Preoperative profiles of plasma amino acids and derivatives distinguish periampullary cancer and benign disease

Periampullary cancers, including pancreatic ductal adenocarcinoma, ampullary-, cholangio-, and duodenal carcinoma, are frequently diagnosed in an advanced stage and are associated with poor overall survival. They are difficult to differentiate from each other and challenging to distinguish from benign periampullary disease preoperatively. To improve the preoperative diagnostics of periampullary neoplasms, clinical or biological markers are warranted.In this study, 28 blood plasma amino acids and derivatives from preoperative patients with benign (N = 45) and malignant (N = 72) periampullary disease were analyzed by LC-MS/MS.Principal component analysis and consensus clustering both separated the patients with cancer and the patients with benign disease. Glutamic acid had significantly higher plasma expression and 15 other metabolites significantly lower plasma expression in patients with malignant disease compared with patients having benign disease. Phenylalanine was the only metabolite associated with improved overall survival (HR = 0.50, CI 0.30-0.83, P < 0.01).Taken together, plasma metabolite profiles from patients with malignant and benign periampullary disease were significantly different and have the potential to distinguish malignant from benign disease preoperatively.

Corrigendum: Effect of five hours of mixed exercise on urinary nitrogen excretion in healthy moderate-to-well-trained young adults

[This corrects the article DOI: 10.3389/fnut.2024.1345922.].

Effect of five hours of mixed exercise on urinary nitrogen excretion in healthy moderate-to-well-trained young adults

Introduction

Carbohydrates and fats are the primary energy substrates during exercise, but proteins can also contribute. When proteins are degraded in the body, the amino groups are mainly converted to urea and excreted. Therefore, nitrogen excretion has been used as a marker of protein degradation, but a clear conclusion has yet to be reached on the effect of exercise on nitrogen excretion. Thus, we tested whether exercise increases nitrogen excretion.

Methods

Fifteen young, healthy, moderate-to-well-trained participants (4 females, 11 males, VO2max 54.4 ± 1.7 mL·kg-1·min-1; mean ± SEM) participated in a randomized, balanced cross-over design investigation consisting of 1 day with 5 h of exercise (exercise day, EX) and 1 day with no exercise (control day, CON). The participants recorded their dietary intake the day before from 16:00 and throughout the intervention day. They then repeated these dietary intakes on the second trial day. A standardized lunch was provided on both days. In addition, participants were allowed to consume almost protein-free snacks in EX to ensure the same energy balance during both trial days. Urine was collected throughout the whole testing period, and urinary 3-methylhistidine (3-MH) excretion was measured to examine muscular catabolism. The sweat rate was calculated during the exercise period.

Results and discussion

The urinary nitrogen and 3-MH excretions did not differ significantly between EX and CON (p = 0.764 and p = 0.953). The sweat rate was 2.55 ± 0.25 L in EX and 0.14 ± 0.15 L in CON (p < 0.001), and by estimating sweat nitrogen excretion, total nitrogen excretion was shown to differ with exercise. Our results showed that 5 hours of mixed exercise did not significantly impact urinary nitrogen and 3-MH excretions in healthy moderate-to-well-trained young adults.

Ghrelin is related to lower brain reward activation during touch

The gut hormone ghrelin drives food motivation and increases food intake, but it is also involved in the anticipation of and response to rewards other than food. This pre-registered study investigated how naturally varying ghrelin concentrations affect the processing of touch as a social reward in humans. Sixty-seven volunteers received slow caressing touch (so-called CT-targeted touch) as a social reward and control touch on their shins during 3T functional imaging on two test days. On one occasion, participants were fasted, and on another, they received a meal. On each occasion, plasma ghrelin was measured at three time points. All touch was rated as more pleasant after the meal, but there was no association between ghrelin concentrations and pleasantness. CT-targeted touch was rated as the most pleasant and activated somatosensory and reward networks (whole brain). A region-of-interest in the right medial orbitofrontal cortex (mOFC) showed lower activation during all touches, the higher the ghrelin concentrations were. During CT-targeted touch, a larger satiety response (ghrelin decrease after the meal) was associated with higher mOFC activation, and this mOFC activation was associated with higher experienced pleasantness. Overall, higher ghrelin concentrations appear to be related to a lower reward value for touch. Ghrelin may reduce the value of social stimuli, such as touch, to promote food search and intake in a state of low energy. This suggests that the role of ghrelin goes beyond assigning value to food reward.

Carbohydrate Ingestion during Prolonged Cycling Improves Next-Day Time Trial Performance and Alters Amino Acid Concentrations

INTRODUCTION

Exercise with low carbohydrate availability increases protein degradation, which may reduce subsequent performance considerably. The present study aimed to investigate the effect of carbohydrate ingestion during standardized exercise with and without exhaustion on protein degradation and next-day performance.

METHODS

Seven trained male cyclists (V̇O 2max 66.8 ± 1.9 mL·kg -1 ·min -1 ; mean ± SEM) cycled to exhaustion (~2.5 h) at a power output eliciting 68% of V̇O 2max (W 68% ). This was followed by repeating 1-min work/1-min recovery intervals at 90% of V̇O 2max (W 90% ) until exhaustion. During W 68% , cyclists consumed a placebo water drink (PLA) the first time and a carbohydrate drink (CHO), 1 g carbohydrate·kg -1 ·h -1 , the second time. The participants performed the same amount of work under the two conditions, separated by at least 1 wk. A standardized diet was provided to the participants so that the two conditions were isoenergetic. To test the impact of carbohydrates on recovery, participants completed a time trial (TT) the next day.

RESULTS

Carbohydrate ingestion maintained carbohydrate availability during W 68% and W 90% : total carbohydrate oxidation was significantly higher in CHO ( P = 0.022), and plasma glucose concentration was maintained compared with PLA ( P = 0.025). Next-day performance during TT was better after CHO ingestion (CHO, 41:49 ± 1:38 min; PLA, 42:50 ± 1:46 min; P = 0.020; effect size d = 0.23, small), as was gross efficiency (CHO, 18.6% ± 0.3%; PLA, 17.9% ± 0.3%; P = 0.019). Urinary nitrogen excretion ( P = 0.897) and urinary 3-methylhistidine excretion ( P = 0.673) did not significantly differ during the study period. Finally, tyrosine and phenylalanine plasma concentrations increased in PLA but not in CHO ( P = 0.018).

CONCLUSIONS

Carbohydrate ingestion during exhaustive exercise reduced deterioration in next-day performance through reduced metabolic stress and development of fatigue. In addition, some parameters point toward less protein degradation, which would preserve muscle function.

Cancer risk and survival according to body mass index in hepatobiliary malignancies: a nationwide registry-based cohort study

BACKGROUND

The aim of this study was to explore the associations between BMI and cancer of the liver, bile ducts, and gallbladder.

METHODS

A registry-based cohort study was performed by linking data from several national registries in Norway.

RESULTS

The cohort comprised 1 723 692 individuals including 4768 hepatobiliary cancer cases during 55 743 509 person-years of follow-up. In men, we found increased risk of cancer per 5 kg/m2 BMI increase for hepatocellular carcinoma and extrahepatic cholangiocarcinoma. In women there was increased risk of extrahepatic cholangiocarcinoma and gallbladder cancer. Women with high BMI in early adulthood had increased risk of intrahepatic cholangiocarcinoma. Reduced cancer-specific survival was found for all hepatobiliary malignancies in women with overweight and obesity. In men, reduced survival was observed in individuals with obesity for all hepatobiliary cancers, except gallbladder cancer. Increased risk of cancer-death per 5 kg/m2 BMI increase was found for hepatocellular carcinoma, intra-, and extrahepatic cholangiocarcinoma in women. For men, 5 kg/m2 BMI increase was positively associated with cancer-death from intrahepatic cholangiocarcinoma.

DISCUSSION

This study supports the notion of an increased risk of hepatobiliary cancers with increasing BMI, with sex and age variations. The findings also suggest a higher risk of cancer-death with increasing BMI.

