title: Pivotal role of cardiac lineage protein-1 (CLP-1) in transcriptional elongation factor P-TEFb complex formation in cardiac hypertrophy.
abstract: OBJECTIVE
  Our aim was to determine if the expression pattern of CLP-1 in developing heart is consistent with its role in controlling RNA transcript elongation by transcriptional elongation factor b (P-TEFb) and if the inhibitory control exerted over P-TEFb by CLP-1 is released under hypertrophic conditions.
  
  
  METHODS
  We performed immunoblot and immunofluorescence analysis of CLP-1 and the P-TEFb components cdk9 and cyclin T in fetal mouse heart and 2 day post-natal mouse cardiomyocytes to determine if they are co-localized. We induced hypertrophy in rat cardiomyocytes either by mechanical stretch or treatment with hypertrophic agents such as endothelin-1 and phenylephrine to determine if CLP-1 is released from P-TEFb in response to hypertrophic stimuli. The involvement of the Jak/STAT signal transduction pathway in this process was studied by blocking this pathway with the Jak2 kinase inhibitor, AG490, and assessing the association of CLP-1 with P-TEFb complexes.
  
  
  RESULTS
  We found that CLP-1 is expressed along with P-TEFb components in developing heart during the period in which knockout mice lacking the CLP-1 gene develop cardiac hypertrophy and die. Under conditions of hypertrophy induced by mechanical stretch or agonist treatment, CLP-1 dissociates from the P-TEFb complex, a finding consistent with the de-repression of P-TEFb kinase activity seen in hypertrophic cardiomyocytes. Blockage of Jak/STAT signaling by AG490 prevented release of CLP-1 from P-TEFb despite the ongoing presence of hypertrophic stimulation by mechanical stretch.
  
  
  CONCLUSIONS
  CLP-1 expression in developing heart and isolated post-natal cardiomyocytes colocalizes with P-TEFb expression and therefore has the potential to regulate RNA transcript elongation by controlling P-TEFb cdk9 kinase activity in heart. We further conclude that the dissociation of CLP-1 from P-TEFb is responsive to hypertrophic stimuli transduced by cellular signal transduction pathways. This process may be part of the genomic stress response resulting in increased RNA transcript synthesis in hypertrophic cardiomyocytes.
authors: Center for Cardiovascular and Muscle Research and Department of Anatomy and Cell Biology, State University of New York Downstate Medical Center, Brooklyn, New York, 11203, USA.
authors: Jorge
authors: J
authors: Espinoza-Derout
authors: Michael
authors: M
authors: Wagner
authors: Katayoun
authors: K
authors: Shahmiri
authors: Eduardo
authors: E
authors: Mascareno
authors: Brahim
authors: B
authors: Chaqour
authors: M A Q
authors: MA
authors: Siddiqui
mesh_terms: D000818:Animals; D009320:Atrial Natriuretic Factor / Q000235:genetics / Q000378:metabolism; D015152:Blotting, Northern; D006332:Cardiomegaly / Q000378:metabolism*; D056906:Cyclin T; D042863:Cyclin-Dependent Kinase 9 / Q000032:analysis; D016213:Cyclins / Q000032:analysis; D005455:Fluorescent Antibody Technique; D018507:Gene Expression Regulation, Developmental; D007150:Immunohistochemistry; D053614:Janus Kinase 2 / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000378:metabolism*; D042925:Positive Transcriptional Elongation Factor B / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins; D051381:Rats; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics / Q000502:physiology*
chemical_list: C503685:Ccnt1 protein, mouse; D056906:Cyclin T; D016213:Cyclins; C118642:Hexim1 protein, mouse; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D009320:Atrial Natriuretic Factor; D053614:Janus Kinase 2; D042925:Positive Transcriptional Elongation Factor B; D042863:Cyclin-Dependent Kinase 9