Cholera toxin potentiates TPA-induced mitogenesis and c-fos expression in BALB/c-3T3-derived proadipocytes

Phospholipase A2 is necessary for tumor necrosis factor alpha-induced ceramide generation in L929 cells

The role of cytosolic phospholipase A2 (cPLA2) in the regulation of ceramide formation was examined in a cell line (L929) responsive to the cytotoxic action of tumor necrosis factor alpha (TNFalpha). In L929 cells, the addition of TNFalpha resulted in the release of arachidonate, which was followed by a prolonged accumulation of ceramide occurring over 5-12 h and reaching 250% over base line. The formation of ceramide was accompanied by the hydrolysis of sphingomyelin and the activation of three distinct sphingomyelinases (neutral Mg2+-dependent, neutral Mg2+-independent, and acidic enzymes). The variant cell line C12, which lacks cPLA2, is resistant to the cytotoxic action of TNFalpha. TNFalpha was able to activate nuclear factor kappaB in both the wild-type L929 cells and the C12 cells. However, TNFalpha was unable to cause the release of arachidonate or the accumulation of ceramide in C12 cells. C6-ceramide overcame the resistance to TNFalpha and caused cell death in C12 cells to a level similar to that in L929 cells. The introduction of the cPLA2 gene into C12 cells resulted in partial restoration of TNFalpha-induced arachidonate release, ceramide accumulation, and cytotoxicity. This study suggests that cPLA2 is a necessary component in the pathways leading to ceramide accumulation and cell death.

Rat preadipocyte adenylyl cyclase: influence of fat localization and androgenic status

The influence of androgenic status on basal and stimulated cAMP production, adenylyl cyclase activities and immunoblot quantified GS alpha and Gi alpha 2 subunits of the adenylyl cyclase regulatory proteins were compared in confluent preadipocytes from subcutaneous (SC) and deep-intraabdominal (epididymal) fat deposits. Maximal cAMP response to isoproterenol was lower in SC than in epididymal preadipocytes. After castration, this site-specific difference was suppressed. cAMP response to 2-chloroadenosine, which was identical in the two types of preadipocytes, was decreased by castration in epididymal cells but not in SC cells. The catalytic activity of adenylyl cyclase and its maximal response to GTP were higher in epididymal than in SC preadipocytes. This response to GTP was decreased by castration in epididymal preadipocytes while it remained unchanged in SC preadipocytes. The catalytic activity of adenylyl cyclase was unchanged by androgenic status whatever the cell localization. Levels of GS alpha quantified by immunoblotting were not modified whatever the androgenic status and cell origin. Levels of Gi alpha 2 were not affected by the androgenic status as well, but were lower in SC than in epididymal cells. This study shows that components of the adenylyl cyclase system in preadipocytes are differently regulated by the androgenic status depending on the anatomical origin of the cells.