Diversity in secreted PLA2-IIA activity among inbred mouse strains that are resistant or susceptible to ApcMin/+ tumorigenesis

The secreted phospholipase A(2) type IIA (Pla2g2a) gene was previously identified as a modifier of intestinal adenoma multiplicity in Apc(Min/+) mice. To determine if intestinal secreted phospholipase A(2) (sPLA(2)) activity was also attenuated in susceptible strains, we developed a sensitive assay to directly quantitate sPL2 activity in the murine intestinal tract utilizing a fluorescent BODIPY-labeled phospholipid substrate. Here, we report assay conditions that distinguish between secreted and cytosolic PLA(2) enzyme activities in extracts of intestinal tissue. The small intestine exhibited higher activity levels than the large intestine. Consistent with predictions from the sPLA(2)-IIA gene sequence in inbred strains, we detected low levels of enzyme activity in inbred strains containing sPLA(2)-IIA mutations; these strains were also associated with greater numbers of intestinal polyps. Additionally, the assay was able to distinguish differences in levels of sPLA(2) activity between neoplasia-resistant strains, which were then shown by sequencing to carry variant wild-type sPLA(2)-IIA alleles. Immunohistochemical analyses of intestinal tissues were consistent with sPLA(2)-IIA activity levels. This approach enables further studies of the mechanisms of sPLA(2) action influencing the development and tumorigenesis of the small intestine and colon in both mice and humans.