Stabilization of C/EBP beta through direct interaction with STAT3 in H-Ras transformed human mammary epithelial cells

Abstract

Signal transducer and activator of transcription 3 (STAT3) plays important roles in cancer-associated inflammation by controlling expression of proinflammatory cytokines and chemokines. Recent studies suggest that C/EBP13 (CCAAT-enhancer binding protein beta) and STAT3 synergistically stimulate cancer cell proliferation and epithelial-mesenchymal transition. C/EBP13 is a leucine-zipper transcription factor that regulates expression of a variety of inflammatory cytokines or chemokines, such as IL-8, G-CSF (granulocyte colony stimulating factor), and GM-CSF (granulocyte macrophage colony stimulating factor) which induce neutrophil infiltration and differentiation. However, molecular mechanisms by which STAT3 and C/EBP13 cooperatively interact had not been fully elucidated. In this study, we found that the level of C/EBP13 protein, but not that of its mRNA transcript, was decreased in the absence of STAT3 in H Ras transformed human mammary epithelial (H -Ras MCF10A) cells. In addition, silencing STAT3 dramatically induced ubiquitination of C/EBP13 for proteasomal degradation. Furthermore, direct inter action between STAT3 and C/EBP13 was confirmed by immunoprecipitation and proximity ligation assays. Taken together, these results suggest that STAT3 stabilizes C/EBP13, thereby promoting cancer-associated inflammation. (c) 2021 Elsevier Inc. All rights reserved.