MUC1 siRNA SILENCING IMPACT IN GASTRIC CANCER CELLS PHENOTYPE N. Costa, P. Paulo, R. Barbosa, H. Tsutsumida, T. Caffrey, M.A. Hollingsworth, F. Santos-Silva* Eppley Cancer Institute, UNMC, Omaha, NE, USA IPATIMUP, Rua Dr Roberto Frias s/n, 4200-465 Porto, Portugal *[email protected] INTRODUCTION. MUC1 is a trans-membrane glycoprotein expressed on epithelial surfaces that was been associated with protection, cell signaling, cellcell interactions and cell migration (1). Over-expression and abnormal glycosylation of MUC1 has been reported in several cancer models, including gastric cancer (2). We evaluated the relevance of MUC1 for gastric cancer tumorigenicity using a siRNA silencing strategy. METHOD. We used small interfering RNAs (siRNA) to knock down MUC1 expression in MKN45 gastric cancer cell line. MUC1 expression levels in silenced clones were confirmed by immunofluorescence and western-blot using HMFG1 MAb and by real-time PCR. MUC1 silenced clones were evaluated for proliferation (MTT assay), apoptosis (TUNEL assay) and invasion (Matrigel invasion assay). Signaling pathways were evaluated with KinetworksTM protein kinase multiblot analysis. RESULTS. Using the RNAi strategy we stably down–regulated MUC1 expression. The MUC1 silenced clones (C1, C2) had significantly increased rates of growth (proliferation), apoptosis and invasion activity when compared with scramble control (SC) (figure 1). Furthermore these clones also showed alterations in phosphorylation of proteins involved in oncogenic signaling pathways: Erk1, decreased phosphorylation of T202 and Y204; Erk2, increased phosphorylation of T185 and Y187; and cell cycle CDK1/2, increased phosphorylation of T14, Y15, and T160/T161. Figure 1 DISCUSSION. MKN45 is a gastric cell line with high levels of MUC1 expression. This study showed that down-regulation of MUC1 in MKN45 cells promotes oncogenesis-associated events (proliferation, apoptosis and invasion). Alterations in phosporylation of signaling targets implicate the involvement of proliferation related cascades (CDK1/2). These findings are opposite from those described in breast and pancreatic models (3, 4), which suggests the need to identify MUC1 signaling partners in gastric cancer cells. Our RNAi model is the first to show that MUC1 affects the transformed status of gastric cancer cells, through effects on oncogenic signaling pathways. ACKNOWLEDGMENT. This work was supported by Fundação para a Ciência e Tecnologia (grants: POCTI/CBO/44812/2002, POCI/SAU-IMI/ 56895/2004 and SFRH/BD/27669/2006) and Fundação Luso-Americana para o Desenvolvimento. REFERENCES 1. Hollingsworth, M.A., Swanson, B.J. (2004) Nat. Rev. Cancer. 4:45-60. 2. Silva, F. et al (2001) Eur. J. Hum. Genet. 9:548-52. 3. Tsutsumida, H. et al (2006) Clin. Cancer Res. 12:2976-87. 4. Hattrup, C.L., Gendler, S.J. (2006) Breast Cancer Res. 8(4):R37.