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Rescue of osteoclast function by transgenic expression of kinase-deficient Src in src-/- mutant mice
P L Schwartzberg1, L Xing, O Hoffmann
1National Cancer Institute, University of Texas Health Science Center, San Antonio, Texas 78284, USA. pams@mhgri.nih.gov
Abstract:
The Src tyrosine kinase has been implicated in a wide variety of signal transduction pathways, yet despite the nearly ubiquitous expression of c-src, src-/- mice show only one major phenotype-osteopetrosis caused by an intrinsic defect in osteoclasts, the cells responsible for resorbing bone. To explore further the role of Src both in osteoclasts and other cell types, we have generated transgenic mice that express the wild-type and mutated versions of the chicken c-src proto-oncogene from the promoter of tartrate resistant acid phosphatase (TRAP), a gene that is expressed highly in osteoclasts. We demonstrate here that expression of a wild-type transgene in only a limited number of tissues can fully rescue the src-/- phenotype. Surprisingly, expression of kinase-defective alleles of c-src also reduces osteopetrosis in src-/- animals and partially rescues a defect in cytoskeletal organization observed in src-/- osteoclasts. These results suggest that there are essential kinase-independent functions for Src in vivo. Biochemical examination of osteoclasts from these mice suggest that Src may function in part by recruiting or activating other tyrosine kinases.
Insights
The Src tyrosine kinase plays a crucial role in bone resorption. Kinase-defective Src partially rescues osteopetrosis, suggesting essential kinase-independent functions in osteoclasts.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Src tyrosine kinase (c-src) is involved in numerous signaling pathways.
- Src knockout (src-/-) mice exhibit osteopetrosis due to osteoclast dysfunction.
- Osteoclasts are critical for bone resorption.
Purpose of the Study:
- To investigate the role of Src in osteoclasts and other cell types.
- To generate transgenic mice expressing wild-type and mutated chicken c-src using the TRAP promoter.
- To explore kinase-dependent and independent functions of Src in vivo.
Main Methods:
- Generation of transgenic mice expressing chicken c-src under the TRAP promoter.
- Analysis of osteopetrosis phenotype in src-/- mice rescued by transgenes.
- Assessment of cytoskeletal organization in src-/- osteoclasts.
- Biochemical analysis of osteoclasts.
Main Results:
- Expression of wild-type c-src transgene in limited tissues fully rescued the src-/- osteopetrosis phenotype.
- Expression of kinase-defective c-src alleles reduced osteopetrosis and partially rescued cytoskeletal defects in src-/- osteoclasts.
- Biochemical data suggest Src recruits or activates other tyrosine kinases in osteoclasts.
Conclusions:
- Src possesses essential kinase-independent functions in vivo.
- Src signaling in osteoclasts is critical for bone resorption.
- Src may function by interacting with other tyrosine kinases.