Antibody blockade of Jagged1 attenuates choroidal neovascularization

Antibody-based blocking of vascular endothelial growth factor (VEGF) reduces choroidal neovascularization (CNV) and retinal edema, rescuing vision in patients with neovascular age-related macular degeneration (nAMD). However, poor response and resistance to anti-VEGF treatment occurs. We report that targeting the Notch ligand Jagged1 by a monoclonal antibody reduces neovascular lesion size, number of activated phagocytes and inflammatory markers and vascular leakage in an experimental CNV mouse model. Additionally, we demonstrate that Jagged1 is expressed in mouse and human eyes, and that Jagged1 expression is independent of VEGF signaling in human endothelial cells. When anti-Jagged1 was combined with anti-VEGF in mice, the decrease in lesion size exceeded that of either antibody alone. The therapeutic effect was solely dependent on blocking, as engineering antibodies to abolish effector functions did not impair the therapeutic effect. Targeting of Jagged1 alone or in combination with anti-VEGF may thus be an attractive strategy to attenuate CNV-bearing diseases.

Identification of SNPs associated with methotrexate treatment outcomes in patients with early rheumatoid arthritis

Methotrexate is one of the cornerstones of rheumatoid arthritis (RA) therapy. Genetic factors or single nucleotide polymorphisms (SNPs) are responsible for 15%–30% of the variation in drug response. Identification of clinically effective SNP biomarkers for predicting methotrexate (MTX) sensitivity has been a challenge. The aim of this study was to explore the association between the disease related outcome of MTX treatment and 23 SNPs in 8 genes of the MTX pathway, as well as one pro-inflammatory related gene in RA patients naïve to MTX. Categorical outcomes such as Disease Activity Score (DAS)-based European Alliance of Associations for Rheumatology (EULAR) non-response at 4 months, The American College of Rheumatology and EULAR (ACR/EULAR) non-remission at 6 months, and failure to sustain MTX monotherapy from 12 to 24 months were assessed, together with continuous outcomes of disease activity, joint pain and fatigue. We found that the SNPs rs1801394 in the MTRR gene, rs408626 in DHFR gene, and rs2259571 in AIF-1 gene were significantly associated with disease activity relevant continuous outcomes. Additionally, SNP rs1801133 in the MTHFR gene was identified to be associated with improved fatigue. Moreover, associations with p values at uncorrected significance level were found in SNPs and different categorical outcomes: 1) rs1476413 in the MTHFR gene and rs3784864 in ABCC1 gene are associated with ACR/EULAR non-remission; 2) rs1801133 in the MTHFR gene is associated with EULAR response; 3) rs246240 in the ABCC1 gene, rs2259571 in the AIF-1 gene, rs2274808 in the SLC19A1 gene and rs1476413 in the MTHFR gene are associated with failure to MTX monotherapy after 12–24 months. The results suggest that SNPs in genes associated with MTX activity may be used to predict MTX relevant-clinical outcomes in patients with RA.

T Cell Metabolism in Infection

T lymphocytes (T cells) are divided into two functionally different subgroups the CD4+ T helper cells (Th) and the CD8+ cytotoxic T lymphocytes (CTL). Adequate CD4 and CD8 T cell activation to proliferation, clonal expansion and effector function is crucial for efficient clearance of infection by pathogens. Failure to do so may lead to T cell exhaustion. Upon activation by antigen presenting cells, T cells undergo metabolic reprograming that support effector functions. In this review we will discuss how metabolic reprograming dictates functionality during viral infections using severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and human immunodeficiency virus (HIV) as examples. Moreover, we will briefly discuss T cell metabolic programs during bacterial infections exemplified by Mycobacterium tuberculosis (MT) infection.

Identification and characterization of a novel glutaminase inhibitor

In humans, there are two forms of glutaminase (GLS), designated GLS1 and GLS2. These enzymes catalyse the conversion of glutamine to glutamate. GLS1 exists as two isozymes: kidney glutaminase (KGA) and glutaminase C (GAC). Several GLS inhibitors have been identified, of which DON (6‐diazo‐5‐oxonorleucine), BPTES (bis‐2‐(5‐phenylacetamido‐1, 3, 4‐thiadiazol‐2‐yl) ethyl sulphide), 968 (5‐(3‐Bromo‐4‐(dimethylamino)phenyl)‐2,2‐dimethyl‐2,3,5,6‐tetrahydrobenzo[a]phenanthridin‐4(1H)‐one) and CB839 (Telaglenastat) are the most widely used. However, these inhibitors have variable efficacy, specificity and bioavailability in research and clinical settings, implying the need for novel and improved GLS inhibitors. Based on this need, a diverse library of 28,000 compounds from Enamine was screened for inhibition of recombinant, purified GAC. From this library, one inhibitor designated compound 19 (C19) was identified with kinetic features revealing allosteric inhibition of GAC in the µm range. Moreover, C19 inhibits anti‐CD3/CD28‐induced CD4+ T‐cell proliferation and cytokine production with similar or greater potency as compared to BPTES. Taken together, our data suggest that C19 has the potential to modulate GLS1 activity and alter metabolic activity of T cells.

Activated, Pro-Inflammatory Th1, Th17, and Memory CD4+ T Cells and B Cells Are Involved in Delayed-Type Hypersensitivity Arthritis (DTHA) Inflammation and Paw Swelling in Mice

Delayed-type hypersensitivity arthritis (DTHA) is a recently established experimental model of rheumatoid arthritis (RA) in mice with pharmacological values. Despite an indispensable role of CD4+ T cells in inducing DTHA, a potential role for CD4+ T cell subsets is lacking. Here we have quantified CD4+ subsets during DTHA development and found that levels of activated, pro-inflammatory Th1, Th17, and memory CD4+ T cells in draining lymph nodes were increased with differential dynamic patterns after DTHA induction. Moreover, according to B-cell depletion experiments, it has been suggested that this cell type is not involved in DTHA. We show that DTHA is associated with increased levels of B cells in draining lymph nodes accompanied by increased levels of circulating IgG. Finally, using the anti-rheumatoid agents, methotrexate (MTX) and the anti-inflammatory drug dexamethasone (DEX), we show that MTX and DEX differentially suppressed DTHA-induced paw swelling and inflammation. The effects of MTX and DEX coincided with differential regulation of levels of Th1, Th17, and memory T cells as well as B cells. Our results implicate Th1, Th17, and memory T cells, together with activated B cells, to be involved and required for DTHA-induced paw swelling and inflammation.

The tails of PKA

The catalytic subunit of PKA is regulated by two tails that each wrap around the N- and C-lobes of the kinase core. While the Ct-Tail is classified as an intrinsically disordered region (IDR), the Nt-Tail is dominated by a strong helix that is flanked by short IDRs. In contrast to the Ct-Tail, which is a conserved and highly regulated feature of all AGC kinases, the Nt-Tail has evolved more recently and is not even conserved in non-mammalian PKAs. In addition, and most importantly, there is a large family of Cb subunits that are highly expressed in mammalian cells in a tissue-specific manner. While we know so much about the Ca1 subunit, we know almost nothing about these Cb isoforms where Cb2 is highly expressed in lymphocytes and Cb3 and Cb4 isoforms account for ~50% of PKA signaling in brain. Based on recent disease mutations, the Cb proteins appear to be functionally important and non-redundant with the Ca isoforms. Imaging in retina also supports non-redundant roles for Cb as well as isoform-specific localization to mitochondria. This represents a new frontier in PKA signaling. Significance Statement How tails and adjacent domains regulate each protein kinase is a fundamental challenge for the biological community. Here we highlight how the N- and C-terminal tails of PKA (Nt-Tails/Ct-Tails) regulate the structure and function of the kinase core and show the combinatorial variations that are introduced into the Nt-Tail of the Ca and Cb subunits of PKA in contrast to the Ct-Tail which is conserved across the entire AGC subfamily of protein kinases.

Inflammatory activation of endothelial cells increases glycolysis and oxygen consumption despite inhibiting cell proliferation

Endothelial cell function and metabolism are closely linked to differential use of energy substrate sources and combustion. While endothelial cell migration is promoted by 2‐phosphofructokinase‐6/fructose‐2,6‐bisphosphatase (PFKFB3)‐driven glycolysis, proliferation also depends on fatty acid oxidation for dNTP synthesis. We show that inflammatory activation of human umbilical vein endothelial cells (HUVECs) by interleukin‐1β (IL‐1β), despite inhibiting proliferation, promotes a shift toward more metabolically active phenotype. This was reflected in increased cellular glucose uptake and consumption, which was preceded by an increase in PFKFB3 mRNA and protein expression. However, despite a modest increase in extracellular acidification rates, the increase in glycolysis did not correlate with extracellular lactate accumulation. Accordingly, IL‐1β stimulation also increased oxygen consumption rate, but without a concomitant rise in fatty acid oxidation. Together, this suggests that the IL‐1β‐stimulated energy shift is driven by shunting of glucose‐derived pyruvate into mitochondria to maintain elevated oxygen consumption in HUVECs. We also revealed a marked donor‐dependent variation in the amplitude of the metabolic response to IL‐1β and postulate that the donor‐specific response should be taken into account when considering targeting dysregulated endothelial cell metabolism.

