Receptor activator of NF-B ligand (RANKL) is a transmembrane glycoprotein that has an essential role in the development of osteoclasts. The extracellular portion of RANKL is cleaved proteolytically to produce soluble RANKL, but definite RANKL sheddase(s) and the physiologic function of RANKL shedding have not yet been determined. In the present study, we found that matrix metalloproteinase (MMP) 14 and a disintegrin and metalloproteinase (ADAM) 10 have strong RANKL shedding activity. In Western blot analysis, soluble RANKL was detected as two different molecular weight products, and RNA interference of MMP14 and ADAM10 resulted in a reduction of both the lower and higher molecular weight products. Suppression of MMP14 in primary osteoblasts increased membrane-bound RANKL and promoted osteoclastogenesis in cocultures with macrophages. Soluble RANKL produced by osteoblasts from MMP14-deficient mice was markedly reduced, and their osteoclastogenic activity was promoted, consistent with the findings of increased osteoclastogenesis in vivo. RANKL shedding is an important process that down-regulates local osteoclastogenesis.Receptor activator of NF-B ligand (RANKL), 2 also known as TNF-related activation-induced cytokine, osteoprotegerin ligand, and osteoclast differentiation factor, is a type II transmembrane glycoprotein of the TNF ligand family. RANKL is expressed on the plasma membrane of osteoblasts, bone marrow stromal cells, and T-lymphocytes (1-5) and exerts its activity through binding to its TNF family receptor RANK, which is expressed on monocyte-macrophage lineage osteoclast precursors (3, 4, 6). Consequently, RANK activates downstream signaling pathways such as NF-B, p38 mitogen-activated protein kinase, c-Jun N-terminal kinase, and nuclear factor of activated T cells c1 and leads to the differentiation, activation, and survival of osteoclasts (6 -9). Both RANKL-and RANK-deficient mice develop severe osteopetrosis due to a lack of osteoclasts (10, 11). Conversely, a deficiency of osteoprotegerin (OPG), a natural inhibitor of RANKL, causes severe osteoporosis due to enhanced osteoclastogenesis (12). These findings suggest a crucial role for the RANKL/RANK/OPG axis in osteoclast development.A number of transmembrane proteins undergo proteolysis and are released from the plasma membrane, a process called ectodomain shedding. The biologic and pathologic significance of ectodomain shedding varies between substrate proteins. For example, cytokines such as TNF-␣ and epidermal growth factor are released from local environments and exert their activity in paracrine and endocrine signaling by ectodomain shedding (13-15). In some cases, ectodomain shedding is necessary even for the local effects of growth factors such as epidermal growth factor (16). Although membrane-bound RANKL is converted to a soluble form through ectodomain shedding (17, 18) similar to other TNF family members, such as TNF-␣ (13, 14) and Fas ligand (19), the RANKL sheddases involved in physiologic and pathologic bone resorption, and the role of...

Tendon harvest causes significant weakness of hamstring muscle strength at high knee flexion angles, but such weakness can be minimized if the gracilis tendon is preserved.

Transforming growth factor-β (TGF-β) ligand is a multifunctional growth factor that regulates various cell behavior, such as cell proliferation, differentiation, migration, and apoptosis. Because TGF-β is a potent growth inhibitor, abnormalities in TGF-β signaling result in carcinogenesis. In addition to tumor suppressor function, TGF-β acts as an oncogenic factor. In particular, TGF-β signaling plays an important role during metastasis of breast cancer. Recently, epithelial-mesenchymal transition (EMT) has been shown to confer malignant properties such as cell motility and invasiveness to cancer cells and plays crucial roles during cancer metastasis. Moreover, breast stem-like cells exhibit EMT properties. Because TGF-β is a potent regulator of EMT as well as cell stemness, TGF-β signaling might play a crucial role in the regulation of breast cancer stem cells.

In articular chondrocytes, the inflammatory cytokine tumor necrosis factor-␣ (TNF-␣) induces the expression of bone morphogenetic protein-2 (BMP-2), a growth factor known to be involved in the induction of cartilage and bone. A study was performed to clarify the mechanism(s) underlying the induction of BMP-2 in chondrogenic ATDC5 cells and primary cultured adult human articular chondrocytes. In ATDC5 cells, the endogenous BMP-2 expression was consistently low throughout the process of chondrogenic differentiation, and TNF-␣ induced BMP-2 expression only after the cells acquired the chondrogenic phenotype. The results of nuclear run-off assay and cycloheximide treatment consistently indicated that ATDC5 cells acquire the capacity to synthesize BMP-2 mRNA in the nuclei during the differentiation process. In an attempt to explain the discrepancy between the active nuclear mRNA synthesis and the observed low expression level in differentiated ATDC5 cells, the stability of BMP-2 mRNA was evaluated, and the cells were found to regulate the expression of BMP-2 at the post-transcriptional level. Human chondrocytes were confirmed to have a similar post-transcriptional regulation. The result of 3-rapid amplification of cDNA end revealed that both human and mouse BMP-2 mRNAs contain multiple pentameric AUUUA motifs in a conserved manner in the 3-untranslated regions, and transient transfection experiments demonstrated that TNF-␣ increases the stability of BMP-2 mRNA through the pentameric motifs. Further experiments revealed that TNF-␣ modulates mRNA stability via p38 signal transduction pathway, whereas the cytokine also augmented the expression of BMP-2 through transcriptional up-regulation via the transcriptional factor NF-B.