Dissociation of Epidermal Growth Factor Receptor and ErbB2 Heterodimers in the Presence of Somatostatin Receptor 5 Modulate Signaling Pathways

Epidermal growth factor through the stimulation of epidermal growth factor receptor (EGFR) plays a critical role in the activation of MAPKs and phosphatidylinositol-3-protein kinase/AKT cell survival pathways attributed in many pathological conditions. At the cellular level, such functions involve EGFR overactivation and phosphorylation. In the present study, we describe that human embryonic kidney-293 cells transfected with somatostatin (SST) receptor 5 (SSTR5) exhibit inhibition of EGFR phosphorylation and modulate MAPK and phosphatidylinositol-3-protein kinase/AKT cell survival signaling. Furthermore, suppression of EGFR by using small interference RNA and an antagonist (AG1478) potentiates the SST effect via activation of SSTR5 on signaling molecules. In wild-type human embryonic kidney-293 cells, EGFR/ErbB2 exists as constitutive heterodimers. The presence of SSTR5 leads to the dissociation of the heteromeric complex of EGFR/ErbB2 and display preferential heterodimerization between SSTR5 and EGFR in an agonist-dependent manner. These findings highlight a new undiscovered mechanism and potential role of SSTR5 to attenuate the EGFR mediated signaling pathways involved in tumorigenesis. Our data indicate that the activation and/or overexpression of SST receptors along with the inhibition of EGFR will serve as an important therapeutic approach in the treatment of ErbB-positive tumors. (Endocrinology 152: 931-945, 2011)