Negative Regulation of Kruppel-Like Factor 4 on microRNA-106a at Upstream Transcriptional Level and the Role in Gastric Cancer Metastasis.

Abstract

MicroRNAs are classes of endogenous noncoding RNAs that play a substantial role in tumor processes through regulating the targets atposttranscriptional level. However, little is known about the upstream transcription regulatory mechanism although it is a prerequisite for investigation of its aberrant expression and function. This report evaluates miR-106a's direct transcriptional factor from upstream level to in depth elucidate their communication in gastric cancer development. Gastric cancer tissues were collected to analyze the miR-106a expression using real-time PCR methods. The combination of Kruppel (or Krüppel)-like factor 4 (KLF4) to miR-106a promoter was testified through bioinformatics followed by construction of luciferase reporter plasmid and chromatin immunoprecipitation assay. Functional experiments and mouse models for evaluating cell growth and metastasis were conducted to observe the biological effect of KLF4 on miR-106a. The interplay between KLF4 and miR-106a was tested with Wnt activator and confirmed in clinical specimens. The up-regulated miR-106a linked to gastric cancer metastasis and epithelial-mesenchymal transition. UCSC and JASPAR predicted the promoter sequence of miR-106a and its binding site with transcriptional factor KLF4. Construction of reporter gene further verified their direct combination at upstream level. Moreover, the inhibitory effect of KLF4 on the phenotype of gastric cancer cells could be restored by miR-106a. CHIR-induced experiment and clinical specimens confirmed the negative regulation of KLF4 on miR-106a. Our findings provide novel direct insights into molecular mechanisms for interaction of KLF4 and miR-106a at upstream level and new ways for clinical application of KLF4-miR-106a axis in advanced gastric cancer metastasis.