Novel Evidence of Expression and Activity of Ecto-Phospholipase C
1 in Human T Lymphocytes
Sebastiano Miscia,
Angela Di Baldassarre,
Amelia Cataldi,
Rosa Alba Rana,
Valerio Di Valerio, and
Giuseppe Sabatino
From the Istituto di Morfologia Umana Normale and Cattedra di
Neonatologia, Università G. D'Annunzio, Chieti, Italy.
Although much is known about the intracellular phospholipase C (PLC)
specific for inositol phospholipids, few data are available about the
presence of a less common PLC at the external side of the membrane
bilayer of some cell types. This ectoenzyme seems to play particular
roles in cellular function by hydrolyzing inositol lipids located on
the outer leaflet of the plasma membrane. Here, we provide the first
evidence that peripheral T lymphocytes express a discrete level of a
PLC
1 at the outer leaflet of the plasma membrane. Flow cytometry
showed that the PLC1-positive (PLC1+) cells
(~37%) were CD8+ and CD45RA+.
Biochemical evidence indicated that (1) this ectoenzyme displays a mass
similar to the cytoplasmic form, (2) it is phosphorylated on tyrosine
residues, and (3) its activity is Ca2+-dependent. In
addition, this enzyme appeared to be correlated with the proliferative
state of the cell, since stimulation with phytohemagglutinin (PHA)
downregulated both its expression and activity, which were restored by
treatment with an antiproliferative agent like natural interferon beta.
Moreover, the different kinetics of formation of its hydrolytic
products, inositol 1 phosphate and inositol 1:2 cyclic phosphate
(Ins(1)P and Ins(1:2 cycl)P), formed upon incubation of the lymphocytes
with [3H]-lyso-phosphatidylinositol (PI), allow the hypothesis of a
selective involvement of the two inositol phosphates in the mechanisms
regulating the metabolism of particular T-lymphocyte subsets.
Blood, Vol. 91 No. 10 (May 15), 1998:
pp. 3833-3840
© 1998 by The American Society of Hematology.
