Effect of the regulatory subunit of cAMP-dependent protein kinase on the genetic activity of eukaryotic cells

MicroRNA-802 Inhibits Cell Proliferation and Induces Apoptosis in Human Laryngeal Cancer by Targeting cAMP-Regulated Phosphoprotein 19

BACKGROUND/AIMS

miR-802 plays a key role in cancer progression and development. The purpose of this work is to investigate the functional role of miR-802 in laryngeal cancer and to elucidate the function of miR-802 and cAMP-regulated phosphoprotein 19 (ARPP19) on laryngeal cancer.

METHODS

RT-qPCR was applied to study the expression level of ARPP19 and miR-802 in the laryngeal carcinoma cell lines and tissues. CCK-8, colony formation, flow cytometry (FACS) assay were used to study the effect of ARPP19 and miR-802 on apoptosis, proliferation, and cell cycle of laryngeal carcinoma cells. Target gene prediction and luciferase reporter gene assay were applied to identify target gene of miR-802. The transcriptional mRNA and protein expression levels of ARPP19 were measured by RT-qPCR or Western blotting.

RESULTS

miR-802 was down-regulated in laryngeal carcinoma cell lines and tissues. Laryngeal cancer cells transfected by miR-802 mimic were significantly inhibited in the terms of cell colony formation and proliferation. Furthermore, miR-802 can inhibit the expression level of ARPP19 by directly targeting the 3' untranslated region (3'-UTR) of ARPP19. Overexpression of the ARPP19 gene can reverse the suppressive effect of miR-802 on laryngeal cancer cells.

CONCLUSION

miR-802 can exert tumor suppressor effects in laryngeal carcinoma by targeting ARPP19, indicating that miR-802 protein may play a role of potential therapeutic target for clinical laryngeal cancer.

Protein kinase A: regulation and receptor-mediated delivery of antisense oligonucleotides and cytotoxic drugs

Protein kinases help regulate eukaryotic cell division. We investigated the regulation of cAMP-dependent protein kinase A (PKA) and casein kinase (CK) type I activity in normal cells and in cancer. To assess this activity in biopsies we suggest a new parameter--the ratio of CK activity and total PKA activity divided by cAMP concentration: CK/PKA/cAMP. In 98 samples of colon mucosa in normal, inflamed, polyp, and adenocarcinoma cells, we found this parameter to be fairly constant in normal conditions and increased 10-fold in colon cancer; the ratio does not depend on the place of biopsy or the patient's age or sex. Experiments with model systems of concanavalin A-stimulated lymphocytes and regenerating rat liver showed that in normal cell proliferation the parameter increases 2-3-fold, as compared to a 30-fold increase in cancer. Unlike normal cells, malignant cells show CK activation and decrease of cAMP; therefore, PKA activity decreases. This suggests a correlation of CK and PKA activity and significant damage to their regulation at pathological changes of tissue proliferation. To further study concerted CK and PKA regulation we used monoclonal antibodies (mAbs) against cAMP-dependent protein kinase regulatory subunit RKII beta. We produced 11 antibodies in three groups: inhibiting, which block cAMP binding with RII beta and inhibit holoenzyme formation (RS6); activating, which enhance cAMP binding and do not affect holoenzyme formation (RS28); and neutral (RS17). To investigate mAb influence on protein kinase regulation in live cells we permeabilized pheochromocytoma PC12 by digitonin. When used at 5-microM concentration for 5 min, digitonin allowed us to deliver mAb into PC12 cells at 30-34-nM concentration, leaving 68-75% viable cells. Protein kinase activity was measured within 0.5 and 4 h after incorporation of mAbs into cells. After 30 min incorporation, mAb RS6 blocked PKA activation in PC12 cells under the influence of cAMP; other mAbs showed no effect. mAb RS6 caused a 4-fold increase of free C subunit activity 4 h after incorporation. mAb RS38 decreased R2C2 activity and did not influence C subunit activity. The change of free C subunit activity caused by mAb incorporation was followed by a synchronized, well-balanced change of CK type I activity, which suggests a correlation between the two phosphorylation systems of cell proteins.

