The Role of HOXA5 in Breast Cancer

描述（由申请人提供）：我们观察到，与正常乳腺上皮细胞（HMEC）相比，同源异型基因HOXA 5在乳腺癌细胞系和原发性乳腺肿瘤中的表达降低。我们以前已经证明了它能够调节p53和孕酮受体的表达。最近，使用两种不同的技术，我们已经确定了对HOXA 5有反应或与HOXA 5相互作用的基因。1)通过对表达人HOXA 5的酿酒酵母进行微阵列分析，我们已经确定了可能受HOXA 5蛋白调控的新的推定靶基因。在酵母中被HOXA 5上调的基因之一是DNA错配修复基因，其人类同源基因被鉴定为MutL-1（hMLH 1）。hMLH 1的启动子区含有4个推测的HOXA 5结合位点。我们现在已经证明HOXA 5的过表达上调乳腺癌细胞系MCF- 7中的hMLH 1。我们现在将评估HOXA 5对hMLH 1的调节及其在维持细胞基因组完整性的关键功能中的作用。2)使用酵母双杂交分析，我们已经确定了一个抗凋亡基因，扭曲，作为HOXA 5蛋白的相互作用。我们已经证明：a）Twist在乳腺癌细胞系中的表达引起p27[Kip 1]水平的降低，同时增加细胞在血清饥饿期间存活的能力，和B）在功能测定中，HOXA 5可以部分恢复Twist对p53靶基因的抑制作用。我们将充分表征HOXA 5/Twist相互作用的性质。除了研究这些蛋白质之间的生物化学相互作用外，我们还想揭示乳腺中HOXA 5的生物学。HOXA 5的表达缺失发生在60%的乳腺癌中。然而，很少有人知道它的表达在整个正常乳腺发育，或其与其他预后因素的关系。3)我们将使用免疫组织化学（IHC）来表征HOXA 5在正常乳腺从青春期前到绝经后阶段的发展过程中的表达和癌症。通过IHC检测乳腺肿瘤阵列，我们想确定HOXA 5的缺失是否与高级别乳腺肿瘤形成相关。因此，我们建议深入研究HOXA 5在乳腺癌中的作用。这些研究将对HOXA 5的肿瘤抑制作用产生新的见解，并进一步阐明HOXA 5在乳腺肿瘤发生中的分子功能。

DESCRIPTION (provided by applicant): We observed that the homeotic gene, HOXA5 has decreased expression in breast cancer cell lines and in primary breast tumors, when compared to normal mammary epithelial cells (HMEC). We have previously demonstrated its ability to modulate the expression of p53 and the progesterone receptor. Recently, using two separate technologies, we have identified genes that are responsive to, or interact with HOXA5. 1) By performing microarray analysis of Saccharomyces cerevisiae that express human HOXA5, we have identified novel putative target genes that may be regulated by HOXA5 protein. One of the genes that is up-regulated by HOXA5 in yeast is a DNA mismatch repair gene whose human paralog was identified as MutL-1 (hMLH1). The promoter region of hMLH1 contains four putative HOXA5 binding sites. We have now demonstrated that over-expression of HOXA5 up-regulates hMLH 1 in a breast cancer cell line, MCF- 7. We will now evaluate the regulation of hMLH1 by HOXA5 and its role in the critical function of maintaining the integrity of the cellular genome. 2) Using yeast two-hybrid analysis, we have identified an anti-apoptotic gene, Twist, as an interactor of HOXA5 protein. We have shown that: a) expression of Twist in a breast cancer cell line caused a decrease in p27[Kip1] levels while increasing the cell's ability to survive during serum starvation and, b) in functional assays, HOXA5 can partially restore the suppressive effects of Twist on p53 target genes. We will fully characterize the nature of the HOXA5/Twist interaction. In addition to studying the biochemical interactions between these proteins, we would like to shed light on the biology of HOXA5 in the breast. Loss of expression of HOXA5 occurs in 60% of breast cancers. However, little is known regarding its expression throughout normal breast development, or its relationship with other prognostic factors. 3) We will use immunohistochemistry (IHC) to characterize HOXA5 expression in normal breast during development from pre-pubertal to postmenopausal stages and in cancer. By examining breast tumor arrays by IHC, we would like to determine if loss of HOXA5 correlates with high grade breast tumor formation. Thus, we propose to examine, in depth, the role of HOXA5 in breast cancer. These studies will yield new insights into the tumor suppressor role of HOXA5 and further elucidate the molecular functions of HOXA5 in breast tumorigenesis.