E3 Ubiquitin Ligase FBW7 Regulates KLF10 Stability And Biological Functions

FBW7(F-box and WD repeat domain-containing 7), the substrate-binding subunit of E3 ubiquitin ligase SCFFBW7 (a complex of SKPl,cullin-1 and FBW7). It can recognize the CPD of the substrate and thus promote its degradation via ubiquitin-proteasome pathway. The tumor suppressor function of FBW7 has been widely accepted.SCFFBW7 targets a set of well-known oncoproteins and plays important roles in various physiological and pathological processes, such as cell cycle, cell proliferation, cellular metabolism, differentiation and apoptosis. There are more and more evidence show that FBW7 palys an important role in stem cell self-renewal, differentiation, and survival. So it’s crucial to find the new substrate of FBW7 for its biological function and its mechanism to inhibit tumorigenesis.KLF10 is an important member of the Kruppel-like zinc finger transcription factors. It can regulate its target gene transduction by its zinc finger domain. KLF10 is also called TGF-P inducible early gene 1 (TIEG1), it has been shown to be rapidly induced by TGFβ1, epidermal growth factor, and bone morphogenetic protein-2. It has been reported that Kruppel-like factor 10 constitutes an important regulator of T regulatory cell suppressor function and CD4+CD25-T cell activetion through distinct mechanisms involving transforming growth factor TGFβ1 and Foxp3. KLF10 overexpressing CD4+CD25-T cells induced both TGFβ1 and Foxp3 expression. As a TGF-β-induced gene, the function of KLF10 in innate immune cells such as macrophages has also been studied. It can regulate the production of inflammatory cytokines in M-BMMs. KLF10 has been implicated in cell differentiation, as a target gene for a variety of signaling pathways, and in serving as a potential marker for human diseases. So the understanding of KLF10’s function is a focus of biological research field.In our research, we calculated that KLF10 containing FBW7 CPDs through bioinformatics method, so we speculated that it may the new substrate of FBW7. Further we use exogenous and endogenous experiments to confirm that FBW7 can regulate KLF10 protein stability. In our results, we find that FBW7 can promote KLF10 ubiquitination through trigger KLF10 degradation in proteasome-dependent manner. We detect the interaction between KLF10 and FBW7 not only in vivo but also in vitro. We find the importantant role of KLF10 CPD in the degradation by a series of point mutations, and we also explicitly find the amino acids in CPD play an important role in phosphorylation. We put forward a new molecular mechanism that FBW7 regulate the substrate stability. Because KLF11 is strongly homologous with KLF10 and we predicted that KLF11 also contains CPD, so we also do some reasearchs in the degradation of KLF11 by FBW7,but the function has not finished.Collectively, we present a new mechamism that regulating KLF10 and KLF11 stability and give a new insight into FBW7 study. Most importantly, we may uncover an unkown function of FBW7 in immune system and plays an important role in some diseases.