Grb2 Interacts with SGEF and Antagonizes the Ability of SGEF to Enhance EGF-Induced ERK1/2 Activation

Mol Cell Biochem (2014) 389:239–247 DOI 10.1007/s11010-013-1945-7

Grb2 interacts with SGEF and antagonizes the ability of SGEF to enhance EGF-induced ERK1/2 activation

Hongtao Wang • Shanhu Li • Hailiang Li • Peng Wang • Fang Huang • Yali Zhao • Lan Yu • Guolan Luo • Xiaoqing Zhang • Jian Wang • Jianguang Zhou

Received: 22 September 2013 / Accepted: 18 December 2013 / Published online: 8 January 2014 Ó Springer Science+Business Media New York 2014

Abstract Previously, we demonstrated that SGEF enhan- Introduction ces EGFR stability; however, SGEF-mediated downstream signaling of EGFR is not well understood. Here, we show Epidermal growth factor receptor (EGFR), the best char- that SGEF enhances EGF-induced ERK1/2 activation inde- acterized member of the ErbB receptor tyrosine kinase pendent of its guanine nucleotide exchange (GEF) activity. (RTK) family, plays crucial roles in numerous cellular We further show that SGEF interacts with Grb2, a critical functions including cell proliferation, survival, differenti- downstream transducer of EGFR. Surprisingly, we found ation, and migration [1]. Aberrant EGFR signaling has that interaction of Grb2 to SGEF antagonizes the ability of been associated with human cancers in which high SGEF to enhance EGF-induced ERK1/2 activation. Taken expression and/or abnormal activation of EGFR are fre- together, this study reports a novel function of SGEF that quently observed [2]. After binding to EGF, EGFR excludes GEF and also provides important insights into the undergoes dimerization which promotes auto-phosphory- complex role of Grb2 in EGFR signal transduction. lation of multiple tyrosine residues in the cytoplasmic tail of the receptor. These phosphorylated tyrosines serve as Keywords SGEF Grb2 EGF EGFR ERK1/2 docking sites for specific downstream effectors, containing PTB or SH2 domains [3], such as PI3K and Src enzymes or Abbreviations Grb2 and Nck adaptor proteins which link EGFR to SGEF SH3-containing guanine nucleotide exchange downstream signaling pathways [4]. factor The adaptor protein Grb2 plays a critical role in EGF- EGFR Epidermal growth factor receptor activated Ras–ERK1/2 signaling pathway [5], which is one EGF Epidermal growth factor of the most important signaling cascades downstream of GEF Guanine nucleotide exchange factor EGFR. Grb2 contains a single SH2 domain flanked by two PTB Phosphotyrosine binding SH3 domains. Through its SH2 domain, which is a conserved SH2 Src homology 2 sequence of 100 amino acids, Grb2 recognizes and binds to SH3 Src homology 3 the phosphorylated residues Tyr-1068 and Tyr-1086 in the Pro Proline-rich domain cytoplasmic domain of EGFR [6]. The SH3 domain, which is a conserved sequence that binds to proline-rich sequences within interacting proteins, constitutively associates with SOS, a guanine nucleotide exchange factor (GEF), which H. Wang S. Li H. Li P. Wang F. Huang Y. Zhao L. Yu catalyzes GDP–GTP exchange on Ras [7, 8]. In this manner, G. Luo X. Zhang J. Wang (&) J. Zhou (&) Grb2 is recruited near the cell membrane by binding to Laboratory of Medical Molecular Biology, Beijing Institute of phosphorylated EGFR, which also brings Sos to the mem- Biotechnology, 27 Taiping Road, Haidian, Beijing 100850, People’s Republic of China brane-bound Ras, resulting in the activation of Ras–ERK1/2 e-mail: [email protected] cascade, after EGFR activation [9]. J. Zhou Recently, we reported that SGEF, a RhoG-specific GEF, e-mail: [email protected] enhanced EGFR stability