250 Experimental Oncology 26, 250-255, 2004 (December) REVIEWS Exp Oncol 2004 26, 4, 250-255 Although multicellular organisms have very complex organization, the size of their genomes is relatively small in comparison with unicellular species [40]. One explanation for such discrepancy is the availability of mechanisms that allow synthesis of several proteins from one gene (for ex- ample, through alternative splicing). But even these mech- anisms could not explain functional variability of proteomes in higher eukaryotes. Recently discovered concept of mul- tifunctional proteins is special characteristic of mammalian cells that can significantly expand a number of encoded functions. Three dimensional protein structure could con- tain motifs that allow it to perform different functions with very insignificant structural changes. It is becoming clear that functions of protein could vary greatly depending on its intracellular localization and on general physiological state of the cell [10]. Obviously, both alternative splicing and post- translational mechanisms responsible for protein variability are not exclusive and functional variability of most verte- brate proteins is regulated by both mechanisms [12]. Malignant transformation is an example of drastic changes in cellular state and it is characterized by patho- logical changes in structure and function of many onco- genes and suppressor genes encoded proteins ultimately leading to malfunctioning of many biochemical and signal- ing pathways. Apart from oncogene-encoded proteins, many other housekeeping proteins of cytoskeleton, cellu- lar adhesion and different biochemical and gene expres- sion pathways are also involved in transformation process. One of the families of multifunctional proteins is represent- ed by some aminoacyl-tRNA synthetases and cofactors CYTOKINE-LIKE ACTIVITIES OF SOME AMINOACYL-tRNA SYNTHETASES AND AUXILIARY p43 COFACTOR OFAMINOACYLATION REACTION AND THEIR ROLE IN ONCOGENESIS Serhiy S. Ivakhno, Alexander I. Kornelyuk* Institute of Molecular Biology and Genetics, NAS of Ukraine, Kyiv, Ukraine Multifunctionality of proteins is among mechanisms accounting for the complexity of interactome networks in higher eukaryotes. During oncogenesis and other pathologic conditions many proteins perform additional functions without changes in three dimensional structures. One family of these moonlighting proteins is represented by enzymes and cofactors of aminoacylation reactions, by means of which tRNAs are attached to their cognate amino acids. Tyrosyl-tRNA synthetase (TyrRS), tryptophanyl-tRNA synthetases (TrpRS) and auxiliary factor of mam- malian multi-aminoacyl-tRNA synthetases, p43 (precusor of endothelial monocyte activating polypeptide II — EMAP II) upon their release in intracellular environment become proinflammatory cytokines with multiple activi- ties during apoptosis, angiogenesis and inflammation. In addition, these proteins play important role in cancer progression, modulating tumor angiogenesis and its escape from surveillance by immune system. Key Words: moonlighting proteins, endothelial-monocyte activating polypeptide II, tyrosyl-tRNA synthetase, tryp- tophanyl-tRNA synthetase, apoptosis, tumor angiogenesis. of aminoacylation reaction. The major housekeeping func- tion of aminoacyl-tRNA synthetases is attachment of ami- noacids to their cognate tRNAs during translation. In mam- mals additional cofactors — proteins p18, p38 and p43 form the core of aminoacyl-tRNA synthetase complex, which assist the aminoacylation. However, two synthetases in mammals, tyrosyl-tRNA synthetase (TyrRS) and tryp- tophanyl-tRNA synthetase (TrpRS) and p43 cofactor (Figure), upon release in intracellular space gain additional activities and began to act as cytokines, regulating migra- tion, division, differentiation and apoptosis of various cells of immune system and endothelial cells, and participating in malignant transformation. Although cytokine functions of these proteins have been investigated for more than 12 years, the mechanisms of their multifunctionality have yet to be discovered. In this article we will briefly review present state of research on cytokine activities of these proteins and their implication in carcinogenesis. EMAP II/p43. Cytokine activity of p43 has been dis- covered in 1992 when it was purified from methylcholant- ren A induced (Meth A) mouse fibrosarcoma and named endothelial and monocyte activating polypeptide II (EMAP II) [13]. Endothelial cells of mouse fibrosarcoma have very high sensitivity to many cytokines, and consequently can be used as a good model for studying angiogenesis fac- tors. EMAP II, purified from these tumors, appeared to be a small protein with molecular weight of 22 kDa, but cDNA of the gene cloned later suggested the existence of 34 kDa EMAP II precursor (proEMAP II). Purified recombinant EMAP II elevated expression of P and E-selectins on the surface of endothelial cells, raised level of intracellular cal- cium and induced tissue factor. Also EMAP II activated neu- trophils (chemotaxis, release of intracellular calcium and peroxidase) and monocytes (stimulation of chemotaxis, induction of tumor necrosis factor (TNF) and tissue factor) [14]. Local intratumoral injection of EMAP II led to bleeding and significant reduction in tumor size. Tumors, treated with EMAP II, also demonstrated higher sensitivity to TNF-in- Received: May 27, 2004. *Correspondence: Fax +38 (044) 266-0759 E-mail: kornelyuk@imbg.org.ua Abbreviations used: EGF — endothelial growth factor; EMAP II — endothelial monocyte activating polypeptide ²²; IFN-γ — inter- feron-γ; RMSD — root mean square deviation; TNF — tumor ne- crosis factor; TrðRS — tryptophanyl-tRNA synthetase; TyrRS — tyrosyl-tRNA synthetase.