Insulin regulation of lipoprotein lipase activity in 3T3-L1 adipocytes is mediated at posttranscriptional and posttranslational levels.
Insulin is a major regulator of lipoprotein lipase (LPL) activity. The molecular events associated with LPL regulation by insulin in 3T3-L1 adipocytes were studied by determining LPL enzyme activity, mRNA levels, protein synthetic rate, and transcription run-off activity. Adipocytes treated with insulin (10(-6) M for 48 h) had substantially higher LPL activity (mean difference compared to carrier-treated cells 146%) with little difference in LPL mRNA levels (mean level 109% of control). Insulin regulation of LPL activity was dose-dependent but changes in LPL mRNA were not. Within 2 h of hormone addition, LPL activity was higher in insulin-treated versus carrier-treated adipocytes although their LPL mRNA levels were similar. In [35S]methionine pulse-labeled adipocytes, insulin decreased LPL protein synthetic rate measured by immunoprecipitation 42-48%, although increases (75-340%) in heparin-releasable LPL activity were detected in the same cells. In contrast, during differentiation of 3T3-L1 fibroblasts to the adipocyte state, 5-80-fold increases of heparin-releasable LPL activity were closely associated with similar (8-60-fold) increases in LPL mRNA levels. LPL synthetic rate was 16-fold greater, and LPL gene transcription initiation measured by transcriptional run-off was 10-fold higher in adipocytes than in undifferentiated cells. Differentiation of 3T3-L1 fibroblasts increases transcription of the LPL gene leading to increased LPL mRNA, protein synthetic rate, and enzyme activity. Insulin regulation of LPL activity in 3T3-L1 adipocytes, however, is mediated entirely at posttranscriptional and posttranslational levels.
Semenkovich
C F
CF
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
Wims
M
M
Noe
L
L
Etienne
J
J
Chan
L
L
D000273:Adipose Tissue / Q000201:enzymology*; D000818:Animals; D015152:Blotting, Northern; D002454:Cell Differentiation; D002478:Cells, Cultured; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008071:Lipoprotein Lipase / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects*; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics
D007328:Insulin; D012333:RNA, Messenger; D008071:Lipoprotein Lipase