Cyclic AMP-dependent protein kinase-mediated desensitisation of adrenal tumour cells

Abstract

Y-l mouse adrenal cortical tumour cells increase their production of steroids and cAMP while decreasing cell population growth in response to treatment with ACTH. With a fluorescent conjugate of the heat-stable protein kinase inhibitor, the time- and dose-dependent dissociation of cAMP-dependent protein kinase can be demonstrated following ACTH stimulation of Y-1 adrenal tumour cells, and the kinetics of its free catalytic subunits can be followed. After 60 min ACTH (6 × 10 −10 M) stimulation, a 4-fold rise in catalytic subunits was detected in the nucleus while a 2-fold increase was noted in the cytoplasm. When Y-1 cells had been previously treated with ACTH, they no longer secreted steroids to the same level in response to a subsequent exposure to ACTH. In addition to the altered steroidogenic response the cells become resistant to the effect of subsequent ACTH treatment on cell division and cAMP production as measured by protein kinase dissociation. Y-1 adrenal cells, that had been pretreated with ACTH, had an altered activation of protein kinase. Although there was an increase in cytoplasmic dissociation following subsequent ACTH stimulation of the pretreated cell, this increase was negligible when compared to that in the non-pretreated cultures. The nucleus of the ACTH-pretreated cell failed to significantly dissociate protein kinase following subsequent ACTH treatment. The data suggest that the phenomenon of desensitisation may be due to a decrease in dissociation of cAMP-dependent protein kinase, especially in the nucleus.