Leupaxin is a critical adaptor protein in the adhesion zone of the osteoclast.
Leupaxin is a cytoskeleton adaptor protein that was first identified in human macrophages and was found to share homology with the focal adhesion protein, paxillin. Leupaxin possesses several protein-binding domains that have been implicated in targeting proteins such as focal adhesion kinase (pp125FAK) to focal adhesions. Leupaxin can be detected in monocytes and osteoclasts, both cells of hematopoietic origin. We have identified leupaxin to be a component of the osteoclast podosomal signaling complex. We have found that leupaxin in murine osteoclasts is associated with both PYK2 and pp125FAK in the osteoclast. Treatment of osteoclasts with TNF-alpha and soluble osteopontin were found to stimulate tyrosine phosphorylation of both leupaxin and leupaxin-associated PYK2. Leupaxin was found to co-immunoprecipitate with the protein tyrosine phosphatase PTP-PEST. The cellular distribution of leupaxin, PYK2, and protein tyrosine phosphorylation-PEST co-localized at or near the osteoclast podosomal complex. Leupaxin was also found to associate with the ARF-GTPase-activating protein, paxillin kinase linker p95PKL, thereby providing a link to regulators of cytoskeletal dynamics in the osteoclast. Overexpression of leupaxin by transduction into osteoclasts evoked numerous cytoplasmic projections at the leading edge of the cell, resembling a motile phenotype. Finally, in vitro inhibition of leupaxin expression in the osteoclast led to a decrease in resorptive capacity. Our data suggest that leupaxin may be a critical nucleating component of the osteoclast podosomal signaling complex.
Gupta
Anandarup
A
Department of Oral and Craniofacial Biological Sciences, University of Maryland, Baltimore, Maryland 21201-1586, USA. ang001@dental.umaryland.edu
Lee
Beth S
BS
Khadeer
Mohammed A
MA
Tang
Zhihui
Z
Chellaiah
Meenakshi
M
Abu-Amer
Yousef
Y
Goldknopf
Joshua
J
Hruska
Keith A
KA
D000818:Animals; D001483:Base Sequence; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D003001:Cloning, Molecular; D051417:Focal Adhesion Kinase 1; D051418:Focal Adhesion Kinase 2; D051416:Focal Adhesion Protein-Tyrosine Kinases; D020690:GTPase-Activating Proteins / Q000378:metabolism; D006801:Humans; D051379:Mice; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D053495:Osteopontin; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D054594:Protein Tyrosine Phosphatase, Non-Receptor Type 12; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D012795:Sialoglycoproteins / Q000494:pharmacology; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D014157:Transcription Factors; D014161:Transduction, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
D015815:Cell Adhesion Molecules; C430213:GIT2 protein, human; D020690:GTPase-Activating Proteins; C112251:LPXN protein, human; C504469:Lpxn protein, mouse; D010750:Phosphoproteins; D012333:RNA, Messenger; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D053495:Osteopontin; D014443:Tyrosine; D012694:Serine; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051418:Focal Adhesion Kinase 2; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; C496051:Ptk2 protein, mouse; C496053:Ptk2b protein, mouse; C516738:PTPN12 protein, human; D054594:Protein Tyrosine Phosphatase, Non-Receptor Type 12; D017027:Protein Tyrosine Phosphatases; C516739:Ptpn12 protein, mouse