Post by Max on Jul 13, 2005 16:40:11 GMT -5
Vitamin A deficiency was found to decrease hippocampal acetylcholine release
In rats fed with a vitamin A-deficient diet, a significant decrease in hippocampal acetylcholine release induced by scopolamine was found, assessed using microdialysis technique. A reduction in the size of hippocampal nuclei of CA1 region in vitamin A-deficient rats, compared to rats fed with a vitamin A-sufficient diet was also found [1].
Suggested inhibition of choline acetyltransferase and Butyrylcholinesterase resulting in reduced formation of acetylcholine
It is shown that ChAT (choline acetyltransferase), an ezyme active in the formation of acetylcholine, activity can be regulated in culture by retinoic acid, an active metabolite of vitamin A, and by sodium butyrate, an organic fatty acid [4]. Butyrylcholinesterase is a serine hydrolase biochemically related to the cholinergic enzyme acetylcholinesterase. It is capable of hydrolyzing esters of choline. Butyrylcholinesterase has unique enzymatic properties and is widely distributed in the nervous system, raising the possibility of its involvement in neural function [3].
Vitamin A and sodium butyrate have two major things in common. 1) They are found to upregulate the ChAT in small doses, which likely, as the butyrylcholinesterase is dependent on a serine hydrolase. 2) Since vitamin A is suggested to bind to serine residues, which possibly also is the case with sodium butyrate, a significant inhibition of the enzymes in larger doses can not be excluded. A possible chemical explanation to this suggested significant inhibition is that the residues get too heavy by the binding of retinoic acid for the hydrolysis to take place at an optimal degree.
Serine 27 of RXRalpha is an unique target for phosphorylation by protein kinase A (PKA) [5]. In the rat pheochromocytoma cell line PC12 The expression of the ChAT and VAChT genes is regulated coordinately at the transcriptional level, and a signaling pathway specifically involving PKA II plays an important role in this process [6].
Suggested decreased promoter activity of the neural acetylcholine receptor
The 4 subunit is a component of the neuronal nicotinic acetylcholine receptors which control catecholamine secretion in bovine adrenomedullary chromaffin cells. The promoter of the gene coding for this subunit was characterized. A proximal region (from 99 to 64) was responsible for the transcriptional activity observed in chromaffin, C2C12, and COS cells. Within this region two cis-acting elements that bind transcription factors Sp1 and NF-Y were identified. Mutagenesis of the two elements indicated that they cooperate for the basal transcription activity of the promoter. The human 4 promoter, that was also characterized, shared structural and functional homologies with the bovine promoter. Thus, two adjacent binding elements for Sp1 and NF-Y were detected. Whereas the Sp1 site was an important determinant of the promoter activity, the NF-Y site may have cell-specific effects [7].
Opioid receptor activity
Previously, several important cis-elements and trans-factors have been shown to play a functional role in the proximal promoter of mouse micro-opioid receptor (MOR) gene. In this study, we defined another functional element located the in -450 to -400 bp (translational start site designated as +1) region of the proximal promoter, which is also essential for the full promoter activity. It is designated as the morAP-2-like element for its sequence homologous to the consensus AP-2 element. Surprisingly, electrophoretic mobility shift analysis (EMSA) revealed that Sp1 and Sp3, but not AP-2 proteins, were specifically bound to the morAP-2-like element. Mutation of the morAP-2-like element, resulting in a loss of Sp binding, led to an approximately 35% decrease in activity, further confirming the positive role of the morAP-2-like element in MOR gene expression. Dephosphorylation of Sp proteins with alkaline phosphatase also decreased Sp binding to the morAP-2-like element in EMSA, suggesting phosphorylation of Sp is essential for its binding to this element. However, direct or indirect activation of PKA, a classical G-protein coupled signaling pathway, resulted in no significant change of Sp binding to the morAP-2-like element, nor of the promoter activity the SH-SY5Y cells, MOR expressing cells, suggesting that phosphorylation of Sp does not involve PKA. These results suggest that the binding of different phosphorylated forms of Sp proteins to the morAP-2-like element may contribute to the fine tuning of MOR expression in different cells [2].