Germline and Mosaic Variants in PRKACA and PRKACB Cause a Multiple Congenital Malformation Syndrome

PRKACA and PRKACB code for two catalytic subunits (Cα and Cβ) of cAMP-dependent protein kinase (PKA), a pleiotropic holoenzyme that regulates numerous fundamental biological processes such as metabolism, development, memory, and immune response. We report seven unrelated individuals presenting with a multiple congenital malformation syndrome in whom we identified heterozygous germline or mosaic missense variants in PRKACA or PRKACB. Three affected individuals were found with the same PRKACA variant, and the other four had different PRKACB mutations. In most cases, the mutations arose de novo, and two individuals had offspring with the same condition. Nearly all affected individuals and their affected offspring shared an atrioventricular septal defect or a common atrium along with postaxial polydactyly. Additional features included skeletal abnormalities and ectodermal defects of variable severity in five individuals, cognitive deficit in two individuals, and various unusual tumors in one individual. We investigated the structural and functional consequences of the variants identified in PRKACA and PRKACB through the use of several computational and experimental approaches, and we found that they lead to PKA holoenzymes which are more sensitive to activation by cAMP than are the wild-type proteins. Furthermore, expression of PRKACA or PRKACB variants detected in the affected individuals inhibited hedgehog signaling in NIH 3T3 fibroblasts, thereby providing an underlying mechanism for the developmental defects observed in these cases. Our findings highlight the importance of both Cα and Cβ subunits of PKA during human development.

Coingestion of protein and carbohydrate in the early recovery phase, compared with carbohydrate only, improves endurance performance despite similar glycogen degradation and AMPK phosphorylation

Endurance athletes competing consecutive days need optimal dietary intake during the recovery period. We report that coingestion of protein and carbohydrate soon after exhaustive exercise, compared with carbohydrate only, resulted in better performance the following day. The better performance after coingestion of protein and carbohydrate was not associated with a higher rate of glycogen synthesis or activation of anabolic signaling compared with carbohydrate only. Importantly, nitrogen balance was positive after coingestion of protein and carbohydrate, which was not the case after intake of carbohydrate only, suggesting that protein synthesis contributes to the better performance the following day.

3PO inhibits inflammatory NFκB and stress-activated kinase signaling in primary human endothelial cells independently of its target PFKFB3

Inhibition of the key glycolytic activator 6-phosphofructokinase 2/fructose-2,6-bisphosphatase-3 (PFKFB3) by 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO) strongly attenuates pathological angiogenesis in cancer and inflammation. In addition to modulating endothelial proliferation and migration, 3PO also dampens proinflammatory activation of endothelial cells and experimental inflammation in vivo, suggesting a potential for 3PO in the treatment of chronic inflammation. The aim of our study was to explore if the anti-inflammatory action of 3PO in human endothelial cells was mediated by inhibition of PFKFB3 and glycolysis and assess if other means of PFKFB3 inhibition reduced inflammatory activation in a similar manner. We found that 3PO caused a rapid and transient reduction in IL-1β- and TNF-induced phosphorylation of both IKKα/β and JNK, thus inhibiting signaling through the NFκB and the stress-activated kinase pathways. However, in contrast to 3PO-treatment, neither shRNA-mediated silencing of PFKFB3 nor treatment with the alternative PFKFB3 inhibitor 7,8-dihydroxy-3-(4-hydroxy-phenyl)-chromen-4-one (YN1) prevented cytokine-induced NFκB signaling and upregulation of the adhesion molecules VCAM-1 and E-selectin, implying off target effects of 3PO. Collectively, our results suggest that the anti-inflammatory action of 3PO in human endothelial cells is not limited to inhibition of PFKFB3 and cellular glycolysis.

The Molecular Basis for Specificity at the Level of the Protein Kinase a Catalytic Subunit

Assembly of multi enzyme complexes at subcellular localizations by anchoring- and scaffolding proteins represents a pivotal mechanism for achieving spatiotemporal regulation of cellular signaling after hormone receptor targeting [for review, see (1)]. In the 3' 5'-cyclic adenosine monophosphate (cAMP) dependent protein kinase (PKA) signaling pathway it is generally accepted that specificity is secured at several levels. This includes at the first level stimulation of receptors coupled to heterotrimeric G proteins which through stimulation of adenylyl cyclase (AC) forms the second messenger cAMP. Cyclic AMP has several receptors including PKA. PKA is a tetrameric holoenzyme consisting of a regulatory (R) subunit dimer and two catalytic (C) subunits. The R subunit is the receptor for cAMP and compartmentalizes cAMP signals through binding to cell and tissue-specifically expressed A kinase anchoring proteins (AKAPs). The current dogma tells that in the presence of cAMP, PKA dissociates into an R subunit dimer and two C subunits which are free to phosphorylate relevant substrates in the cytosol and nucleus. The release of the C subunit has raised the question how specificity of the cAMP and PKA signaling pathway is maintained when the C subunit no longer is attached to the R subunit-AKAP complex. An increasing body of evidence points toward a regulatory role of the cAMP and PKA signaling pathway by targeting the C subunits to various C subunit binding proteins in the cytosol and nucleus. Moreover, recent identification of isoform specific amino acid sequences, motifs and three dimensional structures have together provided new insight into how PKA at the level of the C subunit may act in a highly isoform-specific fashion. Here we discuss recent understanding of specificity of the cAMP and PKA signaling pathway based on C subunit subcellular targeting as well as evolution of the C subunit structure that may contribute to the dynamic regulation of C subunit activity.

Th17 Polarization under Hypoxia Results in Increased IL-10 Production in a Pathogen-Independent Manner

The IL-17-producing CD4⁺ T helper cell (Th17) differentiation is affected by stimulation of the aryl hydrocarbon receptor (AhR) pathway and by hypoxia-inducible factor 1 alpha (HIF-1α). In some cases, Th17 become non-pathogenic and produce IL-10. However, the initiating events triggering this phenotype are yet to be fully understood. Here, we show that such cells may be differentiated at low oxygen and regardless of AhR ligand treatment such as cigarette smoke extract. Hypoxia led to marked alterations of the transcriptome of IL-10-producing Th17 cells affecting genes involved in metabolic, anti-apoptotic, cell cycle, and T cell functional pathways. Moreover, we show that oxygen regulates the expression of CD52, which is a cell surface protein that has been shown to suppress the activation of other T cells upon release. Taken together, these findings suggest a novel ability for Th17 cells to regulate immune responses in vivo in an oxygen-dependent fashion.

Observed correlation between the expression levels of catalytic subunit, Cβ2, of cyclic adenosine monophosphate-dependent protein kinase and prostate cancer aggressiveness

BACKGROUND

Today overtreatment of indolent prostate cancers and undertreatment of aggressive prostate cancer are a major concern for patients, their families, and the health care system. New biomarkers distinguishing indolent and aggressive prostate cancer are needed to improve precision medicine. In prostate cancer, protein kinase A (PKA) is known to activate the androgen receptor and published data indicate that PKA subunits can act as predictive markers for response to radiation and chemotherapy. We have previously shown that the catalytic subunit, Cβ2, of PKA is up-regulated in prostate cancer and we would in this study investigate the potential of Cβ2 to become a prognostic biomarker in prostate cancer.

METHODS

Data were sampled from a total of 241 patients from 3 independent cohorts. We measured and compared Cβ2 messenger RNA (mRNA) levels in prostate tumor and nontumor samples (n = 22), and exon levels in a cohort of 50 tumor samples, as well as acquiring mRNA data from the publicly available database The cancer genome atlas (n = 169).

