Overexpression of IL-6 and STAT3 may provide new insights into ovine pulmonary adenocarcinoma development.

Background: Ovine pulmonary adenocarcinoma (OPA) is caused by Jaagsiekte sheep retrovirus (JSRV) and is considered an important potential animal model for human lung cancer. The precise mechanisms of OPA oncogenesis are still uncertain. The transcription factor signal transducer and activator of transcription 3 (STAT3) is activated by interleukin-6 (IL-6) in many cancers, but this aspect is unknown in OPA. We therefore aimed to evaluate the expression of IL-6 and STAT3 in OPA for its potential role in pulmonary carcinogenesis.

Results: Lung tissues from 9 grossly normal and JRSV-negative sheep and 20 cases of JSRV-positive OPA sheep were included in the study. Tissue samples were stained with antibodies against IL-6, STAT3, and JSRV-MA. IL-6 and STAT3 were further quantified in both groups using Western Blot (WB). Immunohistochemically, IL‑6 was expressed in stromal, inflammatory, and epithelial cells in all cases of OPA, while STAT3 immunoexpression was restricted to epithelial cells. In the OPA group, the percentage of immunolabelled cells for STAT3 accounted for a mean value of 96%. Using the H-SCORE method, 95% of cases were considered positive for STAT3 expression. Control tissues showed multifocal and weak immunoexpression for both markers. Using WB analyses, a highly significant amount of both IL-6 (p = 0.0078) and STAT3 (p < 0.0001) proteins were present in lung neoplasms, by comparison to the control lungs.

Conclusions: Our data showed overexpression of IL-6 and STAT3 in lung tissues from OPA compared to lungs from JSRV-negative sheep. These results suggest a potential role of IL6-STAT3 in OPA carcinogenesis.