Tohoku J. Exp. Med., 2008, 216(1)

Ras-mediated Up-regulation of Survivin Expression in Cytokine-dependent Murine Pro-B Lymphocytic Cells

TETSUHARU SHINJYO,¹ HIDEMITSU KUROSAWA,² JUN-ICHI MIYAGI,¹ KIYOTO OHAMA,¹ MASATO MASUDA,¹ AKITOSHI NAGASAKI,¹ HIROTAKA MATSUI,³ TOSHIYA INABA,³ YUSUKE FURUKAWA⁴ and NOBUYUKI TAKASU¹

¹Department of Endocrinology and Metabolism, Department of Internal Medicine, University of the Ryukyus, School of Medicine, Okinawa, Japan
²Department of Pediatrics, Dokkyo Medical University, Tochigi, Japan
³Department of Developmental Biology and Molecular Oncology, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, Japan
⁴Division of Stem Cell Regulation Center for Molecular Medicine, Jichi Medical School, Tochigi, Japan

Survivin, a member of the inhibitor of apoptosis protein (IAP) family, has been widely studied because of its aberrant expression in human cancer. Survivin has multiple functions, including cell-cycle regulation at mitosis, inhibition of apoptosis and caspase-independent cytoprotection. Clinical studies have shown that survivin is associated with resistance to treatment and its expression is linked to poor prognosis. Recent studies indicated that Ras pathways up-regulate survivin expression in hematopoietic cells. Here we analyzed downstream pathways of Ras in interleukin-3 (IL-3)-dependent Baf-3 murine-derived pro-B lymphocytic cells that express constitutively active Ras mutants, using signaling pathway-specific inhibitors. Both mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI3-K) pathways are involved in the induction of survivin. Downstream of PI3-K, the signaling pathway is composed of two kinases, Akt and mammalian target of rapamycin (mTOR) pathways. In the downstream targets of PI3-K, mTOR but not Akt is responsible for survivin expression. Using a counterflow centrifugal elutriator, we observed G2/M phase-dominant survivin expression in Baf-3 cells. Interestingly, constitutively active Ras mutants also induced survivin in a cell cycle-dependent manner. Reporter assays of the survivin gene promoter revealed a transcriptional regulatory cis-acting region that is responsible for Ras signaling, indicating that Ras increases the transcription of the survivin gene through specific enhancer elements. These data illustrate the pathways regulating survivin expression by Ras. Ras activates the MAPK, PI3-K and mTOR pathways, and these signals enhance survivin transcription. Our data will provide the new information about mechanisms of survivin expression by Ras-signalling pathways.

keywords —— survivin; ras; Baf-3 cell; IL-3; MAPK; PI3-K.

© 2008 Tohoku University Medical Press

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Tohoku J. Exp. Med., 2008, 216, 25-34

Correspondence: Tetsuharu Shinjyo, Department of Endocrinology and Metabolism, Department of Internal Medicine, University of the Ryukyus, School of Medicine 207, Uehara, Nakagami-Nishihara, Okinawa 903-0215, Japan.

e-mail: tshinjo@ryudai2nai.com