Ma. Deeg et Cb. Verchere, REGULATION OF GLYCOSYLPHOSPHATIDYLINOSITOL-SPECIFIC PHOSPHOLIPASE-D SECRETION FROM BETA-TC3 CELLS, Endocrinology, 138(2), 1997, pp. 819-826
Glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) is abu
ndant in mammalian serum, but the source of the circulating enzyme is
unknown. Pancreatic islets have been reported to contain and secrete G
PI-PLD. In this report we examined the regulation of GPI-PLD secretion
from beta TC3 cells, a mouse insulinoma cell line. In the absence of
glucose, phorbol myristic acid (0.1 mu M) stimulated insulin secretion
by 2.5-fold and GPI-PLD secretion by a-fold. Carbachol (5 mu M), gluc
agon-like peptide I-(7-36) amide (0.1 mu M), and isobutylmethylxanthin
e (0.1 maa) had no significant effect on insulin or GPI-PLD secretion
in the absence of glucose. Glucose (16.7 mM) stimulated both GPI-PLD a
nd insulin secretion from beta TC3 cells by 55% and 235%, respectively
. In addition, glucose potentiated the secretagogue effect of isobutyl
methylxanthine, phorbol myristic acid, and glucagon-like peptide I on
both insulin and GPI-PLD secretion. By immunohistochemistry and confoc
al microscopy, beta TC3 cells contain both insulin and GPI-PLD, which
generally colocalized intracellularly. However, GPI-PLD secretion diff
ered from insulin secretion by a higher rate of basal release (2.8% us
. 0.23%/h), a lower magnitude of response to secretagogues, and a more
prolonged period of increased secretion. These results demonstrate th
at beta TC3 cells secrete GPI-PLD in response to insulin secretagogues
and suggest that GPI-PLD may be secreted via the regulated pathway in
these cells.