Interleukin-1 increases protein kinase A activity by a cAMP-independent mechanism in AtT-20 cells

Conditional inactivation of Akt three isoforms causes tau hyperphosphorylation in the brain

BACKGROUND

Tau hyperphosphorylation plays a critical role in neurodegenerative diseases [EMBO Mol Med. 6:1142-60, 2014; Annu Rev Neurosci. 24:1121-59, 2001]. Recent evidence has shown that Akt is down-regulated in AD [J Pathol. 225:54-62, 2011]. However, it remained unknown which pathological process, e.g. tau pathology or neuron death, Akt may contribute to. In this study, Cre-loxP technique was employed to generate a viable Akt three isoforms conditional knockout (Akt cTKO) mouse in which total Akt levels were dramatically reduced in the adult brain.

RESULTS

Significantly increased levels of tau phosphorylated (p-tau) at various sites were observed in Akt cTKO mice as compared to age-matched littermate controls. Increased levels for phosphorylated GSK3α and phosphorylated PKA substrates were detected in Akt cTKO brains. In contrast, no significant changes on p-tau levels were found in Akt1(-/-), Akt2(-/-) or Akt3(-/-) mice.

CONCLUSIONS

Akt may regulate tau phosphorylation in the adult brain by affecting activities for PKA and GSK3α.

Regulation of electrolyte transport with IL-1beta in rabbit distal colon

Interletrkin-1beta levels are elevated in inflammatory bowel disease. In this study the mechanism by which interleukin-1beta affects electrolyte transport in the rabbit distal colon, was investigated. Interleukin-1beta caused a delayed increase in short-circuit current (I(sc)) which was attributed to protein synthesis since the effect was inhibited by cycloheximide. The interleukin-1beta induced increase in I(sc) was not affected by amiloride treatment but was completely inhibited by bumetanide or in chloride-free buffer and by indomethacin. Prostaglandin E(2) levels increased in tissue treated with interleukin-1beta, but this increase was reversed by cycloheximide. These data suggest that interleukin-1beta causes its effect via a yet to be identified second messenger, by increasing chloride secretion through a prostaglandin E(2) mediated mechanism.

Menaquinone-4 enhances testosterone production in rats and testis-derived tumor cells

Background

Vitamin K is essential for the posttranslational modification of various Gla proteins. Although it is widespread in several organs, including the testis, the function of vitamin K in these organs is not well characterized. In this study, we investigated the function of vitamin K in the testis and analyzed its role in steroidogenesis.

Methods

Eight-week-old male Wistar rats were fed a diet supplemented with menaquinone-4 (MK-4, 75 mg/kg diet), one of the predominant K₂ vitamins present in the testis, for 5 weeks. In vivo testosterone levels of the rats' plasma and testes were measured by enzyme-linked immunosorbent assay, and in vitro testosterone levels of testis-derived tumor cells (I-10 cells) maintained in Ham's F-10 medium with 10% fetal bovine serum were measured following treatment with MK-4 (0 to 100 μM) at several time points. Testosterone and cellular protein levels were analyzed with respect to their effects on steroidogenesis.

Results

Testosterone levels in the plasma and testes of MK-4-fed rats were significantly increased compared to those of control rats, with no obvious differences in plasma luteinizing hormone levels. Secreted testosterone levels from I-10 cells were elevated by MK-4, but not by vitamin K₁, in a dose-dependent manner independent of cAMP treatment. Western blot analysis revealed that expression of CYP11A, the rate-limiting enzyme in steroidogenesis, and phosphorylation levels of protein kinase A (PKA) and the cAMP response element-binding protein were all stimulated by the presence of MK-4. Enhancement of testosterone production was inhibited by H89, a specific inhibitor of PKA, but not by warfarin, an inhibitor of γ-glutamylcarboxylation.

Conclusions

MK-4 stimulates testosterone production in rats and testis-derived tumor cells via activation of PKA. MK-4 may be involved in steroidogenesis in the testis, and its supplementation could reverse the downregulation of testosterone production in elders.

Shiga toxin (Stx)1B and Stx2B induce von Willebrand factor secretion from human umbilical vein endothelial cells through different signaling pathways

Diarrhea-associated hemolytic uremic syndrome (D(+)HUS) is caused by the ingestion of Escherichia coli that produce Shiga toxin (Stx), which is composed of a cytotoxic A subunit and pentameric B subunits that bind globotriaosylceramide on susceptible cells. Stx occurs in 2 types, Stx1 and Stx2. B subunits of either type stimulate von Willebrand factor (VWF) secretion from human umbilical vein endothelial cells (HUVECs), and Stx2B can cause thrombotic microangiopathy in Adamts13(-/-) mice. We have now determined that Stx1B and Stx2B activate different signaling pathways in HUVECs. VWF secretion induced by Stx1B is associated with a transient rise in intracellular Ca(2+) level that is blocked by chelation with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester, removal of extracellular Ca(2+), the phospholipase C inhibitor U73122, the protein kinase inhibitor staurosporine, or small interfering RNA knockdown of protein kinase Cα. In contrast, Stx2B-induced VWF secretion is associated with activation of protein kinase A (PKA) and is blocked by the PKA inhibitor H89 or small interfering RNA knockdown of PKA. Stx2B does not increase cAMP levels and may activate PKA by a cAMP-independent mechanism. The activation of distinct signaling pathways may be relevant to understanding why E coli that express Stx2 are more likely to cause D(+)HUS than are E coli expressing only Stx1.

