scholarly journals Compartment-specific regulation of phosphoinositide 3-kinase by platelet-derived growth factor and insulin in 3T3-L1 adipocytes

1996 ◽  
Vol 318 (1) ◽  
pp. 55-60 ◽  
Author(s):  
Barbara T. NAVÉ ◽  
RichardHAIGH J ◽  
Amanda C HAYWARD ◽  
Kenneth SIDDLE ◽  
Peter R. SHEPHERD
Keyword(s):  
Growth Factors ◽  
Growth Factor ◽  
Tyrosine Phosphorylation ◽  
Kinase Activity ◽  
Specific Activity ◽  
Subcellular Fractionation ◽  
Platelet Derived Growth Factor ◽  
Specific Regulation ◽  
Phosphoinositide 3 Kinase ◽  
Stimulation Of

To understand how the stimulation of phosphoinositide 3-kinase (PI 3-kinase) by different growth factors can activate different subsets of downstream responses, growth-factor regulation of PI 3-kinase activity at different intracellular locations was investigated in 3T3-L1 adipocytes. Insulin caused a large stimulation of glucose transport and stimulated recruitment of transferrin receptors to the plasma membrane (PM) in these cells, whereas platelet-derived growth factor (PDGF)-bb was virtually without effect on these responses. Subcellular fractionation studies after stimulation with PDGF-bb or insulin revealed a differential effect of these growth factors on subcellular localization of PI 3-kinase activity. PDGF was more effective than insulin in stimulating PI 3-kinase activity and recruiting the p85α PI 3-kinase adaptor subunit in the fraction containing the PM. However, in the microsomal fraction insulin significantly increased PI 3-kinase activity and p85α levels, whereas PDGF was almost without effect. In the microsomal membrane fraction the insulin-stimulated recruitment of p85α closely matched the increase PI 3-kinase activity, indicating that insulin stimulation of PI 3-kinase in this fraction is largely due to recruitment of PI 3-kinase enzyme rather than alterations in specific activity. Insulin-stimulated recruitment of p85α to the microsomal membranes was not inhibited by wortmannin, indicating that PI 3-kinase activity was not required for this process. A further level of compartment-specific regulation of PI 3-kinase in response to PDGF was revealed by the finding that tyrosine phosphorylation of the p85α adaptor was restricted to the PM-containing fraction. Insulin had no effect on p85 tyrosine phosphorylation in either fraction. In summary, these results suggest a basis by which insulin and PDGF could both use PI 3-kinase signalling cascades but achieve different signalling outcomes.

scholarly journals The Q43L mutant of neuregulin 2β is a pan-ErbB receptor antagonist

2012 ◽  
Vol 443 (1) ◽  
pp. 133-144 ◽  
Author(s):  
Kristy J. Wilson ◽  
Christopher P. Mill ◽  
Richard M. Gallo ◽  
Elizabeth M. Cameron ◽  
Henry VanBrocklin ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Tyrosine Phosphorylation ◽  
Kinase Activity ◽  
Growth Factor Receptor ◽  
Erbb Receptor ◽  
Pharmacological Agents ◽  
Akt Phosphorylation ◽  
Agonist Stimulation ◽  
Phosphoinositide 3 Kinase ◽  
Stimulation Of

The ErbB4 receptor tyrosine kinase possesses both tumour suppressor and oncogenic activities. Thus pharmacological agents are needed to help elucidate ErbB4 functions. However, limitations of existing ErbB4 agonists and antagonists have led us to seek novel ErbB4 antagonists. The Q43L mutant of the ErbB4 agonist NRG2β (neuregulin 2β) stimulates ErbB4 tyrosine phosphorylation, yet fails to stimulate ErbB4 coupling to cell proliferation. Thus in the present paper we hypothesize that NRG2β/Q43L may be an ErbB4 antagonist. NRG2β/Q43L competitively antagonizes agonist stimulation of ErbB4 coupling to cell proliferation. NRG2β/Q43L stimulates less ErbB4 tyrosine phosphorylation than does NRG2β. In addition, NRG2β stimulation of cell proliferation requires PI3K (phosphoinositide 3-kinase) activity and NRG2β stimulates greater Akt phosphorylation than does NRG2β/Q43L. Moreover, EGFR [EGF (epidermal growth factor) receptor] kinase activity (but not that of ErbB4) is critical for coupling ErbB4 to proliferation. Experiments utilizing ErbB4 splicing isoforms and mutants suggest that NRG2β and NRG2β/Q43L may differentially stimulate ErbB4 coupling to the transcriptional co-regulator YAP (Yes-associated protein). Finally, NRG2β/Q43L competitively antagonizes agonist stimulation of EGFR and ErbB2/ErbB3, indicating that NRG2β/Q43L is a pan-ErbB antagonist. Thus we postulate that NRG2β/Q43L and other antagonistic ligands stimulate ErbB tyrosine phosphorylation on a set of residues distinct from that stimulated by agonists, thus suggesting a novel mechanism of ErbB receptor regulation. Moreover, NRG2β/Q43L and related ligand-based antagonists establish a paradigm for the discovery of anti-ErbB therapeutics.

scholarly journals A complex interplay between Akt, TSC2 and the two mTOR complexes

2009 ◽  
Vol 37 (1) ◽  
pp. 217-222 ◽  
Author(s):  
Jingxiang Huang ◽  
Brendan D. Manning
Keyword(s):  
Growth Factor ◽  
Kinase Activity ◽  
Mammalian Target Of Rapamycin ◽  
Inhibitory Effects ◽  
Complex Interplay ◽  
Additional Level ◽  
Phosphoinositide 3 Kinase ◽  
The Relationship ◽  
Stimulation Of ◽  
In Cells

