The p85 regulatory subunit controls sequential activation of phosphoinositide 3-kinase by Tyr kinases and Ras.
Class IA phosphoinositide 3-kinase (PI3K) is a heterodimer composed of a p85 regulatory and a p110 catalytic subunit that regulates a variety of cell responses, including cell division and survival. PI3K is activated following Tyr kinase stimulation and by Ras. We found that the C-terminal region of p85, including the C-Src homology 2 (C-SH2) domain and part of the inter-SH2 region, protects the p110 catalytic subunit from Ras-induced activation. Although the p110 activity associated with a C-terminal p85 deletion mutant increased significantly in the presence of an active form of Ras, purified wild type p85-p110 was only slightly stimulated by active Ras. Nonetheless, incubation of purified p85-p110 with Tyr-phosphorylated peptides, which mimic the activated platelet-derived growth factor receptor, restored Ras-induced p85-p110 activation. In conclusion, p85 inhibits p110 activation by Ras; this blockage is released by Tyr kinase stimulation, showing that the classical mechanism of class IA PI3K stimulation mediated by Tyr kinases also regulates Ras-induced PI3K activation.
Department of Immunology and Oncology, Centro Nacional de Biotecnologia, Universidad Autónoma de Madrid, Cantoblanco, Spain.
Concepcion
C
Jimenez
Carmen
C
Hernandez
Belen
B
Pimentel
Ana C
AC
Carrera
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000502:physiology*; D010766:Phosphorylation; D021122:Protein Subunits; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism; D018631:ras Proteins / Q000737:chemistry / Q000502:physiology*; D018909:src Homology Domains
D047908:Intracellular Signaling Peptides and Proteins; D021122:Protein Subunits; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C509248:Ptpn6 protein, mouse; D018631:ras Proteins