Endoplasmic reticulum stress prolongs GH-induced Janus kinase (JAK2)/signal transducer and activator of transcription (STAT5) signaling pathway.
The desensitization of the GH-induced Janus kinase 2 (JAK2) and signal transducer and activator of transcription 5 (STAT5) signaling pathway plays a crucial role in GH regulation of hepatic genes. Previous studies have demonstrated that the inactivation of the GH-induced JAK2/STAT5 pathway is regulated by protein translation and suppressors of cytokine signaling (SOCS). In this study we sought to explore the relationships between endoplasmic reticulum stress, GH-induced JAK2/STAT5 activity and SOCS expression. 1,2-bis(o-Aminophenoxy)ethane-N,N,N,N-tetraacetic acid (acetoxymethyl)ester (BAPTA-AM), used to provoke endoplasmic reticulum stress, caused a drastic inhibition of protein translation that correlated with the phosphorylation of the eukaryotic translation initiation factor 2alpha. Both GH and BAPTA-AM caused a rapid induction of the transcription factor C/EBP homology protein (CHOP) and an additive effect was observed with combined treatment, which suggests a regulatory role of GH on endoplasmic reticulum stress. Endoplasmic reticulum stress did not interfere with the rapid GH activation of STAT5 DNA binding activity. However, BAPTA-AM prolonged the DNA binding activity of STAT5 without affecting STAT5 or JAK2 protein levels. GH-induced phosphorylation of JAK2 and STAT5 DNA binding activity were prolonged in the presence of BAPTA-AM, suggesting that endoplasmic reticulum stress prevents the inactivation of STAT5 DNA binding activity by modulating the rate of JAK2/STAT5 dephosphorylation. Like BAPTA-AM, the endoplasmic reticulum stressors dithiothreitol and A23187 also prolonged the GH-induced STAT5 DNA binding activity. We were not able to correlate BAPTA-AM effects to the GH-dependent expression of SOCS proteins or SOCS mRNA, suggesting that endoplasmic reticulum stress modulates the rate of JAK2/STAT5 dephosphorylation through mechanisms other than inhibition of SOCS expression. This study indicates that cellular stress may modulate transcription through the JAK/STAT pathway.
Flores-Morales
A
A
Department of Molecular Medicine, Karolinska Institute, 17176 Stockholm, Sweden. Amilca.Flores@molmed.ki.se
Fernández
L
L
Rico-Bautista
E
E
Umana
A
A
Negrín
C
C
Zhang
J G
JG
Norstedt
G
G
D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002458:Cell Fractionation; D002460:Cell Line; D002614:Chelating Agents / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019382:Human Growth Hormone / Q000494:pharmacology*; D053614:Janus Kinase 2; D008894:Milk Proteins; D014176:Protein Biosynthesis / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012097:Repressor Proteins; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000378:metabolism*; D051742:Transcription Factor CHOP; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins; D002614:Chelating Agents; D004268:DNA-Binding Proteins; C497251:Ddit3 protein, rat; D004791:Enzyme Inhibitors; D008894:Milk Proteins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; D050799:STAT5 Transcription Factor; C491589:Socs1 protein, rat; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D019382:Human Growth Hormone; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D051742:Transcription Factor CHOP; D004533:Egtazic Acid; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507927:Jak2 protein, rat; D053614:Janus Kinase 2