title: Direct interaction of major histocompatibility complex class II-derived peptides with class Ia phosphoinositide 3-kinase results in dose-dependent stimulatory effects.
abstract: Peptides corresponding to residues 65-79 of human lymphocyte antigen class II sequence (DQA*03011) are cell-permeable and at high concentrations block activation of protein kinase B/Akt and p70-S6 kinase in T-cells, effects attributed to inhibition of phosphoinositide (PI) 3-kinase activity. To understand the molecular basis of this, we analyzed the effect this peptide had on activity of class I PI 3-kinases. Although there was no effect on the activity of class Ib PI 3-kinase or on the protein kinase activity of class I PI 3-kinases, there was a biphasic effect on lipid kinase activity of the class Ia enzymes. There was an inhibition of activity at higher peptide concentrations because of a formation of insoluble complexes between peptide and enzyme. Conversely, at lower peptide concentrations there was a profound activation of PI 3-kinase activity of class Ia PI 3-kinases. Studies of peptide variants revealed that all active peptides conform to heptad repeat motifs characteristic of coiled-coil helices. Surface plasmon resonance studies confirmed direct sequence-specific binding of active peptide to the p85alpha adapter subunit of class Ia PI 3-kinase. Active peptides also activated protein kinase B and extracellular signal-regulated kinase (ERK) in vivo in a wortmannin-sensitive manner while reducing recoverable cellular p85 levels. These results indicate that the human lymphocyte antigen class II-derived peptides regulate PI 3-kinase by direct interaction, probably via the coiled-coil domain. These peptides define a novel mechanism of regulating PI 3-kinase and will provide a useful tool for specifically dissecting the function of class Ia PI 3-kinase in cells and for probing structure-function relationships in the class Ia PI 3-kinase heterodimers.
authors.affiliation: Department of Biochemistry and Molecular Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Lazaros C
authors.initials: LC
authors.lastname: Foukas
authors.forename: George
authors.initials: G
authors.lastname: Panayotou
authors.forename: Peter R
authors.initials: PR
authors.lastname: Shepherd
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000494:pharmacology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000145:classification / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins; D017385:Sequence Homology; D020349:Surface Plasmon Resonance
chemical_list: D000949:Histocompatibility Antigens Class II; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins