EGF and IGF-I synergistically stimulate proliferation of human esophageal epithelial cells

Proliferation of esophageal mucosal cells is important in repair of reflux-induced injury. We studied the effects of EGF, IGF-I, and IGF- I/binding protein-3 (BP-3) complex on immortalized esophageal epithelial (HET-1A) cells and searched for synergy between the growth factors. HET-1A cells were plated at 5 x 10⁴ in 12 well plates. After 2 days in optimal media, they were maintained in basal media with or without the test peptides: EGF at 0.05-5 nM, IGF-I at 0.1-10 nM, IGF-I/BP-3 at 0.1-10 nM, and a combination of EGF at 5 nM and IGF-I or IGF-I/BP-3 at 1 and 10 nM. In comparison to basal media EGF and IGF-I stimulated cell proliferation over baseline at 5 and 10 nM, respectively. The combination of EGF at 5 nM and IGF-I at 1 and 10 nM worked synergistically, increasing cell counts over baseline to 10.3 ± 0.2 and 14.6 ± 0.8 x 10⁵, respectively. The calculated additive effect of EGF and IGF-I at 1 and 10 nM individually increased cell counts to 8.2 ± 0.2 and 10.4 ± 0.6 x 10⁵, respectively. The difference between the observed and the calculated values was significant at P < 0.05, ANOVA, Tukey test. IGF-I/BP-3 complex enhanced this synergy at low levels of IGF-I but not at 10 nM IGF-I. EGF, IGF, and IGF-I/BP-3 independently promote HET-1A proliferation. IGF and EGF in combination demonstrate synergism with potentiated interaction presumably because of their different roles in the cell cycle, EGF being a competence factor and IGF being a progression factor. This combination may have potential as a treatment for esophageal mucosal injury, and IGF-I/BP-3 may further enhance their benefit.