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J. Biol. Chem., Vol. 279, Issue 35, 36680-36688, August 27, 2004

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Oncogenic Ras Promotes Butyrate-induced Apoptosis through Inhibition of Gelsolin Expression^*

Lidija Klampfer, Jie Huang, Takehiko Sasazuki¶, Senji Shirasawa¶, and Leonard Augenlicht

From the Albert Einstein Cancer Center, Montefiore Medical Center, Department of Oncology, Bronx, New York 10467 and the ^¶Research Institute, International Medical Center of Japan, Toyama 1-21-1, Shinjuku-ku, Tokyo 162-8655, Japan

Activation of Ras promotes oncogenesis by altering a multiple of cellular processes, such as cell cycle progression, differentiation, and apoptosis. Oncogenic Ras can either promote or inhibit apoptosis, depending on the cell type and the nature of the apoptotic stimuli. The response of normal and transformed colonic epithelial cells to the short chain fatty acid butyrate, a physiological regulator of epithelial cell maturation, is also divergent: normal epithelial cells proliferate, and transformed cells undergo apoptosis in response to butyrate. To investigate the role of k-ras mutations in butyrate-induced apoptosis, we utilized HCT116 cells, which harbor an oncogenic k-ras mutation and two isogenic clones with targeted inactivation of the mutant k-ras allele, Hkh2, and Hke-3. We demonstrated that the targeted deletion of the mutant k-ras allele is sufficient to protect epithelial cells from butyrate-induced apoptosis. Consistent with this, we showed that apigenin, a dietary flavonoid that has been shown to inhibit Ras signaling and to reverse transformation of cancer cell lines, prevented butyrate-induced apoptosis in HCT116 cells. To investigate the mechanism whereby activated k-ras sensitizes colonic cells to butyrate, we performed a genome-wide analysis of Ras target genes in the isogenic cell lines HCT116, Hkh2, and Hke-3. The gene exhibiting the greatest down-regulation by the activating k-ras mutation was gelsolin, an actin-binding protein whose expression is frequently reduced or absent in colorectal cancer cell lines and primary tumors. We demonstrated that silencing of gelsolin expression by small interfering RNA sensitized cells to butyrate-induced apoptosis through amplification of the activation of caspase-9 and caspase-7. These data therefore demonstrate that gelsolin protects cells from butyrate-induced apoptosis and suggest that Ras promotes apoptosis, at least in part, through its ability to down-regulate the expression of gelsolin.

Received for publication, May 10, 2004 , and in revised form, June 7, 2004.

^* This work was supported by a Montefiore Medical Center new research initiative award (to L. K.), American Cancer Society Institutional Research Grant ACS IRG 98-274-01 (to L. K.), NCI, National Institutes of Health Grant UO1 CA88104 (to L. A.), and Cancer Center Grant PO13330. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Albert Einstein Cancer Center, Montefiore Medical Center, 111 E. 210th St., Bronx, NY 10467. Tel.: 718-920-6579; Fax: 718-882-4464; E-mail: lklampf{at}aecom.yu.edu.

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