Functional Regulation of Erb B family by N-glycosylation

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Glycosylation is one of the most common post-translational modification, and is known to change physico-chemical properties of proteins. In this study, I examine the function of N-glycan of ErbB family and adenylyl cyclase.ErbB3 has 10 potential glycosylation sites in its extracellular domain. A series of human ErbB3 molecules devoid of N-glycan were prepared and transfected to Flp-In-CHO cells for stable expression. It was revealed that the Asn 418 to Gln mutant (N418Q) mutant of ErbB3 underwent ligand-independent homodimerization. When overexpressed with ErbB2, ligand-independent hetero-dimerization was observed and Erk and Akt phosphorylation was upregulated in the absence of of ErbB3 coexpressed with ErbB2 promoted cell proliferation and colony formation in soft agar in an Erk and Akt-dependent manner. The N418Q mutation also promoted the growth of tumors in athymic mice when injected subcutaneously. Thus, Asn 418-linked N-glycan in ErbB3 plays an essential role in regulating receptor heterodimerization with ErbB2 and might have an effect on transforming activity.Adenylyl cyclase III (ACIII) has 2 potential glycosylation sites in its extracellular domain, and it was suggested that glycosylation is involved in its enzymatic activity. When processing of glycosylation was suppressed by introducing GnT-III, one of glycosyltransferases, forskolin-induced ACIII activation and downstream signaling such as the synthesis of cAMP and the phosphorylation of CREB were significantly upregulated. Now the mechanisms of the regulation of ACIII by the structure of N-glycan is being investigated.