Cloning and characterization of the monkey histamine H3 receptor isoforms.
We have recently identified three splice isoforms of the histamine H(3) receptor in multiple brain regions of cynomolgus monkey (Macaca fascicularis). Two of the novel isoforms displayed a deletion in the third intracellular loop (H(3)(413) and H(3)(410)), the third isoform H(3)(335) displayed a deletion in the i3 intracellular loop and a complete deletion of the putative fifth transmembrane domain TM5. We have confirmed by RT-PCR the expression of full-length H(3)(445) mRNA as well as H(3)(413), H(3)(410), and H(3)(335) splice isoform mRNA in multiple monkey brain regions including the frontal, parietal and occipital cortex, parahippocampal gyrus, hippocampus, amygdala, caudate nucleus, putamen, thalamus, hypothalamus, and cerebellum. The full-length isoform H(3)(445) was predominant in all of the regions tested, followed by H(3)(335), with the H(3)(413) and H(3)(410) being of low abundance. When expressed in C6 cells, H(3)(445), H(3)(413), and H(3)(410) exhibit high affinity binding to the agonist ligand [(3)H]-(N)-alpha-methylhistamine with respective pK(D) values of 9.7, 9.7, and 9.6. As expected, the H(3)(335) isoform did not display any saturable binding with [(3)H]-(N)-alpha-methylhistamine. The histamine H(3) receptor agonists histamine, (R)-alpha-methylhistamine, imetit and proxyfan were able to activate calcium mobilization responses through H(3)(445), H(3)(413) and H(3)(410) receptors when they were co-expressed with the chimeric G alpha(qi5)-protein in HEK293 cells, while no response was elicited in cells expressing the H(3)(335) isoform. The existence of multiple H(3) receptor splice isoforms across species raises the possibility that isoform specific properties including ligand affinity, signal transduction coupling, and brain localization may differentially contribute to observed in vivo effects of histamine H(3) receptor antagonists.
Strakhova
Marina I
MI
Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories, R-4MN, AP9A, 100 Abbott Park Road, Abbott Park, Illinois 60064, USA. marina.strakhova@abbott.com
Fox
Gerard B
GB
Carr
Tracy L
TL
Witte
David G
DG
Vortherms
Timothy A
TA
Manelli
Arlene M
AM
Miller
Thomas R
TR
Yao
Betty B
BB
Brioni
Jorge D
JD
Esbenshade
Timothy A
TA
D000818:Animals; D001921:Brain / Q000378:metabolism; D002460:Cell Line; D003001:Cloning, Molecular; D015870:Gene Expression; D017442:Histamine Agonists / Q000494:pharmacology; D006801:Humans; D008024:Ligands; D008252:Macaca fascicularis; D008297:Male; D011485:Protein Binding; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000378:metabolism*; D018100:Receptors, Histamine H3 / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013045:Species Specificity
D017442:Histamine Agonists; D008024:Ligands; D020033:Protein Isoforms; D012333:RNA, Messenger; D018100:Receptors, Histamine H3