GJA1 and breast cancer: ▪Tumour suppressor and antitumour properties by increased ABCA1, PTEN, HBP1 and GJA1 expression in miR‐19 transfected and non‐transfected BC cells▪Modified methylation status of promoter CPG sites▪Decreased cell colonies and proliferation (by increasing ABCA1, PTEN, HBP1, and GJA1 genes expression) in miR‐19 transfected cells▪ROS scavenger suppressed gas plasma effects on miR‐19a cells and its target genes