Expression of enhancing factor/phospholipase A₂ in ICRC mice

Abstract

Enhancing factor (EF), a growth factor modulator, recently identified as the mouse secretory phospholipase A₂ (PLA₂), has been isolated in our laboratory from the intestines of mice. EF modulates the action of epidermal growth factor (EGF) by mediating an almost 2-fold increase in EGF binding in a radioreceptor assay. EF has been localized immunohistochemically to the Paneth cells of the intestine, adjacent to the proliferating stem cell population. Although very weak staining was observed in the intestines of ICRC mice (ICRC is an inbred strain of mouse developed at this Institute) as compared to Balb/c mice, the enhancing activity was not detected in the partially purified, acid soluble intestinal proteins of the ICRC strain. However, studies using polyclonal antibodies against purified EF demonstrated that EF from Balb/c and ICRC intestines are either immunologically identical or closely related to each other although, quantitatively, EF was very low in ICRC mice. RFLP studies indicated that ICRC mice carry a mutation in the coding region of the EF gene resulting in loss of the BamHI. restriction site. On sequencing, a T insertion was found at position 166 from the ATG site thereby causing a disruption in the ORF. This probably results in undetectable levels of enhancing activity. In this paper we report the molecular characterization of the ICRC mouse with respect to theenhancing factor gene