Bacillus Calmette-Guerin initiates intracellular signaling in a transitional carcinoma cell line by cross-linking alpha 5 beta 1 integrin.
OBJECTIVE
The adherence of bacillus Calmette-Guerin (BCG) to the surface of transitional carcinoma tumor cells initiates nuclear factor (NF)-kappa B signal transduction pathways that modulate the expression of proteins important in the antitumor response to BCG. We tested the hypothesis that BCG initiates NF-kappa B signaling as a consequence of cross-linking alpha 5 beta 1 integrin receptors present on the tumor cell surface.


METHODS
The effect of alpha 5 beta 1 antibody mediated cross-linking on interleukin (IL)-6 mRNA expression, IL-6 promoter activation and activation of a specific NF-kappa B reporter construct was determined. A series of reporter constructs containing nonfunctional mutations in the AP-1, NF-IL-6 and NF-kappa B sites were used to determine the relative importance of these response elements in alpha 5 beta 1 cross-linking mediated activation of the IL-6 promoter. A final series of experiments assessed the role of alpha 5 beta 1 receptor occupancy by fibronectin (FN) in initiating antibody or BCG mediated signaling.


RESULTS
Anti alpha 5 and anti beta 1 mediated cross-linking of alpha 5 beta 1 integrin initiated NF-kappa B signaling, IL-6 promoter activation and IL-6 mRNA expression. Deletion mutants demonstrated that alpha 5 beta 1 cross-link initiated, IL-6 promoter transactivation required intact NF-kappa B and AP-1 response elements. Receptor occupancy by FN was required for BCG but not for antibody initiated signaling.


CONCLUSIONS
Cross-linking the alpha 5 beta 1 receptor present on the surface of human transitional carcinoma cells lines initiates signal transduction in a manner identical to that observed for BCG. We propose a model in which multiple FN binding sites present on BCG interact with alpha 5 beta 1 receptor bound FN molecules to cross-link alpha 5 beta 1 receptors and initiate intracellular signaling.
Chen
Fanghong
F
Department of Urology, Medical College of Wisconsin, Milwaukee, 53226, USA.
Zhang
Guangjian
G
Iwamoto
Yoshiki
Y
See
William A
WA
D001422:Bacterial Adhesion; D002295:Carcinoma, Transitional Cell / Q000378:metabolism* / Q000382:microbiology; D005353:Fibronectins / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D039081:Integrin alpha5beta1 / Q000378:metabolism*; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D009163:Mycobacterium bovis / Q000502:physiology*; D016328:NF-kappa B / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000382:microbiology; D001749:Urinary Bladder Neoplasms / Q000378:metabolism* / Q000382:microbiology
D005353:Fibronectins; D039081:Integrin alpha5beta1; D015850:Interleukin-6; D016328:NF-kappa B; D012333:RNA, Messenger; D018808:Transcription Factor AP-1