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The multiple neoplasia syndrome Carney complex (CNC) is caused by heterozygote mutations in the gene, which codes for the RIα regulatory subunit (PRKAR1A) of protein kinase A. Inactivation of PRKAR1A and the additional loss of the normal allele lead to tumors in CNC patients and increased cyclic AMP signaling in their cells, but the oncogenetic mechanisms in affected tissues remain unknown. Previous studies suggested that PRKAR1A down-regulation may lead to increased mitogen-activated protein kinase (MAPK) signaling. Here, we show that, in lymphocytes with PRKAR1A-inactivating mutations, there is increased extracellular signal-regulated kinase (ERK) 1/2 and B-raf phosphorylation and MAPK/ERK kinase 1/2 and c-Myc activation, whereas c-Raf-1 is inhibited. These changes are accompanied by increased cell cycle rates and decreased apoptosis that result in an overall net gain in proliferation and survival. In conclusion, inactivation of PRKAR1A leads to widespread changes in molecular pathways that control cell cycle and apoptosis. This is the first study to show that human cells with partially inactivated RIα levels have increased proliferation and survival, suggesting that loss of the normal allele in these cells is not necessary for these changes to occur. (Cancer Res 2006; 66(21): 10603-12)

Supplementary Figure 1 from PRKAR1A Inactivation Leads to Increased Proliferation and Decreased Apoptosis in Human B Lymphocytes

Supplementary Table 1 from PRKAR1A Inactivation Leads to Increased Proliferation and Decreased Apoptosis in Human B Lymphocytes

Supplementary Figure 1 Legend from PRKAR1A Inactivation Leads to Increased Proliferation and Decreased Apoptosis in Human B Lymphocytes

Cell signaling is known to be involved in the development and activation of many cancers, and has been the subject of abundant research in the field of cancer (Levitzki & Klein, 2010; Robinson-White & Stratakis, 2002). In response to extracellular and intracellular stimuli, protein kinase mediated pathways orchestrate the activation of cell signaling cascades to control cell growth, proliferation, differentiation and survival. However, there is tremendous complexity in tumor cell signaling (Iqbal et al., 2010). Signaling experiments have demonstrated that many different stimuli may activate the same pathways and many pathways interact (“cross talk”) to modify and influence the outcome of a specific extracellular signal. In particular, the protein kinase A (PKA) pathway has been viewed as the central hub in the mediation of signals in endocrine tumorigenesis (Robinson-White & Stratakis, 2002). Depending on the species, tissue, cell type and ligand involved, the PKA hub interacts with high versatility with the mitogen activated protein kinase (MAPK), protein kinase B (akt/PKB), protein kinase C (PKC) and Wnt pathways to promote endocrine and other tumor cell development and progression (Almeida et al., 2010; Robinson-White & Stratakis, 2002). The purpose of this review is to highlight recent findings on the involvement of the PKA cell signaling pathway in endocrine tumorigenesis, and to define current clinical strategies and future perspectives for the treatment of endocrine and other tumors.

Little is known about the mechanism of action of anesthetics at the biochemical level. The present work, however, gives evidence that barbiturates inhibit inositol phospholipid hydrolysis in both intact and permeabilized rat basophilic leukemia (RBL-2H3) cells by an effect on GTP-binding proteins (G-proteins). Inhibition of hydrolysis was observed when intact cells were stimulated with antigen (DNP24 BSA) or with oligomers of IgE. The inhibition was dependent on the concentration and type of barbiturate used with an order of inhibitory action of secobarbital less than S(-) pentobarbital less than pentobarbital less than R(+) pentobarbital less than phenobarbital. The relatively inactive analogue, (1'RS, 3'SR) 3-hydroxypentobarbital caused little (less than 30% at 1 mM) or no inhibition (at 0.1-0.5 mM). In permeabilized cells, the hydrolysis induced by DNP24 BSA and the nonhydrolyzable analogue of GTP, GTP gamma S (2-100 microM), was also inhibited by pentobarbital. The inhibition of hydrolysis was decreased as pH increased, and was no longer apparent at pH 7.8, a possible indication that the inhibitory effect was due to the unionized form of the drug. In permeabilized cells, the inhibition by pentobarbital occurred in the presence or absence of Ca2+ and was uncompetitive in nature (Km = 7.1 microM for GTP in controls vs. 1.6 microM in the presence of 0.5 mM pentobarbital). Taken together, the data suggest that barbiturates alter the activity of G-proteins independently of Ca2+, and the inhibition may depend on both the hydrophobic properties and the stereospecific and structural features of the molecule.

Barbiturates alter cardiovascular function, in part by an effect on vascular cells. However, a biochemical mechanism for the effect is unknown. We have, therefore, studied the effect of barbiturates on inositol phospholipid hydrolysis in cultured rat aortic endothelial cells. Hydrolysis was stimulated by angiotensin II, norepinephrine and phenylephrine. Pentobarbital, and other barbiturates, inhibited hydrolysis at pharmacological and clinical concentrations (0.1–0.5 mM). The inhibition by pentobarbital was concentration-dependent, reversed by washing, and was decreased by high concentrations of angiotensin II. Kinetic studies gave an apparent K m of hydrolysis by angiotensin II of 1.2 nM, which showed mixed inhibition by pentobarbital (K i = 0.45 mM). Schild analysis of data obtained from pentobarbital inhibition curves also showed a deviation from a competitive type inhibition. [ 125 I]Angiotensin II was bound to a high-affinity receptor (K d = 1.2 mM), which showed a competitive type inhibition of binding by pentobarbital (0.5 mM). Although inhibition of [ 125 I]angiotensin II binding appeared to be competitively inhibited by pentobarbital, the data, taken together, point to a deviation from a simple competitive type inhibition.