The natural antisense transcript HAS2-AS1 regulates breast cancer cells aggressiveness independently from hyaluronan metabolism

•The survival probability of patients with estrogen receptor (ER) negative breast cancer is higher when the expression of HAS2-AS1 is elevated.•HAS2-AS1 overexpression reduces cell aggressiveness only of ER negative and not of ER positive cell lines.•HAS2-AS1 regulates neither hyaluronan accumulation nor hyaluronan synthases expression in ER negative breast cancer cells.•Microarray gene expression profiling reveals that HAS2-AS1 has a pivotal role to regulate the expression of several genes involved in tumorigenesis.•Overexpression of the Long isoform of HAS2-AS1 exon 2 induces mesenchymal to epithelial transition in ER negative breast cancer cells.