IQ Motif-Containing GTPase-Activating Proteins (IQGAPs) Are an Extremely Sensitive and Specific Biomarker of Hepatocellular Carcinoma
H Khurana, CD White, DB Sacks, VA Schmidt, RD Odze. Brigham and Women's Hospital, Boston, MA; State University of New York, New York, NY
Background: IQGAPs are multidomain proteins that integrate Rho GTPase and Ca2+/calmodulin signaling, and are involved in cell adhesion and cytoskeletal reorganization. In mammals, three homologous IQGAPs (IQGAP1, IQGAP2 and IQGAP3) have been identified. In a mouse model, IQGAP2 downregulation results in IQGAP1 amplification and the development of hepatocellular carcinoma (HCC). The aim of the study was to determine the role of these proteins in human hepatocellular carcinogenesis, and as tissue biomarkers for this tumor.
Design: A total of 20 biopsy and 56 surgical resection specimens from 76 patients (M/F ratio: 2/1, Mean age: 60 years) were selected. These included 36 HCC, 4 benign hepatic adenomas (HA), 23 cirrhosis cases (mostly hepatitis C related) and 13 normal liver samples. Immunohistochemical staining for IQGAP1 and IQGAP2 was performed using well-characterized, highly specific antibodies. The rabbit polyclonal IQGAP1 antibody was generated in our laboratory by injecting a purified fusion protein against the N-terminal region of IQGAP1 into rabbits prior to exsanguination (Open Biosystems, AL). The mouse monoclonal antibody against IQGAP2 was purchased from Upstate Biotechnology (MA). The specimens were evaluated for the presence and degree of staining (grade 0: less than 5% tumor cells positive, grade 1: 5% to 25%, grade 2: 26% to 50%, grade 3: 51% to 75%, grade 4: > 75%) and compared between the different specimens.
Results: Cytoplasmic staining for IQGAP1 was detected in 36/36 (100%) HCCs, and all cases exhibited strongly diffuse positivity (grade 4). In contrast, none of the hepatic adenomas, cirrhosis or normal liver tissues showed IQGAP1 staining (100% grade 0; p= <0.000001). IQGAP2 was not expressed in any of the 36 HCC cases (0%) whereas 4 (100%) HA, 23 (100%) cirrhosis and 13 (100%) normal liver tissue samples showed IQGAP2 immunoreactivity (p<0.000001 for all comparisons versus HCC). The sensitivity and specificity of positive IQGAP1 staining for detection of HCC was 100 % and 100% respectively.
Conclusions: Upregulation of IQGAP1 and down-regulation of IQGAP2 play a role in hepatocellular carcinogenesis. IQGAP1 immunostaining is a highly sensitive and specific marker of HCC in tissue specimens. Pharmacological manipulation of IQGAPs may provide a novel therapeutic approach for the treatment of HCC.
Monday, March 22, 2010 1:00 PM
Poster Session II # 89, Monday Afternoon