The effect of lutropin on specific protein synthesis in tumour Leydig cells and in Leydig cells from immature rats

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Abstract
The amount of 35S incorporated into the various proteins after separation by electrophoresis on sodium dodecyl sulfate/polyacrylamide gels was used as an estimate of their synthesis in Leydig cells. Increased synthesis of proteins with apparent MW 27,000 and 29,000 was observed 3 h after addition of lutropin with Leydig tumor cells. Incubation of Leydig cells from immature rats with lutropin (100 ng/ml) for 2 h or longer resulted in increased synthesis of proteins with apparent MW 11,000, 21,000, 27,000 and 29,000. At higher concentrations (.gtoreq. 100 ng/ml) of lutropin there was a decrease in the synthesis of a protein with apparent MW 13,000. The amount of lutropin required for the stimulation of protein synthesis in both types of Leydig cells was similar to that needed for stimulation of steroidogenesis. Lutropin-stimulated specific protein synthesis was not due to increased concentrations of testosterone because addition of testosterone to the cells had no effect on the synthesis of proteins, and inhibition of steroidogenesis with elipten phosphate (an inhibitor of the cholesterol side chaincleavage enzyme complex) did not abolish the effect of lutropin. The stimulation of specific protein synthesis was also not due to contaminating follitropin in the lutropin preparation. Addition of actinomycin D to the cells at the start of incubation prevented the effect of lutropin on specific protein synthesis, indicating that mRNA synthesis may be needed for this effect of lutropin. Incubation of cells with cycloheximide for 30 min after labeling of the proteins did not result in a detectable decrease in the amounts of the lutropin-induced proteins, indicating that their half-life is longer than 30 min.