期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 281, 期 1, 页码 187-198出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M509105200
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资金
- NCRR NIH HHS [P41 RR000954-30, P41-RR00954, P41 RR000954] Funding Source: Medline
- NHLBI NIH HHS [P01-HL57278, P01 HL057278] Funding Source: Medline
- NIDDK NIH HHS [P30 DK056341-069003, P30 DK056341, R37-DK34388, P30 DK056341-06, P30 DK056341-05S2, P60 DK020579, R37 DK034388-23, P60 DK020579-269005, P30-DK56341, P60-DK20579, R37 DK034388] Funding Source: Medline
- NIGMS NIH HHS [P41 GM103422] Funding Source: Medline
- PHS HHS [R01-69455] Funding Source: Medline
Studies involving pharmacologic inhibition or transient reduction of Group VIA phospholipase A(2) (iPLA(2)beta) expression have suggested that it is a housekeeping enzyme that regulates cell 2-lysophosphatidylcholine (LPC) levels, rates of arachidonate incorporation into phospholipids, and degradation of excess phosphatidylcholine (PC). In insulin-secreting islet beta-cells and some other cells, in contrast, iPLA(2)beta signaling functions have been proposed. Using retroviral vectors, we prepared clonal INS-1 beta-cell lines in which iPLA(2)beta expression is stably suppressed by small interfering RNA. Two such iPLA(2)beta knockdown (iPLA(2)beta-KD) cell lines express less than 20% of the iPLA(2)beta of control INS-1 cell lines. The iPLA(2)beta-KD INS-1 cells exhibit impaired insulin secretory responses and reduced proliferation rates. Electrospray ionization mass spectrometric analyses of PC and LPC species that accumulate in INS-1 cells cultured with arachidonic acid suggest that 18:0/20:4-glycerophosphocholine (GPC) synthesis involves sn-2 remodeling to yield 16:0/20:4-GPC and then sn-1 remodeling via a 1-lyso/20:4-GPC intermediate. Electrospray ionization mass spectrometric analyses also indicate that the PC and LPC content and composition of iPLA(2)beta-KD and control INS-1 cells are nearly identical, as are the rates of arachidonate incorporation into PC and the composition and remodeling of other phospholipid classes. These findings indicate that iPLA(2)beta plays signaling or effector roles in beta-cell secretion and proliferation but that stable suppression of its expression does not affect beta-cell GPC lipid content or composition even under conditions in which LPC is being actively consumed by conversion to PC. This calls into question the generality of proposed housekeeping functions for iPLA(2)beta in PC homeostasis and remodeling.
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