Localization of cAMP-dependent signal transducers in early rat liver carcinogenesis

Reconstruction of an integrated genome-scale co-expression network reveals key modules involved in lung adenocarcinoma

Our goal of this study was to reconstruct a “genome-scale co-expression network” and find important modules in lung adenocarcinoma so that we could identify the genes involved in lung adenocarcinoma. We integrated gene mutation, GWAS, CGH, array-CGH and SNP array data in order to identify important genes and loci in genome-scale. Afterwards, on the basis of the identified genes a co-expression network was reconstructed from the co-expression data. The reconstructed network was named “genome-scale co-expression network”. As the next step, 23 key modules were disclosed through clustering. In this study a number of genes have been identified for the first time to be implicated in lung adenocarcinoma by analyzing the modules. The genes EGFR, PIK3CA, TAF15, XIAP, VAPB, Appl1, Rab5a, ARF4, CLPTM1L, SP4, ZNF124, LPP, FOXP1, SOX18, MSX2, NFE2L2, SMARCC1, TRA2B, CBX3, PRPF6, ATP6V1C1, MYBBP1A, MACF1, GRM2, TBXA2R, PRKAR2A, PTK2, PGF and MYO10 are among the genes that belong to modules 1 and 22. All these genes, being implicated in at least one of the phenomena, namely cell survival, proliferation and metastasis, have an over-expression pattern similar to that of EGFR. In few modules, the genes such as CCNA2 (Cyclin A2), CCNB2 (Cyclin B2), CDK1, CDK5, CDC27, CDCA5, CDCA8, ASPM, BUB1, KIF15, KIF2C, NEK2, NUSAP1, PRC1, SMC4, SYCE2, TFDP1, CDC42 and ARHGEF9 are present that play a crucial role in cell cycle progression. In addition to the mentioned genes, there are some other genes (i.e. DLGAP5, BIRC5, PSMD2, Src, TTK, SENP2, PSMD2, DOK2, FUS and etc.) in the modules.

PRKAR1A overexpression is associated with increased ECPKA autoantibody in liver fluke-associated cholangiocarcinoma: application for assessment of the risk group

Cholangiocarcinoma (CCA) associated with Opisthorchis viverrini (Ov) chronic infection is the most frequent primary liver cancer in Thailand, and current approaches to early diagnosis and curative treatments are largely disappointing. We hypothesize a role for protein kinase A (PKA) in Ov-induced CCA. First, we studied the PKA isozyme switching in the liver from the hamster CCA model using quantitative (q) PCR, in situ hybridization, and immunohistochemical and western blot analysis. Second, the presence of extracellular PKA (ECPKA) in CCA cell lines and their conditioned media was demonstrated by western blot and PKA activity assay. Third, we determined the association between PRKAR1A expression and serum ECPKA autoantibody in patients with CCA by ELISA. We demonstrated that an increased PRKAR1A expression is restricted to the biliary cells starting from week 1, with remarkable up-regulation when CCA has completely developed by week 24. The switching of the PKA regulatory subunit isoforms from PRKAR2B/PKAII to PRKAR1A/PKAI is significantly associated with cholangiocyte proliferation. Further, we observed that human CCA cell lines express PRKAR1A but not PRKAR2B and excrete ECPKA. Finally, ECPKA autoantibodies are detected in serum of patients with CCA, adenocarcinoma, and Ov infection with periductal fibrosis, but not from Ov-infected subjects without periductal fibrosis lesion and healthy controls. We conclude that PKA isozyme switching and the PRKAR1A/PKAI pathway might contribute to the induction of cholangiocyte transformation and proliferation in Ov-induced CCA. Overexpression of PRKAR1A leads to secretion of ECPKA which is associated with serum autoantibody that may constitute a biomarker for human CCA genesis.

NOX2 activated by α1-adrenoceptors modulates hepatic metabolic routes stimulated by β-adrenoceptors

The NADPH oxidase (NOX) family of enzymes oxidase catalyzes the transport of electrons from NADPH to molecular oxygen and generates O(2)(•-), which is rapidly converted into H(2)O(2). We aimed to identify in hepatocytes the protein NOX complex responsible for H(2)O(2) synthesis after α(1)-adrenoceptor (α(1)-AR) stimulation, its activation mechanism, and to explore H(2)O(2) as a potential modulator of hepatic metabolic routes, gluconeogenesis, and ureagenesis, stimulated by the ARs. The dormant NOX2 complex present in hepatocyte plasma membrane (HPM) contains gp91(phox), p22(phox), p40(phox), p47(phox), p67(phox) and Rac 1 proteins. In HPM incubated with NADPH and guanosine triphosphate (GTP), α(1)-AR-mediated H(2)O(2) synthesis required all of these proteins except for p40(phox). A functional link between α(1)-AR and NOX was identified as the Gα(13) protein. Alpha(1)-AR stimulation in hepatocytes promotes Rac1-GTP generation, a necessary step for H(2)O(2) synthesis. Negative cross talk between α(1)-/β-ARs for H(2)O(2) synthesis was observed in HPM. In addition, negative cross talk of α(1)-AR via H(2)O(2) to β-AR-mediated stimulation was recorded in hepatocyte gluconeogenesis and ureagenesis, probably involving aquaporine activity. Based on previous work we suggest that H(2)O(2), generated after NOX2 activation by α(1)-AR lightening in hepatocytes, reacts with cAMP-dependent protein kinase A (PKA) subunits to form an oxidized PKA, insensitive to cAMP activation that prevented any rise in the rate of gluconeogenesis and ureagenesis.