In rats fed with a vitamin A-deficient diet, a significant decrease in hippocampal acetylcholine release induced by scopolamine was found, assessed using microdialysis technique. A reduction in the size of hippocampal nuclei of CA1 region in vitamin A-deficient rats, compared to rats fed with a vitamin A-sufficient diet was also found [1].
Suggested inhibition of choline acetyltransferase and Butyrylcholinesterase resulting in reduced formation of acetylcholine
It is shown that ChAT (choline acetyltransferase), an ezyme active in the formation of acetylcholine, activity can be regulated in culture by retinoic acid, an active metabolite of vitamin A, and by sodium butyrate, an organic fatty acid [4]. Butyrylcholinesterase is a serine hydrolase biochemically related to the cholinergic enzyme acetylcholinesterase. It is capable of hydrolyzing esters of choline. Butyrylcholinesterase has unique enzymatic properties and is widely distributed in the nervous system, raising the possibility of its involvement in neural function [3].
Vitamin A and sodium butyrate have two major things in common. 1) They are found to upregulate the ChAT in small doses, which likely, as the butyrylcholinesterase is dependent on a serine hydrolase. 2) Since vitamin A is suggested to bind to serine residues, which possibly also is the case with sodium butyrate, a significant inhibition of the enzymes in larger doses can not be excluded. A possible chemical explanation to this suggested significant inhibition is that the residues get too heavy by the binding of retinoic acid for the hydrolysis to take place at an optimal degree.
Serine 27 of RXRalpha is an unique target for phosphorylation by protein kinase A (PKA) [5]. In the rat pheochromocytoma cell line PC12 The expression of the ChAT and VAChT genes is regulated coordinately at the transcriptional level, and a signaling pathway specifically involving PKA II plays an important role in this process [6].
Suggested decreased promoter activity of the neural acetylcholine receptor
The 4 subunit is a component of the neuronal nicotinic acetylcholine receptors which control catecholamine secretion in bovine adrenomedullary chromaffin cells. The promoter of the gene coding for this subunit was characterized. A proximal region (from 99 to 64) was responsible for the transcriptional activity observed in chromaffin, C2C12, and COS cells. Within this region two cis-acting elements that bind transcription factors Sp1 and NF-Y were identified. Mutagenesis of the two elements indicated that they cooperate for the basal transcription activity of the promoter. The human 4 promoter, that was also characterized, shared structural and functional homologies with the bovine promoter. Thus, two adjacent binding elements for Sp1 and NF-Y were detected. Whereas the Sp1 site was an important determinant of the promoter activity, the NF-Y site may have cell-specific effects [7].
Opioid receptor activity
Previously, several important cis-elements and trans-factors have been shown to play a functional role in the proximal promoter of mouse micro-opioid receptor (MOR) gene. In this study, we defined another functional element located the in -450 to -400 bp (translational start site designated as +1) region of the proximal promoter, which is also essential for the full promoter activity. It is designated as the morAP-2-like element for its sequence homologous to the consensus AP-2 element. Surprisingly, electrophoretic mobility shift analysis (EMSA) revealed that Sp1 and Sp3, but not AP-2 proteins, were specifically bound to the morAP-2-like element. Mutation of the morAP-2-like element, resulting in a loss of Sp binding, led to an approximately 35% decrease in activity, further confirming the positive role of the morAP-2-like element in MOR gene expression. Dephosphorylation of Sp proteins with alkaline phosphatase also decreased Sp binding to the morAP-2-like element in EMSA, suggesting phosphorylation of Sp is essential for its binding to this element. However, direct or indirect activation of PKA, a classical G-protein coupled signaling pathway, resulted in no significant change of Sp binding to the morAP-2-like element, nor of the promoter activity the SH-SY5Y cells, MOR expressing cells, suggesting that phosphorylation of Sp does not involve PKA. These results suggest that the binding of different phosphorylated forms of Sp proteins to the morAP-2-like element may contribute to the fine tuning of MOR expression in different cells [2].