Data from Locked Nucleic Acid <i>In situ</i> Hybridization Analysis of miR-21 Expression during Colorectal Cancer Development

Abstract

&lt;div&gt;Abstract&lt;p&gt;&lt;b&gt;Purpose:&lt;/b&gt; To better understand microRNA miR-21 function in carcinogenesis, we analyzed miR-21 expression patterns in different stages of colorectal cancer development using &lt;i&gt;in situ&lt;/i&gt; hybridization (ISH).&lt;/p&gt;&lt;p&gt;&lt;b&gt;Experimental Design:&lt;/b&gt; Locked nucleic acid (LNA)/DNA probes and a biotin-free tyramide signal amplification system were used in ISH analyses of miRNA expression. Conditions for specific detection of miR-21 were determined using human cell lines and miR-21–expressing lentiviral vectors. Expression was determined in 39 surgically excised colorectal tumors and 34 endoscopically resected colorectal polyps.&lt;/p&gt;&lt;p&gt;&lt;b&gt;Results:&lt;/b&gt; In the surgical samples, miR-21 expression was much higher in colorectal cancers than in normal mucosa. Strong miR-21 expression was also observed in cancer-associated stromal fibroblasts, suggesting miR-21 induction by cancer-secreted cytokines. Protein expression of PDCD4, a miR-21 target, was inversely correlated with miR-21 expression, confirming that miR-21 is indeed a negative regulator of PDCD4 &lt;i&gt;in vivo&lt;/i&gt;. In the endoscopic samples, miR-21 expression was very high in malignant adenocarcinomas but was not elevated in nontumorigenic polyps. Precancerous adenomas also frequently showed miR-21 up-regulation.&lt;/p&gt;&lt;p&gt;&lt;b&gt;Conclusion:&lt;/b&gt; Using the LNA-ISH system for miRNA detection, miR-21 was detectable in precancerous adenomas. The frequency and extent of miR-21 expression increased during the transition from precancerous colorectal adenoma to advanced carcinoma. Expression patterns of miR-21 RNA and its target, tumor suppressor protein PDCD4, were mutually exclusive. This pattern may have clinical application as a biomarker for colorectal cancer development and might be emphasized by self-reinforcing regulatory systems integrated with the &lt;i&gt;miR-21&lt;/i&gt; gene, which has been previously shown in cell culture.&lt;/p&gt;&lt;/div&gt;