by delaying its lysosomal sorting 123 240 Mol Cell Biochem (2014) 389:239–247 and degradation [10]. We also demonstrated that SGEF pCDNA-3.1–SGEF and subcloned into pCMV-2B vector at was overexpressed during prostate cancer and therefore BamHI and EcoRI sites. The primers are as follows: contributed to cancer development and progression [11], For SGEF: most likely by enhancing EGFR stability. However, SGEF- 50-CGGGATCCGACGGCGAGAGCGAGGTGG-30 mediated downstream signaling of EGFR has not been (forward) elucidated. The various roles of SGEF, reported thus far, 50-GGGAATTCCTACACGTTGGTCTCCAGTCC-30 require the GEF activity of SGEF. These include various (reverse) physiologic and pathologic processes such as macropino- For SGEF-N terminus: cytosis, leukocyte transendothelial migration, and uptake 50-CGGGATCCGACGGCGAGAGCGAGGTGG-30 of Salmonella by epithelial cells [12–14]. In addition, (forward) recent studies have demonstrated that SGEF contributes to 50-GGGAATTCTTGGCTCCATGTGGATCTC-30 the invasive capacity of HPV-16 and HPV-18 transformed (reverse) cell [15]. For SGEFDSH3: In this study, we determined the role of SGEF in EGFR- 50-CGGGATCCGACGGCGAGAGCGAGGTGG-30 mediated signal transduction and showed that SGEF sig- (forward) nificantly enhances EGF-induced ERK1/2 activation inde- 50-GGGAATTCTCAGTGAGGTTCGGTCTG-30 pendent of its GEF activity. In addition, we demonstrated (reverse) that SGEF interacts with Grb2, a critical downstream For SGEFDDH: transducer of EGFR. By interacting with SGEF, Grb2 50-CGGGATCCGACGGCGAGAGCGAGGTGG-30 antagonizes the ability of SGEF to enhance EGF-induced (forward1) ERK1/2 activation. Taken together, our work not only 50-GGGAATTCCTACACGTTGGTCTCCAGTCC-30 identifies a new role for SGEF in EGFR-mediated ERK1/2 (reverse1) activation but also provides novel insights into the com- 50-GCCAGGAGGAAAGAAAGAGAAGCAAGTTGG plexity of Grb2 in EGFR-mediated signal transduction. TTCGACTATGC-30 (forward2) 50-GCATAGTCGAAC- CAACTTGCTTCTCTTTCTTTCCTCCTGGC-30 Materials and methods (reverse2) SGEFDPro: Antibodies and reagents 50-CGGGATCCGACGGCGAGAGCGAGGTGG-30 (forward1) Antibodies for Flag and GFP were obtained from Sigma 50-GGGAATTCCTACACGTTGGTCTCCAGTCC-30 (St. Louis, MO, USA). Anti-EGFR, anti-RhoG, anti-Grb2, (reverse1) and anti-tubulin antibodies were purchased from Santa 50-GAGTACAGGGCTGCCTCTACTG- Cruz (CA, USA). Anti-ERK1/2 and phospho-ERK1/2 CAAATGGCCTTGCC-30 (forward2) (Thr202/Tyr204) antibodies were obtained from Cell Sig- 50-GGCAAGGCCATTTGCAGTAGAGGCAGCCCTG- naling Technology (Beverly, MA, USA). Recombinant TACTC-30 (reverse2) EGF was obtained from ProSpec (Rehovot, Israel). SGEF–P1M: PD98058 was purchased from Cell Signaling Technology 50-CGGGATCCGACGGCGAGAGCGAGGTGG-30 (Beverly, MA, USA). (forward1) 50-GGGAATTCCTACACGTTGGTCTCCAGTCC-30 Plasmid constructs (reverse1) 50-GGTGACCTTGCCTGCGGCGGCGGCGGCGGC All vectors including pcDNA3–EGFR, pGEX-4T–Grb2, GGTTCTGCGCCCCCCGC-30 (forward2) pEGFP–Grb2, pEGFP–Grb2–W36, pEGFP–Grb2–R86K, 50-GCGGGGGGCGCAGAACCGCCGCCGCCGCCG and pEGFP–Grb2–W193A were gifts from Dr. Wannian CCGCAGGCAAGGTCACC-30 (reverse2) Yang (Weis Center for Research, Geisinger Clinic, Dan- SGEF–P2M: ville, PA, USA). Full-length, truncated, and point mutations 50-CGGGATCCGACGGCGAGAGCGAGGTGG-30 of SGEF were constructed by inserting PCR-amplified (forward1) fragments into the corresponding vectors. 50-GGGAATTCCTACACGTTGGTCTCCAGTCC-30 SGEF, SGEF-N terminus (1–420 amino acid), SGEF (reverse1) DSH3, SGEFDDH, SGEFDPro, SGEF–P1M, and SGEF– 50-CTGGGTTGACTGCCAGCGCGGTGGCTTCGCC- P2M were PCR or overlapping PCR amplified from CACTGCAAATGGCC-30 (forward2)

