FIG. 5.

G₁/S arrest increases Erk phosphorylation under attached and suspended conditions. (A) Expression of p16^INK4a enhances Erk phosphorylation in attached cells and following detachment. MCF-10A cells transduced with control vector (BABE) or BABE encoding p16^INK4a were placed under attached or suspended conditions following selection. After 24 h in suspension, cell lysates were harvested and immunoblotted with antiserum against total Erk2 or against phosphorylated Erk1/2 (p-Erk1/2). (B) Mimosine treatment enhances Erk phosphorylation under attached and suspended conditions. MCF-10A cells were treated as described for Fig. 2A, except the lysates were immunoblotted with the Erk antibodies described for Fig. 5A. (C) Aphidicolin treatment enhances Erk phosphorylation in attached and suspended cells. MCF-10A cells were treated as described for Fig. 2B, except the lysates were immunoblotted with the Erk antibodies described for panel A.