Title : Functional effects of glycosylation at
Asn-579 of the
epidermal growth factor receptor
Abstract :
- We have investigated functional effects of glycosylation at N(579) of the epidermal growth factor receptor ( EGFR )
- Our previous study showed that the population of cell-surface expressed EGFRs in A431 cells, a human epidermoid carcinoma cell line, is composed of two subpopulations that differ by glycosylation at N(579) [Zhen et al. (2003) Biochemistry 42, 5478-5492]
- To characterize the subpopulation of receptors not glycosylated at N(579) , we established a 32D cell line expressing a point mutant of the EGFR (N579Q) N579Q ), which cannot be glycosylated at this position
- Analysis of epitope accessibility suggests that the lack of glycosylation at N(579) weakens auto-inhibitory tether interactions, and cross-linking experiments suggest a somewhat elevated level of preformed N579Q- EGFR dimers in the absence of ligand relative to wild-type EGFR ( WT-EGFR )
- However, ligand drives the majority of N579Q- EGFR dimerization , suggesting that untethering, while necessary, is not sufficient to drive dimerization
- Ligand-binding experiments reveal a much greater fraction of N579Q-EGFRs in a high-affinity state compared to the fraction of WT-EGFRs in a high-affinity state
- However, differences in the kinetic association and dissociation rates indicate that the high-affinity states of the WT and the N579Q receptors are distinct
- EGF-stimulated phosphorylation in cells expressing N579Q-EGFRs results in notable differences in the pattern of tyrosine phosphorylated proteins compared with that obtained in cells expressing WT-EGFRs
- Moreover, although WT-EGFRs confer cell survival in 32D cells in the absence of interleukin-3 and EGF , we found that receptors lacking glycosylation at N(579) do not
- This is the first study of which we are aware to show that selective glycosylation of a specific N-glycosylation site can produce two functionally distinct receptors