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50-GGCCATTTGCAGTGGGCGAAGCCACCGCGCT To suppress the expression of RhoG, HEK293T cells GGCAGTCAACCCAG-30 (reverse2) were infected with lentivirus carrying RhoG shRNA (GeneChem Co., Shanghai, China). 12 h later, virus-con- SGEF-(1–420 amino acid), SGEF-(1–200 amino acid), taining medium was replaced with fresh medium, and SGEF-(13–216 amino acid), SGEF-(216–420 amino acid), infected cells were then selected on 2 lg/ml puromycin SGEF–DH, SGEF–PH, and SGEF–SH3 were PCR ampli- after an additional 48 h. fied from pCDNA-3.1–SGEF and subcloned into pGEX– KG vector at BamHI and HindIII sites. The primers are as GST pull-down assay follows: For SGEF-(1–420 amino acid): GST or GST-tagged proteins expressed in bacteria were 50-CGGGATCCGACGGCGAGAGCGAGGTGG-30 immobilized on glutathione-Sepharose 4B beads (Amer- (forward) sham) and then incubated with cell lysates with gentle 50-CCAAGCTTTTGGCTCCATGTGGATCTC-30 rotation at 4 °C for 3 h. After washing three times with cell (reverse) lysis buffer, the beads were resolved on 10 % SDS-PAGE For SGEF-(1–200 amino acid): and subjected to Western blot analysis. 50-CGGGATCCGACGGCGAGAGCGAGGTGG-30 (forward) Western blotting and immunoprecipitation 50-CCAAGCTTCCGTTCGGGGTCCTTTGC-30 (reverse) Western blotting was performed as described previously For SGEF-(13–216 amino acid): [11]. 50-CGGGATCCAGCATAACCCCTTTGTG-30 For immunoprecipitation, precleared cell lysates were (forward) incubated with primary antibody at 4 °C for 2 h with gentle 50-CCAAGCTTGGGGAGTTTTTGTTCCG-30 (reverse) rotation followed by further incubation with protein A/G For SGEF-(216–420 amino acid): plus agarose beads for another 2 h at 4 °C. After washing 50-CGGGATCCCCCCTCCAAAGGCTGCC-30 three times with cell lysis buffer, the precipitated beads (forward) were eluted in SDS-PAGE loading buffer, resolved on 50-CCAAGCTTTTGGCTCCATGTGGATCTC-30 10 % SDS-PAGE, and subsequently used for western (reverse) blotting. For SGEF–DH: 50-CGGGATCCGCGGTGAAAAGAAAGGG-30 (forward) Results 50-CCAAGCTTAGTCCTTTCCATCTTCCG-30 (reverse) SGEF enhances EGF-induced ERK1/2 activation For SGEF–PH: independent of its GEF activity 50-CGGGATCCACAGCCTATGTTGAAGAC-30 (forward) Our previous studies demonstrated that SGEF attenuates 50-CCAAGCTTCTTCCCTCTGCTGTG-30 (reverse) EGFR degradation and enhances EGFR stability [10]. For SGEF–SH3: Given that the reduction in EGFR degradation is associated 50-CGGGATCCCCTGCAGACCGAACCTC-30 with abnormal EGFR signal transduction, we investigated (forward) whether SGEF regulates EGF-induced ERK1/2 activation, 50-CCAAGCTTCTACACGTTGGTCTCCAGTCC-30 a major effector downstream of EGFR. As shown in (reverse) Fig. 1a, b, SGEF overexpression significantly enhanced EGF-induced phosphorylation of ERK1/2 in both HEK293T and ZR-75-1 cells. To confirm the effect of Cells and cell culture SGEF on EGF-induced ERK1/2 activation, we silenced SGEF expression in HEK293T and ZR-75-1 cells and HEK293T cells were cultured in Dulbecco’s modified Eagle’s detected ERK1/2 phosphorylation after treating with EGF. medium (DMEM; Gibco) containing 8 % fetal bovine serum As shown in Fig. 1c, EGF-induced phosphorylation of