Inhibition of the mitochondrial permeability transition by protein kinase A in rat liver mitochondria and hepatocytes

NO and cGMP administered at reperfusion after ischaemia prevent injury to hepatocytes mediated by the MPT (mitochondrial permeability transition). To characterize further the mechanism of protection, the ability of hepatic cytosol in combination with cyclic nucleotides to delay onset of the calcium-induced MPT was evaluated in isolated rat liver mitochondria. Liver cytosol plus cGMP or cAMP dose-dependently inhibited the MPT, required ATP hydrolysis for inhibition and did not inhibit mitochondrial calcium uptake. Specific peptide inhibitors for PKA (protein kinase A), but not PKG (protein kinase G), abolished cytosol-induced inhibition of MPT onset. Activity assays showed a cGMP- and cAMP-stimulated protein kinase activity in liver cytosol that was completely inhibited by PKI, a PKA peptide inhibitor. Size-exclusion chromatography of liver cytosol produced a single peak of cGMP/cAMP-stimulated kinase activity with an estimated protein size of 180-220 kDa. This fraction was PKI-sensitive and delayed onset of the MPT. Incubation of active catalytic PKA subunit directly with mitochondria in the absence of cytosol and cyclic nucleotide also delayed MPT onset, and incubation with purified outer membranes led to phosphorylation of a major 31 kDa band. After ischaemia, administration at reperfusion of membrane-permeant cAMPs and cAMP-mobilizing glucagon prevented reperfusion injury to hepatocytes. In conclusion, PKA in liver cytosol activated by cGMP or cAMP acts directly on mitochondria to delay onset of the MPT and protect hepatocytes from cell death after ischaemia/reperfusion.

Regulation of rat alveolar type 2 cell proliferation in vitro involves type II cAMP-dependent protein kinase

To elucidate the role of cAMP and different cAMP-dependent protein kinases (PKA; A-kinase) in lung cell proliferation, we investigated rat alveolar type 2 cell proliferation in relation to activation or inhibition of PKA and PKA regulatory subunits (RIIalpha and RIalpha). Both the number of proliferating type 2 cells and the level of different regulatory subunits varied during 7 days of culture. The cells exhibited a distinct peak of proliferation after 5 days of culture. This proliferation peak was preceded by a rise in RIIalpha protein level. In contrast, an inverse relationship between RIalpha and type 2 cell proliferation was noted. Activation of PKA increased type 2 cell proliferation if given at peak RIIalpha expression. Furthermore, PKA inhibitors lowered the rate of proliferation only when a high RII level was observed. An antibody against the anchoring region of RIIalpha showed cell cycle-dependent binding in contrast to antibodies against other regions, possibly related to altered binding to A-kinase anchoring protein. Following activation of PKA, relocalization of RIIalpha was confirmed by immunocytochemistry. In conclusion, it appears that activation of PKA II is important in regulation of alveolar type 2 cell proliferation.

HIP/PAP, a C-type lectin overexpressed in hepatocellular carcinoma, binds the RII alpha regulatory subunit of cAMP-dependent protein kinase and alters the cAMP-dependent protein kinase signalling

HIP/PAP is a C-type lectin overexpressed in hepatocellular carcinoma (HCC). Pleiotropic biological activities have been ascribed to this protein, but little is known about the function of HIP/PAP in the liver. In this study, therefore, we searched for proteins interacting with HIP/PAP by screening a HCC cDNA expression library. We have identified the RII alpha regulatory subunit of cAMP-dependent protein kinase (PKA) as a partner of HIP/PAP. HIP/PAP and RII alpha were coimmunoprecipitated in HIP/PAP expressing cells. The biological relevance of the interaction between these proteins was established by demonstrating, using fractionation methods, that they are located in a same subcellular compartment. Indeed, though HIP/PAP is a protein secreted via the Golgi apparatus we showed that a fraction of HIP/PAP escaped the secretory apparatus and was recovered in the cytosol. Basal PKA activity was increased in HIP/PAP expressing cells, suggesting that HIP/PAP may alter PKA signalling. Indeed, we showed, using a thymidine kinase-luciferase reporter plasmid in which a cAMP responsive element was inserted upstream of the thymidine kinase promoter, that luciferase activity was enhanced in HIP/PAP expressing cells. Thus our findings suggest a novel mechanism for the biological activity of the HIP/PAP lectin.