HOTAIR induces the ubiquitination of Runx3 by interacting with Mex3b and enhances the invasion of gastric cancer cells

Long non-coding RNAs (LncRNAs) exert their functions mainly by binding to their corresponding proteins. Runt-related transcription factor 3 (Runx3) is an important transcription factor that functions as a tumor suppressor in gastric cancer. Whether there is an interplay between LncRNAs and Runx3 remains unclear. RPISeq was applied to screen the LncRNAs that potentially bind to Runx3. The interaction between LncRNA HOX antisense intergenic RNA (HOTAIR) and Runx3 was validated by RNA Immunoprecipitation and RNA pull-down assays. The role of Mex3b in the ubiquitination of Runx3 induced by HOTAIR was assessed by immunoprecipitation. Pearson's correlation between HOTAIR mRNA expression and Runx3 protein expression was analyzed. Cell migration and invasion were explored by transwell assays. We found that HOTAIR was bound to Runx3 protein and identified the fragment of HOTAIR spanning 1951-2100 bp as the specific binding site. In addition, mex-3 RNA binding family member B (Mex3b) was an E3 ligase involved in HOTAIR-induced ubiquitous degradation of Runx3. Silencing the expression of HOTAIR or Mex3b attenuated the degradation of Runx3. In human gastric cancer tissues, HOTAIR was negatively associated with the expression level of Runx3 protein (Pearson coefficient - 0.501, p = 0.025). Inhibition of HOTAIR significantly suppressed gastric cancer cell migration and invasion through upregulating claudin1, which could be reversed by co-deficiency of Runx3. These results uncovered the novel interaction between HOTAIR and Runx3, and provided potential therapeutic targets on the metastasis of gastric cancer.