(FBS; Hyclone) in a 37 °C/5 % CO2 incubator. Transfection ERK1/2 is suppressed in SGEF-depleted HEK293T and of plasmids was performed using Lipofectamine 2000 ZR-75-1 cells. (Invitrogen) according to the manufacturers’ instructions. The best known role of SGEF is its function as GEF for Before EGF treatment, cells were serum starved for 12–18 h RhoG signaling. To evaluate whether RhoG function is and then stimulated with EGF for the indicated times. required for SGEF-mediated EGFR/ERK1/2 signaling, we 123 242 Mol Cell Biochem (2014) 389:239–247

Fig. 1 SGEF enhances EGF-induced ERK1/2 activation independent overnight and then treated with 10 ng/ml EGF for indicated times, of its GEF activity. a, b HEK293T cells or ZR-75-1 cells were followed by immunoblot analysis. d Control and RhoG-depleted transiently co-transfected with EGFR and control vector or Flag– HEK293T cells were transiently co-transfected with EGFR and SGEF and 24 h post-transfection cells were serum starved for 12 h control vector or Flag–SGEF and 24 h post-transfection cells were and stimulated with EGF (100 ng/ml) for indicated times followed by serum starved for 12 h and stimulated with EGF (100 ng/ml) for immunoblotting of cell lysates with indicated antibodies. c Control indicated times by immunoblot analysis and SGEF-depleted HEK293T and ZR-75-1 cells were starved suppressed RhoG expression in HEK293T cells and examined the effects of SGEF overexpression on EGF- induced ERK1/2 phosphorylation. As shown in Fig. 1b, downregulation of RhoG had little effect on SGEF-mediated ERK1/2 activation, indicating that SGEF-mediated EGFR/ERK1/2 signaling is independent of its GEF activity.

Grb2 interacts with SGEF

Grb2 plays a critical role in EGFR-mediated ERK1/2 activation and may be involved in SGEF-mediated ERK1/2 activation. To determine whether Grb2 interacts with Fig. 2 Grb2 interacts with SGEF. a Lysates of HEK293T cells SGEF, GST pull-down assays were ﬁrst performed with transfected with Flag–SGEF were incubated with GST or GST–Grb2, GST–Grb2. As expected, we observed an interaction precipitated with glutathione-sepharose 4B beads, and the bound proteins were detected with anti-Flag antibody. b, c HEK293T cells between SGEF and GST–Grb2, but not with GST alone were co-transfected with Flag–SGEF and GFP–Grb2 or control that was used as the control (Fig. 2a). To validate this vector. 24 h after transfection, cell lysates were immunoprecipitated interaction, immunoprecipitation assays were performed with anti-GFP or anti-Flag antibody and detected on immunoblots where HEK293 cells were co-transfected with pCMV2B– using anti-Flag and anti-GFP antibodies. d Lysates of HEK293T cells were immunoprecipitated with normal IgG or anti-Grb2 antibodies SGEF and pEGFP–Grb2 or pEGFP, which was used as and detected using anti-Grb2 and anti-SGEF antibodies control. Cell lysates were then immunoprecipitated with anti-GFP antibody and subjected to Western blot analysis co-expressing GFP–Grb2 and Flag–SGEF, but not in cells to detect bound SGEF using anti-Flag antibody. Using anti- with GFP and Flag–SGEF (Fig. 2b), indicating that SGEF GFP for immunoprecipitation, SGEF was detected in cells interacts with Grb2. A reciprocal experiment was also

