Division of Diagnostic Molecular Pathology, Kobe University Graduate School of Medicine, Kobe, Japan.
Mol Cell Biochem. 2011 Apr;350(1-2):29-38. doi: 10.1007/s11010-010-0679-z. Epub 2010 Dec 14.
Receptor activator of NF-κB (RANK) is a member of the tumor necrosis factor receptor (TNFR) family expressed in osteoclast precursors, and RANK-RANK ligand (RANKL) signaling is a key system for differentiation, activation and survival of osteoclasts. Here, we report the identification of a novel alternative splicing variant of mouse RANK gene (vRANK) that contains a new intervening exon between exon 1 and exon 2 of mouse full-length RANK (fRANK) mRNA. Since this novel exon contains the stop codon, vRANK encodes truncated amino acids that have a portion of the signal peptide of fRANK and an additional 19 amino acids that show no homology to previously reported domains. By transient transfection studies with vRANK-GFP and -Flag expressing constructs, vRANK was found localized mostly in the cytoplasm and partly in the cell membrane, but was not secreted into the culture supernatant. Under the stimulation of various factors, the expression of vRANK mRNA was almost parallel to that of fRANK in RAW264.7 cells not treated with M-CSF. Overexpression of vRANK, on the other hand, decreased TRACP (a marker of osteoclasts) mRNA expression as well as the number of TRACP-positive multinucleated giant cells. While the mRNA expression levels of NFATc1 (a master transcriptional factor of the osteoclast differentiation program) were not affected, apoptotic cells increased significantly in vRAN K-transfected cells treated with sRANKL. Taken together, these results suggest that vRANK is a novel osteoclast suppressor that reduces the number of RANKL-induced mature osteoclasts mainly by negating the anti-apoptotic effect of RANKL.
核因子-κB 受体激活剂（RANK）是肿瘤坏死因子受体（TNFR）家族的成员，表达于破骨细胞前体细胞中，而 RANK-RANK 配体（RANKL）信号通路是破骨细胞分化、激活和存活的关键系统。在这里，我们报告了一种新型的小鼠 RANK 基因（vRANK）的剪接变体的鉴定，该变体在小鼠全长 RANK（fRANK）mRNA 的外显子 1 和外显子 2 之间包含一个新的内含子。由于这个新的内含子包含终止密码子，vRANK 编码的截断氨基酸具有 fRANK 的信号肽的一部分和另外 19 个与先前报道的结构域没有同源性的氨基酸。通过 vRANK-GFP 和 -Flag 表达构建体的瞬时转染研究，发现 vRANK 主要定位于细胞质中，部分定位于细胞膜中，但未分泌到培养上清液中。在 RAW264.7 细胞中，在未用 M-CSF 处理的情况下，各种因素刺激下 vRANK mRNA 的表达几乎与 fRANK 平行。另一方面，vRANK 的过表达降低了 TRACP（破骨细胞的标志物）mRNA 的表达以及 TRACP 阳性多核巨细胞的数量。虽然 NFATc1（破骨细胞分化程序的主要转录因子）的 mRNA 表达水平不受影响，但在用 sRANKL 处理的转染 vRAN K 的细胞中，凋亡细胞显著增加。总之，这些结果表明，vRANK 是一种新型的破骨细胞抑制剂，主要通过否定 RANKL 的抗凋亡作用来减少 RANKL 诱导的成熟破骨细胞的数量。
