title: hRpn13, a newly identified component of the 19S particle, regulates proliferation, differentiation, and function in the human osteoblast-like cell line MG63. [corrected].
abstract: The 26S proteasome is a key component of the ubiquitin-proteasome system, a process responsible for the majority of cellular protein degradation. The function of the proteasomal ubiquitin receptor hRpn13, a component of the 26S proteasome, is not completely understood. To investigate the role of hRpn13 in the ubiquitin-proteasome system in osteoblasts, the effects of suppressing and overexpressing the hRpn13 gene on proliferation, differentiation, and function of human osteoblast-like MG63 cells were examined. After knockdown of hRpn13 by small interfering RNA, changes in osteoblast proliferation were evaluated by methyl-thiazolyl-tetrazolium assay. There was an increase in markers for osteoblast proliferation, specifically alkaline phosphatase activity, and elevated protein levels of osteocalcin, proliferating cell nuclear antigen (PCNA), and ubiquitin. Furthermore, hRpn13 knockdown also resulted in a decrease in the ratio between the gene expressions of RANKL and OPG, key players in the pathogenesis of bone diseases that influence the normal balance between bone formation and resorption. In contrast, overexpression of hRpn13 inhibited the proliferation of MG63 cells, and decreased alkaline phosphatase activity as well as protein levels of osteocalcin, PCNA, and ubiquitin while the ratio of RANKL to OPG expression increased. To confirm the function of hRpn13 in the ubiquitin-proteasome pathway, osteoblast proliferation enhancement and ubiquitin accumulation after hRpn2 knockdown was assessed. The results suggest that overexpression of hRpn13 negatively influences proliferation and osteogenic differentiation in MG63 cells. The evidence implies that hRpn13 modulates the influence of osteoblasts on osteoclasts by controlling the stability of regulatory proteins in osteoblasts. In summary, overexpression of hRpn13 promoted the activity of the ubiquitin-proteasome system.
authors: State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan 610041, China.
authors: Xi
authors: X
authors: Zhao
authors: Yonglie
authors: Y
authors: Chao
authors: Pixiu
authors: P
authors: Chen
authors: Die
authors: D
authors: Liu
authors: Peng
authors: P
authors: Su
authors: Jian
authors: J
authors: Sun
authors: Xuqin
authors: X
authors: Cui
authors: Yaxiong
authors: Y
authors: Tang
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000943:Antigens, Differentiation / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D049109:Cell Proliferation; D005786:Gene Expression Regulation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010006:Osteoblasts / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D015675:Osteocalcin / Q000378:metabolism; D053244:Osteoprotegerin / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D053245:RANK Ligand / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: C500781:ADRM1 protein, human; D000943:Antigens, Differentiation; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D053244:Osteoprotegerin; D018809:Proliferating Cell Nuclear Antigen; D053245:RANK Ligand; C505688:TNFSF11 protein, human; D025801:Ubiquitin; D015675:Osteocalcin; D000469:Alkaline Phosphatase; D046988:Proteasome Endopeptidase Complex; C119011:26S proteasome non-ATPase regulatory subunit 13