Chromosome 11q and its association with CCND1 gene amplification and tamoxifen resistance in premenopausal breast cancer

Background: The amplification event occurring at chromosome locus 11q13, reported in several different cancers, includes a number of potential oncogenes. We have previously reported amplification of one such oncogene, CCND1, to be correlated with an adverse effect of tamoxifen in premenopausal breast cancer patients. Overexpression of cyclin D1 protein however, confers tamoxifen resistance but not a tamoxifen induced adverse effect. Potentially, co-amplification of an additional 11q13 gene, with a resulting protein overexpression, is required to cause an agonistic effect. Moreover, during 11q13 amplification a deletion of the distal 11q region has been described. In order to assess the potential impact of the deletion we have examined a selected marker for this event. Methods: Array CGH analysis was employed to identify and confirm changes in the gene expression of a number of different genes mapping to the 11q chromosomal region, associated with CCND1 amplification. The subsequent protein expression of these candidate genes was then examined in a clinical material of 500 primary breast cancers from premenopausal patients randomized to either tamoxifen or no adjuvant treatment. The protein expression was also compared to the CGH data in a subset of 56 breast cancer samples. Results: Cortactin and FADD overexpression was linked to CCND1 amplification, determined by FISH, but was not associated with a diminished effect of tamoxifen. However, deletion of distal chromosome 11q, defined as downregulation of the marker Chk1, was associated with an impaired tamoxifen response, and interestingly, also with low proliferative breast cancer of low grade. For Pak1 and cyclin D1 the protein expression corresponded to the gene expression data from the CGH analysis. Conclusions: The results indicate that many 11q13 associated gene products are overexpressed in conjunction with cyclin D1 but not linked to an agonistic effect of tamoxifen. Finally, the deletion of distal 11q, linked to 11q13 amplification, might be an important event affecting breast cancer outcome and tamoxifen response. Keywords: comparative genomic hybridisation 56 samples with 11q13 amplification have been analysed and compared with protein expression results from immunohistochemical analyses.

【背景】在多种不同癌症中均有报道的11q13染色体位点（chromosome locus 11q13）扩增事件，包含多个潜在致癌基因。本团队此前曾报道，细胞周期蛋白D1基因（CCND1）的扩增与绝经前乳腺癌患者他莫昔芬治疗的不良预后相关。然而，细胞周期蛋白D1（cyclin D1）蛋白过表达仅会引发他莫昔芬耐药，而非他莫昔芬诱导的不良效应。理论上，需同时扩增11q13区域内的另一基因并使其编码蛋白过表达，才会产生激动效应。此外，已有研究显示，11q13扩增过程中会伴随11q远端区域的缺失。为评估该缺失事件的潜在影响，我们针对这一事件选择了相关标志物进行检测。
【方法】本研究采用阵列比较基因组杂交（array comparative genomic hybridisation, CGH）技术，对与CCND1扩增相关的11号染色体区域内多个基因的表达变化进行鉴定与验证。随后，我们在500例绝经前原发性乳腺癌患者的临床样本中检测了这些候选基因的蛋白表达水平，这些患者被随机分配接受他莫昔芬治疗或无辅助治疗。同时，我们还在56例乳腺癌样本的亚组中，将蛋白表达结果与CGH数据进行了比对分析。
【结果】经荧光原位杂交（fluorescence in situ hybridization, FISH）确认，皮层肌动蛋白（Cortactin）与Fas相关死亡结构域蛋白（FADD）的过表达与CCND1扩增相关，但二者均与他莫昔芬治疗效果减弱无关联。然而，以标志物细胞周期检查点激酶1（Chk1）表达下调定义的11号染色体长臂远端区域缺失，与他莫昔芬治疗应答受损相关；有趣的是，该缺失还与低级别、低增殖性乳腺癌相关。对于p21激活激酶1（Pak1）与细胞周期蛋白D1，其蛋白表达水平与CGH分析得到的基因表达数据相符。
【结论】本研究结果表明，诸多与11q13相关的基因产物会伴随细胞周期蛋白D1一同过表达，但均与他莫昔芬的激动效应无关。最终，伴随11q13扩增出现的11q远端区域缺失，可能是影响乳腺癌患者预后及他莫昔芬治疗应答的重要事件。
【关键词】比较基因组杂交（comparative genomic hybridisation）；本研究共分析56例携带11q13扩增的样本，并将其与免疫组化分析得到的蛋白表达结果进行比对。