Goals and Objectives: The overall goal of this program of research is to understand the biology of tumor-induced skeletal muscle wasting, specifically the role of proinflammatory cytokines and cyclooxygenase (COX) activity. Prior experiments indicated that tumor growth increased the expression of ubiquitin ligases (Mafbx and Murf1) in muscles of tumor-bearing mice. The purpose of the present study is to examine the effect of tumor-growth in Mafbx gene knockout mice. Research Significance: Cancer cachexia is a syndrome of progressive weight loss and skeletal muscle wasting that occurs in 50% or more of cancer patients with metastatic or recurrent disease. Cachexia negatively impacts functional status, symptom distress, and survival of cancer patients. Studies conducted in our lab and others suggest that tumor growth triggers increased expression of proinflammatory cytokines, and increased synthesis of proinflammatory prostanoids. Others and we have also demonstrated that skeletal muscle wasting is associated with increased expression of proteins involved in degradation of skeletal muscle, which is mediated in part by selected cytokines. Treatment of tumor-bearing mice with nonsteroidal anti-inflammatory drugs will slow weight loss and preserve muscle mass in mice, reducing muscle levels of Mafbx in treated animals bearing the Lewis Lung, but not the B16 melanoma. Understanding the role of cytokines in protein degradation of muscle wasting should facilitate the development of interventions to treat cancer cachexia. Methods: Male and female homozygote and heterozygote Mafbx gene knockout and wild type mice are inoculated with tumor cells and sacrificed at 17 days of tumor growth. Muscle weight relative to body weight is used to determine muscle mass in the three genotypes. Muscles are homogenized to determine levels of cytokine receptors and Mafbx expression using techniques of ELISA, western blotting, and realtime PCR. Scientific Advances: We have recently demonstrated that treatment with indomethacin preserves muscle mass in mice bearing the colon26 or the Lewis lung carcinoma, but not the B16 melanoma. Indomethacin also reduced levels of Mafbx and Murf1 in muscles of mice bearing the colon26, but not the B16 melanoma. Both the colon26 and Lewis lung tumor cell lines consitutively express IL-6 and COX2, while the B16 melanoma cell line does not. These data suggest that patients bearing tumors that express COX2 may benefit from treatment with inhibitors of COX2 activity. We have also observed that tumor-induced muscle wasting is not altered in Mafbx gene knockout mice, suggesting that Mafbx activity is not required for muscle protein degradation in the tumor-bearing mice. Future Plans: Experiments are underway to examine the effects of indomethacin on levels of Mafbx and Murf in muscles of mice bearing the Lewis lung carcinoma. We will also examine expression levels of these ubiquitin ligases in muscles of Mafbx gene knockout mice. If muscle mass is not preserved in the Mafbx knockout mice, animals will be treated with inhibitors of COX activity and effects on muscle mass and mediators of protein degradation will be determined. These experiments will be repeated using Murf1 gene knockout mice.