Dynamic changes of Jab1 and p27kip1 expression in injured rat sciatic nerve.

Jun activation domain-binding protein (Jab1) is a multifunctional protein that participates in affecting signaling pathway, controlling cell proliferation and apoptosis, and regulating genomic instability and DNA repair, and acts as a key subunit of COP9 signalosome. p27kip1, a member of the Cip/Kip family of cyclin-dependent kinase inhibitors, was shown to inhibit the enzymatic activity of cyclin-CDK complexes, resulting in cell-cycle arrest at G1. Recent studies have shown that Jab1 directly binds to p27kip1 and induces nuclear export and subsequent degradation in a variety of human cancers, while the association and function of Jab1 and p27kip1 in nervous system lesion and regeneration remain unclear. Here, we performed a sciatic nerve injury model in adult rats and studied the dynamic changes of Jab1 and p27kip1 expression by Western blot. Sciatic nerve crush (SNC) resulted in a significant upregulation of Jab1 and a downregulation of p27kip1. Besides, we observed that Jab1 was expressed widely in Schwann cells (SCs) and had few co-localization in axons by double immunofluorescence staining. In addition, the peak expression of Jab1 was parallel with proliferating cell nuclear antigen (PCNA), and numerous SCs expressing Jab1 were PCNA-positive. Results obtained by co-immunoprecipitation and double labeling further showed their interaction in the sciatic nerve. Thus, these results suggested that Jab1 and p27kip1 may be involved in the pathophysiology of sciatic nerve after SNC.