Interaction between nuclear-translocated cellular communication network factor 2 and purine-rich box 1 regulates the expression of fibrosis-related genes

Cellular communication network factor 2 (CCN2) with a nuclear localization signal-like peptide is known to promote fibrosis. However, translocation of CCN2 into the nucleus and its role in fibrosis remain unclear. We hypothesized that nuclear-translocated CCN2 is associated with purine-rich box 1 (PU.1), which is a transcription factor regulating the differentiation of myofibroblasts. Western blot analysis of the cytoplasmic and nuclear fractions of cell lysate and immunofluorescence analysis revealed that CCN2 was detectable in both the cytoplasm and nuclei of murine fibroblastic NIH3T3 cells. Additionally, chromatin immunoprecipitation (IP)-PCR and an electrophoretic mobility shift assay revealed that recombinant CCN2 protein bound to the regulatory region of Spi1, which encodes PU.1. Furthermore, IP-Western blot analysis showed that CCN2 interacted with PU.1. Finally, the forced expression of both Ccn2 and Spi1 significantly promoted the production of angiotensin II, and increased fibrosis-related molecules, such as Col1a1 and Acta2, at the gene and protein levels. These findings indicate that CCN2 translocated to the nucleus interacts with PU.1 and that the complex promotes the markers of myofibroblast differentiation, suggesting that CCN2 plays an important role in fibrosis via cooperation with PU.1, as a transcription co-factor.