Nur77 induction and activation are necessary for interleukin-1 stimulation of proopiomelanocortin in AtT-20 corticotrophs

Nur77 and Nurr1 are critical for proopiomelanocortin (POMC) regulation by corticotrophin releasing hormone (CRH) in corticotrophs. We analyze the regulation and activity of Nur77 by interleukin (IL)-1 in AtT-20 corticotrophic cells and its consequences on POMC regulation. IL-1 induces Nur77 and not Nurr1 mRNA and shows an increased transcriptional activity on the NurRE site, an effect dependent of p38 protein kinase activity. A NurRE mutation abrogates POMC promoter transcription by IL-1 and a stable AtT-20 clone overexpressing a dominant negative form of Nur77 is unresponsive to IL-1-dependent POMC induction and adrenocorticotrophin (ACTH) secretion. These results demonstrate that Nur77 is essential for POMC stimulation by IL-1 in corticotrophs.

Genes expressed in the mouse pituitary corticotrope AtT-20/D-16v tumor cell line

The pituitary corticotrope AtT-20 stable cell line has been used as a model system to study peptide secretion, glucocorticoid regulation, and several other processes. In order to better understand this model cell line, a phage cDNA library was generated from AtT-20/D-16v cell mRNA and cDNA sequences were obtained for 317 clones representing 203 known genes and 48 novel cDNAs. The sequencing results revealed the prevalence of the mouse leukemia virus in this cell line and also identified a number of putatively secreted molecules that were not previously recognized as being secreted from AtT-20/D-16v cells or pituitary corticotropes. Nine completely novel cDNAs and 39 cDNAs homologous to known ESTs were also identified. A listing of other genes known to be expressed in AtT-20/D-16v cells is also provided.

A comparison of the effects of signal transduction inhibitors on oxidative burst and degranulation in IL-I beta stimulated bovine neutrophils

There is little information available on IL-1 mediated signal transduction in neutrophils from species other than humans. In this study, signal transduction pathway inhibitors were used to compare signaling pathways for the oxidative burst and degranulation in bovine neutrophils stimulated with rBoIL-1 beta. Protein kinase C inhibitors (staurosporine and chelerythine), DL-propranolol, pertussis toxin (PT), genistein and verapamil significantly inhibited rBoIL-1 beta (10 ng/ml) stimulated luminol-dependent chemiluminescence (LDCL) in a dose-dependent manner, while indomethacin and zileuton had no effect. Propranolol significantly decreased both primary and secondary granule release in response to rBoIL-1 beta. Staurosporine enhanced secondary but not primary granule release, and PT increased primary and secondary granule release. In addition, propranolol inhibited the shape change induced by rBoIL-1 beta and zymosan-activated serum, whereas PT markedly decreased the response induced by zymosan-activated serum, but not rBoIL-1 beta. These findings suggest that rBoIL-1 beta stimulation of the oxidative burst, degranulation, and shape change of bovine neutrophils are mediated through distinct signal transduction pathways.

Human and murine pituitary expression of leukemia inhibitory factor. Novel intrapituitary regulation of adrenocorticotropin hormone synthesis and secretion

Leukemia inhibitory factor (LIF) gene expression was detected in human fetal pituitary tissue by expression of LIF mRNA transcripts, protein immunocytochemistry, and immunoelectron microscopy. Fetal LIF immunoreactivity colocalized with 30% of ACTH-expressing cells, approximately 20% of somatotrophs, and approximately 15% of non-hormone-expressing cells. LIF was also strongly expressed in normal adult pituitary and in four growth hormone-producing and two ACTH-producing adenomas, but not in eight nonfunctioning pituitary tumors. Culture of fetal cells expressing surface LIF-binding sites demonstrated predominance of in vitro ACTH secretion as compared with other pituitary hormones. In AtT-20 murine cells, LIF (ED50 10 pM) stimulated basal proopiomelanocortin mRNA levels by 40% and corticotropin-releasing hormone-induced ACTH secretion (two- to threefold), as did oncostatin M (ED50 30 pM), a related peptide. ACTH responses were not further enhanced by both cytokines together, which is consistent with their shared receptor. Anti-LIF antiserum neutralized basal and LIF-induced ACTH secretion, suggesting autocrine regulation of ACTH by LIF. The results show that human pituitary cells express the LIF gene and LIF-binding sites, predominantly in corticotrophs. Pituitary LIF expression and LIF regulation of proopiomelanocortin and ACTH reflect an intrapituitary role for LIF in modulating early embryonic determination of specific human pituitary cells and as a paracrine or autocrine regulator of mature ACTH.