Endocrine Abstracts

The cyclic AMP/PKA signalling cascade is involved in the pathogenesis of cortisol-secreting adrenocortical tumors (ACT). Defects in cell cycle checkpoints play a major role in oncogenesis. The PKA regulatory subunits PRKARIA and PRKARIIb are involved in cell survival and steroidogenesis in the adrenocortical carcinoma H295R cell line. We have previously shown that their inactivation enhances the accumulation of cells in the G2 phase and activates PKA and MAPkinases pathways.

This study investigates the correlation between the cell cycle phases and the adrenal steroid secretion, as well as their control by PKA.

Methods: Using pharmacologic drugs, H295R cells were synchronized at specific cell cycle check point (G1 phase), (S phase) and (G2 phase). The cell cycle distribution (Cytometry), the expression of cyclins, PKA subunits, cell signalling pathways, StAR and steroidogenic enzymes were analysed. The effect of PKA activation either by the different PKA subunits, or cAMP, PKA inactivation by H89 and PKI along the cell cycle synchronization were studied.

Results: Cells synchronized at G2 phase increased the expression of the steroidogenic enzymes and steroid secretion. Arresting H295R in G1 phase decreased the steroidogenic enzymes expression and cortisol secretion. PKA subunits distribution and PKA activity modulation were cell cycle dependent. PKA activation by PRKARIA inactivation counteracted specifically the decrease of steroidogenesis in cells arrested in G1 phase: StAR/luc reporter gene activity and cell progression in G2 phase were stimulated. PRKARIIb inactivation and PRKACA overexpression or cAMP increased the StAR/luc reporter gene activity, independently of the cell cycle check point arrest. The H89 and PKI differentially reduced StAR/luc reporter gene activity, and both reversed the cell cycle in the G2 arrested cells.

Conclusion: Inactivation of the Carney complex gene stimulates steroidogensis in the low steroidogenic G1 phase arrested cells. This study shows a link between the cell cycle check points and the regulation of steroidogenesis, in which the PRKARIA subunit is a key regulator of both cell cycle and steroidogenesis.