Nuclear translocation of the catalytic subunit of protein kinase A induced by an antisense oligonucleotide directed against the RIalpha regulatory subunit

PIP2 Alteration Caused by Elastic Modulus and Tropism of Electrospun Scaffolds Facilitates Altered BMSCs Proliferation and Differentiation

Aligned submicron fibers have played an essential role in inducing stem cell proliferation and differentiation. In this study, it is aimed to identify the differential causes of stem cell proliferation and differentiation between bone marrow mesenchymal stem cells (BMSCs) on aligned-random fibers with different elastic modulus, and to change the differential levels through a regulatory mechanism mediated by B-cell lymphoma 6 protein(BCL-6) and miRNA-126-5p(miR-126-5p). The results showed that phosphatidylinositol(4,5)bisphosphate alterations are found in the aligned fibers compared with the random fibers, which has a regular and oriented structure, excellent cytocompatibility, regular cytoskeleton, and high differentiation potential. The same trend is actual for the aligned fibers with a lower elastic modulus. The level of proliferative differentiation genes in cells is altered by BCL-6 and miR-126-5p mediated regulatory mechanisms to make the cell distribution nearly consistent with the cell state on low elastic modulus aligned fibers. This work demonstrates the reason for the difference of cells between the two kinds of fibers and on fibers with different elastic modulus. These findings provide more insights for understanding the gene-level regulation of cell growth in tissue engineering.

Diarylpropionitrile inhibits melanogenesis via protein kinase A/cAMP-response element-binding protein/microphthalmia-associated transcription factor signaling pathway in α-MSH-stimulated B16F10 melanoma cells

Diarylpropionitrile (DPN), a selective agonist for estrogen receptor β (ERβ), has been reported to regulate various hormonal responses through activation of ERβ in tissues including the mammary gland and brain. However, the effect of DPN on melanogenesis independent of ERβ has not been studied. The aim of this study is to examine the possibility of anti-melanogenic effect of DPN and its underlying mechanism. Melanin contents and cellular tyrosinase activity assay indicated that DPN inhibited melanin biosynthesis in alpha-melanocyte stimulating hormone-stimulated B16F10 melanoma cell line. However, DPN had no direct influence on in vitro tyrosinase catalytic activity. On the other hand, 17β-estradiol had no effect on inhibition of melanogenesis, suggesting that the DPN-mediated suppression of melanin production was not related with estrogen signaling pathway. Immunoblotting analysis showed that DPN down-regulated the expression of microphthalmia-associated transcription factor (MITF), a central transcription factor of melanogenesis and its down-stream genes including tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2. Also, DPN attenuated the phosphorylation of protein kinase A (PKA) and cAMP-response element-binding protein (CREB). Additionally, DPN suppressed the melanin synthesis in UVB-irradiated HaCaT conditioned media culture system suggesting that DPN has potential as an anti-melanogenic activity in physiological conditions. Collectively, our data show that DPN inhibits melanogenesis via down-regulation of PKA/CREB/MITF signaling pathway.

Prominin-1-Radixin axis controls hepatic gluconeogenesis by regulating PKA activity

Prominin-1 (Prom1) is a major cell surface marker of cancer stem cells, but its physiological functions in the liver have not been elucidated. We analyzed the levels of mRNA transcripts in serum-starved primary WT (Prom1+/+ ) and KO (Prom1-/- ) mouse hepatocytes using RNA sequencing (RNA-seq) data, and found that CREB target genes were downregulated. This initial observation led us to determine that Prom1 deficiency inhibited cAMP response element-binding protein (CREB) activation and gluconeogenesis, but not cyclic AMP (cAMP) accumulation, in glucagon-, epinephrine-, or forskolin-treated liver tissues and primary hepatocytes, and mitigated glucagon-induced hyperglycemia. Because Prom1 interacted with radixin, Prom1 deficiency prevented radixin from localizing to the plasma membrane. Moreover, systemic adenoviral knockdown of radixin inhibited CREB activation and gluconeogenesis in glucagon-treated liver tissues and primary hepatocytes, and mitigated glucagon-elicited hyperglycemia. Based on these results, we conclude that Prom1 regulates hepatic PKA signaling via radixin functioning as an A kinase-anchored protein (AKAP).

