TY - JOUR
T1 - Glucose-responsitivity and expression of an ATP-stimulatable, Ca2+-independent phospholipase A2 enzyme in clonal insulinoma cell lines
AU - Ramanadham, Sasanka
AU - Wolf, Matthew J.
AU - Li, Bingbing
AU - Bohrer, Alan
AU - Turk, John
N1 - Funding Information:
The authors would like to thank the expert technical assistance of Dr. Mary Mueller and Ms. Patricia Jett. This work was supported by grants from Juvenile Diabetes Foundation International (194165) and from National Institutes of Health (DK-34388 and RR-00954).
PY - 1997/1/21
Y1 - 1997/1/21
N2 - We have previously reported that pancreatic islet β-cells and clonal HIT insulinoma cells express an ATP-stimulatable Ca2+-independent phospholipase A2 (ASCI-PLA2) enzyme and that activation of this enzyme appears to participate in glucose-stimulated insulin secretion. To further examine this hypothesis, glucose-responsitivity and expression of ASCI-PLA2 activity in various insulinoma cell lines were examined. Secretagogue-stimulated insulin secretion was observed with βTC6-f7 and early passage (EP)-βTC6 cells. In contrast, RIN-m5f, βTC3, and late passage (LP)-βTC6 cells exhibited little secretagogue-induced secretion. A haloenollactone suicide substrate (HELSS) which inhibits ASCI-PLA2 activity ablated secretagogue-induced insulin secretion from βTC6-f7 and EP-βTC6 cells. All insulinoma cell lines studied expressed both cytosolic and membrane-associated Ca2+-independent PLA2 activities which were inhibited by HELSS. The cytosolic enzymatic activity in the glucose-responsive βTC6-f7 and EP-βTC6 cells was activated by ATP and protected against thermal denaturation by ATP, but this was not the case in the glucose-unresponsive RIN-m5f, βTC3, or LP-βTC6 cells, Comparison of the distribution of Ca2+-independent PLA2 activity revealed that membrane-associated activity was higher than cytosolic activity in βTC6-f7 and EP-βTC6 cells but not in RIN-m5f, βTC3, or LP-βTC6 cells. Insensitivity of cytosolic activity to ATP may prevent association of the PLA2 activity with membrane substrates and contribute to attenuated glucose-responsitivity in the RIN-m5f, βTC3, or LP-βTC6 cells. HIT insulinoma cells were also found to undergo a decline in both glucose-responsitivity and membrane-associated Ca2+-independent PLA2 activity upon serial passage in culture, and this was associated with a reduction in membrane content of arachidonate-containing phospholipids. These and previous results suggest that the ATP-stimulatable PLA2 enzyme may participate in glucose-induced insulin secretion.
AB - We have previously reported that pancreatic islet β-cells and clonal HIT insulinoma cells express an ATP-stimulatable Ca2+-independent phospholipase A2 (ASCI-PLA2) enzyme and that activation of this enzyme appears to participate in glucose-stimulated insulin secretion. To further examine this hypothesis, glucose-responsitivity and expression of ASCI-PLA2 activity in various insulinoma cell lines were examined. Secretagogue-stimulated insulin secretion was observed with βTC6-f7 and early passage (EP)-βTC6 cells. In contrast, RIN-m5f, βTC3, and late passage (LP)-βTC6 cells exhibited little secretagogue-induced secretion. A haloenollactone suicide substrate (HELSS) which inhibits ASCI-PLA2 activity ablated secretagogue-induced insulin secretion from βTC6-f7 and EP-βTC6 cells. All insulinoma cell lines studied expressed both cytosolic and membrane-associated Ca2+-independent PLA2 activities which were inhibited by HELSS. The cytosolic enzymatic activity in the glucose-responsive βTC6-f7 and EP-βTC6 cells was activated by ATP and protected against thermal denaturation by ATP, but this was not the case in the glucose-unresponsive RIN-m5f, βTC3, or LP-βTC6 cells, Comparison of the distribution of Ca2+-independent PLA2 activity revealed that membrane-associated activity was higher than cytosolic activity in βTC6-f7 and EP-βTC6 cells but not in RIN-m5f, βTC3, or LP-βTC6 cells. Insensitivity of cytosolic activity to ATP may prevent association of the PLA2 activity with membrane substrates and contribute to attenuated glucose-responsitivity in the RIN-m5f, βTC3, or LP-βTC6 cells. HIT insulinoma cells were also found to undergo a decline in both glucose-responsitivity and membrane-associated Ca2+-independent PLA2 activity upon serial passage in culture, and this was associated with a reduction in membrane content of arachidonate-containing phospholipids. These and previous results suggest that the ATP-stimulatable PLA2 enzyme may participate in glucose-induced insulin secretion.
KW - Insulin secretion
KW - Insulinoma cell
KW - Phospholipase A
UR - http://www.scopus.com/inward/record.url?scp=0031581646&partnerID=8YFLogxK
U2 - 10.1016/S0005-2760(96)00139-7
DO - 10.1016/S0005-2760(96)00139-7
M3 - Article
C2 - 9030192
AN - SCOPUS:0031581646
SN - 0005-2760
VL - 1344
SP - 153
EP - 164
JO - Biochimica et Biophysica Acta - Lipids and Lipid Metabolism
JF - Biochimica et Biophysica Acta - Lipids and Lipid Metabolism
IS - 2
ER -