PF4 attenuates EGF-induced pRb phosphorylation. HUVEC lysates, collected at the specified times after stimulation with 20 ng/mL EGF in the absence (−) or presence (+) of 2 μg/mL PF4, were separated by SDS-PAGE and immunoblotted for pRb as described in Materials and Methods. Results shown are representative of three independent experiments.