Chromogenic in situ hybridization reveals specific expression pattern of long non-coding RNA DRAIC in formalin-fixed paraffin-embedded specimen

Long non-coding RNA (lncRNA) plays an important role in the regulation of gene expression in normal and cancer cells. We previously discovered a novel tumor-suppressive lncRNA, DRAIC, in prostate cancer cells. Subsequent studies have demonstrated that DRAIC is dysregulated in various malignancies and exhibits a tumor-suppressive or pro-oncogenic function. However, details regarding its expression pattern in normal and cancerous tissues remain largely unknown. In this study, we performed chromogenic in situ hybridization (CISH) using RNAscope technology to assess DRAIC expression in formalin-fixed paraffin-embedded (FFPE) specimens. In the neuroendocrine-differentiated cancer cell line VMRC-LCD, CISH revealed a diffuse localization of DRAIC in the cytoplasm as well as specific accumulation in the nuclear compartment. DRAIC expression was comprehensively analyzed using tissue microarrays containing 89 normal and 155 tumor tissue samples. DRAIC was weakly expressed in normal epithelial cells of the colon, bronchiole, kidney, prostate, and testis. Conversely, DRAIC was moderately to highly expressed in some cancer tissues, including prostate adenocarcinoma, invasive ductal carcinoma of the breast, neuroendocrine carcinoma of the esophagus, lung adenocarcinoma, and small cell lung carcinoma. While DRAIC knockdown did not affect VMRC-LCD cellular viability and invasive ability, gene expression related to the neuroendocrine and cancer-related pathways was altered. Our expression analysis revealed the specific expression pattern of DRAIC in normal and cancerous FFPE tissues. The results presented here may lead to the elucidation of additional novel functions of DRAIC.