The role of ErbB3 N-glycan in dimer formation: Implications for transforming activity

Abstract

The ErbB2/ErbB3 heterodimer elicits potent mitogenic and transforming signals, and clinical studies indicate that these receptors play an important role in tumor incidence and progression. In this study, a series of human ErbB3 mutants devoid of N-glycans expressed in Flp-In-CHO cells were used to determine whether N-glycosylation is involved in the function of ErbB3. A crosslinking study showed that the Asn⁴¹⁸ to Gln mutant (N418Q) of ErbB3 underwent heregulin (HRG)-independent autodimerization. Furthermore, ErbB3-N418Q autodimerized with ErbB2 in the absence of HRG, and receptor tyrosine phosphorylation and subsequent extracellular signal-regulated kinase (ERK) and Akt phosphorylation were promoted. A cell proliferation assay and a soft agar colony formation assay demonstrated that ErbB2/ErbB3-N418Q co-expression promoted cell proliferation and colony formation in soft agar in ERK- and Akt-dependent manners. ErbB2/ErbB3-N418Q co-expression also promoted the growth of tumors in athymic nude mice when injected subcutaneously. These results suggest that the Asn⁴¹⁸-linked N-glycan in ErbB3 plays a crucial role in regulating receptor dimer formation and transforming activity.