👤 Andrea L Bauman

Current conventions, partly derived from self-reported data, typically equate 1 minute of vigorous physical activity (VPA) to 2 minutes of moderate physical activity (MPA). Using accelerometer-derived intensity classification in 73,485 UK Biobank participants (mean follow-up: 8.0 [1.0] years), we assess the equivalence of light activity (LPA) and MPA to 1 minute of VPA for all-cause (ACM) and cardiovascular (CVD) mortality, major adverse cardiovascular events (MACE), type 2 diabetes, and cancer outcomes. For a standardised 5%-35% risk reduction, the median MPA equivalent per minute of VPA is 4.1 (ACM, 95% CI: 4.1-4.2), 7.8 (CVD mortality, 7.7-8.0), 5.4 (MACE, 5.3-5.5), 9.4 (type 2 diabetes, 9.3-9.6), and 3.5 (cancer mortality, 3.4-3.5) minutes. For non-cancer outcomes, the median LPA equivalent per 1 minute of VPA ranges from 53 (ACM) to 94 minutes (type 2 diabetes), reflecting generally weaker dose-response curves of LPA with all outcomes. These findings indicate a substantial departure from self-reported estimates and support integrating device-based equivalence into guidelines and wearables. Show less

The concentration of the second messenger cAMP is tightly controlled in cells by the activity of phosphodiesterases. We have previously described how the protein kinase A-anchoring protein mAKAP serves as a scaffold for the cAMP-dependent protein kinase PKA and the cAMP-specific phosphodiesterase PDE4D3 in cardiac myocytes. PKA and PDE4D3 constitute a negative feedback loop whereby PKA-catalyzed phosphorylation and activation of PDE4D3 attenuate local cAMP levels. We now show that protein phosphatase 2A (PP2A) associated with mAKAP complexes is responsible for reversing the activation of PDE4D3 by catalyzing the dephosphorylation of PDE4D3 serine residue 54. Mapping studies reveal that a C-terminal mAKAP domain (residues 2085-2319) binds PP2A. Binding to mAKAP is required for PP2A function, such that deletion of the C-terminal domain enhances both base-line and forskolin-stimulated PDE4D3 activity. Interestingly, PP2A holoenzyme associated with mAKAP complexes in the heart contains the PP2A targeting subunit B56delta. Like PDE4D3, B56delta is a PKA substrate, and PKA phosphorylation of mAKAP-bound B56delta enhances phosphatase activity 2-fold in the complex. Accordingly, expression of a B56delta mutant that cannot be phosphorylated by PKA results in increased PDE4D3 phosphorylation. Taken together, our findings demonstrate that PP2A associated with mAKAP complexes promotes PDE4D3 dephosphorylation, serving both to inhibit PDE4D3 in unstimulated cells and also to mediate a cAMP-induced positive feedback loop following adenylyl cyclase activation and B56delta phosphorylation. In general, PKA.PP2A.mAKAP complexes exemplify how protein kinases and phosphatases may participate in molecular signaling complexes to dynamically regulate localized intracellular signaling. Show less

mAKAPbeta is the scaffold for a multimolecular signaling complex in cardiac myocytes that is required for the induction of neonatal myocyte hypertrophy. We now show that the pro-hypertrophic phosphatase calcineurin binds directly to a single site on mAKAPbeta that does not conform to any of the previously reported consensus binding sites. Calcineurin-mAKAPbeta complex formation is increased in the presence of Ca(2+)/calmodulin and in norepinephrine-stimulated primary cardiac myocytes. This binding is of functional significance because myocytes exhibit diminished norepinephrine-stimulated hypertrophy when expressing a mAKAPbeta mutant incapable of binding calcineurin. In addition to calcineurin, the transcription factor NFATc3 also associates with the mAKAPbeta scaffold in myocytes. Calcineurin bound to mAKAPbeta can dephosphorylate NFATc3 in myocytes, and expression of mAKAPbeta is required for NFAT transcriptional activity. Taken together, our results reveal the importance of regulated calcineurin binding to mAKAPbeta for the induction of cardiac myocyte hypertrophy. Furthermore, these data illustrate how scaffold proteins organizing localized signaling complexes provide the molecular architecture for signal transduction networks regulating key cellular processes. Show less

Common challenges to any cell are the processing of the extracellular stimuli it receives into intracellular signaling cascades that initiate a multitude of diverse biological functions. However, many of these stimuli act via a common signaling pathway, suggesting the cell must somehow discriminate between different stimuli and respond accordingly. Subcellular targeting through the association with adaptor and scaffolding proteins has emerged as a key mechanism by which cells maintain signaling specificity. Compartmentation of cAMP signaling is maintained by the clustering of cAMP signaling enzymes in discrete units by the scaffolding protein A-kinase anchoring proteins (AKAP). In doing so, AKAPs provide the molecular architecture for the cAMP micordomains that underlie the spacial-temporal control of cAMP signaling. Show less

Cardiac hypertrophy is regulated by a large intracellular signal transduction network. Each of the many signaling pathways in this network contributes uniquely to the control of cell growth. In the last few years, it has become apparent that multimolecular signaling complexes or 'signalosomes' are important for mediating crosstalk between different signaling pathways. These complexes integrate upstream signals and control downstream effectors. In the cardiac myocyte, the protein mAKAPbeta serves as a scaffold for a large signalosome that is responsive to upstream cAMP, Ca(2+), and mitogen-activated protein kinase signaling. The mAKAPbeta signalosome is important for the control of NFATc transcription factor activity and for the overall induction of myocyte hypertrophy. Show less

Maladaptive cardiac hypertrophy can progress to congestive heart failure, a leading cause of morbidity and mortality in the United States. A better understanding of the intracellular signal transduction network that controls myocyte cell growth may suggest new therapeutic directions. mAKAP is a scaffold protein that has recently been shown to coordinate signal transduction enzymes important for cytokine-induced cardiac hypertrophy. We now extend this observation and show mAKAP is important for adrenergic-mediated hypertrophy. One function of the mAKAP complex is to facilitate cAMP-dependent protein kinase A-catalyzed phosphorylation of the ryanodine receptor Ca2+-release channel. Experiments utilizing inhibition of the ryanodine receptor, RNA interference of mAKAP expression and replacement of endogenous mAKAP with a mutant form that does not bind to protein kinase A demonstrate that the mAKAP complex contributes to pro-hypertrophic signaling. Further, we show that calcineurin Abeta associates with mAKAP and that the formation of the mAKAP complex is required for the full activation of the pro-hypertrophic transcription factor NFATc. These data reveal a novel function of the mAKAP complex involving the integration of cAMP and Ca2+ signals that promote myocyte hypertrophy. Show less