| Budget Amount *help |
¥6,500,000 (Direct Cost: ¥6,500,000)
Fiscal Year 1998: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1997: ¥5,100,000 (Direct Cost: ¥5,100,000)
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| Research Abstract |
Many peptide hormone and neurotransmitter receptors belonging to the seven membrane-spanning G protein-coupled receptor family have been demonstrated to transmit ligand-dependent mitogenic signals in vitro. The physiological roles of the mitogenic activity through G protein-coupled receptors in vivo had remained to be elucidated. By generating G protein-coupled cholecystokinin (CCK)-B/gastrin receptor deficient-mice by gene targeting, we have clearly demonstrated that the G protein-coupled CCK-B/gastrin receptor is essential for the physiological as well as pathological cell growth in vivo.
CCK-B/gastrin receptor have been shown to be expressed in various lineages of human leukaemia cell lines and be able to promote their growth by an autocrine mechanism. We evaluated the expression of CCK-B/gastrin receptor mRNA in peripheral mononuclear cells of eight patients suffering from de novo acute leukaemia by reverse transcription-polymerase chain reaction. All patients examined (four myeloid
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, three lymphoid and one mixed-lineage) possessed receptor transcript. Among them, five samples also expressed gastrin mRNA.Thus, the autocrine stimulation through the CCK-B/gastrin receptor might be exist in de novo leukaemia cells.
Moreover, the expression of the gastrin and its receptor genes in human colon tumor cells was examined by RT-PCR.Buman colon tumors resected surgically were xenografted to nude mice to eliminate cells other than proliferative carcinoma cells. Unexpectedly, all human colon carcinoma cells (10 samples) grown in nude mice expressed the CCK-B/gastrin receptor transcript. These carcinomas include all sort of differentiation stages. These results suggest that all human colon carcinoma may be derived from the colon mucosa cells expressing CCK-B/gastrin receptors physiologically. Moreover, gastrin mRNA was expressed in the tumor cells as well as in the normal colon mucosa. A gastrin autocrine loop could be present in human colon cancer cells in vivo
The brain CCK-B receptor is identical to the gastrin receptor of the stomach mucosa. However, the affinities for two peptide ligands, CCK-8 and gastrin I, as well as non-peptide ligands vary depend on the animal spieces. Thus, it is important to evaluate the spieces specificity of receptor antagonists. Here, we examined the antagonistic potency of new CCK-B/gastrin receptor antagonists on mouse NIE 3T3 fibroblasts ectopically expressing human CCK-B/gastrin receptors (N-hCCKBR) by determining radioligand binding, intracellular calcium [Ca^<2+>]i and inositol phosphate concentrations. Among several benzodiazepine derivatives, AG-041R had the most potent activities in the competition of [^<125>I]-CCK-8 or [^<125I>]-gastrin I binding, the inhibition of CCK-8- or gastrin I-induced phosphoinositide hydrosis and cytoplasmic free calcium increase. AG-041R is a specific antagonist for human CCK-B/gastrin receptors. Less
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