Transcriptional down-regulation by insulin of the beta 3-adrenergic receptor expression in 3T3-F442A adipocytes: a mechanism for repressing the cAMP signaling pathway.

Abstract

Modulation of the three -adrenergic receptor subtypes (1&ARs) by Insulin was investigated in mouse 3T3-F442A adipocytes. Saturation and competition experiments measuring binding of 12I-abeled (-)-cyanopindolol to adipocyte membranes demonstrated that cell exposure to insulin for 4 days caused a 3.5-fold decrease in the density of the major P-AR component of the adipocyte, the #3-AR, while 1i-AR sites remained unchanged and P2-ARs were undetectable. This correlated with a lower potency of the 13-ARselective agonists CGP12177, IC1201651, and BRL37344 in stimulating adenylate cyclase. Northern blotting analysis indicated that insulin induced a rapid and sharp decrease in 13-AR mRNA levels. This effect was detectable at low insulin concentrations (EC5o = 3 nM) and was not observed in the presence of insulin-like growth factor I, sugging an insulin receptormediated phenomenon. Reverse transcriptase-PCR analysis showed that, in contrast to Its dramatic down-regulatory effect on (3-AR mRNA, insulin did not modify the levels of JR,-and SE-AR transcripts. As as d by nuclear run-on assays, insulin inhibited the 13-AR gene transcription rate by 90% within 30 min. mRNA turnover experiments showed that the half-life of P3-AR mRNA was short (90 min) and remained unaffected by insulin. These findings demonstrate the genetic control of a 3-AR subtype expression by insulin and reveal a mechanism for the regulation by this hormone of cAMPdependent biological processes in adipocytes.

Fat accumulation in the rat during early pregnancy is modulated by enhanced insulin responsiveness

“…Present findings, showing an augmented adipose tissue responsiveness to the antilipolytic action of insulin at early pregnancy, provide an explanation for the decrease in both ␤ 3 -adrenoceptor protein and activity, since these variables are known to be interconnected (14,18). This is in agreement with results showing that the lipolytic response to catecholamines is impaired in biopsies of subcutaneous femoral adipose tissue in late first trimester pregnant women (48).…”

“…In contrast, the antilipolytic action of insulin is a multistep process, so acute effects of insulin are related to activation of cGMP-inhibited phosphodiesterase (PDE3) (12), activation of a phosphatase, and/or sequestration of ␤ 3 -adrenoceptors from the cell surface (15). The mechanisms by which long-term insulin treatment reduces ␤-adrenergic sensitivity are less documented, although it is known that long-term exposure to insulin induces a decrease of mRNA ␤ 3 -adrenoceptor expression in both isolated adipocytes (14) and 3T3-F442A preadipocytes (18).…”

Emerging role of protein kinase C in energy homeostasis: A brief overview

“…Results presented argue strongly in favor of an inverse relationship between PKCβ and β3-adrenergic receptor expression [26] . The proposed relationship is consistent with earlier reports showing that sustained PKC activation suppressed β-ARs expression at the transcriptional level [31][32][33] . The net consequence of PKCβ-mediated adipose dysfunction could have profound clinical consequences because of the large size of the fat organ and its central metabolic role.…”

Insulin and Sterol-regulatory Element-binding Protein-1c (SREBP-1C) Regulation of Gene Expression in 3T3-L1 Adipocytes

“…However, the lack of stimulation observed with the dominant positive questions about the ability of SREBP-1c to mimic insulin regulation, raises the possibility that, for a limited number of genes, the effects of insulin might not be achieved through SREBP-1c only. Another example is the ␤ 3 -adrenoreceptor gene, whose transcription is repressed by insulin (48). Our study shows that indeed, the ␤ 3 -adrenoreceptor mRNA was down-regulated in cells treated by insulin as well as in those overexpressing the DP mutant of SREBP-1c.…”