Enhanced antiproliferative and proapoptotic effects on prostate cancer cells by simultaneously inhibiting androgen receptor and cAMP-dependent protein kinase A

The androgen-signaling pathway with the androgen receptor (AR) as its key molecule is widely understood to influence prostate tumor growth significantly even after androgen ablation. Under androgen-deprived conditions, the AR may be activated inappropriately through interaction with other molecules, including cyclic AMP-dependent protein kinase A (PKA). In a previous study, we have shown that knocking down the AR significantly inhibits prostate tumor growth. In this study, we show that combined inhibition of the AR and the regulatory subunit I alpha of PKA (RIalpha) with small interference RNAs significantly increased the growth-inhibitory and proapoptotic effects of AR knockdown. This treatment strategy was effective in androgen-sensitive and in androgen ablation-resistant prostate cancer cells. In addition, we report that downregulating PKA RIalpha was sufficient to inhibit PKA signaling and interestingly also impaired AR expression and activation. Vice versa, AR knockdown induced a decline in PKA RIalpha, associated with reduced PKA activity. This mutual influence on expression level was specific, because siRNAs against the AR did not affect expression of PKA RIalpha in AR negative DU-145 cells and a siRNA control did not affect protein expression. Another important finding of our study was that depletion of PKA RIalpha also potentiated the antiproliferative effect of the antiandrogen bicalutamide in androgen-sensitive LNCaP. We therefore concluded that combined inhibition of PKA RIalpha and AR may be a promising new therapeutic option for prostate cancer patients and might be superior to solely preventing AR expression.

Imaging cyclic AMP changes in pancreatic islets of transgenic reporter mice

Cyclic AMP (cAMP) and Ca(2+) are two ubiquitous second messengers in transduction pathways downstream of receptors for hormones, neurotransmitters and local signals. The availability of fluorescent Ca(2+) reporter dyes that are easily introduced into cells and tissues has facilitated analysis of the dynamics and spatial patterns for Ca(2+) signaling pathways. A similar dissection of the role of cAMP has lagged because indicator dyes do not exist. Genetically encoded reporters for cAMP are available but they must be introduced by transient transfection in cell culture, which limits their utility. We report here that we have produced a strain of transgenic mice in which an enhanced cAMP reporter is integrated in the genome and can be expressed in any targeted tissue and with tetracycline induction. We have expressed the cAMP reporter in beta-cells of pancreatic islets and conducted an analysis of intracellular cAMP levels in relation to glucose stimulation, Ca(2+) levels, and membrane depolarization. Pancreatic function in transgenic mice was normal. In induced transgenic islets, glucose evoked an increase in cAMP in beta-cells in a dose-dependent manner. The cAMP response is independent of (in fact, precedes) the Ca(2+) influx that results from glucose stimulation of islets. Glucose-evoked cAMP responses are synchronous in cells throughout the islet and occur in 2 phases suggestive of the time course of insulin secretion. Insofar as cAMP in islets is known to potentiate insulin secretion, the novel transgenic mouse model will for the first time permit detailed analyses of cAMP signals in beta-cells within islets, i.e. in their native physiological context. Reporter expression in other tissues (such as the heart) where cAMP plays a critical regulatory role, will permit novel biomedical approaches.

