Clone-specific expression, transcriptional regulation, and action of interleukin-6 in human colon carcinoma cells.
BACKGROUND
Many cancer cells produce interleukin-6 (IL-6), a cytokine that plays a role in growth stimulation, metastasis, and angiogenesis of secondary tumours in a variety of malignancies, including colorectal cancer. Effectiveness of IL-6 in this respect may depend on the quantity of basal and inducible IL-6 expressed as the tumour progresses through stages of malignancy. We therefore have evaluated the effect of IL-6 modulators, i.e. IL-1beta, prostaglandin E2, 17beta-estradiol, and 1,25-dihydroxyvitamin D3, on expression and synthesis of the cytokine at different stages of tumour progression.


METHODS
We utilized cultures of the human colon carcinoma cell clones Caco-2/AQ, COGA-1A and COGA-13, all of which expressed differentiation and proliferation markers typical of distinct stages of tumour progression. IL-6 mRNA and protein levels were assayed by RT-PCR and ELISA, respectively. DNA sequencing was utilized to detect polymorphisms in the IL-6 gene promoter.


RESULTS
IL-6 mRNA and protein concentrations were low in well and moderately differentiated Caco-2/AQ and COGA-1A cells, but were high in poorly differentiated COGA-13 cells. Addition of IL-1beta (5 ng/ml) to a COGA-13 culture raised IL-6 production approximately thousandfold via a prostaglandin-independent mechanism. Addition of 17beta-estradiol (10-7 M) reduced basal IL-6 production by one-third, but IL-1beta-inducible IL-6 was unaffected. Search for polymorphisms in the IL-6 promoter revealed the presence of a single haplotype, i.e., -597A/-572G/-174C, in COGA-13 cells, which is associated with a high degree of transcriptional activity of the IL-6 gene. IL-6 blocked differentiation only in Caco-2/AQ cells and stimulated mitosis through up-regulation of c-myc proto-oncogene expression. These effects were inhibited by 10-8 M 1,25-dihydroxyvitamin D3.


CONCLUSIONS
In human colon carcinoma cells derived from well and moderately differentiated tumours, IL-6 expression is low and only marginally affected, if at all, by PGE2, 1,25-dihydroxyvitamin D3, and 17beta-estradiol. However, IL-6 is highly abundant in undifferentiated tumour cells and is effectively stimulated by IL-1beta. In case of overexpression of an IL-6 gene variant with extreme sensitivity to IL-1beta, massive release of the cytokine from undifferentiated tumour cells may accelerate progression towards malignancy by paracrine action on more differentiated tumour cells with a still functioning proliferative IL-6 signalling pathway.
Brozek
Wolfgang
W
Department of Pathophysiology, Medical University of Vienna, Vienna, Austria. wolfgang.brozek@meduniwien.ac.at
Bises
Giovanna
G
Fabjani
Gerhild
G
Cross
Heide S
HS
Peterlik
Meinrad
M
D018938:Caco-2 Cells; D045744:Cell Line, Tumor; D002999:Clone Cells / Q000378:metabolism / Q000473:pathology; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics* / Q000502:physiology; D011110:Polymorphism, Genetic / Q000502:physiology; D000090063:Proto-Oncogene Mas; D015398:Signal Transduction / Q000235:genetics; D014158:Transcription, Genetic
D015850:Interleukin-6; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas