Developmental expression and functional activity of beta 1- and beta 3-adrenoceptors in murine 3T3-F442A differentiating adipocytes.
Beta 1- and beta 3-adrenoceptor mRNA and protein expression, and contribution of each subtype to the catecholamine-sensitive adenylyl cyclase system were studied during the adipose conversion of the murine 3T3-F442A cell line. Northern and reverse transcriptase-polymerase chain reaction analyses indicated that emergence of beta 3-adrenoceptor transcripts was concomittant with that of the gene encoding adipsin, a very late marker of adipose differentiation. Conversely, the induction of the beta 1-adrenoceptor mRNA occurred early after cell commitment towards adipose conversion. Changes in beta-subtype gene expression were accompanied by parallel modifications in receptor expression and function. 125I-cyanopindolol saturation and competition binding experiments showed a 3-fold increase in beta 1-adrenoceptor density in day 3 post-confluent cells. The beta 3-subtype population became detectable later and represented approximately 95% of total beta-adrenoceptors in day 8 and day 12 post-confluent cells. Adenylyl cyclase activity in response to the beta 3-adrenoceptor-selective agonists CGP12177 (4-(3-t-butylamino-2-hydroxypropoxy)-benzimidazol-2-one), ICI201651 ([(R)-4-(2 hydroxy-3-phenoxypropylamino-ethoxy)-N-(2- methoxyethyl)phenoxy-acetamide]) and cyanopindolol was virtually absent in young adipocytes, but dramatically increased in mature cells. The respective contributions of the beta 1- and the beta 3-subtypes to the production of cAMP were resolved by an Eadie-Hofstee computer analysis of isoproterenol and norepinephrine concentration-response curve of adenylyl cyclase activity. Agonist response curves in the presence of beta 1- and beta 2-adrenoceptor antagonist indicated that the beta 1-subtype accounted for the totality of beta-adrenoceptor-mediated adenylyl cyclase activation in young adipocytes. In mature adipose cells approximately 90% of this response was due to an activation of the beta 3-adrenoceptor. In addition, approximately 84% of the maximal norepinephrine-stimulated lipolysis was mediated by the beta 3-adrenoceptor in fully differentiated adipocytes. The differentiation-dependent expression of beta-subtypes in adipocytes is a biphasic process involving an initial and moderate induction of beta 1-adrenoceptors followed by the emergence of a prominent beta 3-adrenoceptor population. Compared analysis of both receptor occupancy and cAMP production shows that the beta 3-subtype is more efficiently coupled to the adenylyl cyclase system than the beta 1-adrenoceptor. Thus in mature adipose cells this receptor subtype represents the core of cAMP-dependent regulation of the lipolytic, antilipogenic and thermogenic effects of catecholamines.
El Hadri
K
K
Institut National de la Santé et de la Recherche Médicale U 282, Hôpital Henri Mondor, Créteil, France.
Fève
B
B
Pairault
J
J
D000262:Adenylyl Cyclases; D017667:Adipocytes / Q000201:enzymology / Q000502:physiology*; D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D008066:Lipolysis / Q000502:physiology; D008566:Membranes / Q000378:metabolism; D008969:Molecular Sequence Data; D010869:Pindolol / Q000031:analogs & derivatives; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*; D018342:Receptors, Adrenergic, beta-1 / Q000187:drug effects / Q000502:physiology*; D022702:Receptors, Adrenergic, beta-3; D015398:Signal Transduction / Q000502:physiology
D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D018342:Receptors, Adrenergic, beta-1; D022702:Receptors, Adrenergic, beta-3; C047975:cyanopindolol; D010869:Pindolol; D000262:Adenylyl Cyclases