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COLON CANCER CELL ANOIKIS RESISTANCE: EGFR-DEPENDENT SUSTAINED ACTIVATION OF THE SRC-MEK/ERK PATHWAY CAN OVERRIDE FAK, PI3-K/AKT-1 DEPENDENCE FOR SURVIVAL
PH Vachon, M-J Demers
Département d’anatomie et de biologie celllaire, FMSS, Université de Sherbrooke, QC
Background/Aims: Anoikis resistance is a landmark of invasive cancer cells. In the present study, we investigated the cell surviving properties of colon cancer cells with regards to anoikis resistance.
METHODS: Colon cancer cells HCT116 and HT29, which do not differentiate, and T84, which polarize but not differentiate, were compared to undifferentiated (-2 PC) and differentiated (30 PC) enterocyte-like Caco-2/15 cells, as well as to normal human crypt cells (HIEC). HCT116, HT29 and T84 cells are known for their high EGF/TGFalpha autocrine secretory activities, in sharp contrast to Caco-2/15 and HIEC cells. EGFR, Fak, Src, the MEK/Erk and/or PI3-K/Akt-1 pathways were inhibited either pharmacologically or by overexpression of dominant negative mutants. Cells were also kept in suspension on poly-HEMA for 0-24 hrs. Anoikis was evaluated by ISEL and/or DNA laddering. Activation parameters of Fak, Src, Erk-1/Erk-2 and Akt-1 were analyzed. All experiments were performed under serum-free conditions.
RESULTS: 1- Differentiated enterocytes are more susceptible to anoikis than undifferentiated/crypt ones. However, HCT116, HT29 and T84 cells displayed significantly greater anoikis resistance overall. 2- Differentiated and undifferentiated enterocytes require Fak and the PI3-K/Akt-1 pathway for their survival. However, T84 cells do not require Fak, whereas HCT116 do not require PI3-K/Akt-1. 3- As in the case of differentiated enterocytes, HCT116, T84 and HT29 cells require Src and MEK/Erk for their survival, whereas undifferentiated/crypt enterocytes require Src only. 4- In contrast to both undifferentiated and differentiated enterocytes, HT29, T84 and HCT116 exhibit a sustained activation of Src and MEK/Erk while kept under anoikis-inducing conditions. 5- The inhibition of EGFR activity abrogated anoikis resistance in HCT116, HT29 and T84 cells, by causing a drop of Src-MEK/Erk activation.
CONCLUSIONS: These data indicate that an illicit activation of EGFR in colon cancer cells through high secretion of EGF/TGFalpha under anoikis conditions will result in a sustained activation of the Src-MEK/Erk pathway, thus overriding a Fak, PI3-K/Akt-1 dependance for survival and consequently conferring high anoikis resistance.
Supported by the CRS & FRSQ