| Summary: | <p>Abstract</p> <p>Background</p> <p>The <it>DLX </it>gene family encodes for homeobox transcription factors involved in the control of morphogenesis and tissue homeostasis. Their expression can be regulated by Endothelin1 (ET1), a peptide associated with breast cancer invasive phenotype. Deregulation of <it>DLX </it>gene expression was found in human solid tumors and hematologic malignancies. In particular, <it>DLX4 </it>overexpression represents a possible prognostic marker in ovarian cancer. We have investigated the role of <it>DLX </it>genes in human breast cancer progression.</p> <p>Methods</p> <p>MDA-MB-231 human breast carcinoma cells were grown in vitro or injected in nude mice, either subcutaneously, to mimic primary tumor growth, or intravenously, to mimic metastatic spreading. Expression of <it>DLX2</it>, <it>DLX5 </it>and <it>DLX6 </it>was assessed in cultured cells, either treated or not with ET1, tumors and metastases by RT-PCR. <it>In situ </it>hybridization was used to confirm <it>DLX </it>gene expression in primary tumors and in lung and bone metastases. The expression of <it>DLX2 </it>and <it>DLX5 </it>was evaluated in 408 primary human breast cancers examining the GSE1456 and GSE3494 microarray datasets. Kaplan-Meier estimates for disease-free survival were calculated for the patients grouped on the basis of <it>DLX2</it>/<it>DLX5 </it>expression.</p> <p>Results</p> <p>Before injection, or after subcutaneous growth, MDA-MB-231 cells expressed <it>DLX2 </it>but neither <it>DLX5 </it>nor <it>DLX6</it>. Instead, in bone and lung metastases resulting from intravenous injection we detected expression of <it>DLX5/6 </it>but not of <it>DLX2</it>, suggesting that <it>DLX5/6 </it>are activated during metastasis formation, and that their expression is alternative to that of <it>DLX2</it>. The <it>in vitro </it>treatment of MDA-MB-231 cells with ET1, resulted in switch from <it>DLX2 </it>to <it>DLX5 </it>expression. By data mining in microarray datasets we found that expression of <it>DLX2 </it>occurred in 21.6% of patients, and was significantly correlated with prolonged disease-free survival and reduced incidence of relapse. Instead, <it>DLX5 </it>was expressed in a small subset of cases, 2.2% of total, displaying reduced disease-free survival and high incidence of relapse which was, however, non-significantly different from the other groups due to the small size of the <it>DLX+ </it>cohort. In all cases, we found mutually exclusive expression of <it>DLX2 </it>and <it>DLX5</it>.</p> <p>Conclusions</p> <p>Our studies indicate that <it>DLX </it>genes are involved in human breast cancer progression, and that <it>DLX2 </it>and <it>DLX5 </it>genes might serve as prognostic markers.</p>
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