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Fig. 3 SH3 domain of Grb2 and Pro domain of SGEF mediate the Flag antibody. d Immunoprecipitation assays were performed with interaction between Grb2 and SGEF. a GST pull-down assays were anti-Flag antibody using cell extracts from HEK293T cells transfec- performed using cell extracts from HEK293T cells transfected with ted with Flag–SGEF and GFP–Grb2 or its mutants, and the SGEF or the deletion mutants shown in the schematic diagram, and immunoprecipitates were detected with anti-GFP antibody and anti- the bound proteins were detected with anti-Flag antibody. b Lysates Flag antibody. W36K, R86K, or W193A, respectively, represents the of HEK293T cells transfected with GFP–Grb2 were incubated with N-terminal SH3 domain-defective, the SH2 domain-defective, or the GST or GST fusion proteins shown in the schematic diagram, and the C-terminal SH3 domain-defective mutants. The mutant positions are bound proteins were detected with anti-GFP antibody. c Immunopre- shown with the star markers in the schematic diagram. e GST pull- cipitation assays were performed with anti-Flag antibody using cell down assays were performed using lysates of HEK293T cells extracts from HEK293T cells transfected with GFP–Grb2 and Flag– transfected with GFP–Grb2 or its mutants, and the bound proteins SGEF or its mutants shown in the schematic diagram, and the were detected with anti-GFP antibody immunoprecipitates were detected with anti-GFP antibody and anti-

123 244 Mol Cell Biochem (2014) 389:239–247 performed, where Grb2 was co-immunoprecipitated with These data indicate that the SH3 domains of Grb2 and SGEF proteins (Fig. 2c). These data prove that exogenous the Pro domain of SGEF mediate the interaction between Grb2 interacts with exogenous SGEF in vitro. We next Grb2 and SGEF. asked whether endogenous Grb2 could interact with endogenous SGEF. For this, HEK293 cells were collected, Impaired interaction between Grb2 and SGEF does and cell lysates were immunoprecipitated with anti-Grb2 not eliminate SGEF-mediated ERK1/2 activation antibody and subjected to immunoblot analysis with anti- SGEF antibody. Indeed, SGEF was detected with anti- The above experiments show that SGEF interacts with Grb2, but not with control IgG in immunoprecipitation Grb2 and it is well known that Grb2 plays a critical role in assays (Fig. 2d). These results unequivocally demonstrate EGFR-mediated ERK1/2 activation. Therefore, it is likely that endogenous Grb2 could interact with SGEF in vivo. that the interaction between Grb2 and SGEF is essential for SGEF-mediated EGFR/ERK1/2 activation. To test this SH3 domain of Grb2 and Pro domain of SGEF mediate hypothesis, we expressed EGFR and wild-type SGEF or the interaction between Grb2 and SGEF two Grb2-binding defective SGEF mutants (SGEFDPro and SGEF–P1M) and examined the phosphorylation of To map the regions involved in the interaction between ERK1/2 after EGF treatment. Surprisingly, impaired Grb2 and SGEF, we made a series of SGEF deletion mutant interaction between Grb2 and SGEF did not eliminate constructs (Fig. 3a) and examined the binding of these SGEF-mediated ERK1/2 activation, but further enhanced it constructs to Grb2 by GST pull-down assays. The results (Fig. 4a). These unexpected results indicate that it is pos- show that the N terminus was sufficient for SGEF to bind sible that the interaction between Grb2 and SGEF antag- Grb2 (Fig. 3a). To further investigate the specific