ABSTRACT
PURPOSE: The HER2 gene encodes a 185-kd transmembrane glycoprotein receptor (p185(HER2)) that has partial homology with the epidermal growth factor receptor (EGFR) and shares intrinsic tyrosine kinase activity. The HER2 gene has been found to be amplified in various human cancers and to be associated with poor prognosis. The authors investigated the correlation between clinicopathologic factors and the overexpression of the p185(HER2) in Korean gastric adenocarcinoma patients, and determined whether the antiproliferative effects of anti- p185(HER2) antibody can also be observed on gastric cancer cell lines that overexpress this growth factor receptor. MATERIALS AND METHODS: We evaluated the relationship between p185(HER2) overexpression and clinicopathological features in 94 (M: F=52: 42) gastric adenocarcinoma patients (median age 59 years). Protein expression was analysed by immunohistochemical staining in paraffin embedded tissues with monoclonal antibody for p185(HER2). To explore the role of humanized anti-p185(HER2) monoclonal antibody trastuzumab (Herceptin ) in vitro, the growth curve of Korean gastric cancer cells that overexpress the p185(HER2) protein was studied and a cell cycle analysis was performed. RESULTS: p185(HER2) overexpression correlates positively with lymph node metastasis (p=0.002), distant metastasis (p=0.01), AJCC classification (p=0.01), higher relapse rate p=0.001), and a tendential association with the pT stage (p=0.054). p185(HER2) overexpression was found to be more frequent in advanced gastric cancer than early gastric cancer (54.1% vs 24.2%, p=0.008). Patients with overexpression of p185(HER2) were found to have significantly lower relapse-free (p=0.003) and overall survival (p= 0.0004) than patients without overexpression. Among several Korean gastric cancer cell lines, SNU-1, SNU-5, and SNU-620 overexpress p185(HER2). Trastuzumab inhibited the proliferation of p185(HER2) overexpressed Korean gastric cancer cell line by 21% with down-regulation of p185(HER2) protein expression. DNA fluorescence flow cytometry of propidium iodide-stained nuclei showed a reduction in the fraction of the S phase following treatment with trastuzumab. CONCLUSIONS: Taken together, our observations suggest the potential prognostic significance of p185(HER2) overexpression in Korean gastric adenocarcinoma patients and point to the need for further research on this mechanism. This suggests the possible use of p185(HER2) as a therapeutic target in gastric cancer.
Subject(s)
Humans , Adenocarcinoma , Cell Cycle , Cell Line , Classification , DNA , Down-Regulation , Flow Cytometry , Fluorescence , Genes, erbB-2 , Glycoproteins , Lymph Nodes , Neoplasm Metastasis , Paraffin , Prognosis , Propidium , Protein-Tyrosine Kinases , ErbB Receptors , Recurrence , S Phase , Stomach Neoplasms , TrastuzumabABSTRACT
PURPOSE: Anti-p185HER2/neu monoclonal antibody (mAb) that can induce phenotypic reversion and monoclonal antibodies specific for the p185HER2/neu growth factor receptor that are able to diminish its kinase-signaling properties represent a specific advance in the therapy for p185HER2/neu-expressing human cancers. With mAb treatment, down-regulation of p185HER2/neu surface receptors and attenuation of the kinase-signaling properties have been observed and regarded as a basic phenomenon; however, the mechanisms for mAb-induced phenotypic reversion are not clear. METHODS: We used human tumor-cell lines of SK-BR-3, T6-17, and U373MG. With immunoprecipitation and Western blotting, we investigated the changes in p185HER2/neu receptor phosphorylation and the expression of signal-regulatory proteins (SIRPs) after mAb treatment. To identify the proteins interacting with Tat-binding protein-1 (TBP1), we used the Clonotech Gal4 matchmaker two-hybrid system. RESULTS: Minimal to moderate reduction in phosphotyrosine (pTyr) content was observed in SK-BR-3 and T6-17 cells with short-term (10-30 minutes) incubation after mAb treatment, but that did not alter total p185HER2/neu receptor density. SIRPs phosphorylation after peptide treatment was increased. With mAb treatment, three proteins were shown to interact with TBP1, and all of the interacting proteins are subunits of proteasome 26S. Collectively, anti- p185HER2/neu mAb or peptide down-regulates the surface receptors and attenuates the kinase signaling, which then both induces higher proteasome activity through increased TBP1 and increases SIRPs expres sion. CONCLUSION: Increased proteasomal activity may degrade abnormal proteins and increased SIRPs may regulate signal transduction toward the norm. Therefore, activation of a protein-degradation pathway and induction of signal-regulatory proteins may be possible mechanisms for the ultimate anti-tumor effects of the anti-p185HER2/neu mAb or peptide.