Role of cholinergic neuromuscular transmission in the neuroregulation of the autophosphorylatable regulatory subunit of cyclic AMP-dependent protein kinase type II and the acetylcholine receptor content in skeletal muscle

Previously, we found that the in vitro [32P]-autophosphorylation of the regulatory subunit of cyclic AMP-dependent protein kinase type II in rat soleus muscles is subject to a nerve-stump-length-dependent neuroregulation which indicates that this event is dependent upon some neural signal other than the impulse-directed release of acetylcholine. In this investigation, tetrodotoxin and alpha-bungarotoxin were also administered to further differentiate the effect of impulse-directed and spontaneously released acetylcholine upon this event and also upon the appearance of new acetylcholine receptors as measured by the binding of radioiodinated bungarotoxin. A 24 h blockade of cholinergic transmission with either neurotoxin did not change the phosphorylation level of the regulatory subunit, while a significant increase is observed when solei are surgically denervated for this period. The phosphorylation level and also the acetylcholine receptor content were increased only after more prolonged (48-96 h) muscle inactivity was produced with the neurotoxins. However, then their effects may not be solely related to alterations in cholinergic transmission. Taken together, our results do not support a trophic role for spontaneously released acetylcholine with respect to the two neurotrophic events studied.

Calcium, cyclic AMP and protein kinase C--partners in mitogenesis

Evidence is steadily mounting that the proto-oncogenes, whose products organize and start the programs that drive normal eukaryotic cells through their chromosome replication/mitosis cycles, are transiently stimulated by sequential signals from a multi-purpose, receptor-operated mechanism (consisting of internal surges of Ca2+ and bursts of protein kinase C activity resulting from phosphatidylinositol 4,5-bisphosphate breakdown and the opening of membrane Ca2+ channels induced by receptor-associated tyrosine-protein kinase activity) and bursts of cyclic AMP-dependent kinase activity. The bypassing or subversion of the receptor-operated Ca2+/phospholipid breakdown/protein kinase C signalling mechanism is probably the basis of the freeing of cell proliferation from external controls that characterizes all neoplastic transformations.

Altered autophosphorylation of adenosine 3',5'-phosphate-dependent protein kinase in the dunce memory mutant of Drosophila melanogaster

The phosphorylation-dephosphorylation, in the presence of adenosine 5'-[gamma-32P]triphosphate, of a polypeptide of apparent molecular mass 53,000 has been compared in head homogenates of wild type and memory mutant dunceM11 strains of Drosophila melanogaster. In both strains, labelling of the 53 kilodalton protein required exogenous adenosine 3',5'-phosphate (cAMP), but in dunceM11 cAMP at higher concentration (above approximately 3 microM) caused the rapid disappearance of the label. This differential dephosphorylation can be attributed to the lack of a cAMP-specific phosphodiesterase isoenzyme in the mutant. Several lines of evidence indicate that the 53 kilodalton protein is identical with the regulatory subunit of cAMP-dependent protein kinase. The findings suggest that in the mutant's nerve cells the state of phosphorylation of the regulatory subunit of cAMP-dependent protein kinase is altered, which may contribute to the biochemical disorder leading to the memory deficit.

Phosphorylative neuromodulation of the regulatory subunit of cyclic AMP-dependent protein kinase type II in skeletal muscle

The phosphorylative neuromodulation of the regulatory subunit of protein kinase type II (R-II) in cytosolic fractions from denervated and sham-operated, contralateral soleus muscles of the rat was evaluated. The denervation-induced increase in the 32P-phosphorylation of R-II is not related to an increased dephosphorylation by cation-dependent or cation-independent protein phosphatases in the cytosolic fractions. The level of 32P-phosphorylation of an exogenous heptapeptide substrate (Kemptide) by dissociated catalytic subunits of cyclic AMP-dependent protein kinase in cytosolic fractions from denervated and sham-operated solei did not differ. Also, no change in the concentration of cytosolic R-II assessed by competitive enzyme-linked immunosorbent assays (ELISA) was found after denervation. However, the in vitro 32P-phosphorylation of R-II in these samples was increased. Taken together, our results suggest that the increased availability of autophosphorylatable sites reflects an in vivo modulation of R-II phosphorylation rather than a significant change in total R-II content.