Stimulation of p21ras upon T-cell activation

Downward, Julian; Graves, Jonathan D.; Warne, Patricia H.; Rayter, Sydonia; Cantrell, Doreen A.

doi:10.1038/346719a0

Cited by 865 publications

(580 citation statements)

References 20 publications

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“…Activation of protein kinase C downstream of PLCg could contribute to activation of MAP kinase through protein kinase C phosphorylation of Raf (SoÈ zeri et al, 1992). Alternatively, a protein kinase C pathway could contribute to the activation of Ras itself: while this has been reported previously in lymphocytes (Downward et al, 1990), in most cell types PKC activation is not su cient to cause Ras activation. However, in PC12 cells activation of PKC by phorbol esters has been shown to result in elevation of GTP levels bound to Ras (Nakafuku et al, 1992).…”

Section: Discussionmentioning

confidence: 80%

Nerve growth factor induced stimulation of Ras requires Trk interaction with Shc but does not involve phosphoinositide 3-OH kinase

et al. 1998

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The TrkA receptor protein tyrosine kinase is involved in signalling PC12 cell di erentiation and cessation of cell division in response to nerve growth factor (NGF). To assess the importance of adaptor proteins and Ras in NGF control of phosphoinositide 3-OH kinase (PI 3-kinase), speci®c receptor mutations in Trk have been employed. We show that phosphorylation of tyrosine 490, but not 785, of Trk is essential for activation of both Ras and PI 3-kinase in vivo, correlating with tyrosine phosphorylation of Shc and binding of Shc to the adaptor Grb2 and the Ras exchange factor Sos. A mutant receptor that lacks Y490 and Y785, but contains an introduced YxxM motif which binds the regulatory domain of PI 3-kinase, is unable to activate Ras despite causing increased PI 3-kinase activity. This indicates clearly that activation of PI 3-kinase by itself is not su cient to cause activation of Ras, arguing against a model in which PI 3-kinase acts upstream of Ras. The Shc site of Trk is thus crucial for the activation of Ras and PI 3-kinase.

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Section: Discussionmentioning

confidence: 80%

Nerve growth factor induced stimulation of Ras requires Trk interaction with Shc but does not involve phosphoinositide 3-OH kinase

et al. 1998

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“…This e ect could be a result of either increased guanine nucleotide exchange or a decrease in RasGAP activity, an e ect previously documented in T-cells (Downward et al, 1990). Several reports have detailed the use of the RasN17 dominant negative mutant to demonstrate the Ras-independence of phorbol ester-dependent Raf regulation (Arai and Escobedo, 1996;Zou et al, 1996).…”

Section: Discussionmentioning

confidence: 87%

Oncogenes, growth factors and phorbol esters regulate Raf-1 through common mechanisms

et al. 1998

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We have uniformly examined the regulatory steps required by oncogenic Ras, Src, EGF and phorbol 12-myristate 13-acetate (PMA) to activate Raf-1. Speci®-cally, we determined the role of Ras binding and the phosphorylation of serines 338/339, tyrosines 340/341 and the activation loop (491 ± 508) in response to these stimuli in COS-7 cells. An intact Ras binding domain was found to be essential for Raf-1 kinase activation by each stimulus, including PMA. Brief treatment of COS-7 cells with PMA was found to rapidly promote accumulation of the active, GTP-bound form of Ras. Furthermore, loss of the serine 338/339 and tyrosine 340/341 phosphorylation sites also blocked Raf-1 activation by all stimuli tested. Loss of the serine 497 and serine 499 PKCa phosphorylation sites failed to signi®cantly reduce Raf-1 activation by any stimulus including PMA. Alanine substitution of all other potential phosphorylation sites within the Raf-1 activation loop had little or no e ect on kinase regulation by Ras[V12] or vSrc although some mutants were less responsive to PMA. These results suggest that in mammalian cells, Raf-1 can be regulated by a variety of di erent stimuli through a common mechanism involving association with Ras-GTP and multiple phosphorylations of the amino-terminal region of the catalytic domain. Phosphorylation of the activation loop does not appear to be a signi®cant mechanism of Raf-1 kinase regulation in COS-7 cells.

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“…This observation is not unique to C3H10T1/2 ®broblasts since Downward et al (1990) observed that T-lymphocytes contained little, if any, c-Ha-ras protein. C3H10T1/2 cells are readily transformed by the ectopic expression of either activated (G12V)Ha-ras (V12H10 cells) or (Q61K)Nras (K61N10 cells), as characterized by the acquisition of a refractile cell morphology and the ability to form foci in soft agar (data not shown).…”

Section: Expression Of Activated Ras In C3h10t1/2 ®Broblastsmentioning

confidence: 91%

Ha-ras and N-ras regulate MAPK activity by distinct mechanisms in vivo

Hamilton

Wolfman

1998

Oncogene

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The Ras GTPases function as molecular switches, regulating a multiplicity of biological events. However the contribution, if any, of a speci®c c-Ras isoform (Ha-, N-, or Ki-ras A or B) in the regulation of a given biological or biochemical process, is unknown. Murine C3H10T1/2 ®broblasts transformed with activated (G12V)Ha-ras or (Q61K)N-ras proliferate in serum-free media and have constitutive MAPK activity. The growth factor antagonist, suramin, inhibited the serum-independent proliferation of Ha-ras transformed ®broblasts, but not the serum-independent proliferation of N-ras transformed cells. The inhibition of cell proliferation was concomitant with the abrogation of the constitutive MAPK activity in the Ha-ras transformed ®broblasts. Analysis of the Ras-signalling complexes in immunoprecipitates from Ha-ras transformed cells revealed that Raf-1 co-immunoprecipitated with endogenous c-N-ras but not (G12V)Ha-ras. Pretreatment with suramin resulted in the loss of Raf-1 from c-N-ras immunoprecipitates. A c-N-ras antisense oligonucleotide, which down-regulated c-N-ras protein levels, abrogated the constitutive MAPK activity and serum-independent proliferation of (G12V)Ha-ras transformed cells. The data suggest that Raf-1 has a higher a nity for N-ras then Ha-ras in vivo, and c-N-ras function is required for the serum-independent proliferation of Ha-ras transformed cells.

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Stimulation of p21ras upon T-cell activation

Cited by 865 publications

References 20 publications

Nerve growth factor induced stimulation of Ras requires Trk interaction with Shc but does not involve phosphoinositide 3-OH kinase

Nerve growth factor induced stimulation of Ras requires Trk interaction with Shc but does not involve phosphoinositide 3-OH kinase

Oncogenes, growth factors and phorbol esters regulate Raf-1 through common mechanisms

Ha-ras and N-ras regulate MAPK activity by distinct mechanisms in vivo

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