| 1. |
- Bakke, Marit
(författare)
-
Regulation of steroidogenesis : cAMP-dependent transcription in adrenocortical cells
- 1996
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Optimal steroid hormone output from the adrenal cortex depends on the peptide hormone ACTH which elicits its effect by increasing the intracellular levels of the second messenger cAMP, and a subsequent activation of the cAMP-dependent protein kinase. An important aspect of ACTH action is the ability of this hormone to increase transcription of a group of genes that encodes the steroid hydroxylases, enzymes that catalyze the conversion of cholesterol to biologically active steroids. A general feature of these genes is that they depend on atypical cAMP-responsive sequences not found in other genes that are regulated by this second messenger. A major focus of this thesis was to investigate the molecular mechanisms underlying cAMP-induced transcription of the gene encoding cytochrome P450 17alpha-hydroxylase (CYP17). This enzyme is necessary for syntbesis of cortisol and adrenal androgens. CYP17 contains two sequences in its promoter region that mediate cAMP-responsiveness on reporter genes when transfected into steroidogenic cells. These sequences, which are designated cAMP-responsive sequences 1 and 2 (CRS1 and CRS2), display differences with regard to nucleotide sequence and protein interactions. CRS1 and CRS2 are also differently regulated by the protein kinase C signal transduction pathway, since treatment of adrenocortical cells with phorbol esters represses cAMP-induced transcription mediated by CRS1, but has no effect on transcription conferred by CRS2. The mouse VL30 elements constitute a family of retrotransposons that are highly inducible by various physiological stimuli, and in steroidogenic tissues, VL30 expression is induced in response to tropic hormones. We identified DNA regulatory elements that mediated the ACTH-dependent transcription of a VL30 retrotransposon in mouse adrenal cells. These elements were related to classical cAMP regulatory elements (CREs) but exhibited differences in protein binding both with respect to affinity and specificity, suggesting that steroidogenic-cell specific gene expression in response to cAMP can be mediated both through DNA sequences related to classical CREs as well as through atypical cAMP-responsive sequences present in the steroid hydroxylase genes. Taken together, the results presented in this thesis provide new insights into the molecular aspects of ACTH action on steroid hormone biosynthesis, and also unravel novel aspects of cAMP-dependent gene regulation.
|
|
| 2. |
- Gucek, Alenka, et al.
(författare)
-
Fusion pore regulation by cAMP/Epac2 controls cargo release during insulin exocytosis
- 2019
-
Ingår i: eLIFE. - : ELIFE SCIENCES PUBLICATIONS LTD. - 2050-084X. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Regulated exocytosis establishes a narrow fusion pore as initial aqueous connection to the extracellular space, through which small transmitter molecules such as ATP can exit. Co-release of polypeptides and hormones like insulin requires further expansion of the pore. There is evidence that pore expansion is regulated and can fail in diabetes and neurodegenerative disease. Here, we report that the cAMP-sensor Epac2 (Rap-GEF4) controls fusion pore behavior by acutely recruiting two pore-restricting proteins, amisyn and dynamin-1, to the exocytosis site in insulin-secreting beta-cells. cAMP elevation restricts and slows fusion pore expansion and peptide release, but not when Epac2 is inactivated pharmacologically or in Epac2(-/-) (Rapgef4(-/-)) mice. Consistently, overexpression of Epac2 impedes pore expansion. Widely used antidiabetic drugs (GLP-1 receptor agonists and sulfonylureas) activate this pathway and thereby paradoxically restrict hormone release. We conclude that Epac2/cAMP controls fusion pore expansion and thus the balance of hormone and transmitter release during insulin granule exocytosis.
|
|
| 3. |
- Hoivik, Erling A., et al.
(författare)
-
DNA Methylation of Alternative Promoters Directs Tissue Specific Expression of Epac2 Isoforms
- 2013
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:7, s. e67925-
-
Tidskriftsartikel (refereegranskat)abstract
- Epac 1 and Epac 2 (Epac1/2; exchange factors directly activated by cAMP) are multidomain proteins that mediate cellular responses upon activation by the signaling molecule cAMP. Epac1 is ubiquitously expressed, whereas Epac2 exhibits a restricted expression pattern. The gene encoding Epac2 gives rise to at least three protein isoforms (Epac2A, Epac2B and Epac2C) that exhibit confined tissue and cell specific expression profiles. Here, we describe alternative promoter usage for the different isoforms of Epac2, and demonstrate that the activity of these promoters depend on the DNA methylation status. Bisulfite sequencing demonstrated that the level of methylation of the promoters in different tissues correlates with Epac2 isoform expression. The presented data indicate that the tissue-specific expression of the Epac2 isoforms is epigenetically regulated, and identify tissue-specific differentially methylated promoter regions within the Epac2 locus that are essential for its transcriptional control.
|
|
| 4. |
- Höglund, Erik, et al.
(författare)
-
Suppression of aggressive behaviour in juvenile Atlantic cod (Gadus morhua) by L-tryptophan supplementation
- 2005
-
Ingår i: AQUACULTURE. ; 249:1-4, s. 525-531
-
Tidskriftsartikel (refereegranskat)abstract
- Aggressive interactions and cannibalism of juvenile Atlantic cod may cause substantial production losses under conditions of intensive rearing. In other teleosts, chronically increased brain concentrations and turnover of the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) are associated with suppressed aggression. Further, dietary supplementation with the serotonin precursor, L-tryptophan (TRP) suppresses aggression in juvenile rainbow trout (Onchorhyncus mykiss) and reduces cannibalism in juvenile grouper (Epinephelus coioides). In the present study, the behavioural effect of dietary TRP supplementation was observed in pairs of juvenile Atlantic cod subjected to repeated encounters for 10 days. After 3 days, one group was given TRP-supplemented feed (28 g/kg). A significant (P < 0.01) decrease in aggressive acts (from 40 +/- 2.7/ 10 min to 17 +/- 2.0/10 min, mean +/- standard error of mean) was seen after changing to TRP-supplemented feed. The mean number of aggressive acts was also significantly (P<0.05) lower in the TRP-treated group (17 +/- 2.0/10 min) compared to a control group not receiving TRP treatment (29 3.3/10 min). A second experiment examined the effect of TRP-supplemented feed (28 g/kg) on the activity of central 5-HT, quantified as the concentration ratio between the 5-HT metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and 5-HT. In this experiment, the TRP-treated group ([5-HIAA]/[5-HT]=0.56 +/- 0.04) showed elevated values (P<0.038) compared with the control group ([5-HIAA]/[5-HT]=0.43 +/- 0.03). In conclusion, this study shows that juvenile Atlantic cod are highly aggressive and that supplementing the feed with TRP affects central 5-HT signalling systems and reduces this behaviour. (c) 2005 Elsevier B.V. All rights reserved.
|
|
