Endocrine Abstracts

Introduction: The inactivating mutations of the Carney complex gene PRKAR1A (regulatory subunit RIA of PKA) cause bilateral adrenocortical tumors (PPNAD: Primary Pigmented Nodular Adrenocorticel disease) over-secreting cortisol. This leads to stimulation of PKA activity, however the mechanisms of adrenal tumorigenesis and cortisol dysregulation are not fully understood. In order to identify target genes of PRKAR1A inactivation in adrenal cortex we undertook a comparative transcriptome analysis. This work aims to understand the role of the major identified target in cortisol dysregulation and PPNAD development.

Methods: Comparison of the transcriptome of PPNAD tissues, normal human adrenals, and H295R adrenal cortical cells with and without inactivation of PRKAR1A identified a main gene whose expression is decreased following PRKAR1A inactivation: KCTD20 (potassium channel tetramerization domain containing). The H295R and HEK293 cells were used to understand the transcriptional regulation of KCTD20 by PKA RIA and evaluate the consequences of the inactivation (siKCTD20) and the overexpression of KCTD20 (vector-KCTD20).

Results: The decreased KCTD20 expression after PRKAR1A inactivation is independent of PKA activity. Overexpression of KCTD20 increases apoptosis and decreases proliferation. Inactivation of KCTD20 protects against apoptosis (P<0.01), increases the activity of the Star-Luc reporter (P<0.001), the expression of the Star (P=0.01) and CYP11B1 genes (P=0.05), and cortisol production of H295R cells (P<0.05). These effects seem independent of PKA activity. Invalidation of KCTD20 results in membrane depolarization in response to KCL and increases intracellular calcium (P<0.001).

Conclusion: PKA RIA acts on KCTD20 via a PKA independent pathway. KCTD20 may play a role in adrenal Cushing by mechanisms independent of PKA activity. Its role in calcium signalling could be an important element to study.