RB1 and colon carcinoma: Comparative analysis of different signal transduction pathways in HGUE-C-1 versus HT-29 colon carcinoma cell lines show that lack of APC activity, low expression and activity of Rb protein together with an over-expression and high activation of p70S6K and constitutive activation of Erk1/2, may be the driving force of HGUE-C-1 carcinogenesis.