Background: CCAAT-enhancer binding protein beta (C/EBPβ) is a transcription factor playing a critical role in mammary gland development and breast cancer progression. Loss of C/EBPβ increases metastatic dissemination of mouse mammary tumor cells. However, the mechanism, by which C/EBPβ expression affects metastasis formation remains unknown.
Aim: The aim of the study was to determine the relationship between C/EBPβ and survival of breast cancer patients, as well as to elucidate the mechanism linking C/EBPβ with metastasis formation.
Methods: C/EBPβ expression was evaluated in 137 cases of human breast cancer and correlated with overall survival by Kaplan-Meier analysis. Additionally, the mouse 4T1 tumor model was used to discover the mechanism explaining the effect of C/EBPβ on metastasis formation.
Results: Here we report that decreased C/EBPβ expression is associated with shorter overall survival of breast cancer patients. We also demonstrate that in the murine 4T1 model loss of C/EBPb affects tumor growth and morphology, as well as promotes metastatic spread to the lungs. Immunohistochemical analyses showed that C/EBPβ inhibition leads to increased expression of MHCII, followed by accumulation of CD45, CD3 and CD4-positive lymphocytes in the tumors. Inflammation involvement in C/EBPβ-mediated metastasis formation was confirmed by DNA microarray and experiments on CD4+ cell-deprived nude mice. Additionally, anti-CD3 and anti-CD4 treatments of C/EBPβ-silenced tumor-bearing mice resulted in reverting C/EBPβ effect on tumor growth.
Conclusions: Altogether, C/EBPβ is a predictor of overall survival in breast cancer patients, and affects tumor growth, morphology and lung metastasis formation in murine 4T1 model. The mechanism of metastasis formation, we have discovered, involves immunological response depending on C/EBPβ-mediated activation of MHCII and accumulation of CD4+ lymphocytes in the tumor.