region in onizes SGEF-mediated EGFR/ERK1/2 activation. the N terminus of SGEF that is required for the interaction with Grb2, HEK293 cells transiently transfected with GFP– The interaction of Grb2 with SGEF antagonizes SGEF- Grb2 were collected and cell lysates were pulled down with mediated EGFR/ERK1/2 activation a series of GST-fused truncated SGEF constructs. The resulting data suggest that in SGEF the amino acid sequence To test the hypothesis that the interaction of Grb2 with SGEF from 13 to 200 was required for binding to Grb2. This inhibits SGEF-mediated EGFR/ERK1/2 activation, we first region includes a proline-rich (Pro) domain, which is well co-expressed EGFR and wild-type Grb2 or Grb2 mutant known to recognize SH3 domains. Given that Grb2 contains (Grb2W36K) without the ability to bind SGEF in HEK293T two SH3 domains [16], we speculated that the Pro domain cells transfected with control or Flag–SGEF vectors and of SGEF was critical to bind Grb2. Therefore, we con- determined ERK1/2 phosphorylation after stimulating with structed an SGEF Pro domain deletion mutant (SGEFDPro) EGF for 5 min. As shown in Fig. 4b, exogenous GFP–Grb2 and two additional mutants SGEF–P1M or SGEF–P2M weakened SGEF-mediated ERK1/2 activation. However, (Fig. 3c) and determined the binding of these constructs to the SGEF-binding defective Grb2 mutant (Grb2W36K) Grb2 by immunoprecipitation assays. As expected, the could not suppress SGEF-mediated ERK1/2 activation, interaction between SGEF and Grb2 is impaired when the indicating that interaction of Grb2 to SGEF antagonizes the Pro domain is deleted from SGEF (Fig. 3c). It also dem- ability of SGEF to enhance EGF-induced ERK1/2 activa- onstrates that the motif containing 137–141 proline in tion. To confirm this result, we co-transfected EGFR and SGEF is vital for the interaction between SGEF and Grb2. control or Flag–SGEF vectors in control or Grb2-depleted We next mapped the binding region of Grb2 with SGEF HEK293T cells and determined ERK1/2 phosphorylation by immunoprecipitation assays. The results show that after treating with EGF for 5 min. The results presented in mutation of the N-terminal SH3 domain or the C-terminal Fig. 4c indicate that Grb2 depletion further enhances SGEF- SH3 of Grb2 impaired its binding to SGEF, indicating that mediated ERK1/2 activation, confirming that Grb2 antago- the two SH3 domains of Grb2 are essential for binding to nizes SGEF-mediated EGFR/ERK1/2 activation. To further SGEF (Fig. 3d). To further confirm that the Pro domain of investigate whether the interaction of Grb2 with SGEF is SGEF and the SH3 domains of Grb2 are critical for the required for this antagonistic effect, we co-expressed EGFR interaction between Grb2 and SGEF, we expressed the full- and wild-type SGEF or SGEF mutant (SGEFDPro) without length Grb2 and three Grb2 mutants (Grb2W36K, the ability to bind Grb2 into control or Grb2-depleted Grb2R86K, and Grb2W193A) and examined the binding of HEK293T cells and determined ERK1/2 phosphorylation these constructs to SGEF Pro domain by GST pull-down after stimulating with EGF for 5 min. As shown in Fig. 4d, in assays. The results presented in Fig. 3e confirm that the Pro comparison with wild-type SGEF, SGEF mutant (SGEFD- domain of SGEF and SH3 domains of Grb2 are required for Pro) further enhanced EGF-induced ERK1/2 activation in the interaction between Grb2 and SGEF. control HEK293T cells. However, in Grb2-depleted 123 Mol Cell Biochem (2014) 389:239–247 245

