Regulation of glucose transport as well as glucose transporter and immediate early gene expression in 3T3-L1 preadipocytes by 8-bromo-cAMP.
In the present study we have examined the ability of 8-bromoadenosine cyclic 3',5'-phosphate (8-bromo-cAMP; the membrane permeant analog of cAMP which can activate protein kinase A) to mimic hormone action and stimulate glucose transport and glucose transporter (GLUT-1) gene expression as well as the expression of several growth-related protooncogenes in quiescent 3T3-L1 fibroblasts. 8-Bromo-cAMP induced a rapid and prolonged increase in the rate of hexose transport. Early activation of hexose transport (within 30 min) was associated with increased plasma membrane immunoreactive glucose transporters, which corresponded to a doubling in the number of D-glucose-displaceable, plasma membrane cytochalasin B binding sites. The time course for 8-bromo-cAMP-induced hexose transport preceded the accumulation of GLUT-1 mRNA, which peaked between 4 and 8 h after exposure to the agent, and subsequently declined to approach basal (control) levels. Expression of the immediate-early genes c-fos and jun-B was induced by 8-bromo-cAMP on a rapid, but sustained time course, whereas induction of c-jun expression was delayed. Alterations in specific mRNAs following exposure to 8-bromo-cAMP were due to increased gene transcription (as judged by nuclear transcription run-on assays), although with respect to GLUT-1, an increase in mRNA stability was also observed. Treatment of the cells with forskolin resulted in the induction of GLUT-1 expression as well as expression of the immediate early genes. Exposure of quiescent 3T3-L1 fibroblasts to 8-bromo-cAMP resulted in a substantial increase in rates of total protein and RNA synthesis, but had little effect on DNA synthesis. The results demonstrate that 8-bromo-cAMP initiated a G0/G1 transition, but did not permit progression into S-phase. The results further suggest that increased cytosolic cAMP results in the stimulation of glucose transport by three distinct mechanisms to include translocation of pre-existing transporters, increased transcription of the GLUT-1 gene and increased stability of GLUT-1 mRNA.
Cornelius
P
P
Department of Biochemistry, School of Medicine, East Carolina University, Greenville, North Carolina 27858.
Marlowe
M
M
Call
K
K
Pekala
P H
PH
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology*; D000273:Adipose Tissue / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002455:Cell Division / Q000235:genetics; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D005947:Glucose / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D014176:Protein Biosynthesis / Q000187:drug effects; D011519:Proto-Oncogenes / Q000187:drug effects*; D012333:RNA, Messenger / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014529:Uridine / Q000378:metabolism
D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D007930:Leucine; D005947:Glucose; D013936:Thymidine; D014529:Uridine