G-protein coupled receptor-associated sorting protein 1 (GASP-1), a potential biomarker in breast cancer

Abstract

An innovative “2-D high performance liquid electrophoresis” (2-D HPLE) technology was used to identify serum biomarkers associated with the early stage of breast cancer in addition to other more advanced stages. 2-D HPLE is a newly developed electrophoretic technology that separates 100s of serum albumin complexes on a polyvinyl membrane based on their surface charges. Association of cancer proteins or their fragments (biomarkers) with pre-existing albumin complexes in the blood of cancer patients results in altered mobility on the membrane. Using 2-D HPLE we identified that a specific fragment of G-protein coupled receptor-associated sorting protein 1 (GASP-1) was present in the sera of patients with early stage disease but absent in sera of normal patients. GASP-1 has been shown to modulate lysosomal sorting and functional down-regulation of a variety of G-protein coupled receptors in neuronal cells. However, no reports have linked GASP-1 to breast cancer pathogenesis. GASP-1 was detected in tumor extracts of 7 cases of Stage 2 and Stage 3 breast cancers, but not in adjacent normal tissue as revealed by western blot analysis using an antibody developed against a GASP-1 peptide identified by our 2-D HPLE technology. Using this antibody, we immunohistochemically detected over-expression of GASP-1 in all of 107 cases of archived ductal breast carcinoma tumor samples, while normal adjacent breast tissue from 12 cases of ductal carcinoma showed little or no staining. Additionally, all 10 cases of metastatic breast carcinoma present in lymph nodes were positive. Strong positive GASP-1 staining was observed in all tumor tissue including ductal carcinoma in situ (DCIS) and invasive ductal carcinoma. Additionally, we observed a wide spectrum of enhanced staining of premalignant ductal epithelial cells present in benign ducts and those found in atypical ductal hyperplasia (ADH). These studies identify GASP-1 as a potential new serum and tumor biomarker for breast cancer and suggest that GASP-1 may be a novel target for the development of breast cancer therapeutics.