Quantitation of the mRNA expression of the epidermal growth factor system: selective induction of heparin-binding epidermal growth factor-like growth factor and amphiregulin expression by growth factor stimulation of prostate stromal cells.

The epidermal growth factor (EGF) system is a rapidly expanding system of growth factors involved in many aspects of normal and cancerous growth. We have developed a method for the quantitation of mRNA coding for all six growth factors activating the human EGF receptor (HER-1) and for the quantitation of mRNA for the receptors HER-1 and its preferred dimerization partner, HER-2. The method is based on the generation of specific RNA standards, which are amplified by reverse transcriptase-polymerase chain reaction (RT-PCR) with the sample RNA and a set of calibrators. The resulting calibration curve is used to quantitate the unknown samples, which require only a single RT-PCR reaction. Our method has the advantage that quantitation is based on coamplification of an internal RNA standard, thereby controlling both the PCR and RT reactions. In addition, the RNA standards for all growth factors and receptors are combined in a single RT reaction, which minimizes variation and allows the quantitation of all eight mRNA species with only 0.1 microg RNA. This makes the method suitable for studies in which the supply of material is limited. The developed method has enabled us to demonstrate that prostate stromal cells in primary culture express EGF, heparin-binding EGF (HB-EGF), amphiregulin, betacellulin, and epiregulin as well as the HER-1 and HER-2 receptors, whereas no transforming growth factor-alpha mRNA is found. Furthermore, activation of the EGF system in these cells by stimulation with HB-EGF or EGF in mitogenic doses causes a selective increase in the expression of amphiregulin and HB-EGF mRNA (more than 15-fold and 25-fold, respectively), whereas there is no increase in the expression of mRNA for the other growth factors or receptors. In accord with the increase in amphiregulin mRNA, the amount of amphiregulin peptide released from the cells is also increased. The selective induction of amphiregulin and HB-EGF by growth factor stimulation may represent a mechanism to amplify the initial growth factor signal in prostate stromal cells.