Variant in the Regulatory Subunit of Phosphatidylinositol 3 - Kinase ( p 85 ) Preliminary

P hosphatidylinositol 3-kinase (PI 3-kinase), a sig-naling molecule activated by insulin receptor sub-strate (IRS)-1, has a role in both insulin-stimulated glucose uptake and in basal glucose transporter recycling. PI 3-kinase is also responsible for phosphorylating phosphatidylinositol, PI-4-P, PI-4,5-P 2 , and PI-3,4,5-P 3 , w h i c h function as intracellular second messengers. The structure of PI 3-kinase is heterodimeric, consisting of a catalytic subunit (p110) and a regulatory subunit, which is one of several alternatively spliced products of the p85 gene (G R B 1) (1). Since inhibitors of PI 3-kinase block insulin-stimulated glucose uptake (2), we initially investigated the p85 gene as a candidate gene for the decrease in the rate of insulin-stimulated glucose uptake that is observed in Pima Indians before the onset of type 2 diabetes. However, our preliminary fin d i n g s indicate that a variation in p85 does not alter insulin-stimulated glucose uptake, but rather affects the acute insulin response in Pima women. In addition, since an association with the acute insulin response was only observed in women, we hypothesize that p85 may be differentially expressed in men and women. Sequence analysis of muscle cell cDNA from insulin-sensitive and insulin-resistant Pima subjects identified one previously reported missense polymorphism at codon 326 (AT G to ATA), which predicts a Met to an Ile substitution (3). This polymorphism was genotyped in 1,182 Pima subjects and in 53 North American Caucasians (Centre d'Etude Polymor-phism Humain [CEPH]) by sequencing of a 104 base pair (bp) fragment of DNA amplified from this region of genomic DNA. The frequency of the Met-encoding allele was 0.75, and the frequency of the Ile-encoding allele was 0.25 in the Pima population. The frequency of this polymorphism was slightly lower in the CEPH samples (0.83 and 0.17 for the Met-and Ile-encoding alleles, respectively). The allelic frequencies observed in the CEPH population were similar to those previously reported in a Danish Caucasian population (0.84 and 0.16) (3). All of the allelic frequencies were in Hardy-We i n b e r g equilibrium. A second nucleotide variation at codon 330 was also identified in all 1,182 Pima DNA samples and the 53 CEPH DNA samples. This codon (GAT, which encodes Asp) differed from the original published sequence of p85 (A AT, which encodes Asn at codon 330) (4). The prevalence of type 2 diabetes was assessed in individuals whose DNA had been genotyped …