Dok‐3 sequesters Grb2 and inhibits the Ras‐Erk pathway downstream of protein‐tyrosine kinases

• Published in: Genes to cells : devoted to molecular & cellular mechanisms 2006-02, Vol.11 (2), p.143-151
• Main Authors: Honma, Miyuki, Higuchi, Osamu, Shirakata, Masaki, Yasuda, Tomoharu, Shibuya, Hiroshi, Iemura, Shun‐ichiro, Natsume, Tohru, Yamanashi, Yuji
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing - metabolism; Amino Acid Sequence; Animals; Binding Sites; Cells, Cultured; Extracellular Signal-Regulated MAP Kinases - antagonists & inhibitors; Extracellular Signal-Regulated MAP Kinases - metabolism; GRB2 Adaptor Protein - chemistry; GRB2 Adaptor Protein - metabolism; Humans; Mice; Molecular Sequence Data; Oncogene Protein pp60(v-src) - metabolism; Protein Binding; Protein-Tyrosine Kinases - metabolism; Proto-Oncogene Proteins p21(ras) - antagonists & inhibitors; Proto-Oncogene Proteins p21(ras) - metabolism; Shc Signaling Adaptor Proteins; Signal Transduction; Son of Sevenless Proteins - metabolism; Src Homology 2 Domain-Containing, Transforming Protein 1; Tyrosine - metabolism
• ISSN: 1356-9597; 1365-2443
• DOI: 10.1111/j.1365-2443.2006.00926.x

Adaptor proteins are essential in coordinating recruitment and, in a few cases, restraint of various effectors during cellular signaling. Dok‐1, Dok‐2 and Dok‐3 comprise a closely related family of adaptor, which negatively regulates mitogen‐activated protein kinase Erk downstream of protein‐tyrosine kinases (PTKs). Recruitment of p120 rasGAP, a potent inhibitor of Ras, by Dok‐1 and Dok‐2 appears critical in the negative regulation of the Ras‐Erk pathway. However, as Dok‐3 does not bind rasGAP, it has been unclear how Dok‐3 inhibits Erk downstream of PTKs. Here, we identified Grb2 as a Dok‐3‐binding protein upon its tyrosine phosphorylation. This interaction required the intact binding motifs of the Grb2 SH2 domain, and a mutant (Dok‐3‐FF) having a Tyr/Phe substitution at these motifs failed to inhibit Ras and Erk activation downstream of a cytoplasmic PTK Src. Because Grb2 forms a stable complex with Sos, a crucial activator of Ras, these data suggest that Dok‐3 restrains Grb2 and inhibits the ability of the Grb2‐Sos complex to activate Ras. Indeed, forced expression of Dok‐3, but not Dok‐3‐FF, inhibited the recruitment of the Grb2‐Sos complex to Shc downstream of Src, which is an essential event for activation of the Ras‐Erk pathway. These findings indicate that Dok‐3 sequesters Grb2 from Shc and inhibits the Ras‐Erk pathway downstream of PTKs.