RESULTS

Cβ2 mRNA was up-regulated in prostate cancer in all 3 cohorts, measured by 3 different methods. Furthermore, the relative Cβ2 mRNA expression levels were lower in prostate cancer samples with Gleason score 8 to 10 compared with samples with Gleason score<8 (P = 0.004). Finally, low expression of Cβ2 mRNA in prostate cancer biopsies correlated with poor survival (hazard ratio = 0.20; 95% CI: 0.048-0.86; P = 0.031), adjusted for risk group and age.

CONCLUSIONS

We suggest that Cβ2 mRNA expression may be used as a biomarker together with established prognostic markers to more precisely predict aggressiveness in patients diagnosed with prostate cancer.

Serum albumin and HCO3- regulate separate pools of ATP in human spermatozoa

STUDY QUESTION

Do the known capacitating agents HCO(3)(-) and serum albumin regulate the generation of ATP required for sperm motility and capacitation?

SUMMARY ANSWER

Serum albumin and HCO(3)(-) seem to regulate two separate pools of ATP by different mechanisms in human spermatozoa.

WHAT IS KNOWN ALREADY

Sperm capacitation is a maturation process that naturally occurs in the female reproductive tract preparing the sperm cell for fertilization. It is a highly energy-depending process as it involves hyperactive motility and substantial levels of protein phosphorylation.

STUDY DESIGN, SIZE, DURATION

Human sperm cells from four (motility experiments) and three (all other experiments) healthy donors were used. Untreated cells were compared with cells treated with HCO(3)(-) and serum albumin for up to 4 h.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Changes in glycolysis and mitochondrial respiration rates upon treatment with serum albumin and HCO(3)(-) were analysed by metabolic tracing of (13)C-labelled substrates and respirometry studies, respectively. Levels of hyperactive spermatozoa and ATP content were measured during 4 h of incubation under capacitating conditions.

MAIN RESULTS AND THE ROLE OF CHANCE

We found that HCO(3)(-) significantly (P < 0.05) increased glycolytic flux by >3-folds via a cAMP/PKA sensitive pathway. This was accompanied by an increase in hyperactive motility. In contrast, serum albumin significantly increased endogenous ATP levels by 50% without stimulating hyperactive motility or glycolysis, indicating that this pool of ATP is separately located from the HCO(3)(-)-induced ATP. The increase in ATP induced by albumin could be mimicked by treatment with the cholesterol acceptors 2-hydroxypropyl- and methyl-β-cyclodextrin and counteracted by co-incubation with cholesterol sulphate to the level of the non-treated control (P < 0.05), pointing to cholesterol extraction from the sperm cell membrane as the main mechanism. However, the concentration of cyclodextrins needed to directly detect cholesterol extraction from the sperm cells was not compatible with maintenance of sperm viability. The increase in ATP seemed not to be dependent on the sperm-specific Ca(2+) channel CatSper. Finally, we demonstrated that neither HCO(3)(-) nor serum albumin stimulated mitochondrial respiration rates. However, serum albumin increased the respiratory capacity of mitochondria by >50%, an effect that was counteracted by HCO(3)(-).

LIMITATIONS, REASONS FOR CAUTION

Great variation in motility and capacitation is observed between sperm cells from different species. Hence, caution should be taken when extrapolating the findings in this work on human spermatozoa to sperm from other species.

WIDER IMPLICATIONS OF THE FINDINGS

It is already established that an efficient energy-generation is required to support sperm motility and capacitation. However, the mechanisms explaining how ATP production is regulated in spermatozoa are not fully understood. Our findings indicate that HCO(3)(-) stimulates hyperactive motility by increasing glycolytic flux and ATP production in a cAMP/PKA sensitive fashion. On the other hand, serum albumin seems to increase ATP concentration at a different location and by a mechanism different from glycolysis that involves extraction of cholesterol from the sperm cell membrane. These new insights into sperm metabolism may pave the way for both the development of new and improved male contraceptives and optimized assisted reproduction techniques.

STUDY FUNDING

The work was funded by Spermatech AS, The University of Oslo and the Research Council of Norway.

COMPETING INTEREST(S)

T.H.H. and K.R.R. are employees at Spermatech. B.S.S is a shareholder in Spermatech.

Exogenous pyruvate accelerates glycolysis and promotes capacitation in human spermatozoa

BACKGROUND

There has been an ongoing debate in the reproductive field about whether mammalian spermatozoa rely on glycolysis, oxidative phosphorylation or both for their energy production. Recent studies have proposed that human spermatozoa depend mainly on glucose for motility and fertilization but the mechanism behind an efficient glycolysis in human spermatozoa is not well understood. Here, we demonstrate how human spermatozoa utilize exogenous pyruvate to enhance glycolytic ATP production, motility, hyperactivation and capacitation, events that are crucial for male fertility.

METHODS

Purified human spermatozoa from healthy donors were incubated under capacitating conditions (including albumin, bicarbonate and glucose) and tested for changes in ATP levels, motility, hyperactivation and tyrosine phosphorylation after treatment with pyruvate. The experiments were repeated in the presence of sodium cyanide in order to assess the contribution from mitochondrial respiration. The metabolism of ¹³C labeled glucose and pyruvate was traced by a combination of liquid chromatography and mass spectrometry.

RESULTS

The treatment of human spermatozoa with exogenous pyruvate increased intracellular ATP levels, progressive motility and hyperactivation by 56, 21 and 130%, respectively. In addition, added pyruvate induced a significant increase in tyrosine phosphorylation levels. Blocking of the electron transport chain did not markedly affect the results, indicating that the mechanism is independent of oxidative phosphorylation. However, the observed effects could be counteracted by oxamate, an inhibitor of lactate dehydrogenase (LDH). Metabolic tracing experiments revealed that the observed rise in ATP concentration resulted from an enhanced glycolytic flux, which was increased by more than 50% in the presence of exogenous pyruvate. Moreover, all consumed ¹³C labeled pyruvate added was converted to lactate rather than oxidized in the tricarboxylic acid cycle.

CONCLUSIONS

Human spermatozoa seem to rely mainly, if not entirely, on glycolysis as the source of ATP fueling the energy-demanding processes of motility and capacitation. The efficient glycolysis is dependent on exogenous pyruvate, which indirectly feeds the accelerated glycolysis with NAD⁺ through the LDH-mediated conversion of pyruvate to lactate. Pyruvate is present in the human female reproductive tract at concentrations in accordance with our results. As seen in other mammals, the motility and fertility of human spermatozoa seem to be dictated by the available energy substrates present in the conspecific female.

G-patch domain and KOW motifs-containing protein, GPKOW; a nuclear RNA-binding protein regulated by protein kinase A

Background

Post-transcriptional processing of pre-mRNA takes place in several steps and requires involvement of a number of RNA-binding proteins. How pre-mRNA processing is regulated is in large enigmatic. The catalytic (C) subunit of protein kinase A (PKA) is a serine/threonine kinase, which regulates numerous cellular processes including pre-mRNA splicing. Despite that a significant fraction of the C subunit is found in splicing factor compartments in the nucleus, there are no indications of a direct interaction between RNA and PKA. Based on this we speculate if the specificity of the C subunit in regulating pre-mRNA splicing may be mediated indirectly through other nuclear proteins.

Results

Using yeast two-hybrid screening with the PKA C subunit Cbeta2 as bait, we identified the G-patch domain and KOW motifs-containing protein (GPKOW), also known as the T54 protein or MOS2 homolog, as an interaction partner for Cbeta2. We demonstrate that GPKOW, which contains one G-patch domain and two KOW motifs, is a nuclear RNA-binding protein conserved between species. GPKOW contains two sites that are phosphorylated by PKA in vitro. By RNA immunoprecipitation and site directed mutagenesis of the PKA phosphorylation sites we revealed that GPKOW binds RNA in vivo in a PKA sensitive fashion.

Conclusion

GPKOW is a RNA-binding protein that binds RNA in a PKA regulated fashion. Together with our previous results demonstrating that PKA regulates pre-mRNA splicing, our results suggest that PKA phosphorylation is involved in regulating RNA processing at several steps.

