Objective: The Homeobox (HOX) family of genes consists of 39 genes encoding transcription factors important to morphogenesis and cell differentiation. Usually inactive in normal differentiated tissues, dysregulation of HOX genes has been reported in several malignancies. HOX genes have been linked to genes important in malignant transformation including vascular endothelial growth factor, Ras, interleukin-8, and fibroblast growth factor. We have previously reported up-regulation of HOXA2, HOXA7 and HOXB7 in ovarian cancer. Little is known about HOXC6 gene expression in ovarian cancer. In this study we evaluated HOXC6 expression in normal and malignant human ovarian tissue to characterize expression of HOXC6 in serous ovarian cancer.

Methods: Microarray analysis of mRNA from LCM captured cells from human ovarian tissues was performed on 11 samples of normal, and malignant ovarian tissues. These samples were analyzed using the Affymetrix Human EXON 1.0 ST microarray to distinguish the differential pattern of mRNA expression between malignant and normal samples. Real-time reverse transcription PCR was utilized to confirm down-regulation of HOXC6 genes as determined by microarray analysis. HOXC6 protein in tissue was evaluated by immunohistochemistry.

Results: Microarray analysis demonstrated significant down-regulation of the HOXC6 gene in malignant serous ovarian tumor samples compared to normal ovarian epithelial cells of control samples. RT-PCR and immunohistochemistry confirmed HOXC6 down-regulation in malignant samples. A 115-fold difference in malignant and normal primary tissue samples and cell lines was seen in the RT-PCR analysis. By immunohistochemistry nuclear staining of HOXC6 protein was seen in the nuclei of normal ovarian surface epithelial tissues but significantly reduced or absent in malignant ovarian samples.

Conclusion: HOXC6 is significantly differentially expressed comparing normal ovarian tissue and serous malignant ovarian tissue based on both tissue mRNA and protein analysis. This finding of HOXC6 down-regulation in ovarian cancer is unique and opposite of the up-regulation of other HOX genes previously reported. Down-regulation of HOXC6 in serous ovarian cancer may be an important finding relative to oncogenic pathways and biomarker development. This suggests dysregulation of HOXC6 genes may be an early event in malignant transformation and additional studies to validate the role of the HOXC6 gene in ovarian cancer are warranted.

Citation Format: David L. Tait, Zahra Bahrani-Mostafavi, Carol Vestal, Christine Richardson, M. Taghi Mostafavi. Down-regulation of HOXC6 in serous ovarian cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3007. doi:10.1158/1538-7445.AM2013-3007