p63(TP63) elicits strong trans-activation of the MFG-E8|[sol]|lactadherin|[sol]|BA46 gene through interactions between the TA and |[Delta]|N isoforms

摘要

We report here that human MFGE8 encoding milk fat globule-EGF factor 8 protein (MFG-E8), also termed 46?kDa breast epithelial antigen and lactadherin, is transcriptionally activated by p63, or TP63, a p53 (TP53) family protein frequently overexpressed in head-and-neck squamous cell carcinomas, mammary carcinomas and so on. Despite that human MFG-E8 was originally identified as a breast cancer marker, and has recently been reported to provide peptides for cancer immunotherapy, its transcriptional control remains an open question. Observations in immunohistochemical analyses, a tetracycline-induced p63 expression system and keratinocyte cultures suggested a physiological link between p63 and MFGE8. By reporter assays with immediately upstream regions of MFGE8, we determined that the trans-activator (TA) isoforms of p63 activate MFGE8 transcription though a p53/p63 motif at ?370, which was confirmed by a chromatin immunoprecipitation experiment. Upon siRNA-mediated p63 silencing in a squamous cell carinoma line, MFG-E8 production decreased to diminish Saos-2 cell adhesion. Interestingly, the ΔN-p63 isoform lacking the TA domain enhanced the MFGE8-activating function of TA-p63, if ΔN-p63 was dominant over TA-p63 as typically observed in undifferentiated keratinocytes and squamous cell carcinomas, implying a self-regulatory mechanism of p63 by the TA:ΔN association. MFG-E8 may provide a novel pathway of epithelial–nonepithelial cell interactions inducible by p63, probably in pathological processes.