Helix-Loop-Helix Protein p8, a Transcriptional Regulator Required for Cardiomyocyte Hypertrophy and Cardiac Fibroblast Matrix Metalloprotease Induction

Abstract

Cardiomyocyte hypertrophy and extracellular matrix remodeling, primarily mediated by inflammatory cytokine-stimulated cardiac fibroblasts, are critical cellular events in cardiac pathology. The molecular components governing these processes remain nebulous, and few genes have been linked to both hypertrophy and matrix remodeling. Here we show that p8, a small stress-inducible basic helix-loop-helix protein, is required for endothelin-and ␣-adrenergic agonist-induced cardiomyocyte hypertrophy and for tumor necrosis factorstimulated induction, in cardiac fibroblasts, of matrix metalloproteases (MMPs) 9 and 13-MMPs linked to general inflammation and to adverse ventricular remodeling in heart failure. In a stimulus-dependent manner, p8 associates with chromatin containing c-Jun and with the cardiomyocyte atrial natriuretic factor (anf) promoter and the cardiac fibroblast mmp9 and mmp13 promoters, established activator protein 1 effectors. p8 is also induced strongly in the failing human heart by a process reversed upon therapeutic intervention. Our results identify an unexpectedly broad involvement for p8 in key cellular events linked to cardiomyocyte hypertrophy and cardiac fibroblast MMP production, both of which occur in heart failure.The progression to heart failure involves an initial phase of pathological cardiomyocyte hypertrophy, which develops as a consequence of excess hemodynamic work load and may be triggered by ␣-adrenergic agents, angiotensin II, and/or endothelin. Pathological cardiomyocyte hypertrophy is followed by left ventricular decompensation, characterized by cardiomyocyte loss, and interstitial fibrosis-direct contributors to adverse ventricular remodeling. Ultimately, the contractile properties of the heart are compromised, resulting in heart failure (17,18,27). The molecular components and cellular events required for heart failure remain incompletely understood, and few genes have been linked to both pathological hypertrophy of cardiomyocytes and matrix remodeling (9,17,18,27).Post-myocardial infarction, in addition to hypertrophy of surviving cardiomyocytes, remodeling of the extracellular matrix occurs, particularly within the territory of the infarct, as lost myocytes are replaced by fibrous tissue (22, 23). Key to this remodeling process is the production and release of matrix metalloproteases (MMPs) from both resident cells, especially cardiac fibroblasts, and infiltrating leukocytes. Inflammatory cytokine production (especially tumor necrosis factor [TNF], interleukin-1 [IL-1], and IL-6 family members) by these cells is believed to be the major trigger for induction of MMP expression.Studies employing broad-spectrum inhibitors of MMPs have shown that cytokine (TNF)-stimulated upregulation of the expression of MMPs is a central factor leading to left ventricular dilation post-myocardial infarction, a harbinger of heart failure (28,32,48). Studies of mice with a targeted deletion of mmp9 clearly implicate this factor in not only left ventricular dilation but also in inhibition of neo-an...

p38γ MAPK Cooperates with c-Jun in trans-Activating Matrix Metalloproteinase 9

“…Although these different scenarios require further study, the required role of the c-Jun binding activity in p38␥ stimulating c-Jun synthesis, MMP9 transcription, and invasion highlights an essential role of this protein-complex in triggering the invasion cascade. c-Jun was previously shown to bind the MMP9 promoter in cardiac (50) but not in neuronal cells (51), and similarly we showed that c-Jun only binds the MMP9 in the presence of p38␥, indicating a determinant role of c-Jun cofactor abundances in its trans-activation of MMP9. Our results suggest that p38␥ may be one of these critical cofactors to determine c-Jun transcriptional activity by increasing its expression and facilitating its target gene promoter binding.…”

The small chromatin-binding protein p8 coordinates the association of anti-proliferative and pro-myogenic proteins at the myogenin promoter

“…Similar to MyoD, p8 is acetylated by p300, which leads to enhanced transcriptional activity of associated tissue-specific factors such as Pax2 (Hoffmeister et al, 2002). Analysis of p8 secondary structure predicts a HLH motif (Goruppi et al, 2007) towards the C-terminus (positions 46-71), suggesting the potential to dimerize with other HLH proteins, including MyoD (Murre et al, 1989;Benezra et al, 1990). However, the importance of the HLH motif is unresolved because our preliminary studies suggest that overexpression of a mutant p8 lacking helix 2 mimics wild-type p8 in inhibiting the cell cycle as well as MyoD and myogenin expression (S.C., unpublished).…”

“…Partners of p8: p300, p68 and MyoD p8 shares 35% amino acid identity with the HMGA1 (formerly HMGI/Y) chromatin architectural factors (Encinar et al, 2001) and can regulate the activity of different transcription factors, such as Smad (Garcia-Montero et al, 2001), p53 (Clark et al, 2008), Jun and other established AP1 effectors (Goruppi et al, 2007). p8 also binds to p300 and Pax2-transactivation domain interacting protein (PTIP) to regulate the activity of Pax2A and Pax2B on the glucagon promoter (Hoffmeister et al, 2002).…”

“…We identified p8 in a gene-trap screen for loci induced in synchronized myoblasts (Sambasivan et al, 2008). However, this p300-binding phospho-protein has been implicated in the stress response (Vasseur et al, 2004), growth control (Malicet et al, 2003;Vasseur et al, 2002a;Vasseur et al, 1999), tumorigenesis (Vasseur et al, 2002b;Iovanna, 2002), metastasis (Ito et al, 2003) and cardiac hypertrophy (Goruppi et al, 2007). Here, we report a functional analysis of p8 in C2C12 myoblasts using RNA interference (RNAi), overexpression and yeast two-hybrid analysis.…”

Transcription factor TEAD4 regulates expression of Myogenin and the unfolded protein response genes during C2C12 cell differentiation

“…In this study, we show that TEAD4 directly regulates expression of NUPR1 that is required for endothelin-and a-adrenergic agonist-induced cardiomyocyte hypertrophy. 31 Moreover, NUPR1 negatively regulates cardiomyocyte autophagy. Dysfunctional autophagy has been linked to cardiomyopathies and hypertrophy.…”