1. ¹Ikawa Laboratory, RIKEN, Wako, Japan
2. ²Department of Molecular Physiology, Kyoritsu University of Pharmacy, Tokyo, Japan
3. ³Department of Cell Regulation, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan
4. ⁴Department of Redox Response Cell Biology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan
5. ⁵Oral Health Science Research Center, Kanagawa Dental College, Yokosuka, Japan
6. ⁶Department of Immune Regulation, Tokyo Medical and Dental University, Tokyo, Japan
7. ⁷Human Gene Sciences Center, Tokyo Medical and Dental University, Tokyo, Japan
8. ⁸Department of Microbiology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi, Japan
9. ⁹Department of Hematology, Tokyo Medical and Dental University, Tokyo, Japan

Correspondence: Dr I Katoh, Department of Microbiology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi 409-3898, Japan. E-mail: iyoko@yamanashi.ac.jp

Received 24 October 2006; Revised 4 June 2007; Accepted 5 June 2007; Published online 16 July 2007.

Abstract

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 N-p63 isoform lacking the TA domain enhanced the MFGE8-activating function of TA-p63, if N-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:N association. MFG-E8 may provide a novel pathway of epithelial–nonepithelial cell interactions inducible by p63, probably in pathological processes.