sertoli and in germ cells, its action is probably exerted in a context of a local control. As EGF also regulates other parameters involved in glucose metabolism its effect on LDH A might be viewed in a general con text related to the control of energy metabolism by the growth factor in th e testicular cells.