Fig. 4 The interaction of Grb2 with SGEF antagonizes SGEF- EGF for 5 min. Cell lysates were immunoblotted with indicated mediated EGFR/ERK1/2 activation. a HEK293T cells were transfec- antibodies. c Control and Grb2-depleted HEK293T cells were ted with Flag-vector, Flag–SGEF, Flag–SGEF–P1M, or Flag–SGEF– transfected with Flag-vector or Flag–SGEF. 24 h post-transfection, DPro. 24 h post-transfection, cells were serum starved overnight and cells were serum starved for 12 h and stimulated with EGF (100 ng/ then stimulated with 100 ng/ml EGF for indicated times. Cell lysates ml) for indicated times. Cell lysates were immunoblotted using were immunoblotted with indicated antibodies. b Flag-vector or Flag- indicated antibodies. d Control and Grb2-depleted HEK293T cells SGEF was transiently transfected together with GFP, GFP–Grb2, or were transfected with Flag-vector, Flag–SGEF, or Flag–SGEFDPro. GFP–Grb2W36K into HEK293T cells. 24 h post-transfection, cells 24 h post-transfection, the cells were treated similar to b. Cell lysates were serum starved overnight and then stimulated with 100 ng/ml were immunoblotted using indicated antibodies

HEK293T cells, SGEF mutant (SGEFDPro) did not further degradation in general is associated with abnormal EGFR enhance EGF-induced ERK1/2 activation compared with signal transduction, we investigated the effect of SGEF on wild-type SGEF, further indicating that the interaction of EGF-induced ERK1/2 activation, which is one of the most Grb2 with SGEF is critical for endogenous Grb2 to antago- important effectors downstream of EGFR. Our results show nize SGEF-mediated ERK1/2 activation. that overexpression of SGEF enhanced EGF-induced ERK1/ 2 activation. Since the well-characterized function of SGEF is the GEF activity for RhoG, we speculated that the ability of Discussion SGEF to enhance EGF-induced ERK1/2 activation may depend on RhoG function. However, we found that depletion Our previous study demonstrated that SGEF attenuated of RhoG did not abrogate SGEF-mediated EGFR/ERK1/2 ligand-induced EGFR degradation by delaying EGFR traf- activation, suggesting that RhoG function is not essential for ﬁcking to late endosomes. Because deregulation of EGFR SGEF to effect EGF-induced ERK1/2 activation. 123 246 Mol Cell Biochem (2014) 389:239–247

Our study also reveals the interaction of SGEF with mediated EGFR/ERK1/2 activation. If this hypothesis is Grb2 and the critical role of the Grb2 SH3 domains and the true, the interaction between SGEF and Grb2 may be SGEF Pro domain in this interaction. Therefore, it is rea- implicated in determining cell fate by balancing the extent sonable to speculate that this interaction is essential for the and the duration of EGF-induced ERK1/2 signaling. effect of SGEF on EGF-induced ERK1/2 activation. Sur- However, additional studies are required to test this prisingly, our results demonstrate that impairing the inter- hypothesis. We and others have demonstrated that SGEF action between Grb2 and SGEF further improved EGF- contributes to cancer cell migration [10, 15]. In addition, induced ERK1/2 activation rather than weakening it. This the ERK1/2 pathway has been reported to inhibit EGF- unexpected result suggests the possible antagonizing role induced prostate cancer cell migration [24]. Since Grb2 of Grb2 on the enhancement of EGF-induced ERK1/2 inhibits the ability of SGEF to enhance EGF-induced activation by interacting with SGEF. Therefore, we ana- ERK1/2 activation, it is also possible that Grb2 facilitates lyzed the effect of Grb2 overexpression or depletion on SGEF to promote cancer cell migration by avoiding excess SGEF-mediated EGFR/ERK1/2 activation. The results activation of EGF-induced ERK1/2 signaling due to SGEF show that Grb2 overexpression suppresses SGEF-mediated overexpression in cancer cells, which is consistent with the ERK1/2 activation. In addition, Grb2 depletion signifi- critical role of Grb2 in cancer metastasis [25]. cantly enhances SGEF-mediated ERK1/2 activation. In summary, we have shown that SGEF enhances EGF- Moreover, our data further demonstrate that the interaction induced ERK1/2 activation independent of its GEF activ- of Grb2 with SGEF is critical for this antagonistic effect. ity. Further, our study has demonstrated that Grb2 antag- All these observations strongly indicate that Grb2 not only onizes the ability of SGEF to enhance EGF-induced ERK1/ mediates EGF-induced ERK1/2 activation by activating 2 activation by interacting with SGEF, going beyond its Ras but also could negatively regulate it particularly when canonical function as a critical downstream transducer for SGEF is overexpressed. several growth factor receptors. Therefore, our findings not EGF-induced ERK1/2 signaling plays important roles in only identify a novel function of SGEF excluding GEF for numerous cellular activities, such as cellular proliferation, RhoG but also provide important insights into the complex differentiation, metabolism, migration, and programed role of Grb2 in EGFR signal transduction. death [5]. Deregulation of ERK1/2 signaling leads to a wide range of diseases including cancers, cardiovascular Acknowledgments We thank Dr. Wannian Yang for providing diseases, diabetes, and Alzheimer’s disease [17]. There- materials. This work was supported by the grants from the National Natural Science Foundation of China (No. 81372770 to J.Z. and Nos. fore, appropriate activation of ERK1/2 signaling is critical 81172445 and 81372140 to J.W.). for maintaining cellular homeostasis. Our data indicate that Grb2 inhibits the ability of SGEF to enhance EGF-induced ERK1/2 activation through its interaction with SGEF, References which may be crucial to avoid excess activation of ERK1/2 signaling and thereby maintain homeostasis. Moreover, it 1. Jorissen RN, Walker F, Pouliot N, Garrett TP, Ward CW, Burgess is well known that the strength and the duration of ERK1/2 AW (2003) Epidermal growth factor receptor: mechanisms of activation and signalling. 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