The minimal adipose phenotype of hormone-sensitive lipase (HSL)-null mice suggested that other hormonally responsive lipase(s) were present in adipocytes. Recent studies have characterized a new adipose tissue triglyceride lipase, ATGL/PNPLA2/destnutrin/iPLA2ζ/TTS2.2 (ATGL). We had previously cloned a novel adipose-enriched transcript by differential screening and recently determined its identity with murine ATGL. We report here on the regulation of ATGL by TNF-α and insulin in 3T3-L1 adipocytes and identify ATGL as a target for transcriptional activation by the key adipogenic transcription factor PPARγ. Insulin at 100 nM resulted in a marked decrease in ATGL transcript that was effectively blocked by inhibitors for PI 3-kinase and p70 ribosomal protein S6 kinase. TNF-α treatment decreased ATGL transcript in a time-dependent manner that paralleled TNF-α downregulation of PPARγ with a maximal decrease noted by 6 h. TNF-α effects on ATGL were attenuated by pretreatment with PD-98059, LY-294002, or rapamycin, suggesting involvement of the p44/42 MAP kinase, PI 3-kinase, and p70 ribosomal protein S6 kinase signals. To study transcriptional regulation of ATGL, we cloned 2,979 bp of the murine ATGL 5′-flanking region. Compared with promoterless pGL2-Basic, the −2979/+21 ATGL luciferase construct demonstrated 120- and 40-fold increases in activity in white and brown adipocytes, respectively. Luciferase reporter activities for a series of eight ATGL promoter deletions revealed that the −928/+21, −1738/+21, −1979/+21, and −2979/+21 constructs were transactivated by PPARγ. Our findings identify the novel lipase ATGL to be a target gene for TNF-α and insulin action in adipocytes and reveal that it is subject to transcriptional control by PPARγ-mediated signals.
Abnormal regulation of ribosomal protein S6 kinase by insulin in skeletal muscle of insulin-resistant humans.