Osteosarcoma (OS) is the most frequent primary malignant bone tumor in urgent need of better therapies. Using genetically modified mouse models (GEMMs), we demonstrate that Wnt signaling promotes c-Fos-induced OS formation via the actions of the collagen-modifying enzyme Loxl2. c-Fos/AP-1 directly regulates the expression of the Wnt ligands Wnt7b and Wnt9a in OS cells through promoter binding, and Wnt7b and Wnt9a in turn promote Loxl2 expression in murine and human OS cells through the transcription factors Zeb1 and Zeb2. Concordantly, inhibition of Wnt ligand secretion by inactivating the Wnt-less (Wls) gene in osteoblasts in c-Fos GEMMs either early or in a therapeutic setting reduces Loxl2 expression and progression of OS. Wls-deficient osteosarcomas proliferate less, are less mineralized and are enriched in fibroblastic cells surrounded by collagen fibers. Importantly, Loxl2 inhibition using either the pan-Lox inhibitor BAPN or a specific inducible shRNA reduces OS cell proliferation in vitro and decreases tumor growth and lung colonization in murine and human orthotopic OS transplantation models. Finally, OS development is delayed in c-Fos GEMMs treated with BAPN or with specific Loxl2 blocking antibodies. Congruently, a strong correlation between c-FOS, LOXL2 and WNT7B/WNT9A expression is observed in human OS samples, and c-FOS/LOXL2 co-expression correlates with OS aggressiveness and decreased patient survival. Therefore, therapeutic targeting of Wnt and/or Loxl2 should be considered to potentiate the inadequate current treatments for pediatric, recurrent, and metastatic OS.

骨肉瘤（OS）是最常见的原发性恶性骨肿瘤，迫切需要更好的治疗方法。使用转基因小鼠模型 (GEMM)，我们证明 Wnt 信号通过胶原蛋白修饰酶 Loxl2 的作用促进 c-Fos 诱导的 OS 形成。c-Fos/AP-1 通过启动子结合直接调节 OS 细胞中 Wnt 配体Wnt7b和Wnt9a的表达，而 Wnt7b 和 Wnt9a 通过转录因子 Zeb1 和 Zeb2 反过来促进 Loxl2 在鼠和人 OS 细胞中的表达。一致地，通过使Wnt-less ( Wls)失活来抑制 Wnt 配体分泌c-Fos GEMMs 中成骨细胞中的基因在早期或治疗环境中都会降低 Loxl2 的表达和 OS 的进展。Wls 缺陷型骨肉瘤增殖较少，矿化程度较低，并且富含被胶原纤维包围的成纤维细胞。重要的是，使用 pan-Lox 抑制剂 BAPN 或特定的可诱导 shRNA 抑制 Loxl2 可减少体外 OS 细胞增殖，并减少小鼠和人类原位 OS 移植模型中的肿瘤生长和肺定植。最后，用 BAPN 或用特异性 Loxl2 阻断抗体处理的 c-Fos GEMM 的 OS 开发延迟。一致地，在人类 OS 样本中观察到 c-FOS、LOXL2 和 WNT7B/WNT9A 表达之间的强相关性，并且 c-FOS/LOXL2 共表达与 OS 侵袭性和降低的患者存活率相关。所以，