Previous work has indicated that the PDZ domain Tax interacting protein 1 (Tip-1) is a target of the HTLV1 Tax protein and is a potential RhoA effector. We have used the yeast two-hybrid system to show that Tip-1 also interacts with the HPV16 E6 protein. This interaction was confirmed by co-immunoprecipitation from E6 expressing C33A cervical carcinoma cells (C33A-E6) which showed that Tip-1 was not degraded by interaction with the HPV16 E6 oncoprotein. During routine passage we observed that C33A-E6 had a less compact morphology and were less adherent than control vector transfected cells C33A-V cells - a known effect of GTP-RhoA. Comparison of C33A-E6 to C33A-V demonstrated that E6 expressing cells had higher levels of phosphorylated myosin light chains (MLC) and increased cell motility, which was inhibited by antisense silencing of Tip-1 expression and by the RhoA kinase (ROCK) inhibitor Y27632. Both C33A-E6 and C33A-V cells were shown to express GTP activated RhoA. Since ROCKs can be activated by GTP RhoA these data indicate that E6 may increase cell motility by augmenting GTP RhoA mediated activation of ROCKs and that this is dependent on the expression of the Tip-1 protein.

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