8Cl-cAMP modifies the balance between PKAR1 and PKAR2 and modulates the cell cycle, growth and apoptosis in human adrenocortical H295R cells

Abstract

Various types of protein kinase A (PKA) alterations have been observed in adrenocortical tumours and Carney complex (CNC). PKA is a heterotetramer of two regulatory and two catalytic subunits. The R1A and R2B proteins are the most abundant regulatory subunits in endocrine tissues. A decrease in R2B protein levels has been observed in adrenal adenoma, whereas tumours from patients with CNC display a decrease in R1A protein levels. Dysregulation of the balance between R1A and R2B may thus be involved in adrenal tumourigenesis. We investigated the impact of the differences in the balance of PKA subunits on cell growth using specific cAMP analogues. We assessed the effects of 8-chloroadenosine-cAMP (8Cl-cAMP), a site-selective activator of PKA R2B, in H295R adrenocortical cells. 8Cl-cAMP stimulated PKA activity, decreased R1A levels and increased R2B levels. It had no cytotoxic effects, initially stimulating DNA synthesis and then inducing apoptosis by disrupting G 2 /M progression. We observed an initial accumulation of cells in the S phase, translocation of cyclin A to the nucleus, CDK2 activation, sustained DNA synthesis and proliferating cell nuclear antigen accumulation. Cell cycle arrest in the G 2 phase was parallel with the accumulation of cyclin B and the inactivation of CDC2 kinase. The 8CPT-cAMP, which activates the R2B subunit, had similar effects. R2B silencing reduced the apoptosis induced by tumour necrosis factor a and transforming growth factor b. Thus, R2B is a key regulator of proliferation/differentiation in H295R cell line along with the complex balance between the PKA subunits. Activation of PKA R2B and dysregulation of the R1A/R2B balance regulate cell cycle progression and apoptosis in adrenocortical cells by modulating cyclin production and cyclin-dependent kinase activities.

PRKAR2B plays an oncogenic role in the castration-resistant prostate cancer

“…In adrenocortical human cell line, inactivation of PRKAR2B enhanced cell proliferation and reduced apoptosis [16]. Activation of PKAR2B by selective cAMP analogs alters the growth of adrenocortical cells [17]. A dramatic decrease in PKAR2B protein levels is observed in a subset of adrenocortical adenomas, however, its function is not clear [18].…”

The Role of Cyclic Nucleotide Signaling Pathways in Cancer: Targets for Prevention and Treatment

“…While these studies are preliminary, this is a promising approach as it could potentially result in reduced toxicity by lowering the dosage of the PKA activator that would be necessary to observe an effect. It has also been observed that there is a difference in the ratio between PKA-RI and PKA-RII in select cancer types [125,126]. Although more studies need to be conducted to fully understand the difference in the regulatory role of these isoforms these studies provide insight into the means of developing safe and effective inhibitors.…”

Comparison of the Effects of PRKAR1A and PRKAR2B Depletion on Signaling Pathways, Cell Growth, and Cell Cycle Control of Adrenocortical Cells

“…PKA is a holoenzyme that is formed by 2 regulatory subunits, type I (R1A and R1B) and type II (R2A and R2B), and 4 catalytic subunits (Cα, Cβ, Cγ, and Cx). Signaling via cAMP/PKA can either inhibit or stimulate cell proliferation depending on the cell type [1, 2]. Most cells contain both PKAI and PKAII isozymes and their relative abundance varies among species and tissues.…”