cAMP and protein kinase A in endocrine (and other) tumors

Studies of the biological role of cAMP have indicated dual and often opposing effects on proliferation and differentiation. Elevation of the intracellular cAMP in normal and transformed cells may lead to cell proliferation; in other cells, it induces changes in morphology, apoptosis and/or differentiation. The best known mediator of cAMP action in the cell is cAMP-dependent protein kinase or protein kinase A (PKA). PKA exists as two different isozymes, designated type I (PKA-I) and type II (PKA-II); the two isoforms are essentially distinct in their physicochemical properties. The relative ratio of PKA-I and PKA-II varies throughout the cell cycle in cells of the same type, it changes significantly during development and follows different patterns in the various tissues. Disruption of the apparently fine balance between the main two PKA isozymes is strongly associated with tumorigenesis and tumor growth, and vice versa. The enormous variety of cAMP/PKA functions and the net effect of this signaling system on cellular growth, proliferation and differentiation have been the subject of debate for more than 30 years among investigators in the field. The relatively recent identification of PRKAR1A mutations and PKA-I deficiency as a cause of endocrine and other tumors in human and mice was instrumental in advancing our understanding of how cAMP and PKA work in regulating the cell cycle. This article reviews the current state of knowledge in the field; the use of pharmacologic modulation of the cAMP/PKA system with the goal of treating certain tumors appears to be near, although very little has been accomplished so far, at least in terms of studies on humans.

Oligonucleotide-Based Therapeutic Options against Hepatitis C Virus Infection

The hepatitis C virus (HCV) is the cause of a silent pandemic that, due to the chronic nature of the disease and the absence of curative therapy, continues to claim an ever-increasing number of lives. Current antiviral regimens have proven largely unsatisfactory for patients with HCV drug-resistant genotypes. It is therefore important to explore alternative therapeutic stratagems whose mode of action allows them to bypass viral resistance. Antisense oligonucleotides, ribozymes, small interfering RNAs, aptamers and deoxyribozymes constitute classes of oligonucleotide-based compounds designed to target highly conserved or functionally crucial regions contained within the HCV genome. The therapeutic expectation for such compounds is the elimination of HCV from infected individuals. Progress in oligonucleotide-based HCV antivirals towards clinical application depends on development of nucleotide designs that bolster efficacy while minimizing toxicity, improvement in liver-targeting delivery systems, and refinement of small-animal models for preclinical testing.

Melatonin reduces prostate cancer cell growth leading to neuroendocrine differentiation via a receptor and PKA independent mechanism

BACKGROUND

Melatonin, the main secretory product of the pineal gland, inhibits the growth of several types of cancer cells. Melatonin limits human prostate cancer cell growth by a mechanism which involves the regulation of androgen receptor function but it is not clear whether other mechanisms may also be involved.

METHODS

Time-course and dose-dependent studies were performed using androgen-dependent (LNCaP) and independent (PC3) prostate cancer cells. Cell number, cell viability, and cell cycle progression were studied. Neuroendocrine differentiation of these cells was evaluated by studying morphological and biochemical markers. Finally, molecular mechanisms including the participation of melatonin membrane receptors, intracellular cAMP levels, and the PKA signal transduction pathway were also analyzed.

RESULTS

Melatonin treatment dramatically reduced the number of prostate cancer cells and stopped cell cycle progression in both LNCaP and PC3 cells. In addition, it induced cellular differentiation as indicated by obvious morphological changes and neuroendocrine biochemical parameters. The role of melatonin in cellular proliferation and differentiation of prostate cancer cells is not mediated by its membrane receptors nor related to PKA activation.

CONCLUSIONS

The treatment of prostate cancer cells with pharmacological concentrations of melatonin influences not only androgen-sensitive but also androgen-insensitive epithelial prostate cancer cells. Cell differentiation promoted by melatonin is not mediated by PKA activation although it increases, in a transitory manner, intracellular cAMP levels. Melatonin markedly influences the proliferative status of prostate cancer cells. These effects should be evaluated thoroughly since melatonin levels are diminished in aged individuals when prostate cancer typically occurs.

