Abstract
3441
ERBB4 (HER-4) is a receptor tyrosine kinase involved in cell division, migration, adhesion, differentiation, and apoptosis. ERBB4 is frequently over-expressed in breast and colorectal tumors and this over-expression has been associated with good prognosis. To learn about the underlying mechanisms of aberrant ERBB4 expression we searched for genetic variants within the ERBB4 ATG -1000 bp 5'-regulatory region, investigated their possible functional role, established their polymorphic nature and tested their possible involvement in breast and colorectal cancer risk. Mutational analyses of the ERBB4 promoter region was performed on 92 DNA samples of colorectal cancer patients using PCR, denaturing high performance liquid chromatography (DHPLC), and sequencing. Corresponding normal DNA was tested in those patients whose tumor revealed an ERBB4 variant. To investigate the functional role reporter gene assays were performed with the respective plasmid constructs transfected into breast cancer cell lines MDA134 and MDA157. To analyze the binding affinity of nuclear proteins to each allele, electrophoretic mobility shift assay (EMSA) was employed. Polymorphisms were defined following establishment of allele and genotype frequencies in Slovenian and German populations using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Association studies for cancer associated risk estimations were carried out for a colorectal case-control collection from Slovenia (459 patients, 569 controls) and the population-based breast cancer case-control collection GENICA from Germany (1021 patients, 1015 controls) based on the comparison of genotype frequencies between cases and controls. We observed 7 ERBB4 variants in colorectal tumors and showed their germline origin with five variants being novel. Among these we pursued ERBB4 ATG-782 G>T and observed that the promoter activity of the T allele was two times lower compared to the G allele. Furthermore, the binding affinity to nuclear proteins was significantly lower. The variant T allele showed a frequency of 1.6 % and carriers of this allele showed a significantly increased risk for breast (OR 1.58; 95% CI: 1.04-2.33) and colorectal cancer (OR 2.21; 95% CI=1.22-3.99). We conclude that the novel polymorphism ERBB4 -782 G>T is involved in the risk to develop breast and colorectal cancer. This increased risk may be explained by a reduced ERBB4 promoter activity potentially leading to lower ERBB4 expression and compromised protection of normal breast and mucosa.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA