LncRNA MACC1-AS1 sponges multiple miRNAs and RNA-binding protein PTBP1

Long noncoding RNA (lncRNA) represents a class of endogenous RNAs that regulate gene expression in eukaryotes. To date, the function and underlying mechanism of the majority of mammalian lncRNAs remain unknown. Here, we report that MACC1-AS1, a cognate antisense lncRNA of the sixth intron of the MACC1 gene, functions as a cell growth modulator and enhances breast tumor progress. RNA pulldown and luciferase assays showed that MACC1-AS1 contained binding sites for multiple miRNAs, including well-known tumor suppressors miR-384 and miR-145-3p that repress the expression of pleiotrophin (PTN) and c-Myc mRNAs. Binding of miR-384 and miR-145-3p miRNAs to MACC1-AS1 alters the cell growth phenotype through increased expression of PTN and c-Myc mRNAs. MACC1-AS1 also competitively interacted with PTBP1, an RNA-binding protein, via a conserved pyrimidine rich motif within this lncRNA. Binding of PTBP1to MACC1-AS1 not only stabilized MACC1-AS1 and enhanced the sponge effect of MACC1-AS1 on miRNAs, but also decreased PTBP1 availability for binding to target mRNAs. Our results define a new dimension into how a lncRNA is able to regulate cell growth by sponging multiple miRNAs and an RNA-binding protein.