SH3P2 suppresses osteoclast differentiation through restricting membrane localization of myosin 1E

OSTF1 knockdown mitigates IL-1β-induced chondrocyte injury via inhibiting the NF-κB signaling pathway

Osteoarthritis (OA) is an age-related joint disease characterized by progressive heterogeneous changes in articular cartilage and subchondral bone. Osteoclast stimulating factor 1 (OSTF1) is a small intracellular protein involved in bone formation and bone resorption. However, to our best knowledge, its role in OA is still unclear. In this study, an OA rat model was established by anterior cruciate ligament transection (ALCT). OSTF1 was increased in the cartilage tissues of OA patients and OA rats. Next, the role of OSTF1 in interleukin-1β (IL-1β)-induced chondrocyte apoptosis, inflammation and extracellular matrix degradation was explored through loss of function assays. Strikingly, OSTF1 knockdown relieved IL-1β-induced chondrocyte apoptosis, with decreased cleaved caspase-3 and cleaved PARP levels. Besides, OSTF1 knockdown restrained IL-1β-induced inflammation and degradation of extracellular matrix of chondrocytes. Subsequently, the molecular mechanism of OSTF1 was explored. Transcriptomic analysis revealed the potential gene network map regulated by OSTF1 knockdown. Some differentially expressed genes (DEGs) were involved in regulating the NF-κB signaling pathway. Furthermore, our results demonstrated that OSTF1 knockdown inhibited IL-1β-activated the NF-κB signaling pathway. Ultimately, we analyzed the potential gene network map regulated by OSTF1 and its downstream NF-κB. Bioinformatics analysis showed that 18 DEGs in OSTF1-silenced chondrocytes overlapped with the NF-κB downstream targets. Collectively, our findings indicate that OSTF1 knockdown mitigates IL-1β-induced chondrocyte injury via inhibiting the NF-κB signaling pathway.

Membrane binding of endocytic myosin-1s is inhibited by a class of ankyrin repeat proteins

Myosin-1s are monomeric actin-based motors that function at membranes. Myo1 is the single myosin-1 isoform in Schizosaccharomyces pombe that works redundantly with Wsp1-Vrp1 to activate the Arp2/3 complex for endocytosis. Here, we identified Ank1 as an uncharacterized cytoplasmic Myo1 binding partner. We found that in ank1Δ cells, Myo1 dramatically redistributed from endocytic patches to decorate the entire plasma membrane and endocytosis was defective. Biochemical analysis and structural predictions suggested that the Ank1 ankyrin repeats bind the Myo1 lever arm and the Ank1 acidic tail binds the Myo1 TH1 domain to prevent TH1-dependent Myo1 membrane binding. Indeed, Ank1 overexpression precluded Myo1 membrane localization and recombinant Ank1 reduced purified Myo1 liposome binding in vitro. Based on biochemical and cell biological analyses, we propose budding yeast Ank1 and human OSTF1 are functional Ank1 orthologs and that cytoplasmic sequestration by small ankyrin repeat proteins is a conserved mechanism regulating myosin-1s in endocytosis.

Membrane binding of endocytic myosin-1s is inhibited by a class of ankyrin repeat proteins

Myosin-1s are monomeric actin-based motors that function at membranes. Myo1 is the single myosin-1 isoform in Schizosaccharomyces pombe that works redundantly with Wsp1-Vrp1 to activate the Arp2/3 complex for endocytosis. Here, we identified Ank1 as an uncharacterized cytoplasmic Myo1 binding partner. We found that in ank1Δ cells, Myo1 dramatically redistributed from endocytic patches to decorate the entire plasma membrane and endocytosis was defective. Biochemical analysis and structural predictions suggested that the Ank1 ankyrin repeats bind the Myo1 lever arm and the Ank1 acidic tail binds the Myo1 TH1 domain to prevent TH1-dependent Myo1 membrane binding. Indeed, Ank1 over-expression precluded Myo1 membrane localization and recombinant Ank1 blocked purified Myo1 liposome binding in vitro. Based on biochemical and cell biology analyses, we propose budding yeast Ank1 and human OSTF1 are functional Ank1 orthologs and that cytoplasmic sequestration by small ankyrin repeat proteins is a conserved mechanism regulating myosin-1s in endocytosis.

Summary

Fission yeast long-tailed myosin-1 binds Ank1. Ank1 ankyrin repeats associate with the Myo1 lever arm and Ank1 acidic tail binds the Myo1 TH1 domain to inhibit Myo1 membrane binding. Ank1 orthologs exists in budding yeast (Ank1) and humans (OSTF1).