EBV infection renders B cells resistant to growth inhibition via adenylyl cyclase

Cyclic AMP (cAMP) is an important physiological growth inhibitor of lymphoid cells, and the cAMP/protein kinase A (PKA) pathway is disrupted in several immunological disorders and cancers. Epstein Barr virus (EBV) infection of B lymphocytes is responsible for the development of lymphoproliferative disease as well as certain B-lymphoid malignancies. Here we hypothesized that EBV infection might render B lymphocytes resistant to cAMP/PKA-mediated growth inhibition. To test this, we assessed the growth-inhibitory response of cAMP-elevating compounds such as forskolin and isoproterenol, as well as the PKA activator 8-CPT-cAMP in normal B lymphocytes, EBV-infected B cells and in the EBV-negative B lymphoid cell line Reh. We could demonstrate that EBV infection indeed abolished cAMP-mediated growth inhibition of B cells. The defect was pinpointed to defective adenylyl cyclase (AC) activation by forskolin and isoproterenol, resulting in reduced formation of cAMP and lack of PKA activation and CREB phosphorylation. In contrast, 8-CPT-cAMP which directly activates PKA was able to inhibit EBV-infected B cell growth. The physiological implications of these results were underlined by the observation that the ability of forskolin to inhibit camptothecin-induced apoptosis was abolished in EBV-infected B cells. We conclude that EBV infection of B cells abrogates the activation of AC and thereby cAMP formation, and that this dysfunction renders the cells resistant to growth inhibition via the cAMP/PKA pathway.

MEK1 and MEK2 regulate distinct functions by sorting ERK2 to different intracellular compartments

In this study, we provide novel insight into the mechanism of how ERK2 can be sorted to different intracellular compartments and thereby mediate different responses. MEK1-activated ERK2 accumulated in the nucleus and induced proliferation. Conversely, MEK2-activated ERK2 was retained in the cytoplasm and allowed survival. Localization was a determinant for ERK2 functions since MEK1 switched from providing proliferation to be a mediator of survival when ERK2 was routed to the cytoplasm by the attachment of a nuclear export site. MEK1-mediated ERK2 nuclear translocation and proliferation were shown to depend on phosphorylation of S298 and T292 sites in the MEK1 proline-rich domain. These sites are phosphorylated on cellular adhesion in MEK1 but not MEK2. Whereas p21-activated kinase phosphorylates S298 and thus enhances the MEK1-ERK2 association, ERK2 phosphorylates T292, leading to release of active ERK2 from MEK1. On the basis of these results, we propose that the requirement of adhesion for cells to proliferate in response to growth factors, in part, may be explained by the MEK1 S298/T292 control of ERK2 nuclear translocation. In addition, we suggest that ERK2 intracellular localization determines whether growth factors mediate proliferation or survival and that the sorting occurs in an adhesion-dependent manner.

Involvement of the catalytic subunit of protein kinase A and of HA95 in pre-mRNA splicing

Protein kinase A (PKA) is a holoenzyme consisting of two catalytic (C) subunits bound to a regulatory (R) subunit dimer. Stimulation by cAMP dissociates the holoenzyme and causes translocation to the nucleus of a fraction of the C subunit. Apart from transcription regulation, little is known about the function of the C subunit in the nucleus. In the present report, we show that both Calpha and Cbeta are localized to spots in the mammalian nucleus. Double immunofluorescence analysis of splicing factor SC35 with the C subunit indicated that these spots are splicing factor compartments (SFCs). Using the E1A in vivo splicing assay, we found that catalytically active C subunits regulate alternative splicing and phosphorylate several members of the SR-protein family of splicing factors in vitro. Furthermore, nuclear C subunits co-localize with the C subunit-binding protein homologous to AKAP95, HA95. HA95 also regulates E1A alternative splicing in vivo, apparently through its N-terminal domain. Localization of the C subunit to SFCs and the E1A splicing pattern were unaffected by cAMP stimulation. Our findings demonstrate that the nuclear PKA C subunit co-locates with HA95 in SFCs and regulates pre-mRNA splicing, possibly through a cAMP-independent mechanism.

Androgen dependent regulation of protein kinase A subunits in prostate cancer cells

Neuroendocrine (NE) cells may play a role in prostate cancer progression. Both androgen deprivation and cAMP are well known inducers of NE differentiation (NED) in the prostate. Gene-expression profiling of LNCaP cells, incubated in androgen stripped medium, showed that the Cbeta isoform of PKA is up-regulated during NE differentiation. Furthermore, by using semi-quantitative RT-PCR and immunoblotting analysis, we observed that the Cbeta splice variants are differentially regulated during this process. Whereas the Cbeta2 splice variant is down-regulated in growth arrested LNCaP cells, the Cbeta1, Cbeta3 and Cbeta4 variants, as well as the RIIbeta subunit of PKA, are induced in NE-like LNCaP cells. The opposite effect of Cbeta expression could be mimicked by androgen stimulation, implying the Cbeta gene of PKA as a putative new target gene for the androgen receptor in prostate cancer. Moreover, to investigate expression of PKA subunits during prostate cancer progression, we did immunoblotting of several prostatic cell lines and normal and tumor tissue from prostate cancer patients. Interestingly, multiple Cbeta subunits were also observed in human prostate specimens, and the Cbeta2 variant was up-regulated in tumor cells. In conclusion, it seems that the Cbeta isoforms play different roles in proliferation and differentiation and could therefore be potential markers for prostate cancer progression.

Effect of acidosis on IL-8 and MCP-1 during hypoxia and reoxygenation in human NT2-N neurons

Inflammation probably plays a significant role in perinatal brain injury. To study the contribution of locally produced cytokines, the effect on cell death of addition of IL-8 and MCP-1 or antibodies to these, and the impact of acidosis, human postmitotic NT2-N neurons were exposed to 3 h of hypoxia and glucose deprivation and reoxygenated for 21 h. After 3 h of hypoxia with neutral medium, IL-8 was significantly increased compared to controls (150 (100-250)% vs. 100 (85-115)%, p=0.023). After 21 h of neutral reoxygenation, both IL-8 (380 (110-710)% vs. 150 (85-260)%, p=0.041) and monocyte chemoattractant protein-1 (MCP-1) (650 (440-2000)% vs. 310 (230-340)%, p=0.007) were significantly increased compared to controls. After 3 h of hypoxia, both IL-8 (p=0.002) and MCP-1 (p=0.008) were significantly lower in cells with acidotic compared with cells with neutral medium. Acidosis during reoxygenation, however, significantly increased IL-8 release, whereas MCP-1 release was diminished. Similar effects of acidosis were seen in normoxic controls. The cells also secreted RANTES and IP-10, but not 8 other cytokines tested. We found no effect on cell death, measured by MTT assay, of addition of IL-8, MCP-1 or antibodies to these. We conclude that human NT2-N neurons release IL-8 and MCP-1 during 21 h of reoxygenation after 3 h of hypoxia. Acidosis led to a differential effect on IL-8 and MCP-1, with increased IL-8 and decreased MCP-1, both during reoxygenation and in normoxic controls. IL-8 and MCP-1 had no effect on cell death.

Protein kinase A (PKA)--a potential target for therapeutic intervention of dysfunctional immune cells

In several cases of immunodeficiency and autoimmunity, the dysfunctional immune system is associated with either hypo- or hyperactive T and B cells. In autoimmune conditions such as systemic lupus erythematosus (SLE) and immunodeficiencies such as acquired immunodeficiency syndrome (AIDS), it has been demonstrated that the regulatory effect of the signaling pathway of cyclic 3', 5' adenosine monophosphate (cAMP) and cAMP-dependent protein kinase (PKA) is abrogated. PKA is well-known as a key regulator of immune responses in that it inhibits both early and late phases of antigen induced T and B cell activation. Here we will discuss a potential useful strategy for therapeutic interventions of dysfunctional T cells associated with SLE and HIV by modulation of the cAMP-PKA pathway. Therefore, we will describe the components and architecture of the cAMP-PKA signaling pathway in T cells in order to point out one or several steps which potentially may serve as targets for therapeutic intervention.

Identification and characterization of novel PKA holoenzymes in human T lymphocytes

Cyclic AMP-dependent protein kinase (PKA) is a holoenzyme that consists of a regulatory (R) subunit dimer and two catalytic (C) subunits that are released upon stimulation by cAMP. Immunoblotting and immunoprecipitation of T-cell protein extracts, immunofluorescence of permeabilized T cells and RT/PCR of T-cell RNA using C subunit-specific primers revealed expression of two catalytically active PKA C subunits C alpha1 (40 kDa) and C beta2 (47 kDa) in these cells. Anti-RI alpha and Anti-RII alpha immunoprecipitations demonstrated that both C alpha1 and C beta2 associate with RI alpha and RII alpha to form PKAI and PKAII holoenzymes. Moreover, Anti-C beta2 immunoprecipitation revealed that C alpha1 coimmunoprecipitates with C beta2. Addition of 8-CPT-cAMP which disrupts the PKA holoenzyme, released C alpha1 but not C beta2 from the Anti-C beta2 precipitate, indicating that C beta2 and C alpha1 form part of the same holoenzyme. Our results demonstrate for the first time that various C subunits may colocate on the same PKA holoenzyme to form novel cAMP-responsive enzymes that may mediate specific effects of cAMP.

