Department of Orthopaedics, Case Western Reserve University, Cleveland, Ohio, USA.
Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, Ohio, USA.
J Cell Physiol. 2021 Aug;236(8):5686-5697. doi: 10.1002/jcp.30254. Epub 2021 Jan 3.
We previously reported that the evolutionary conserved transcriptional cofactor Jab1/Cops5 is critical for mouse chondrocyte differentiation by selectively repressing BMP signaling. In this study, we first uncovered that the endogenous Jab1 interacts with endogenous Smad1/5/8. Furthermore, although Jab1 did not directly interact with Acvr1 (Alk2), a key Type I BMP receptor, the interaction between endogenous Smad1/5/8 and Acvr1 was increased in Jab1-null chondrocytes. Thus, Jab1 might negatively regulate BMP signaling during chondrocyte differentiation in part by sequestering Smad1/5/8 away from Acvr1. Next, to identity Jab1 downstream targets in chondrocytes, we performed RNA-sequencing analysis of Jab1-null chondrocytes and discovered a total of 1993 differentially expressed genes. Gene set enrichment analysis revealed that key targets inhibited by Jab1 includes p53, BMP/transforming growth factor beta, and apoptosis pathways. We confirmed that endogenous Jab1 interacts with endogenous p53. There was significantly elevated p53 reporter activity, an enhanced expression of phospho-p53, and an increased expression of a key p53 downstream target, Puma, in Jab1-null chondrocytes. Moreover, treatments with a p53-specific inhibitor and/or a BMP Type I receptor-specific inhibitor reversed the elevated p53 and BMP signaling activities in Jab1-null chondrocytes and partially restored columnar growth plate structure in E17.5 Jab1-null mouse tibia explant cultures. Finally, we demonstrated that the chondrocyte-specific Jab1 overexpression in mice resulted in smaller-sized embryos with disorganized growth plates. In conclusion, our data showed that the delicate Jab1-mediated crosstalk between BMP and p53 pathways is crucial to maintain proper chondrocyte survival and differentiation. Moreover, the appropriate Jab1 expression level is essential for proper skeletal development.
我们之前报道过，进化保守的转录共激活因子 Jab1/Cops5 通过选择性抑制 BMP 信号通路，对小鼠软骨细胞分化至关重要。在这项研究中，我们首先发现内源性 Jab1 与内源性 Smad1/5/8 相互作用。此外，尽管 Jab1 并未直接与关键的 I 型 BMP 受体 Acvr1（Alk2）相互作用，但 Jab1 缺失的软骨细胞中内源性 Smad1/5/8 与 Acvr1 的相互作用增加。因此，Jab1 可能通过将 Smad1/5/8 与 Acvr1 隔离，在软骨细胞分化过程中负调控 BMP 信号通路。接下来，为了鉴定软骨细胞中 Jab1 的下游靶标，我们对 Jab1 缺失的软骨细胞进行了 RNA-seq 分析，共发现了 1993 个差异表达基因。基因集富集分析表明，Jab1 抑制的关键靶标包括 p53、BMP/转化生长因子β和细胞凋亡途径。我们证实内源性 Jab1 与内源性 p53 相互作用。在 Jab1 缺失的软骨细胞中，p53 报告基因活性显著升高，磷酸化 p53 的表达增强，p53 的一个关键下游靶标 Puma 的表达增加。此外，用 p53 特异性抑制剂和/或 BMP I 型受体特异性抑制剂处理可逆转 Jab1 缺失的软骨细胞中升高的 p53 和 BMP 信号活性，并部分恢复 E17.5 Jab1 缺失的小鼠胫骨外植体培养物中柱状生长板结构。最后，我们证明了在小鼠中软骨细胞特异性过表达 Jab1 会导致胚胎变小，生长板排列紊乱。总之，我们的数据表明，BMP 和 p53 通路之间精细的 Jab1 介导的串扰对于维持适当的软骨细胞存活和分化至关重要。此外，适当的 Jab1 表达水平对于骨骼的正常发育至关重要。
