Background:Aberrant activities of Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signalling pathways have been implicated in the development and spread of various cancer entities, among them colorectal carcinoma (CRC). Transcription factors STAT3 and STAT1, both downstream effectors of interleukin (IL)-6 and its receptor, are involved in growth and developmental control of CRC cells. Constituents of the signalling network around IL-6 and STAT activation are discussed as potential biomarkers and therapeutic targets in CRC.Methods:By immunohistochemical analysis of a tissue microarray covering >400 CRC biopsies, the expression and activity status of STAT1, STAT3 as well as of IL-6 and the IL-6 receptor α-chain was determined. The outcome was correlated with clinical information and patients' survival data. Colorectal carcinoma biopsies were also analysed for specific DNA-binding activity of STATs.Results:Statistical analysis showed tendential associations between individual STATs, IL-6/IL-6 receptor-α and clinicopathological parameters. The study revealed a significant correlation of high STAT1 activity with longer patient overall survival. Surprisingly, strong STAT3 expression in surgical specimens was correlated with an increase in median overall survival by about 30 months. Statistical analysis revealed that high expression levels of STAT1 and STAT3 were associated. This finding was backed up by biochemical data that showed simultaneous STAT1 and STAT3 DNA-binding activity in randomly selected CRC biopsies.Conclusion:By multivariate data analysis, we could show that STAT3 expression and activity constitutes an independent favourable prognostic marker for CRC.

The role of STAT1 and STAT3 for colorectal carcinoma (CRC) development and progression is controversial. We evaluated 414 CRC patient samples on tissue microarrays for differential expression of STAT1 and STAT3 protein levels and correlated ratios with clinical parameters. Concomitant absence of nuclear STAT1 and STAT3 expression was associated with significantly reduced median survival by ≥33 months (p=0.003). To gain insight into underlying mechanisms, we generated four CRC cell lines with STAT3 knockdown. The cell lines harbor different known mutational drivers and were xenografted into SCID mice to analyze the influence of STAT3 on their tumor growth behavior. Experimental downregulation of STAT3 expression had differential, cell-line specific effects on STAT1 expression levels. STAT1 consistently showed nuclear localization irrespective of its tyrosine phosphorylation status. Two characteristic STAT1/3 expression patterns with opposite growth behavior could be distinguished: cell lines with a low STAT1/high STAT3 ratio showed faster tumor growth in xenografts. In contrast, xenografts of cell lines showing high STAT1 and low STAT3 levels grew slower. Importantly, these ratios reflected clinical outcome in CRC patients as well. We conclude that the ratio of STAT1 to STAT3 expression is a key determinant of CRC progression and that STAT1 counteracts pro-tumorigenic STAT3 signaling. Thus, we suggest that the STAT3/STAT1 ratios are better clinical predictors in CRC as compared to STAT3 or STAT1 levels alone.

The interferon‐inducible transcription factor STAT1 is a tumor suppressor in various malignancies. We investigated sex‐specific STAT1 functions in colitis and colitis‐associated colorectal cancer (CRC) using mice with specific STAT1 deletion in intestinal epithelial cells (STAT1∆IEC). Male but not female STAT1∆IEC mice were more resistant to DSS‐induced colitis than sex‐matched STAT1flox/flox controls and displayed reduced intraepithelial infiltration of CD8+ TCRαβ+ granzyme B+ T cells. Moreover, DSS treatment failed to induce expression of T‐cell‐attracting chemokines in intestinal epithelial cells of male but not of female STAT1∆IEC mice. Application of the AOM‐DSS protocol for induction of colitis‐associated CRC resulted in increased intestinal tumor load in male but not in female STAT1∆IEC mice. A sex‐specific stratification of human CRC patients corroborated the data obtained in mice and revealed that reduced tumor cell‐intrinsic nuclear STAT1 protein expression is a poor prognostic factor in men but not in women. These data demonstrate that epithelial STAT1 is a male‐specific tumor suppressor in CRC of mice and humans.

This article has been corrected: In Figure 2d, the immunofluorescence pictures of Stat1 of the cell line SW620 were accidentally duplicated to the HCT116 cell line. The corrected Figure 2d is shown below. The authors declare that these corrections do not change the results or conclusions of this paper.

Aberrant activities of JAK/STAT signalling pathways have been implicated in the development and spread of various cancer entities, among them colorectal carcinoma (CRC). By immunohistochemical analysis of a tissue microarray covering more than 400 CRC biopsies from patients with full clinical documentation, the expression and activity status of STAT1 and STAT3 was determined. Results were correlated with clinical information. A significant association of high STAT1 activity (as indicated by nuclear location) with longer patient overall survival was observed. Unexpectedly, strong STAT3 expression in surgical specimens could be clearly correlated with an increase in median overall survival by about 30 months. Interestingly, combined consideration of STAT1/3 expression and activity levels in CRC specimens revealed patterns that match the clinical outcome with statistical significance. For instance, tumors with concomitant absence of STAT1 and STAT3 have a worse prognosis, while high STAT1 activity along with low STAT3 activity proved associated with longer patient survival. To address the signal transduction background of these findings, STAT1/3 expression was experimentally modified in CRC cell lines and effects on the growth of xenograft tumors were studied. Mimicking STAT1/3 patterns from patient biopsies in xenografts resulted in alterations in tumor growth well corresponding to clinical data. From these experiments we draw the conclusions that the ratio of nuclear STAT1/STAT3 is a determinant of colon carcinoma progression. Supported by: Deutsche Krebshilfe, IZKF Jena, European Regional Development Fund ERDF Citation Format: Claire Gordziel, Harini Nivarthi, Thomas Knösel, Helmut Dolznig, Richard Moriggl, Karlheinz Friedrich. Individual and combined activities of STAT1 and STAT3 have prognostic relevance for the progression of colorectal carcinoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5458. doi:10.1158/1538-7445.AM2013-5458