Inflammation
promotes colorectal cancer (CRC) tumorigenesis, but the underlying molecular
mechanisms are still being uncovered. Proinflammatory cytokine interleukin-6
(IL-6) stimulates survival signaling in CRC cells. Inflammatory signals
regulate also the production and activity of proteases and their inhibitors. Over-expression
of serine protease inhibitor Kazal type1 (SPINK1) predicts an unfavorable
outcome in many cancers. The SPINK1 gene
contains an IL-6 responsive element and thus, in addition to being a protease
inhibitor, acts also as an acute phase reactant. Expression of trypsin-1 and -2,
the main targets of SPINK1, also correlate with malignancy and metastatic
potential. We assessed the relationship between IL-6, SPINK1 and trypsin-1 and
-2, and the mechanism of this signaling. The following methodologies were used:
qPCR, immunohistochemistry, immunofluorometric assays and Western blotting. The
results show that Colo205 and HT-29 cells express SPINK1 and secrete it into
the culture medium. IL-6 dose-dependently increased the mRNA expression and
protein levels of SPINK1. Conditioned media from fibroblasts had the same effect
and conversely CRC media increased IL-6 secretion in the fibroblasts. In
Colo205 cells the baseline levels of trypsin-1 and -2 and the respective genes PRSS1 and PRSS2 were much higher compared to HT-29 cells. In Colo205 cells IL-6
led to concomitant increase in the secretion of trypsin-1 and -2, whereas in
HT-29 cells these remained constantly low. Mechanistically, addition of IL-6
led to activation of the canonical Stat3 pathway, as indicated by Stat3
phosphorylation. Stat3 inhibitor reduced both SPINK1 and trypsin-1 and -2
levels, demonstrating that Stat3 is the transcription factor driving their
expression. Taken together, our results show a connection between inflammatory
response and increased SPINK1 and trypsin-1 and -2 levels. The study also
strengthens the role of tumor microenvironment in tumor progression and
emphasizes the importance of studying tumor-stroma crosstalk of proteolytic
processing in colorectal and other cancers.