Molecular Biology Reports 26: 95–101, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. 95 Manipulation of the ubiquitin-proteasome pathway in cachexia: pentoxifylline suppresses the activation of 20S and 26S proteasomes in muscles from tumor-bearing rats Lydie Combaret, C´ ecile Ralli` ere, Daniel Taillandier, Keiji Tanaka 1 & Didier Attaix Institut National de la Recherche Agronomique and Centre de la Recherche en Nutrition Humaine de Clermont- Ferrand, 63122 Ceyrat, France; 1 The Tokyo Metropolitan Institute of Medical Science, 18–22, Honkomagome 3-chome, Bunkyo-ku, Tokyo 113, Japan Key words: cancer cachexia, pentoxifylline, protein breakdown, skeletal muscle, ubiquitin-proteasome system, tumor necrosis factor Abstract The development of pharmacological approaches for preventing the loss of muscle proteins would be extremely valuable for cachectic patients. For example, severe wasting in cancer patients correlates with a reduced efficacy of chemotherapy and radiotherapy. Pentoxifylline (PTX) is a very inexpensive xanthine derivative, which is widely used in humans as a haemorheological agent, and inhibits tumor necrosis factor transcription. We have shown here that a daily administration of PTX prevents muscle atrophy and suppresses increased protein breakdown in Yoshida sarcoma-bearing rats by inhibiting the activation of a nonlysosomal, Ca 2+ -independent proteolytic pathway. PTX blocked the ubiquitin pathway, apparently by suppressing the enhanced expression of ubiquitin, the 14-kDa ubiquitin conjugating enzyme E2, and the C2 20S proteasome subunit in muscle from cancer rats. The 19S complex and 11S regulator associate with the 20S proteasome and regulate its peptidase activities. The mRNA levels for the ATPase subunit MSS1 of the 19S complex increased in cancer cachexia, in contrast with mRNAs of other regulatory subunits. This adaptation was suppressed by PTX, suggesting that the drug inhibited the activation of the 26S proteasome. This is the first demonstration of a pharmacological manipulation of the ubiquitin-proteasome pathway in cachexia with a drug which is well tolerated in humans. Overall , the data suggest that PTX can prevent muscle wasting in situations where tumor necrosis factor production rises, including cancer, sepsis, AIDS and trauma. Introduction A prominent feature of cancer cachexia is a pro- gressive weight loss, involving depletion of skeletal muscle proteins and adipose tissue [1]. Wasting is an important indirect cause of death in cancer patients [2], since cachectic patients display a reduced response to radiotherapy and chemotherapy [3]. Furthermore, sus- tained loss of skeletal muscle may have a pronounced negative impact upon rehabilitation or survival of the organism, because of the vital role of muscle in loco- motion and respiratory effort. Thus, the development of pharmacological approaches designed to counter- act the loss of muscle proteins would be extremely valuable for cancer patients, and patients with other wasting diseases [4]. Increased protein breakdown has been shown to contribute to muscle wasting in tumor-bearing animal models and some cancer patients (see [5] for a review). Temparis et al. [6] demonstrated that the activation of the ubiquitin-proteasome proteolytic pathway was responsible for muscle atrophy in Yoshida sarcoma- bearing rats. Indeed, in cancer [5] and other catabolic states [4, 7] this system is the critical process respon- sible for the breakdown of most skeletal muscle pro- teins, including the long-lived contractile components [8–10].