Osteoarthritis
Figure 5 FBXW7 regulates MKK7 ubiquitination and degradation. (A) Quantitative PCR analysis of Mkk7 in articular cartilage from Fbxw7 KO mice and littermate Controls. n=5 per group. P<0.002, 95% CI 1.471 to 1.867. (B) Quantitative PCR analysis of Mkk7 in primary chondrocytes from Fbxw7 KO mice and littermate Controls treated with or without tensile strain loading. n=5 per group. (C) Western blot and quantification of TAK1, MKK4, MKK7, p-JNK and JNK in mechanical stress-treated primary chondrocytes from Fbxw7 KO mice and Controls. (D) Representative images of immunofluorescence of p-JNK in cartilage from Fbxw7 KO mice and Controls, and quantitative analysis of p-JNK-positive chondrocytes compared with total chondrocytes. n=10 per group. Scale bar: 100 µm. (E) MKK7 was immunoprecipitated from ATDC5 cells after transfection with either adenovirus containing Fbxw7 (Ad- Fbxw7 ) or Fbxw7 -siRNA. The presence of MKK7 and FBXW7 in the immunoprecipitates was evaluated by immunoblotting. (F) MKK7 was immunoprecipitated from ATDC5 cells after stimulation with MG-132 and transfection with either Ad- Fbxw7 or Fbxw7 -siRNA. Western blotting detected the ubiquitination level of MKK7. Data are shown as mean±SD. Statistical analyses were conducted using Student’s t-test (A,D), two-way analysis of variance followed by Sidak’s multiple comparison test (B,C). Boxed area is enlarged in the bottom right corner. **P<0.01. Con, control; FBXW7, F-box and WD repeat domain containing 7; IB, immunoblotting; IP, immunoprecipitate; KO, knockout; NS, not significant.
Additionally, FBXW7 has been shown to negatively regulate mTOR signalling, which plays a vital role in OA development, as reported in our previous studies. 40–42 Although FBXW7 has been widely studied, its role in chondrocyte senescence and OA development has not been reported. An interesting finding of
(E3) ligase complex and targets several pathways for the degra- dation of various mammalian oncoproteins that control cell growth, differentiation, and tumorigenesis. 34–37 It has been reported that FBXW7 deletion leads to p16 INK4a and p19 eleva- tion to facilitate the cell cycle and promote cell senescence. 38 39
Zhang H, et al . Ann Rheum Dis 2022; 81 :676–686. doi:10.1136/annrheumdis-2021-221513
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