Intracellular Localization and Content of YB-1 Protein in Multidrug Resistant Tumor Cells

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A. V. Vaiman¹, T. P. Stromskaya¹, E. Yu. Rybalkina¹, A. V. Sorokin², S. G. Guryanov², T. N. Zabotina¹, E. B. Mechetner³, L. P. Ovchinnikov², and A. A. Stavrovskaya^1*

¹Institute of Carcinogenesis, Blokhin Russian Cancer Research Center, Russian Academy of Medical Sciences, Kashirskoe Shosse 24, 115478 Moscow, Russia; E-mail: vaiman@yandex.ru

²Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia; fax: (7-495) 632-7871; E-mail: ovchinn@vega.protres.ru

³Chemicon International, Inc., 28820 Single Oak Drive, Temecula, CA 92590, USA; E-mail: emechetner@cox.net

^* To whom correspondence should be addressed.

Received July 16, 2005; Revision received October 6, 2005

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The multifunctional mammalian protein YB-1 is a member of the large DNA- and RNA-binding protein family with an evolutionarily ancient cold-shock domain. YB-1 is involved in multiple DNA- and mRNA-dependent events and regulates gene expression at various levels. It can be found both in the nucleus and the cytoplasm. Bound to DNA in the cell nucleus, YB-1 functions as a transcription factor interacting with inverted CCAAT-box (Y-box) in promoters and enhancers of multiple genes. In particular, YB-1 regulates activity of the multidrug resistance (MDR) genes MDR1 and LRP. In tumors, YB-1 has been suggested to be an early and global marker of MDR. In this study, we compared amounts of YB-1 mRNAs and intracellular localization of YB-1 protein in six pairs of drug sensitive and drug resistant sublines of diverse tumors. We have shown that neither great increase in the level of YB-1 mRNA nor substantial increase in the number of cells with nuclear localization of YB-1 are obligatory traits of drug resistant tumor cell populations. However, the cells with highest amounts of YB-1 mRNA also demonstrated increased quantities of MDR1, MRP1, BCRP, and LRP mRNAs encoding different MDR proteins. Transfection of two different populations of drug-sensitive cells with YB-1 cDNA led to increase in the amount of YB-1 mRNA. The quantities of MRP1 and LRP mRNAs increased in both populations. Introduction of YB-1 small hairpin RNA (shRNA) resulted in decreased amounts of YB-1 mRNA, as well as MRP1, LRP, and MDR1 mRNAs (in three different cell lines). Our data suggest that although YB-1 regulates several MDR genes, it could not be regarded as a global marker of already formed drug resistant tumor cell populations. It is most likely that at the first steps of MDR development YB-1 activity is necessary for propagation of resistant cell populations rather than for maintenance of drug resistance.

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KEY WORDS: YB-1 protein, mRNA, tumor cell, multidrug resistance, resistant cell, protein localization

DOI: 10.1134/S0006297906020052

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