The Structure and Function of P55^PIK Reveal a New Regulatory Subunit for Phosphatidylinositol 3-Kinase

Abstract

Phosphatidylinositol 3-kinase (PI-3 kinase) is implicated in the regulation of diverse cellular processes, including insulin-stimulated glucose transport. PI-3 kinase is composed of a 110-kDa catalytic subunit and an 85-kDa regulatory subunit. Here, we describe p55 PIK , a new regulatory subunit that was isolated by screening expression libraries with tyrosine-phosphorylated insulin receptor substrate 1 (IRS-1). p55PIK is composed of a unique 30-residue NH 2 terminus followed by a proline-rich motif and two Src homology 2 (SH2) domains with significant sequence identity to those in p85. Phosphatidylinositol 3-kinase (PI-3 kinase) is a common signaling element which plays a role in the regulation of a broad array of biological responses by activated receptors for hormones, growth factors, cytokines, and antigens (6,13,15,42,46,48,61). It is composed of a 110-kDa catalytic subunit (p110) associated with an 85-kDa regulatory subunit (p85) that contains one Src homology 3 (SH3) domain, homology to the breakpoint cluster region (bcr) gene, two proline-rich motifs, and two SH2 domains (11). Interestingly, p110␣ displays dual catalytic specificity, as it phosphorylates the D-3 position of phosphatidylinositol and its phosphorylated derivatives and serine residues in p85 and insulin receptor substrate 1 (IRS-1) (12, 32). Mammalian p110 is homologous to VPS34, a Saccharomyces cerevisiae PI-3 kinase which is involved in vacuolar protein sorting (49); however, the molecular role of PI-3 kinase in mammalian cells is unclear (22).The p85 regulatory subunit has a broad potential to couple the PI-3 kinase to multiple signaling elements by employing its SH3 domain, proline-rich motifs, bcr homology region, or SH2 domains (24). Most activated receptors with tyrosine kinase activity engage the SH2 domains in p85 through phosphorylated YXXM motifs in the receptors themselves or a closely associated subunit (52). The platelet-derived growth factor receptor, one of the best-characterized systems, associates directly with the SH2 domains in p85 at a phosphorylated YMDM motif in the kinase insert region (61). Inhibition of PI-3 kinase catalytic activity with wortmannin or disruption of p85 function by site-directed mutagenesis blocks several growth factor-stimulated processes, including mitogenesis and antiapoptosis (61, 67), differentiation (27), receptor trafficking (23), chemotaxis (31, 45), membrane ruffling (29, 64), and insulin-stimulated glucose transport (7,16,44) and Xenopus oocyte maturation (8, 9). In addition, PI-3 kinase appears to be required for the stimulation of p70S6k by platelet-derived growth factor and insulin and probably other growth factors (7,10,40). On the basis of these results, PI-3 kinase plays a central role in cellular signaling.Insulin regulates PI-3 kinase by tyrosine phosphorylation of IRS-1 and IRS-2, multipotential docking proteins which contain multiple potential tyrosine phosphorylation sites, including several YXXM motifs (41, 58). In addition to insulin and insulin-like growth factor 1 (IGF-1), ...

An oncogenic fusion product of the phosphatidylinositol 3-kinase p85β subunit and HUMORF8, a putative deubiquitinating enzyme

“…The mouse speci®c p85b transcript is depicted as signal C and can be observed in all four NIH3T3 cell derived transfectants ( Figure 2b, lanes 7 ± 10). The size of the mouse p85b transcript matches with the data from Pons et al (1995).…”

Janus Kinase-dependent Activation of Insulin Receptor Substrate 1 in Response to Interleukin-4, Oncostatin M, and the Interferons

“…Activation of PI 3Ј-kinase through association of the p85␣ subunit with IRS-1 is well established (22,(55)(56)(57)(58). Consistent with this ligand and JAK-dependent association of the p85␣ subunit of PI 3Ј-kinase with IRS-1 and PI 3Ј-kinase "activation" were observed here for IL-4, OSM, and less obviously IFN-␣ (Wellferon) (Fig.…”

Lower Phosphoinositide 3-Kinase (PI 3-kinase) Activity and Differential Expression Levels of Selective Catalytic and Regulatory PI 3-Kinase Subunit Isoforms in Prefrontal Cortex and Hippocampus of Suicide Subjects

“…In addition, we observed that changes in PI 3-kinase were present in all suicide subjects whether they were diagnosed with major depression or other psychiatric illnesses, which further suggests that these changes are related to suicide rather than some specific psychopathology. A number of studies have shown that all catalytic and regulatory isoforms of class IA PI 3-kinase, except p110d, are highly expressed in the central nervous system (Pons et al, 1995;Antonetti et al, 1996;Fruman et al, 1996;Inukai et al, 1997). When we examined the relative mRNA distribution of catalytic and regulatory subunit isoforms of PI 3-kinase, an interesting pattern of expression emerged in the human PFC and hippocampus.…”