Mixed-lineage leukaemia 1 contributes to endometrial stromal cells progesterone responsiveness during decidualization.

Studies have reported that non-receptive endometrium or abnormal decidualization was closely related to recurrent implantation failure (RIF). MLL1 is a histone H3 lysine 4 trimethylation (H3K4me3) transferase that regulates the transcriptional activation of target genes. The role of MLL1 has been underexplored during decidualization. In our research, we found the expression of MLL1 was closely related to endometrial receptivity, and it was responsible to hormone stimulation. Inhibiting the function of MLL1 by MM102 reduced the transformation of HESCs. Furthermore, down-regulation of MLL1 by siRNA transfection significantly decreased PGR and its target genes expression. MLL1 act as a co-activator of ERα, and both of them were recruited to PGR regulatory regions, thus promote PGR transcription. Our study showed that MLL1 plays a key role in promoting progesterone signalling transmission.