Article

GRB-7 facilitates HER-2/Neu-mediated signal transduction and tumor formation

Division of Hematology and Medical Oncology, Oregon Health Sciences University, Portland VA Medical Center, Portland, OR 97239, USA.
Carcinogenesis (Impact Factor: 5.27). 04/2008; 29(3):473-9. DOI: 10.1093/carcin/bgm221
Source: PubMed

ABSTRACT Growth factor receptor-bound protein-7 (GRB-7), an adaptor molecule, can interact with multiple signal transduction molecules. GRB-7 is amplified concurrently with HER-2/Neu in most, if not all, of breast cancer with chromosome 17q11-21 amplification. GRB-7 gene amplification is associated with RNA over-expression. We show GRB-7 protein is over-expressed by immunoblotting in breast cancer cell lines and primary breast tumors with HER-2/Neu protein over-expression. Over-expression of GRB-7 in MCF-7 breast cancer cells that over-express HER-2/Neu leads to activation of tyrosine phosphorylation of HER-2/Neu. Knockdown of GRB-7 expression in SKBR-3 breast cancer cells with naturally occurring HER-2/Neu gene amplification decreases tyrosine phosphorylation of HER-2/Neu. Activation of HER-2/Neu phosphorylation is associated with increase in tyrosine phosphorylation of phosphoinositide-specific lipase C-gamma-1 (PLC-gamma-1) and recruitment of PLC-gamma-1 to HER-2/Neu protein molecule. Activation of downstream protein kinase C (PKC) pathway is evidenced by increase in the phosphorylation of a common PKC substrate-myristoylated alanine-rich protein kinase C substrate (MARCKS). In addition, over-expression of GRB-7 in MCF-7 breast cancer cells that over-express HER-2/Neu leads to activation of AKT phosphorylation. Knockdown of GRB-7 expression in MB-453 and SKBR-3 breast cancer cells results in decrease in AKT phosphorylation. GRB-7 over-expression therefore facilitates activation of phosphorylation of HER-2/Neu and AKT in breast cancer cells with HER-2/Neu over-expression. GRB-7 over-expression in MCF-7 cells over-expressing HER-2/Neu leads to morphologic change of cells and promotes tumor xenograft growth in nude mice. GRB-7 over-expression therefore plays pivotal roles in activating signal transduction and promoting tumor growth in breast cancer cells with chromosome 17q11-21 amplification.

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Available from: Shiuh-Wen Luoh, Jul 29, 2015
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    • "In addition to HER-2, there are a number of other chromosome 17q11-12 genes, including closely neighboring GRB7, which may be amplified and over-expressed concurrently with HER-2 (Luoh 2002; Kao & Pollack 2006; Kauraniemi & Kallioniemi 2006; Bai & Luoh 2008; Stein et al. 1994; Glynn et al. 2010). The GRB7 gene codes for a multi-domain signal transduction molecule, and is known to play important roles in tumor growth and migration (Shen & Guan 2004). "
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    ABSTRACT: Testing for human epidermal growth factor receptor-2 (HER-2) in breast cancer is performed by either immunohistochemistry (IHC) or in situ hybridization (ISH). The growth factor receptor-bound protein-7 (GRB7) gene is in close proximity to HER-2 on chromosome 17q11-12 and codes a signal transduction molecule shown to be an independent adverse marker in breast cancer. HER-2 and GRB7 protein expression from 613 frozen breast tumors was determined by Western analysis. HER-2 protein results were confirmed with IHC. Commercial HER-2 FISH was performed on a subset of tumors with multi-probe FISH used to assess the extent of HER-2 gene amplification. mRNA expression was determined by Multi-plex RT-PCR. Seven tumors with GRB7 protein over-expression scored HER-2 FISH amplified but had no HER-2 protein over-expression. Four of the 7 tumors showed elevated GRB7 but not HER-2 mRNA over-expression. The breast cancer cell line HCC3153 did not over-express HER-2 protein but showed HER-2 FISH amplification of a limited segment around the HER-2 gene. Ten breast cancer tumors from the TCGA database had gene copy number increases around HER-2 without HER-2 mRNA or protein over-expression. A subset of human breast cancers that test positive with FISH for HER-2 gene amplification do not over-express HER-2 protein. One mechanism for this discordance is the incomplete amplification of the smallest HER-2 region of chromosome 17q11-12, which includes GRB7. HER-2 gene amplification without protein over-expression is clinically significant because patients with such tumors are unlikely to benefit from HER-2 targeted therapy.
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    • "One of the best studied of these core genes is GRB7. Co-expression of Grb7 and HER2 facilitates HER2 signal transduction and functions synergistically for tumour formation (Stein et al, 1994; Bai and Luoh, 2008). Tumours co-expressing high levels of Grb7 and HER2 have a worse outcome than those with only higher levels of HER2 (Nadler et al, 2010), in line with the clinical data presented here. "
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