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Mol. Cell. Biol., May 1996, 2195-2203, Vol 16, No. 5
DA Antonetti, P Algenstaedt and CR Kahn
We have identified two novel alternatively spliced forms of the p85alpha
regulatory subunit of phosphatidylinositol (PI) 3-kinase by expression
screening of a human skeletal muscle library with phosphorylated
baculovirus- produced human insulin receptor substrate 1. One form is
identical to p85alpha throughout the region which encodes both Src homology
2 (SH2) domains and the inter-SH2 domain/p110 binding region but diverges
in sequence from p85alpha on the 5' side of nucleotide 953, where the
entire break point cluster gene and SH3 regions are replaced by a unique
34-amino-acid N terminus. This form has an estimated molecular mass of
approximately 53 kDa and has been termed p85/AS53. The second form is
identical to p85 and p85/AS53 except for a 24-nucleotide insert between the
SH2 domains that results in a replacement of aspartic acid 605 with nine
amino acids, adding two potential serine phosphorylation sites in the
vicinity of the known serine autophosphorylation site (Ser-608). Northern
(RNA) analyses reveal a wide tissue distribution of p85alpha, whereas
p85/AS53 is dominant in skeletal muscle and brain, and the insert isoforms
are restricted to cardiac muscle and skeletal muscle. Western blot
(immunoblot) analyses using an anti-p85 polyclonal antibody and a specific
anti-p85/AS53 antibody confirmed the tissue distribution of p85/AS53
protein and indicate a approximately 7-fold higher expression of p85/AS53
protein than of p85 in skeletal muscle. Both p85 and p85/AS53 bind to p110
in coprecipitation experiments, but p85alpha itself appears to have
preferential binding to insulin receptor substrate 1 following insulin
stimulation. These data indicate that the gene for the p85alpha regulatory
subunit of PI 3-kinase can undergo tissue-specific alternative splicing.
Two novel splice variants of the regulatory subunit of PI 3-kinase are
present in skeletal muscle, cardiac muscle, and brain; these variants may
have important functional differences in activity and may play a role in
tissue-specific signals such as insulin-stimulated glucose transport or
control of neurotransmitter secretion or action.
Copyright © 1996, American Society for Microbiology
Insulin receptor substrate 1 binds two novel splice variants of the regulatory subunit of phosphatidylinositol 3-kinase in muscle and brain
Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts 02215, USA.
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