Protein kinase A isozyme switching: eliciting differential cAMP signaling and tumor reversion

The cAMP-dependent protein kinase types I (PKA-I) and II (PKA-II), composed of identical catalytic (C) subunits but distinct regulatory (R) subunits (RI versus RII), are expressed in a balance of cell growth and differentiation. Distortion of this balance may underlie tumorigenesis and tumor growth. Here, we used PC3M prostate carcinoma cells as a model to overexpress wild type and mutant R and C subunit genes and examined the effects of differential expression of these genes on tumor growth. Only the RIIbeta and mutant RIalpha-P (a functional mimic of RIIbeta) transfectants exhibited growth inhibition in vitro, reverted phenotype, and apoptosis, and inhibited in vivo tumor growth. DNA microarrays demonstrated that RIIbeta and RIalpha-P overexpression upregulated a cluster of differentiation genes, while downregulating transformation and proliferation signatures. Overexpression of RIalpha and Calpha, which upregulated PKA-I, elicited the expression signatures opposite that elicited by RIIbeta overexpression. Total colocalization of Calpha and RIIbeta seen by confocal microscopy in the RIIbeta cell nucleus supports the opposed genomic regulation demonstrated between Calpha and RIIbeta cells. Differential expression of PKA R subunits may therefore serve as a tumor-target-based gene therapy for PC3M prostate and other cancers.

Antisense protein kinase A RIalpha inhibits 7,12-dimethylbenz(a)anthracene-induction of mammary cancer: blockade at the initial phase of carcinogenesis

PURPOSE

There are two types of cyclic AMP (cAMP)-dependent protein kinase (PKA), type I (PKA-I) and type II (PKA-II), which share a common catalytic (C) subunit but contain distinct regulatory (R) subunits, RI versus RII, respectively. Evidence suggests that increased expression of PKA-I and its regulatory subunit (RIalpha) correlates with tumorigenesis and tumor growth. We investigated the effect of sequence-specific inhibition of RIalpha gene expression at the initial phase of 7,12-dimethylbenz(alphaa)anthracene (DMBA)-induced mammary carcinogenesis.

EXPERIMENTAL DESIGN

Antisense RIalpha oligodeoxynucleotide (ODN) targeted against PKA RIalpha was administered (0.1 mg/day/rat, i.p.) 1 day before DMBA intubation and during the first 9 days post-DMBA intubation to determine the anticarcinogenic effects.

RESULTS

Antisense RIalpha, in a sequence-specific manner, inhibited the tumor production. At 90 days after DMBA intubation, untreated controls and RIalpha-antisense-treated rats exhibited an average mean number of tumors per rat of 4.2 and 1.8, respectively, and 90% of control and 45% of antisense-treated animals had tumors. The antisense also delayed the first tumor appearance. An increase in RIalpha and PKA-I levels in the mammary gland and liver preceded DMBA-induced tumor production, and antisense down-regulation of RIalpha restored normal levels of PKA-I and PKA-II in these tissues. Antisense RIalpha in the liver induced the phase II enzymes, glutathione S-transferase and quinone oxidoreductase, c-fos protein, and activator protein 1 (AP-1)- and cAMP response element (CRE)-directed transcription. In the mammary glands, antisense RIalpha promoted DNA repair processes. In contrast, the CRE transcription-factor decoy could not mimic these effects of antisense RIalpha.

CONCLUSIONS

The results demonstrate that RIalpha antisense produces dual anticarcinogenic effects: (a) increasing DMBA detoxification in the liver by increasing phase II enzyme activities, increasing CRE-binding-protein phosphorylation and enhancing CRE- and Ap-1-directed transcription; and (b) activating DNA repair processes in the mammary gland by down-regulating PKA-I.

