Department of Dental Pharmacology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8525, Japan.
Division of Molecular and Cellular Biology, Department of Radiation Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02115, USA.
Int J Mol Sci. 2020 Dec 8;21(24):9352. doi: 10.3390/ijms21249352.
Rab11b, abundantly enriched in endocytic recycling compartments, is required for the establishment of the machinery of vesicle trafficking. Yet, no report has so far characterized the biological function of Rab11b in osteoclastogenesis. Using in vitro model of osteoclasts differentiated from murine macrophages like RAW-D cells or bone marrow-derived macrophages, we elucidated that Rab11b served as an inhibitory regulator of osteoclast differentiation sequentially via (i) abolishing surface abundance of RANK and c-Fms receptors; and (ii) attenuating nuclear factor of activated T-cells c1 (NFATc-1) upstream signaling cascades, following RANKL stimulation. Rab11b was localized in early and late endosomes, Golgi complex, and endoplasmic reticulum; moreover, its overexpression enlarged early and late endosomes. Upon inhibition of lysosomal function by a specific blocker, chloroquine (CLQ), we comprehensively clarified a novel function of lysosomes on mediating proteolytic degradation of c-Fms and RANK surface receptors, drastically ameliorated by Rab11b overexpression in RAW-D cell-derived osteoclasts. These findings highlight the key role of Rab11b as an inhibitor of osteoclastogenesis by directing the transport of c-Fms and RANK surface receptors to lysosomes for degradation via the axis of early endosomes-late endosomes-lysosomes, thereby contributing towards the systemic equilibrium of the bone resorption phase.
Rab11b 在内涵体再循环隔室中丰富表达，是囊泡运输机制建立所必需的。然而，到目前为止，还没有报道描述 Rab11b 在破骨细胞发生中的生物学功能。在体外模型中，通过 RAW-D 细胞或骨髓来源的巨噬细胞分化为破骨细胞，我们阐明 Rab11b 通过以下两种方式顺序作为破骨细胞分化的抑制调节因子：（i）消除 RANK 和 c-Fms 受体的表面丰度；（ii）在 RANKL 刺激后，减弱 T 细胞激活核因子 c1（NFATc-1）上游信号级联。Rab11b 定位于早期和晚期内涵体、高尔基体和内质网；此外，其过表达会扩大早期和晚期内涵体。通过用特异性抑制剂氯喹（CLQ）抑制溶酶体功能，我们全面阐明了溶酶体在介导 c-Fms 和 RANK 表面受体的蛋白水解降解中的新功能，该功能在 RAW-D 细胞衍生的破骨细胞中通过 Rab11b 的过表达得到了极大改善。这些发现强调了 Rab11b 作为破骨细胞发生抑制剂的关键作用，通过将 c-Fms 和 RANK 表面受体的运输引导到溶酶体进行降解，从而在早期内涵体-晚期内涵体-溶酶体轴上发挥作用，从而促进骨吸收阶段的全身平衡。
