Phospholipase A2 expression in human and rodent insulin-secreting cells

The expression of different isoforms of phospholipase A2 in human and rat islets of Langerhans and in the clonal B-cell lines, HIT-T15 and RINm5F has been investigated, using polyclonal antisera specific to human cytosolic (cPLA2) or human Groups I and II secretory (sPLA2) isoforms. Abundant levels of a 100-kDa protein corresponding to cPLA2 were detected in cytosolic extracts of human islets. A 100-kDa cPLA2 was not detectable in rat islets, RINm5F or HIT-T15 cells using an anti-cPLA2 serum raised against cloned human cPLA2 cDNA, despite the antiserum being cross-reactive with cPLA2 from rat kidney. Human and rat islets were found to express a 21-kDa protein immunoreactive with Group I sPLA2 antiserum. Group II sPLA2 was not detected in human or rat islets. RIN cells did not express detectable levels of either Group I or Group II sPLA2, but HIT cells expressed variable quantities of Group II sPLA2. These differences in PLA2 expression suggest that caution should be exercised when extrapolating conclusions about lipid-derived signalling molecules from insulin-secreting cell lines to normal islets of Langerhans.