Induction of Cβ splice variants and formation of novel forms of protein kinase A type II holoenzymes during retinoic acid-induced differentiation of human NT2 cells

Cyclic AMP (cAMP) and cAMP-dependent protein kinase (PKA) are critical regulators of neuronal differentiation. The expression, levels and activities of PKA subunits were studied prior to and during differentiation of the human neuronal precursor cell line NTera 2 (NT2). Undifferentiated NT2 cells expressed mainly cytoplasmic PKA type I, consisting of the regulatory subunit RIalpha and the catalytic subunit Calpha. Low levels of PKA type II consisting of RIIalpha or RIIbeta associated with Calpha were also detected, mainly in the cytoplasm and in the Golgi-centrosomal area. During retinoic acid-induced differentiation, the RIalpha and RIIalpha expressions remained in the cytoplasm, while we observed a strong upregulation of RIIbeta, located to the whole cytoplasm including neurite extensions. This upregulation coincided with increased PKA-specific activity accompanied by a strong induction of a number of neuronal-specific Cbeta splice variants that together with RIIbeta form novel PKAII holoenzymes. Formation of novel PKAII holoenzymes may imply specific PKA features which may have consequences for the process of neuronal differentiation and nerve cell function.

Identification of novel splice variants of the human catalytic subunit Cbeta of cAMP-dependent protein kinase

Four different isoforms of the catalytic subunit of cAMP-dependent protein kinase, termed Calpha, Cbeta, Cgamma and PrKX have been identified. Here we demonstrate that the human Cbeta gene encodes six splice variants, designated Cbeta1, Cbeta2, Cbeta3, Cbeta4, Cbeta4ab and Cbeta4abc. The Cbeta splice variants differ in their N-terminal ends due to differential splicing of four different forms of exon 1 designated exon 1-1, 1-2, 1-3, 1-4 and three exons designated a, b and c. All these exons are located upstream of exon 2 in the Cbeta gene. The previously identified human Cbeta variant has been termed Cbeta1, and is similar to the Cbeta isoform identified in the mouse, ox, pig and several other mammals. Human Cbeta2, which is the homologue of bovine Cbeta2, has no homologue in the mouse. Human Cbeta3 and Cbeta4 are homologous to the murine Cbeta3 and Cbeta2 splice variants, whereas human Cbeta4ab and Cbeta4abc represent novel isofoms previously not identified in any other species. At the mRNA level, the Cbeta splice variants reveal tissue specific expression. Cbeta1 was most abundantly expressed in the brain, with low-level expression in several other tissues. The Cbeta3 and Cbeta4 splice variants were uniquely expressed in human brain in contrast to Cbeta2, which was most abundantly expressed in tissues of the immune system, with no detectable expression in brain. We suggest that the various Cbeta splice variants when complexed with regulatory subunits may give rise to novel holoenzymes of protein kinase A that may be important for mediating specific effects of cAMP.

CDK1-mediated phosphorylation of the RIIα regulatory subunit of PKA works as a molecular switch that promotes dissociation of RIIα from centrosomes at mitosis

Protein kinase A regulatory subunit RIIα is tightly bound to centrosomal structures during interphase through interaction with the A-kinase anchoring protein AKAP450, but dissociates and redistributes from centrosomes at mitosis. The cyclin B-p34cdc2 kinase (CDK1) has been shown to phosphorylate RIIα on T54 and this has been proposed to alter the subcellular localization of RIIα. We have made stable transfectants from an RIIα-deficient leukemia cell line (Reh) that expresses either wild-type or mutant RIIα (RIIα(T54E)). When expressed, RIIα detaches from centrosomes at mitosis and dissociates from its centrosomal location in purified nucleus-centrosome complexes by incubation with CDK1 in vitro. By contrast, centrosomal RIIα(T54E) is not redistributed at mitosis, remains mostly associated with centrosomes during all phases of the cell cycle and cannot be solubilized by CDK1 in vitro. Furthermore, RIIα is solubilized from particular cell fractions and changes affinity for AKAP450 in the presence of CDK1. D and V mutations of T54 also reduce affinity for the N-terminal RII-binding domain of AKAP450, whereas small neutral residues do not change affinity detected by surface plasmon resonance. In addition, only RIIα(T54E) interacts with AKAP450 in a RIPA-soluble extract from mitotic cells. Finally, microtubule repolymerization from mitotic centrosomes of the RIIα(T54E) transfectant is poorer and occurs at a lower frequency than that of RIIα transfectants. Our results suggest that T54 phosphorylation of RIIα by CDK1 might serve to regulate the centrosomal association of PKA during the cell cycle.

Differential expression and regulation of the PKA signalling pathway in fast and slow skeletal muscle

To identify intracellular signalling pathways that transduce muscle electrical activity, we have investigated the Protein Kinase A (PKA) pathway in fast and slow skeletal muscle. The slow soleus muscle (SOL) displayed approximately twice as much PKA catalytic activity and cAMP-binding compared to the fast Extensor Digitorum Longus (EDL) muscle. These results were confirmed by Western blot analysis using antibodies directed against the catalytic or regulatory subunits of PKA. PKA subunits were concentrated at the neuromuscular junction in innervated and denervated muscle fibers demonstrating that PKA is expressed post-synaptically. In addition, we also detected PKA subunits outside the junctional area, suggesting that PKA functions outside of the synaptic regions. Following denervation, levels of cyclic AMP, PKA C activity, R cAMP-binding and RI alpha protein levels increased significantly in the SOL, in contrast to the EDL where only elevated levels of RI alpha protein were observed. These observations demonstrate that PKA levels in skeletal muscle are subject to control at several levels and suggest that some of the differences may be in the pattern of electrical activity that motoneurons impose on the SOL and EDL.

A novel isoform of human cyclic 3',5'-adenosine monophosphate-dependent protein kinase, c alpha-s, localizes to sperm midpiece

Using rapid amplification of cDNA ends, a cDNA encoding a novel splice variant of the human C alpha catalytic subunit of cAMP-dependent protein kinase (PKA) was identified. The novel isoform differed only in the N-terminal part of the deduced amino acid sequence, corresponding to the part encoded by exon 1 in the previously characterized murine C alpha gene. Sequence comparison revealed similarity to an ovine C alpha variant characterized by protein purification and micropeptide sequencing, C alpha-s, identifying the cloned human cDNA as the C alpha-s isoform. The C alpha-s mRNA was expressed exclusively in human testis and expression in isolated human pachytene spermatocytes was demonstrated. The C alpha-s protein was present in ejaculated human sperm, and immunofluorescent labeling with a C alpha-s-specific antibody indicated that C alpha-s was localized in the midpiece region of the spermatozoon. The majority of C alpha-s was particulate and could not be released from the sperm midpiece by cAMP treatment alone. Furthermore, detergent extraction solubilized approximately two-thirds of the C alpha-s pool, indicating interaction both with detergent-resistant cytoskeletal and membrane structures. In addition, we recently identified the regulatory subunit isoforms RI alpha, RII alpha, and an A-kinase anchoring protein, hAKAP220 in this region in sperm that could target C alpha-s. This novel C alpha-s splice variant appeared to have an independent anchor in the human sperm midpiece as it could not be completely solubilized even in the presence of both detergent and cAMP.

Cyclic-AMP-dependent protein kinase (PKA) in testicular cells. Cell specific expression, differential regulation and targeting of subunits of PKA

LH and FSH regulate via cyclic adenosine 3'5' cyclic monophosphate (cAMP) and cAMP-dependent protein kinase (PKA), steroid biosynthesis is Leydig and Sertoli cells, respectively. Cyclic AMP also regulates a number of different cellular processes such as cell growth and differentiation, ion channel conductivity, synaptic release of neurotransmitters, and gene transcription. The principle intracellular target for cAMP in mammalian cells is the PKA. The fact that this broad specificity protein kinase mediates a number of discrete physiological responses following cAMP engagement, has raised the question of how specificity is maintained in the cAMP/PKA system. Here we describe features of this signaling pathway that may contribute to explain how differential effects of cAMP may occur.

