Effects of CHX on HB-EGF mRNA levels in GM-CSF–treated PMN. CHX did not inhibit, but overinduced, the GM-CSF–dependent upregulation of HB-EGF mRNA, showing that protein synthesis was not required. PMN were pretreated with 20 μg/mL CHX before stimulation with 25 ng/mL GM-CSF for 2 hours. Total RNA was then extracted and analyzed for HB-EGF and actin mRNA levels. The experiment depicted is representative of 2.