Recurrent activating mutation in PRKACA in cortisol-producing adrenal tumors

Richard Lifton and colleagues identify a recurrent activating mutation in PRKACA, which encodes the catalytic subunit of protein kinase A, in cortisol-producing adrenal tumors. They further show that the mutation results in loss of binding by the regulatory subunit PRKAR1A, leading to increased phosphorylation of downstream targets. Adrenal tumors autonomously producing cortisol cause Cushing's syndrome1,2,3,4. We performed exome sequencing of 25 tumor-normal pairs and identified 2 subgroups. Eight tumors (including three carcinomas) had many somatic copy number variants (CNVs) with frequent deletion of CDC42 and CDKN2A, amplification of 5q31.2 and protein-altering mutations in TP53 and RB1. Seventeen tumors (all adenomas) had no somatic CNVs or TP53 or RB1 mutations. Six of these had known gain-of-function mutations in CTNNB1 (β-catenin)5,6 or GNAS (Gαs)7,8. Six others had somatic mutations in PRKACA (protein kinase A (PKA) catalytic subunit) resulting in a p.Leu206Arg substitution. Further sequencing identified this mutation in 13 of 63 tumors (35% of adenomas with overt Cushing's syndrome). PRKACA, GNAS and CTNNB1 mutations were mutually exclusive. Leu206 directly interacts with the regulatory subunit of PKA, PRKAR1A9,10. Leu206Arg PRKACA loses PRKAR1A binding, increasing the phosphorylation of downstream targets. PKA activity induces cortisol production and cell proliferation11,12,13,14,15, providing a mechanism for tumor development. These findings define distinct mechanisms underlying adrenal cortisol-producing tumors.