PKAI as a potential target for therapeutic intervention

We have mapped a molecular mechanism for the impaired T-cell function in HIV infection and common variable immunodeficiency (CVI). Protein kinase A type I (PKAI) has a key role as an inhibitor of immune function in T lymphocytes and is activated following antigen receptor triggering. T cells from patients with HIV infection and CVI have increased activation of PKAI. This inhibits immune function and proliferation of T cells. Selective antagonists that block cAMP action through PKAI improve the immune function of T cells from HIV-infected patients up to 300%. Furthermore, combination of cAMP antagonists with interleukin-2 normalized immune responses of T cells from all patients examined and stimulated immune function of T cells from HIV-infected patients up to 600%. In addition, in vitro experiments indicate that approximately 50% of patients with CVI have a T-cell dysfunction that might benefit from a treatment reversing PKAI hyperactivation. This outlines PKAI as a potentially attractive drug target for immunomodulating therapy in HIV infection, as well as for the treatment of other immunodeficiency disorders such as CVI.

Identification, cloning and characterization of a novel nuclear protein, HA95, homologous to A-kinase anchoring protein 95

Previously, we have identified and characterized nuclear AKAP95 from man which targets cyclic AMP (cAMP)-dependent protein kinase (PKA)-type II to the condensed chromatin/spindle region at mitosis. Here we report the cloning of a novel nuclear protein with an apparent molecular mass of 95 kDa that is similar to AKAP95 and is designated HA95 (homologous to AKAP95). HA95 cDNA sequence encodes a protein of 646 amino acids that shows 61% homology to the deduced amino acid sequence of AKAP95. The HA95 gene is located on chromosome 19p13.1 immediately upstream of the AKAP95 gene. Both HA95 and AKAP95 genes contain 14 exons encoding similar regions of the respective proteins, indicating a previous gene duplication event as the origin of the two tandem genes. Despite their apparent similarity, HA95 does not bind RII in vitro. HA95 contains a putative nuclear localization signal in its N-terminal domain. It is localized exclusively into the nucleus as demonstrated in cells transfected with HA95 fused to either green fluorescence protein or the c-myc epitope. In the nucleus, the HA95 protein is found as complexes directly associated with each other or indirectly associated via other nuclear proteins. In interphase, HA95 is co-localized with AKAP95, but the two proteins are not biochemically associated. At metaphase, both proteins co-localize with condensed chromosomes. The similarity in sequence and localization of HA95 and AKAP95 suggests that the two molecules constitute a novel family of nuclear proteins that may exhibit related functions.

Differential localization of protein kinase A type II isozymes in the Golgi-centrosomal area

Selectivity in the action of cAMP may be mediated by compartmentalized pools of cyclic AMP-dependent protein kinase (PKA). PKA type II is directed to different subcellular loci by interaction of the type II regulatory subunits (RIIalpha, RIIbeta) with A-kinase anchoring proteins. In order to separately investigate the subcellular localization of PKA type II isozymes, monospecific antibodies to human RIIalpha and RIIbeta subunits of PKA were developed. We demonstrate that centrosomes bind both RIIalpha and RIIbeta. Centrosomes were the preferred intracellular anchoring site for RIIbeta. However, centrosomal localization of RIIbeta was observed only in some highly differentiated cells such as keratinocytes, granulosa cells, and macrophages and in all neoplastic cell lines examined. Centrosomal localization of RIIbeta was not observed in normal undifferentiated cells such as fibroblasts, myoblasts, and T and B cells. In contrast, RIIalpha was abundant in the Golgi area and in the trans-Golgi network (TGN). Furthermore, although RIIalpha appeared to colocalize with microtubules in the Golgi/TGN, extractions with nonionic detergent demonstrated that RIIalpha was mainly membrane-associated. In addition, alterations of microtubule dynamics with Nocodazole or Taxol affected the distribution of the detergent-extractable pool of RIIalpha, indicating that RIIalpha may localize with microtubule-associated vesicles. Thus, RIIalpha and RIIbeta clearly localize differently in the Golgi-centrosomal region. This indicates specific roles for PKA isozymes containing either RIIalpha or RIIbeta.

Cyclic-AMP-dependent protein kinase (PKA) in testicular cells. Cell specific expression, differential regulation and targeting of subunits of PKA

LH and FSH regulate via cyclic adenosine 3'5' cyclic monophosphate (cAMP) and cAMP-dependent protein kinase (PKA), steroid biosynthesis is Leydig and Sertoli cells, respectively. Cyclic AMP also regulates a number of different cellular processes such as cell growth and differentiation, ion channel conductivity, synaptic release of neurotransmitters, and gene transcription. The principle intracellular target for cAMP in mammalian cells is the PKA. The fact that this broad specificity protein kinase mediates a number of discrete physiological responses following cAMP engagement, has raised the question of how specificity is maintained in the cAMP/PKA system. Here we describe features of this signaling pathway that may contribute to explain how differential effects of cAMP may be contributed to features of the PKA signaling pathway.

Cloning and characterization of a cDNA encoding an A-kinase anchoring protein located in the centrosome, AKAP450

A combination of protein kinase A type II (RII) overlay screening, database searches and PCR was used to identify a centrosomal A-kinase anchoring protein. A cDNA with an 11.7 kb open reading frame was characterized and found to correspond to 50 exons of genomic sequence on human chromosome 7q21-22. This cDNA clone encoded a 3908 amino acid protein of 453 kDa, that was designated AKAP450 (DDBJ/EMBL/GenBank accession No. AJ131693). Sequence comparison demonstrated that the open reading frame contained a previously characterized cDNA encoding Yotiao, as well as the human homologue of AKAP120. Numerous coiled-coil structures were predicted from AKAP450, and weak homology to pericentrin, giantin and other structural proteins was observed. A putative RII-binding site was identified involving amino acid 2556 of AKAP450 by mutation analysis combined with RII overlay and an amphipatic helix was predicted in this region. Immunoprecipitation of RII from RIPA-buffer extracts of HeLa cells demonstrated co-precipitation of AKAP450. By immunofluorecent labeling with specific antibodies it was demonstrated that AKAP450 localized to centrosomes. Furthermore, AKAP450 was shown to co-purify in centrosomal preparations. The observation of two mRNAs and several splice products suggests additional functions for the AKAP450 gene.

Increased activation of protein kinase A type I contributes to the T cell deficiency in common variable immunodeficiency

The molecular mechanisms underlying the T cell dysfunction often present in common variable immunodeficiency (CVI) are not established. cAMP-dependent protein kinase A type I (PKAI) is an important inhibitor of T cell proliferation after Ag stimulation. We therefore investigated the possibility that activation of PKAI may be involved in the development of T cell dysfunction in CVI. An exogenously added PKAI-selective antagonist (Rp-8-Br-cAMPS) induced a significant increase in anti-CD3-stimulated PBMC proliferation in 20 CVI patients compared with no effect in 15 controls. Purified T cells from 7 CVI patients with strictly defined T cell deficiency had elevated endogenous cAMP levels compared with controls. Treatment of T cells from these CVI patients with Rp-8-bromo-cAMP-phosphorothioate markedly improved anti-CD3-stimulated proliferation (up to 3.7-fold), particularly in CD4+ lymphocytes, reaching proliferation levels comparable to control values. No effect of cAMP antagonist on T cell proliferation was seen in controls. In these CVI patients, cAMP antagonist also increased IL-2 production in anti-CD3-stimulated T cells. However, exogenously added IL-2 at concentrations comparable to the achieved increase in IL-2 levels after addition of cAMP antagonist had no effect on T cell proliferation. Furthermore, the stimulatory effects of exogenously added IL-2 at higher concentrations and cAMP antagonist on T cell proliferation were additive. Our findings indicate that increased PKAI activation may be an important molecular basis for the T cell defect in CVI and suggest that the cAMP/PKAI system may be a potential molecular target for immunomodulating therapy in these patients.