Akt/PKB (protein kinase B) both regulates and is regulated by the TSC (tuberous sclerosis complex) 1–TSC2 complex. Downstream of PI3K (phosphoinositide 3-kinase), Akt phosphorylates TSC2 directly on multiple sites. Although the molecular mechanism is not well understood, these phosphorylation events relieve the inhibitory effects of the TSC1–TSC2 complex on Rheb and mTORC1 [mTOR (mammalian target of rapamycin) complex] 1, thereby activating mTORC1 in response to growth factors. Through negative-feedback mechanisms, mTORC1 activity inhibits growth factor stimulation of PI3K. This is particularly evident in cells and tumours lacking the TSC1–TSC2 complex, where Akt signalling is severely attenuated due, at least in part, to constitutive activation of mTORC1. An additional level of complexity in the relationship between Akt and the TSC1–TSC2 complex has recently been uncovered. The growth-factor-stimulated kinase activity of mTORC2 [also known as the mTOR–rictor (rapamycin-insensitive companion of mTOR) complex], which normally enhances Akt signalling by phosphorylating its hydrophobic motif (Ser473), was found to be defective in cells lacking the TSC1–TSC2 complex. This effect on mTORC2 can be separated from the inhibitory effects of the TSC1–TSC2 complex on Rheb and mTORC1. The present review discusses our current understanding of the increasingly complex functional interactions between Akt, the TSC1–TSC2 complex and mTOR, which are fundamentally important players in a large variety of human diseases.

Characterization of pp85, a target of oncogenes and growth factor receptors

1990 ◽  
Vol 10 (6) ◽  
pp. 2909-2915
Author(s):  
B Cohen ◽  
Y X Liu ◽  
B Druker ◽  
T M Roberts ◽  
B S Schaffhausen
Keyword(s):  
Growth Factor ◽  
Kinase Activity ◽  
Platelet Derived Growth Factor ◽  
Individual Species ◽  
3T3 Cells ◽  
Phosphatidylinositol Kinase ◽  
Common Substrate ◽  
Phosphorylation Analysis ◽  
Stimulation Of

An 85,000-molecular-weight polypeptide (85K polypeptide) has previously been identified as a common substrate for tyrosine phosphorylation upon polyomavirus middle T transformation or upon platelet-derived growth factor stimulation of 3T3 cells. In each case, pp85 has an associated phosphatidylinositol kinase activity. The tissue distribution of pp85 was determined by middle T blotting experiments; the highest levels were found in brain, lung, and spleen tissues. High-resolution examination of 85K by isoelectric focusing demonstrated that there are at least 10 different forms. These were resolved into two families, 85K and 86K; the ratio of the two families changed in different cells. Similar forms were found for pp85 associated with pp60v-src. Individual species within each family differed by phosphorylation. Analysis of pp85 and pp86 by immunoprecipitation with anti-phosphotyrosine antibody showed increasing phosphorylation in response to middle T or pp60v-src transformation. The association of middle T with pp85 and pp60c-src was examined in pulse-chase experiments. Association of middle T with pp60c-src was slow and was accompanied by progressive modification of middle T. pp85 formed a dissociable complex with middle T within 2.5 min.

Platelet-derived growth factor stimulation of GTPase-activating protein tyrosine phosphorylation in control and c-H-ras-expressing NIH 3T3 cells correlates with p21ras activation

1992 ◽  
Vol 12 (9) ◽  
pp. 3903-3909
Author(s):  
C J Molloy ◽  
T P Fleming ◽  
D P Bottaro ◽  
A Cuadrado ◽  
S A Aaronson
Keyword(s):  
Growth Factor ◽  
Tyrosine Phosphorylation ◽  
Platelet Derived Growth Factor ◽  
Gtpase Activating Protein ◽  
3T3 Cells ◽  
Pdgf Stimulation ◽  
Nih 3T3 ◽  
Stimulation Of ◽  
Sustained Increase ◽  
Nih 3T3 Cells

Platelet-derived growth factor (PDGF) stimulation of NIH 3T3 cells leads to the rapid tyrosine phosphorylation of the GTPase-activating protein (GAP) and an associated 64- to 62-kDa tyrosine-phosphorylated protein (p64/62). To assess the functions of these proteins, we evaluated their phosphorylation state in normal NIH 3T3 cells as well as in cells transformed by oncogenically activated v-H-ras or overexpression of c-H-ras genes. No significant GAP tyrosine phosphorylation was observed in unstimulated cultures, while PDGF-BB induced rapid tyrosine phosphorylation of GAP in all cell lines analyzed. In NIH 3T3 cells, we found that PDGF stimulation led to the recovery of between 37 and 52% of GAP molecules by immunoprecipitation with monoclonal antiphosphotyrosine antibodies. Furthermore, PDGF exposure led to a rapid and sustained increase in the levels of p21ras bound to GTP, with kinetics similar to those observed for GAP tyrosine phosphorylation. The PDGF-induced increases in GTP-bound p21ras in NIH 3T3 cells were comparable to the steady-state level observed in serum-starved c-H-ras-overexpressing transformants, conditions in which these cells maintained high rates of DNA synthesis. These results imply that the level of p21ras activation following PDGF stimulation of NIH 3T3 cells is sufficient to support mitogenic stimulation. Addition of PDGF to c-H-ras-overexpressing cells also resulted in a rapid and sustained increase in GTP-bound p21ras. In these cells GAP, but not p64/62, showed increased tyrosine phosphorylation, with kinetics similar to those observed for increased GTP-bound p21ras. All of these findings support a role for GAP tyrosine phosphorylation in p21ras activation and mitogenic signaling.

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