PubMed Journals: J Biol Chem
Source: PMID: 8027066
⇦ ⇨ J Biol Chem. 1994 Jul 8;269(27):18062-71.
The functions of the human insulin receptor
are affected in different ways by mutation
of each of the four N-glycosylation sites
in the beta subunit.
Leconte I(1), Carpentier JL, Clauser E.
(1) INSERM U36, Chaire de Médecine Expérimentale,
Collège de France, Paris.
The functional role of the oligosaccharide
chains linked to the insulin receptor (IR)
beta subunit was investigated by site-directed
mutagenesis of each of the 4 acceptor asparagines
(N1 to N4 from the amino to the carboxyl
terminus) and stable expression of the receptors
in CHO cells. All mutant receptors are expressed
normally at the cell surface, bind insulin
with similar affinity, but have a beta subunit
of smaller molecular mass, and a defect
in ligand-induced internalization as compared
to wild type receptor. In terms of receptor
activation and signal transduction, the
N1 and N2 mutants function normally, whereas
the N4 mutant exhibits major alterations
in in vitro tyrosine kinase activity and
autophosphorylation and is unable to transduce
the signal for either glycogen or DNA synthesis.
By contrast, in vivo autophosphorylation
and IRS-1 phosphorylation appear quantitatively
normal, and only partial alterations of
phosphatidylinositol 3-kinase and mitogen-activated
protein kinase activation are observed.
Mutation of the N3 site results in partial
defect of IR activation. These data provide
evidence for (i) glycosylation of each N-linked
glycosylation site of the IR beta subunit,
(ii) absence of correlation between internalization
and transmembrane signaling, and (iii) a
major role for oligosaccharide side chain(s)
located close to the cell membrane in IR
activation and transmembrane signaling.
PMID: 8027066 [Indexed for MEDLINE]