Functional characterization of two cholecystokinin-B/gastrin receptor isoforms: a preferential splice donor site in the human receptor gene.
The cholecystokinin-B and gastrin receptor is encoded by a single gene composed of five exons and spanning over 10 kilobases on human chromosome 11p 15.5-->15.4. Exon 4 has two possible alternative splicing donor sites that seem to be conserved in other species such as the canine, rat, Mastomys, and mouse. They could generate two receptor isoforms (short- and long-form), which differ in their putative third cytoplasmic domain of the serpentine G-protein-coupled receptors. In the present study, we examined whether an alternative splicing is operated in a tissue-specific manner and whether two receptor isoforms have functional differences. RNase-protection assay and S1 nuclease mapping demonstrated the preferential expression of the short-form in the human brain as well as the digestive organs, stomach and pancreas. The two putative isoforms of the cholecystokinin-B/gastrin receptor expressed in mouse fibroblasts showed the same characteristics in their ligand-bindings, the major signal transduction such as phosphoinositides production, cytoplasmic Ca2+ increase, tyrosine phosphorylation of focal adhesion kinase, activation of mitogen-activated protein kinase, and the induction of early-responsive genes such as c-fos, c-myc, and c-jun. Moreover, the ligand-dependent trophic effect was seen in both receptor isoforms. Taken together with the absence of tissue-specific expression of two receptor isoforms, these results suggest a species-specific dominant splice donor site in exon 4 of the human receptor gene.
Ito
M
M
Department of Medicine, Kobe University School of Medicine, Japan.
Iwata
N
N
Taniguchi
T
T
Murayama
T
T
Chihara
K
K
Matsui
T
T
D016475:3T3 Cells; D017398:Alternative Splicing; D000818:Animals; D001483:Base Sequence; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009928:Organ Specificity / Q000235:genetics; D011949:Receptors, Cholecystokinin / Q000235:genetics*
D011949:Receptors, Cholecystokinin