Bombesin-mediated AP-1 activation in a human gastric cancer (SIIA).
BACKGROUND
Bombesin, a gut tetradecapeptide homologous to the mammalian gastrin-releasing peptide (GRP), stimulates the growth of the human gastric cancer line SIIA through specific GRP receptors (GRP-Rs); the cellular mechanisms are not known. The purpose of our study was to (1) confirm functional GRP-R in SIIA and (2) determine whether bombesin alters the expression and binding activity of the AP-1 transcription factors, c-jun and jun-B.


METHODS
SIIA cells were treated with bombesin, and intracellular calcium mobilization was measured by means of fura-2 spectrofluorometry. To assess changes in c-jun and jun-B, RNA and protein were extracted for Northern and Western blots, respectively; nuclear protein was extracted for gel mobility shifts to determine AP-1 binding activity.


RESULTS
SIIA cells mobilized intracellular calcium in response to bombesin, exhibiting a functional cell-surface GRP-R. Bombesin treatment increased expression of both c-jun and jun-B mRNA by 0.5 hours, with maximal expression at 1 hour; concomitant increases in steady-state levels of c-Jun and JunB protein were identified. Moreover, bombesin increased binding of the AP-1 proteins as shown by gel shifts.


CONCLUSIONS
The SIIA human gastric cancer possesses functional GRP-R coupled to the calcium second messenger pathway. Further, bombesin stimulates expression of c-jun and jun-B mRNA and protein and increases binding activity of AP-1 proteins. Delineating the cellular pathways involved in bombesin-mediated gene activation will provide important insights into the mechanisms responsible for normal and neoplastic gut growth.
Kim
H J
HJ
Department of Surgery, University of Texas Medical Branch, Galveston 77555-0527, USA.
Evers
B M
BM
Guo
Y
Y
Banker
N A
NA
Hellmich
M R
MR
Townsend
C M
CM
D000230:Adenocarcinoma; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D001839:Bombesin / Q000378:metabolism / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D018004:Receptors, Bombesin / Q000378:metabolism*; D013274:Stomach Neoplasms; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects
D004268:DNA-Binding Proteins; D016755:Proto-Oncogene Proteins c-jun; D018004:Receptors, Bombesin; D018808:Transcription Factor AP-1; D001839:Bombesin