Receptor activator of NF-kappaB (RANK) cytoplasmic motif, 369PFQEP373, plays a predominant role in osteoclast survival in part by activating Akt/PKB and its downstream effector AFX/FOXO4.
Receptor activator of NF-kappaB ligand (RANKL) plays a crucial role in osteoclast differentiation, function, and survival. RANKL exerts its effect by activating its receptor RANK (receptor activator of NF-kappaB), which recruits various intracellular signaling molecules via specific motifs in its cytoplasmic tail. Previously, we identified three RANK cytoplasmic motifs (Motif 1, 369PFQEP373; Motif 2, 559PVQEET564; and Motif 3, 604PVQEQG609) mediating osteoclast formation and function. Here, we investigated RANK cytoplasmic motifs involved in osteoclast survival. Motif 1, in contrast to its minimal role in osteoclast formation and function, plays a predominant role in promoting osteoclast survival. Moreover, whereas Motif 2 and Motif 3 are highly potent in osteoclast formation and function, they exert a moderate effect on osteoclast survival. We also investigated the role of these motifs in activating Akt/protein kinase B (PKB), which has been implicated in RANKL-induced osteoclast survival. Motif 1, but not Motif 2 or Motif 3, is able to stimulate Akt/PKB activation. Because Akt/PKB has been shown to utilize distinct downstream effectors (glycogen synthase kinase-3beta, FKHR/FOXO1a, BAD, and AFX/FOXO4) to regulate cell survival, we next determined which downstream effector(s) is activated by Akt/PKB to promote osteoclast survival. Our data revealed that RANKL only stimulates AFX/FOXO4 phosphorylation, indicating that AFX/FOXO4 is a key downstream target activated by Akt/PKB to modulate osteoclast survival. Taken together, we conclude that Motif 1 plays a predominant role in mediating osteoclast survival in part by activating Akt/PKB and its downstream effector AFX/FOXO4.
Liu
Wei
W
Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
Wang
Shunqing
S
Wei
Shi
S
Sun
Li
L
Feng
Xu
X
D020816:Amino Acid Motifs; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000166:cytology; D018797:Cell Cycle Proteins; D002470:Cell Survival; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D051858:Forkhead Transcription Factors; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006023:Glycoproteins / Q000737:chemistry*; D008264:Macrophages / Q000166:cytology; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism*; D053244:Osteoprotegerin; D017434:Protein Structure, Tertiary; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry*; D018124:Receptors, Tumor Necrosis Factor / Q000737:chemistry*; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D012190:Retroviridae / Q000235:genetics; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*
D018797:Cell Cycle Proteins; C108803:FOXO4 protein, human; D051858:Forkhead Transcription Factors; D006023:Glycoproteins; D053244:Osteoprotegerin; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor; D011993:Recombinant Fusion Proteins; C506030:TNFRSF11B protein, human; C506031:Tnfrsf11b protein, mouse; D014157:Transcription Factors; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3