Positive feedback regulation between USP15 and ERK2 inhibits osteoarthritis progression through TGF-β/SMAD2 signaling

Abstract

Background The transforming growth factor-β (TGF-β) signaling pathway plays an essential role in maintaining homeostasis in joints affected by osteoarthritis (OA). However, the specific mechanism of non-SMAD and classical SMAD signaling interactions is still unclear, which needs to be further explored. Methods In ATDC5 cells, USP15 overexpression and knockout were performed using the transfected lentivirus USP15 and Crispr/Cas9. Western blotting and immunofluorescence staining were used to test p-SMAD2 and cartilage phenotype-related molecular markers. In rat OA models, immunohistochemistry, hematoxylin and eosin (HE)/Safranin-O fast green staining, and histology were used to examine the regulatory activity of USP15 in TGF-β/SMAD2 signaling and the cartilage phenotype. Then, ERK2 overexpression and knockout were performed. The expressions of USP15, p-SMAD2, and the cartilage phenotype were evaluated in vitro and in vivo. To address whether USP15 is required for ERK2 and TGF-β/SMAD2 signaling, we performed rescue experiments in vitro and in vivo. Immunoprecipitation and deubiquitination assays were used to examine whether USP15 could bind to ERK2 and affect the deubiquitination of ERK2. Finally, whether USP15 regulates the level of p-ERK1/2 was evaluated by western blotting, immunofluorescence staining, and immunohistochemistry in vitro and in vivo. Results Our results indicated that USP15 stimulated TGF-β/SMAD2 signaling and the cartilage phenotype. Moreover, ERK2 required USP15 to influence TGF-β/SMAD2 signaling for regulating the cartilage phenotype in vivo and in vitro. And USP15 can form a complex with ERK2 to regulate ubiquitination of ERK2. Interestingly, USP15 did not regulate the stability of ERK2 but increased the level of p-ERK1/2 to further enhance the TGF-β/SMAD2 signaling pathway. Conclusions Taken together, our study revealed positive feedback regulation between USP15 and ERK2, which played a critical role in TGF-β/SMAD2 signaling to inhibit OA progression. Therefore, this specific mechanism can guide the clinical treatment of OA.

SOX4 and RELA Function as Transcriptional Partners to Regulate the Expression of TNF- Responsive Genes in Fibroblast-Like Synoviocytes

“…Similarly, differential expression of AP-1 signaling pathway components including Mapk1 (ERK2), Map3k8 (MEKK8) and Junb (AP1) is also expected to contribute to large-scale cellular and molecular changes. Regarding ERK2, Wang et al reported that overexpression of this kinase was involved in maintaining cartilage homeostasis through modulating the TGF-b/SMAD axis via reducing the expression of Col2a1, Aggrecan, and Sox9, which are key molecules for cartilage homeostasis (30). The AP-1 subunit, JunB, has been proposed as a negative regulator of proliferation and production of cytokines in fibroblasts (31,32).…”

Hsa_circ_0008870 suppresses bone formation of growth plate through inhibition of miR-185-3p/ MAPK1 axis in idiopathic short stature

“…Zhao et al indicated that overexpression of MAPK1 reduced the inhibitory effect of miR-320c on articular chondrocyte proliferation and attenuated the promoting effect of miR-320c on apoptosis ( Zhao et al, 2021 ). Wang et al observed that the positive feedback regulation between ERK2 (MAPK1) and USP15 played a critical role in the regulation of TGF-β/SMAD2 signaling and the maintaining of cartilage phenotype ( Wang et al, 2021 ).…”

The roles and regulatory mechanisms of TGF-β and BMP signaling in bone and cartilage development, homeostasis and disease

“… 299 USP15 also inhibits OA progression by deubiquitinating ERK2 and enhancing ERK2-induced TGF-β/SMAD2 signaling. 300 …”