[Genetic modification of the mouse]

Genetic modification of mice by homologous recombination has rapidly become a central tool within molecular medicine and molecular biology. The use of such techniques allows precise mutation of single genes and study of the direct consequences in intact animals. A decade has passed since the a series of landmark studies demonstrated the feasibility of genetically modifying embryonic stem cells in mice by homologous recombination. This initiated the whole field of gene targeting, or "knockout" technology in mice. This article reviews briefly the historical and technical development of knockout technology, and the application to selected mouse models within cancer biology, immunology and neurobiology. Refinements of this type of genetic modification, with tissue- or time-specific genetic ablation or mutations, represent the next step in technology development. The combined use of Cre/loxP and homologous recombination has opened for a wide spectrum of possibilities, reaching far beyond null mutations. The rapid evolvement of the whole field has opened for genetic engineering--in the presise sense of the word--in whole animals.

Isozymes of cyclic AMP-dependent protein kinases (PKA) in human lymphoid cell lines: levels of endogenous cAMP influence levels of PKA subunits and growth in lymphoid cell lines

Activation of the cAMP signaling pathway in lymphoid cells is known to inhibit cell proliferation of T and B cells as well as cytotoxicity of natural killer (NK) cells. In order to find suitable model systems to study cAMP-mediated processes, we have examined the expression of cAMP-dependent protein kinase (PKA), endogenous levels of cAMP, and cell proliferation in eight cell lines of B lineage origin, four cell lines of T lineage origin, and normal human B and T cells. We demonstrated that the expression of mRNA and protein for one of the regulatory (R) subunits of PKA (RIalpha) was present in all the cells investigated, in contrast to the other R subunits (RIbeta, RIIalpha, and RIIbeta). Furthermore, three T cell lines and one B cell line expressed only RIalpha and C, implying these cells to contain solely PKA type I. Moreover, for the RI subunit, we observed an apparent reciprocal relationship between levels of mRNA and protein. Generally, RIalpha protein was low in cell lines where mRNA was elevated and vice versa. This was not the case for the RII subunits, where high levels of mRNA were associated with elevated levels of protein. Interestingly, we demonstrated an inverse correlation between levels of endogenous cAMP and cell growth as determined by [3H]-thymidine incorporation and cell-doubling rate (P < 0.05). Taken together, our results demonstrate great differences in PKA isozyme composition, which should be taken into consideration when using lymphoid cell lines as model system for cAMP/PKA effects in normal lymphocytes.

Protein kinase A type I antagonist restores immune responses of T cells from HIV-infected patients

Cyclic AMP-dependent protein kinase A (PKA) type I has been established as an acute inhibitor of T cell activation. For this reason, we investigated the possible role of PKA type I in HIV-induced T cell dysfunction. T cells from HIV-infected patients have increased levels of cAMP and are more sensitive to inhibition by cAMP analog than are normal T cells. A PKA type I-selective antagonist increases the impaired proliferation of T cells from HIV-infected patients to normal or subnormal levels (up to 2.8-fold). Follow-up of patients after initiation of highly active antiretroviral treatment revealed that a majority of patients have a persistent T cell dysfunction that is normalized by incubation of T cells with Rp-8-Br-cAMPS. These observations imply that increased activation of PKA type I may contribute to the progressive T cell dysfunction in HIV infection and that PKA type I may be a potential target for immunomodulating therapy.

Kinetic properties of the C-terminal Src kinase, p50csk

Csk is an important regulator of tyrosine kinases of the Src family. In this paper, we have characterised the kinetics and catalytic properties of a highly active and stable enzyme obtained in milligram amounts by expressing the enzyme as a fusion protein with glutathione-S-transferase (GST) in Escherichia coli. Using the synthetic polyamino acid poly(Glu, Tyr) as substrate, phosphotransferase activity was linear for 7-8 min with Mg2+ and 5 min with Mn2+. With Mg2+ and Mn2+, respectively, K(m) (ATP) was 56.9 +/- 6.2 and 5.4 +/- 0.6 microM and Vmax was 293 +/- 52 and 217 +/- 38 pmol phosphate transferred (microgram Csk)-1 min-1. Optimal concentrations of Mg2+ and Mn2+ were 4-10 mM and 2-3 mM, respectively, and higher concentrations of both cations were inhibitory. The Csk activity was highly sensitive to monovalent (Na+, K+) and divalent (Ca2+) cations, the sensitivity being 2-5-fold higher with Mg2+ than Mn2+. Physiological concentrations of Ca2+ (less than 10 microM) were without effect. Autophosphorylation of Csk was demonstrated in vitro, but did not influence the catalytic activity. Addition of inorganic phosphate above 100 microM strongly inhibited Csk catalytic activity towards poly(Glu, Tyr) in the presence of Mn2+, but not in the presence of Mg2+. Phosphorylation of a physiological substrate (Lck) and autophosphorylation of Csk was not inhibited by phosphate, indicating that the phosphate-dependent inhibition of Csk activity was substrate specific.

The gene encoding the C gamma catalytic subunit of cAMP-dependent protein kinase is a transcribed retroposon

Three different catalytic isoforms of cAMP-dependent protein kinase have been identified (C alpha, C beta, and C gamma). We report the cloning and characterization of the human and rhesus monkey genes encoding the testis-specific C gamma subunit. The human C gamma gene is intronless with an open reading frame similar to the previously published cDNA sequence. The 3' and 5' flanking regions share high similarity with the C alpha nontranslated regions (82%) also outside the regions corresponding to the C gamma cDNA. The human gene is flanked by an Alu-related sequence in the 5'-end and there are insertions of two Alu-related sequences in the 3' nontranslated region. The observation that the C gamma gene is intronless and colinear with C alpha mRNA, together with the presence of remnants of a poly(A) tail and flanking direct repeats, indicates that the C gamma gene is a C alpha-derived retroposon. The 5' flanking region of this gene has a high G/C content and a putative TATA box situated at -138 compared to the translation initiation codon. Cloning and sequencing of a partial C gamma rhesus monkey gene demonstrate conservation of the sequence in primates. Northern analysis on isolated and fractionated human germ cells of testes from normal and estrogen-treated individuals demonstrates that the C gamma gene is expressed only in germ cells in the human testis. Our results indicate that the C gamma gene is a retroposon specifically transcribed in primate testicular germ cells.

Structure, function, and regulation of human cAMP-dependent protein kinases

A large number of hormones, neurotransmitters, and other signaling substances that bind to G-protein-coupled cell-surface receptors have their signals converge at one sole second messenger, cAMP. The question of how specificity can be maintained in a signal-transduction system in which many extracellular signals leading to a vast array of intracellular responses are all mediated through one second-messenger system has been the subject of thorough investigation and a great deal of speculation. An increasing number of cAK isozymes, consisting of homo- or heterodimers of R subunits (RIalpha, RIbeta, RIIalpha, RIIbeta) with associated catalytic subunits (C alpha, Cbeta, Cgamma), may, at least in part, explain this specificity. The various cAK isozymes display distinct biochemical properties, and the heterogeneous subunits of cAK reveal cell-specific expression and differential regulation at the level of gene transcription, mRNA stability, and protein stability in response to a wide range of hormones and other signaling substances. The existence of a number of anchoring proteins specific to either RIIalpha or RIIbeta, and which localize cAKII isozymes toward distinct substrates at defined subcellular loci, strongly supports the idea that specific functions can be assigned to the various cAK isozymes. The demonstration that selective activation of cAKI is necessary and sufficient for cAMP-mediated inhibition of T-cell proliferation, and the observation that T-cell activation is associated with redistribution and colocalization of cAKI to the TCR, is also compatible with the notion of isozyme-specific effects.

Specificity in the cAMP/PKA signaling pathway. differential expression, regulation, and subcellular localization of subunits of PKA

A large number of hormones, neurotransmitters and other signal substances utilize cyclic adenosine 3 5 cyclic monophosphate (cAMP) as an intracellular second messenger. Cyclic AMP regulates a number of different cellular processes such as cell growth and differentiation, ion channel conductivity, synaptic release of neurotransmitters, and gene transcription The principle intracellular target for cAMP in mammalian cells is the cAMP-dependent protein kinase (PKA). The fact that this broad specificity protein kinase mediates a number of discrete physiological responses following cAMP engagement, has raised the question of how specificity is maintained in the cAMP/PKA system. Here, we will describe features of PKA signaling pathway that may contribute to explain how differential effects of cAMP may be maintained in this pathway.