Production of the long and short forms of MFG-E8 by epidermal keratinocytes

Abstract

Mouse milk fat globule-EGF factor 8, MFG-E8, is the ortholog to the human mammary tumor marker, lactadherin, and comprises two spliced variants, the L and S forms. Recent studies have suggested that MFG-E8-L produced by macrophages and Langerhans cells in the skin serves as a linker between phagocytic cells and apoptotic cells, and that MFG-E8-S, also termed SED1, facilitates sperm-egg interaction for fertilization. However, Mfge8 gene expression occurs in various tissues apparently unrelated to these critical events. Our in situ hybridization study has revealed that Mfge8 is expressed in the periderm (the premature epidermis) on embryonic day-14, well before Langerhans cells begin to grow in the prenatal phase. Mfge8 transcript is detectable in the basal and spinous layers throughout skin development, whereas immunostaining has revealed MFG-E8 protein accumulation in the spinous layer. Cultured keratinocyte stem cells consistently express Mfge8-L and -S mRNAs and produce the L protein, which is primarily detectable in the culture supernatant, and the S protein, which is mostly associated with the cells. Upon Ca(2+)-stimulated differentiation, which is detected by a decrease in keratinocyte stem cell marker p63(p51) and the induction of keratin1, we have observed suppression of Mfge8, and the protein becomes localized to the cell-cell borders. Papillomas and carcinomas caused by chronic UV-B irradiation produce MFG-E8 as determined by immunostaining. Thus, undifferentiated and poorly differentiated keratinocytes produce the L and S forms of MFG-E8 during normal and pathological tissue development, probably to support an as yet unidentified membrane function.

p63(TP63) elicits strong trans-activation of the MFG-E8/lactadherin/BA46 gene through interactions between the TA and ΔN isoforms

“…Total adherent cell count was 35% decreased by p63si-transfection, in which the antibody blocking caused only an 8.3% reduction. Consistent with earlier results (Taylor et al, 1997), western blot analysis of the supernatants detected two broad bands at apparent molecular masses of 42-44 kDa (Figure 7c), indicating secretion of MFG-E8 in poorly glycosylated forms (Oshima et al, 2002;Watanabe et al, 2005). The bands' intensity was decreased to approximately 40% by the p63 suppression.…”

“…MFG-E8-L, the mouse-specific long isoform, having a Pro/Thr-enriched domain, facilitates phagocytosis of apoptotic cells by macrophages as demonstrated by recent studies with MFGE8-deficient mice (Hanayama et al, 2002;Hanayama and Nagata, 2005). However, the other isoform, MFG-E8-S, lacking the phagocytosisfacilitating activity is more ubiquitously, abundantly expressed (Watanabe et al, 2005) and expected to facilitate various types of cell-cell interactions. Importantly, human MFGE8 codes for a protein similar to mouse MFGE8-S, but not an MFG-E8-L-type protein.…”

“…MFG-E8 is a membrane-associated, heavily glycosylated secretory protein with two distinct types of adhesion sites: the Arg-Gly-Asp triplet arranged to bind to integrin a v b 3 or a v b 5 ; and the discoidin domains (C1 and C2) that interact with phosphatidylserine located on the inner side of plasma membrane (Taylor et al, 1997;Shi and Gilbert, 2003). Mouse Mfge8 produces MFG-E8-L and MFG-E8-S, in which the former is mousespecific, and the latter conserved among humans and animals (Watanabe et al, 2005). While the L form containing a Pro/Thr-enriched domain facilitates phagocytosis of apoptotic cells by macrophages (Hanayama et al, 2002(Hanayama et al, , 2004, the S form was reported to support the gamete interaction upon fertilization (Ensslin and Shur, 2003).…”

“…In addition to the increased expression of MFGE8 in lactating and transformed breast epithelial cells (Peterson et al, 1990), steady-state expression also occurs in various tissues (Kruger et al, 2000;Watanabe et al, 2005). However, little is known about the transcriptional control of MFGE8.…”

Milk Fat Globule-EGF Factor VIII in Sepsis and Ischemia-Reperfusion Injury

“…The expression of the two splice variants shows spatial and temporal specificity. MFG-E8S is distributed widely, whereas MFG-E8L has been found in activated mouse macrophages (14,26), as well as in immature dendritic cells (27), Langerhans cells of the skin (27) and in epidermal keratinocytes (28). Recently, MFG-E8L has been identified in a species other than the mice (24,25).…”