Isoproterenol decreased LPL gene transcription and steady-state mRNA levels at 15 minutes, whereas insulin increased LPL mRNA levels without affecting transcription, likely through mRNA stability.
Does isoproterenol or insulin regulate LPL gene expression in rat adipocytes?
Isoproterenol decreases LPL enzyme activity via decreased gene transcription, while insulin increases it likely through mRNA stability changes.
Lipoprotein lipase (LPL) is highly regulated by catecholamines and insulin in adipocytes. Isoproterenol, a beta-adrenergic agonist, decreases LPL enzyme activity, whereas insulin increases LPL activity. We have isolated an 868-basepair rat LPL cDNA clone to assess hormone-mediated changes in LPL steady state mRNA levels and LPL gene transcription rates in adipocytes. Northern blot analysis of isoproterenol-treated (10(-6) M) adipocytes showed that LPL steady state mRNA decreased by 15 min. Nuclear run-on transcription assays in isoproterenol-treated cells indicated that LPL gene transcription was also decreased at 15 min compared to that in control cells. Conversely, insulin (6.7 x 10(-8) M) mediated an increase in LPL steady state mRNA in treated adipocytes, yet LPL gene transcription was not different from that in control cells. Thus, the isoproterenol-mediated decrease in LPL enzyme activity and steady state mRNA levels in adipocytes is associated with decreases in LPL gene transcription. Insulin, which does not affect LPL gene transcription, increases LPL enzyme activity and steady state mRNA levels. The effect of insulin on LPL mRNA is probably due to insulin-induced changes in mRNA stability.
Raynolds et al. (1990) studied this question. Isoproterenol and Insulin vs. Control cells was evaluated on LPL steady state mRNA levels and LPL gene transcription rates. Isoproterenol decreased LPL gene transcription and steady-state mRNA levels at 15 minutes, whereas insulin increased LPL mRNA levels without affecting transcription, likely through mRNA stability.