Signal transduction pathways leading to insulin-induced early gene induction.
We examined the signal transduction pathway leading to insulin stimulation of two immediate early genes, c-fos, and the early growth response gene, Egr-1. In Rat 1 fibroblasts overexpressing normal human insulin receptors (HIRc-B), insulin and IGF-I rapidly and transiently induced the expression of both c-fos and Egr-1 mRNA with maximum accumulation at 30 min, declining to basal levels at 120 min. Insulin (100 ng/mL) increased c-fos and Egr-1 mRNA expression 10-fold (EC50 = 20 ng/mL), whereas IGF-I (100 ng/mL) and serum (20%) led to a 3- and 11.5-fold increase, respectively. Insulin-stimulated c-fos protein expression was maximal at 1 h postinduction and undetectable at 4 h. The effects of insulin and IGF-I on both c-fos mRNA and protein expression were absent in Rat 1 fibroblasts expressing tyrosine kinase-defective human insulin receptors (A/K1018). In cells expressing insulin receptors in which the two C-terminal tyrosines are mutated to phenylalanine (Y/F2 cells), the insulin stimulated increase in Egr-1 and c-fos mRNA was comparable to that of HIRc cells, whereas, in cells expressing C-terminal truncated receptors (delta CT cells), the insulin induced increase in Egr-1 mRNA was normal, but the c-fos mRNA response was severely blunted. As expected, the insulin effect to increase ras GTP formation and MAP kinase activity was negligible in A/K1018 cells but normal, or supernormal, in Y/F2 cells. Importantly, stimulation of ras GTP was increased in delta CT cells, whereas stimulation of MAP kinase activity was almost absent.(ABSTRACT TRUNCATED AT 250 WORDS)
Jhun
B H
BH
Department of Medicine, University of California, School of Medicine San Diego, La Jolla, CA 92093, USA.
Haruta
T
T
Meinkoth
J L
JL
Leitner
W
W
Draznin
B
B
Saltiel
A R
AR
Pang
L
L
Sasaoka
T
T
Olefsky
J M
JM
D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics; D051766:Early Growth Response Protein 1; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D017781:Genes, Immediate-Early / Q000187:drug effects*; D016762:Genes, fos; D006160:Guanosine Triphosphate / Q000378:metabolism; D017874:Immediate-Early Proteins; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D012333:RNA, Messenger; D012194:RNA-Directed DNA Polymerase; D051381:Rats; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486110:Egr1 protein, rat; D017874:Immediate-Early Proteins; D007328:Insulin; D012333:RNA, Messenger; D014157:Transcription Factors; D006160:Guanosine Triphosphate; D012194:RNA-Directed DNA Polymerase; D016283:Proto-Oncogene Proteins p21(ras)