Proteome Analysis and Morphological Studies Reveal Multiple Effects of the Immunosuppressive Drug Mycophenolic Acid Specifically Resulting from Guanylic Nucleotide Depletion

Mafalda Escobar-Henriques, Axelle Balguerie, Chistelle Monribot, Hélian Boucherie, Bertrand Daignan-Fornier
2001 Journal of Biological Chemistry  
Mycophenolic acid (MPA), one of the most promising immunosuppressive drugs recently developed, is a potent inhibitor of IMP dehydrogenase, the first committed step toward GMP synthesis. We found that all the drug effects on yeast cells were prevented by bypassing GMP synthesis, thus confirming the high specificity of MPA. Although the primary target of MPA is clearly identified, we aimed to further understand how GTP depletion leads to growth arrest and developed a new approach based on
more » ... ch based on proteome analysis combined with overexpression studies. Essential proteins down-expressed in the presence of MPA were identified by protein two-dimensional gel analysis and subsequently overexpressed in yeast. Two such proteins, Cdc37p and Sup45p, when overexpressed allowed partial relief of MPA toxicity, strongly suggesting that their lower amount after MPA treatment significantly contributed to the MPA effect. These conserved proteins involved in cell cycle progression and translation are therefore important secondary targets for MPA. Our data establish that MPA effects occur through inhibition of a unique primary target resulting in guanine nucleotides depletion, thereby affecting multiple cellular processes. Mycophenolic acid (MPA) 1 in its morpholinoethyl ester prodrug form, mycophenolate mofetil (Cellcept, Roche), is one of the most promising immunosuppressive drugs recently developed. It is now widely used to prevent allograft rejection and may be an important alternative to cyclosporin A, which was recently demonstrated to induce tumor development (1). MPA specifically inhibits inosine monophosphate dehydrogenase (IMPDH), the enzyme catalyzing the first committed step in GMP biosynthesis (Fig. 1) , and consequently depletes the GTP cellular pool severely (down to 10% of normal levels) (2). Although the primary target of MPA is clearly identified and human IMPDH has been crystallized in the presence of MPA (3), it is not yet clear how MPA treatment leads to immuno-suppression. Two major questions are still unresolved. First, are all of the MPA in vivo effects attributed to decreased synthesis of GMP, and second, what are the consequences on cell physiology of GMP starvation caused by MPA treatment, i.e. which proteins are the secondary targets of MPA? To address these questions, we have used a proteomic approach on yeast as a model eukaryotic system.
doi:10.1074/jbc.m103416200 pmid:11535588 fatcat:mxaxex4junge3mw75p7q2heuui