Temporal regulation of expression of immediate early and second phase transcripts by endothelin-1 in cardiomyocytes.
BACKGROUND
Endothelin-1 stimulates Gq protein-coupled receptors to promote proliferation in dividing cells or hypertrophy in terminally differentiated cardiomyocytes. In cardiomyocytes, endothelin-1 rapidly (within minutes) stimulates protein kinase signaling, including extracellular-signal regulated kinases 1/2 (ERK1/2; though not ERK5), with phenotypic/physiological changes developing from approximately 12 h. Hypertrophy is associated with changes in mRNA/protein expression, presumably consequent to protein kinase signaling, but the connections between early, transient signaling events and developed hypertrophy are unknown.


RESULTS
Using microarrays, we defined the early transcriptional responses of neonatal rat cardiomyocytes to endothelin-1 over 4 h, differentiating between immediate early gene (IEG) and second phase RNAs with cycloheximide. IEGs exhibited differential temporal and transient regulation, with expression of second phase RNAs within 1 h. Of transcripts upregulated at 30 minutes encoding established proteins, 28 were inhibited >50% by U0126 (which inhibits ERK1/2/5 signaling), with 9 inhibited 25-50%. Expression of only four transcripts was not inhibited. At 1 h, most RNAs (approximately 67%) were equally changed in total and polysomal RNA with approximately 17% of transcripts increased to a greater extent in polysomes. Thus, changes in expression of most protein-coding RNAs should be reflected in protein synthesis. However, approximately 16% of transcripts were essentially excluded from the polysomes, including some protein-coding mRNAs, presumably inefficiently translated.


CONCLUSIONS
The phasic, temporal regulation of early transcriptional responses induced by endothelin-1 in cardiomyocytes indicates that, even in terminally differentiated cells, signals are propagated beyond the primary signaling pathways through transcriptional networks leading to phenotypic changes (that is, hypertrophy). Furthermore, ERK1/2 signaling plays a major role in this response.
Cullingford
Timothy E
TE
National Heart and Lung Institute Division, Faculty of Medicine, Imperial College London, Armstrong Road, London SW7 2AZ, UK. t.cullingford@imperial.ac.uk
Markou
Thomais
T
Fuller
Stephen J
SJ
Giraldo
Alejandro
A
Pikkarainen
Sampsa
S
Zoumpoulidou
Georgia
G
Alsafi
Ali
A
Ekere
Collins
C
Kemp
Timothy J
TJ
Dennis
Jayne L
JL
Game
Laurence
L
Sugden
Peter H
PH
Clerk
Angela
A
D000818:Animals; D002478:Cells, Cultured; D019332:Endothelin-1 / Q000494:pharmacology / Q000502:physiology*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D014176:Protein Biosynthesis / Q000187:drug effects / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D014158:Transcription, Genetic
D019332:Endothelin-1; D012333:RNA, Messenger; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3