ABSTRACT
The cytokine TWEAK and its cognate receptor Fn14 are members of the TNF/TNFR superfamily and are upregulated in tumors. We found that Fn14, when expressed in tumors, causes cachexia and that antibodies against Fn14 dramatically extended lifespan by inhibiting tumor-induced weight loss although having only moderate inhibitory effects on tumor growth. Anti-Fn14 antibodies prevented tumor-induced inflammation and loss of fat and muscle mass. Fn14 signaling in the tumor, rather than host, is responsible for inducing this cachexia because tumors in Fn14- and TWEAK-deficient hosts developed cachexia that was comparable to that of wild-type mice. These results extend the role of Fn14 in wound repair and muscle development to involvement in the etiology of cachexia and indicate that Fn14 antibodies may be a promising approach to treat cachexia, thereby extending lifespan and improving quality of life for cancer patients.
Subject(s)
Cachexia/drug therapy , Neoplasms/pathology , Receptors, Tumor Necrosis Factor/antagonists & inhibitors , Amino Acid Sequence , Animals , Antibodies, Monoclonal/administration & dosage , Atrophy/drug therapy , Cachexia/pathology , Cell Death , Colonic Neoplasms/drug therapy , Cytokine TWEAK , Female , Humans , Lung Neoplasms/drug therapy , Mice , Mice, Inbred BALB C , Molecular Sequence Data , Muscle Development , Neoplasms/metabolism , Receptors, Tumor Necrosis Factor/chemistry , Receptors, Tumor Necrosis Factor/metabolism , Sequence Alignment , Signal Transduction , TWEAK Receptor , Tumor Necrosis Factors/metabolismABSTRACT
Tom7 is a component of the translocase of the outer mitochondrial membrane (TOM) and assembles into a general import pore complex that translocates preproteins into mitochondria. We have identified the human Tom7 homolog and characterized its import and assembly into the mammalian TOM complex. Tom7 is imported into mitochondria in a nucleotide-independent manner and is anchored to the outer membrane with its C terminus facing the intermembrane space. Unlike studies in fungi, we found that human Tom7 assembles into an approximately 120-kDa import intermediate in HeLa cell mitochondria. To detect subunits within this complex, we employed a novel supershift analysis whereby mitochondria containing newly imported Tom7 were incubated with antibodies specific for individual TOM components prior to separation by blue native electrophoresis. We found that the 120-kDa complex contains Tom40 and lacks receptor components. This intermediate can be chased to the stable approximately 380-kDa mammalian TOM complex that additionally contains Tom22. Overexpression of Tom22 in HeLa cells results in the rapid assembly of Tom7 into the 380-kDa complex indicating that Tom22 is rate-limiting for TOM complex formation. These results indicate that the levels of Tom22 within mitochondria dictate the assembly of TOM complexes and hence may regulate its biogenesis.
