Endocytosis in mammalian cells involves multiple organelles
and trafficking events. Molecules brought into the cell by receptor-
mediated endocytosis must be sorted and delivered to the
appropriate destinations [1]. In electron microscopy studies, membrane
tubules (60–80 nm in diameter) have been observed extending
from various endosomes [2–4], and various endocytic recycling
receptors accumulate in these tubules [5–10]. It has been suggested
that the role of membrane tubules is to help sort membrane-
bound recycling receptors away form soluble cargo that is
destined for degradation [7,11].
A variety of studies have led to the surprising conclusion that
cytoplasmic phospholipase A2 (PLA2) activities are intimately involved
in the formation of membrane tubules from both the Golgi
complex and various endosomal compartments, and
membrane trafficking pathways leading from these organelles
[12]. In the case of endosomes, recent studies have revealed a
concentration-dependent effect on the recycling of transferrin
(Tf) and its receptor (TfR) when cells are treated with various
cytoplasmic PLA2 antagonists such as ONO-RS-082 (ONO) or
bromoenol lactone (BEL) [13]. High concentrations (10 lM)
block export of Tf/TfR from both peripheral sorting endosomes
(SEs) and the central endocytic recycling compartment (ERC),
whereas low concentrations (1 lM) allow transport to, but