A-kinase-interacting protein localizes protein kinase A in the nucleus

The genetic variability and covalent modifications associated with the amino terminus of the protein kinase A (PKA) catalytic (C) subunit suggest that it may contribute to protein-protein interactions and/or localization. By using a yeast two-hybrid screen, we identified a PKA-interacting protein (AKIP1) that binds to the amino terminus (residues 1-39) of the C subunit of PKA. The interaction was localized to the A helix (residues 14-39) of the C subunit and to the carboxyl terminus of AKIP1. AKIP1 thus defines the amino-terminal A helix of PKA as a protein interaction motif. In normal breast (Hs 578 Bst) and HeLa cells, AKIP1 is present in the nucleus as speckles. A nuclear localization signal (Arg-14 and Arg-15) was identified. Upon stimulation with forskolin, HeLa cells expressing AKIP1 accumulated higher levels of the endogenous C subunit in the nucleus. Deletion of the carboxyl terminus of AKIP1 or overexpression of residues 1-39 of the C subunit abolished nuclear localization of the activated endogenous C subunit. Thus, AKIP1 describes a PKA-interacting protein that can contribute to localization by a mechanism that is distinct from A-kinase anchoring proteins that interact with the regulatory subunits.

Antisense protein kinase A RI alpha-induced tumor reversion: portrait of a microarray

Antisense oligonucleotides can selectively block disease-causing genes due to the specificity of the Watson-Crick base-pairing mechanism of action. A genome-wide view of antisense technology is illustrated via protein kinase A RI alpha antisense. Complementary DNA microarray analysis of the RI alpha antisense-induced expression profile shows the up- and down-regulation of clusters of coordinately expressed genes that define the molecular portrait of a reverted tumor cell phenotype. This global view broadens the horizons of antisense technology; it advances the promise of antisense beyond a single target gene to the whole cell and the whole organism. Along with recent rapid advances in oligonucleotide technologies-including new chemical and biological understanding of more sophisticated nucleic acid drugs-oligonucleotide-based gene silencing offers not only an exquisitely specific genetic tool for exploring basic science but also an exciting possibility for treating and preventing cancer and other diseases.

Growth hormone-releasing hormone and pituitary development, hyperplasia and tumorigenesis

Growth hormone-releasing hormone (GHRH) is essential for expansion of the somatotrope lineage during pituitary development, and excessive GHRH secretion and/or action results in unregulated somatotrope proliferation and neoplastic transformation. Our understanding of the molecular and morphological bases for these effects from both animal and clinical studies has greatly increased during the past decade. However, many features of the cellular pathways remain to be defined, including the interaction of other genes in the multistep process of somatotrope tumorigenesis.

Dissecting the circuitry of protein kinase A and cAMP signaling in cancer genesis: antisense, microarray, gene overexpression, and transcription factor decoy

Expression of the RI alpha subunit of the cAMP-dependent protein kinase type I (PKA-I) is enhanced in human cancer cell lines, in primary tumors, in transformed cells, and in cells upon stimulation of growth. Signaling via the cAMP pathway may be complex, and the biological effects of the pathway in normal cells may depend upon the physiological state of the cells. However, results of different experimental approaches such as antisense exposure, 8-Cl-cAMP treatment, and gene overexpression have shown that the inhibition of RI alpha/PKA-I exerts antitumor activity in a wide variety of tumor-derived cell lines examined in vitro and in vivo. cDNA microarrays have further shown that in a sequence-specific manner, RI alpha antisense induces alterations in the gene expression profile of cancer cells and tumors. The cluster of genes that define the "proliferation-transformation" signature are down-regulated, and those that define the "differentiation-reverse transformation" signature are up-regulated in antisense-treated cancer cells and tumors, but not in host livers, exhibiting the molecular portrait of the reverted (flat) phenotype of tumor cells. These results reveal a remarkable cellular regulation, elicited by the antisense RI alpha, superimposed on the regulation arising from the Watson-Crick base-pairing mechanism of action. Importantly, the blockade of both the PKA and PKC signaling pathways achieved with the CRE-transcription factor decoy inhibits tumor cell growth without harming normal cell growth. Thus, a complex circuitry of cAMP signaling comprises cAMP growth regulatory function, and deregulation of the effector molecule by this circuitry may underlie cancer genesis and tumor progression.