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Differential regulation of elicited-peritoneal macrophage 14 kDa and 85 kDa phospholipase A2(s) by transforming
B Bolognese1, M McCord, L A Marshall
1SmithKline Beecham Pharmaceuticals, Inflammation and Respiratory Pharmacology, King of Prussia, PA 19406-0939, USA.
Abstract:
Elicited guinea pig macrophages collected from inflammatory peritoneal exudate release soluble 14 kDa phospholipase A2 (PLA2) and prostaglandin E2 (PGE2) into surrounding media during culture (Marshall et al. (1994) J. Lipid Med. 10, 295-313). The effect of transformation growth factor beta 1 (TGF beta), an immunoregulatory growth factor, was examined in this system. Exposure of cultured macrophages to TGF beta reduced both the activity and protein levels of 14 kDa PLA2 measured in conditioned media. This inhibition occurred within the first 6-8 h, was prevalent through 72 h of exposure and was dependent on TGF beta concentration. The reduction, however, never reached more than 40-60%. Evaluation of the cellular PLA2 activity confirmed the existence of an immunologically-related 14 kDa PLA2 (ELISA) in the particulate fraction and an 85 kDa PLA2 (Western analysis) in the cytosol. Exposure to TGF beta halved the particulate activity and protein levels of 14 kDa PLA2 which was consistent with the reduction in the secreted form. Alternatively, TGF beta induced an increase in cytosolic 85 kDa PLA2 (activity and protein) which was not apparent until 12 h and significant at 20-24 h of exposure. This demonstrates that TGF beta differentially regulates the production of these two enzymes. Despite this, neither PGE2 synthesis nor the up-regulated cyclooxygenase -II were altered by TGF beta treatment suggesting that maximal prostanoid synthesis had been reached.
Insights
Transforming growth factor beta 1 (TGF beta) differentially regulates phospholipase A2 (PLA2) in guinea pig macrophages. TGF beta inhibits secreted 14 kDa PLA2 while increasing cytosolic 85 kDa PLA2, impacting inflammatory responses.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages play a key role in inflammatory responses by releasing mediators like phospholipase A2 (PLA2) and prostaglandin E2 (PGE2).
- Transforming growth factor beta 1 (TGF beta) is an immunoregulatory cytokine with complex effects on immune cells.
Purpose of the Study:
- To investigate the effect of TGF beta on the production and release of PLA2 and PGE2 by guinea pig macrophages.
- To determine how TGF beta influences the different molecular forms of PLA2 within macrophages.
Main Methods:
- Cultured guinea pig peritoneal macrophages were exposed to TGF beta.
- PLA2 activity and protein levels were measured in conditioned media and cellular fractions using ELISA and Western analysis.
- PGE2 synthesis and cyclooxygenase-II expression were also assessed.
Main Results:
- TGF beta significantly reduced the activity and protein levels of secreted 14 kDa PLA2 in a dose- and time-dependent manner.
- TGF beta also decreased particulate 14 kDa PLA2, but concurrently increased cytosolic 85 kDa PLA2 activity and protein.
- Neither PGE2 synthesis nor cyclooxygenase-II were affected by TGF beta treatment.
Conclusions:
- TGF beta differentially regulates PLA2 isoforms in macrophages, inhibiting the secreted 14 kDa form while upregulating the cytosolic 85 kDa form.
- These regulatory effects on PLA2 do not alter maximal PGE2 synthesis, suggesting other regulatory mechanisms are dominant.
- TGF beta's differential regulation of PLA2 provides insights into immune modulation during inflammation.