c-JUN peptide

Nucleoli are well defined for their function in ribosome biogenesis, but only a small fraction of the nucleolar proteome has been characterized. Here, we report that the proto-oncogene, c-Jun, is targeted to the nucleolus. Using live cell imaging in myogenic cells, we document that the c-Jun basic domain contains a unique, evolutionarily conserved motif that determines nucleolar targeting. Fos family Jun dimer partners, such as Fra2, while nuclear, do not co-localize with c-Jun in the nucleolus. A point mutation in c-Jun that mimics Fra2 (M260E) in its Nucleolar Localization sequence (NoLS) results in loss of c-Jun nucleolar targeting while still preserving nuclear localization. Fra2 can sequester c-Jun in the nucleoplasm, indicating that the stoichiometric ratio of heterodimeric partners regulates c-Jun nucleolar targeting. Finally, nucleolar localization of c-Jun modulates nucleolar architecture and ribosomal RNA accumulation. These studies highlight a novel role for Jun family proteins in the nucleolus, having potential implications for a diverse array of AP-1-regulated cellular processes.

Transcription factor c-Jun is a member of AP-1 transcription complex that can be induced by various pathogens and plays a broad regulatory role in vertebrate immune response. In this study, the complete c-Jun cDNA of large yellow croaker Larimichthys crocea (Lcc-Jun) was cloned, whose open reading frame (ORF) is 984 bp long and encodes a protein of 327 amino acids (aa). The deduced Lcc-Jun protein contains three highly conserved domains, a transactivation domain (TAD, Met1-His118), a DNA binding domain (DBD, Lys218-Arg243), and a Leucine zipper domain (LZD, Leu271-Leu299), as found in other specie c-Jun. Lcc-Jun was constitutively expressed in all examined tissues, with the higher levels in blood, heart, and head kidney. Its transcripts were not only induced in spleen and head kidney by poly (I: C) or LPS, but also up-regulated in primary head kidney leukocytes (PKL), macrophages (PKM), and granulocytes (PKG), suggesting that Lcc-Jun may be involved in immune responses induced by poly (I: C), a viral mimic, and LPS, a Gram-negative bacterial component. Overexpression of Lcc-Jun in PKL increased the expression of cytokines and transcription factors involved in T helper 1 (Th1: TNF-α, IFN-γ, and T-bet) and Th2 (IL-4/13 A/B, IL-6, and GATA3) cell development and differentiation, suggesting that Lcc-Jun may play a role in regulation of Th1/Th2 cell response. These results therefore led us to suggest that the c-Jun-mediated signaling pathways may have an important immune-modulatory function in teleost fish.

Background: Nucleosome assembly protein 1-like 1 (NAP1L1) is highly expressed in various types of cancer and plays an important role in carcinogenesis, but its specific role in tumor development and progression remains largely unknown. In this study, we suggest the potential of NAP1L1 as a prognostic biomarker and therapeutic target for the treatment of ovarian cancer (OC). Methods: In our study, a tissue microarray (TMA) slide containing specimens from 149 patients with OC and 11 normal ovarian tissues underwent immunohistochemistry (IHC) to analyze the correlation between NAP1L1 expression and clinicopathological features. Loss-of- function experiments were performed by transfecting siRNA and following lentiviral gene transduction into SKOV3 and OVCAR3 cells. Cell proliferation and the cell cycle were assessed by the Cell Counting Kit-8, EDU assay, flow cytometry, colony formation assay, and Western blot analysis. In addition, co-immunoprecipitation (Co-IP) and immunofluorescence assays were performed to confirm the relationship between NAP1L1 and its potential targets in SKOV3/OVCAR3 cells. Results: High expression of NAP1L1 was closely related to poor clinical outcomes in OC patients. After knocking down NAP1L1 by siRNA or shRNA, both SKOV3 and OVCAR3 cells showed inhibition of cell proliferation, blocking of the G1/S phase, and increased apoptosis in vitro. Mechanism analysis indicated that NAP1L1 interacted with hepatoma-derived growth factor (HDGF) and they were co-localized in the cytoplasm. Furthermore, HDGF can interact with jun proto-oncogene (C-JUN), an oncogenic transformation factor that induces the expression of cyclin D1 (CCND1). Overexpressed HDGF in NAP1L1 knockdown OC cells not only increased the expression of C-JUN and CCND1, but it also reversed the suppressive effects of si-NAP1L1 on cell proliferation. Conclusions: Our data demonstrated that NAP1L1 could act as a prognostic biomarker in OC and can interact with HDGF to mediate the proliferation of OC, and this process of triggered proliferation may contribute to the activation of HDGF/C-JUN signaling in OC cells.