Hyper-activation of ATM upon DNA-PKcs inhibition modulates p53 dynamics and cell fate in response to DNA damage

A functional DNA damage response is essential for maintaining genome integrity in the presence of DNA double strand breaks. It is mainly coordinated by the kinases ATM, ATR and DNA-PKcs, which control the repair of broken DNA strands and relay the damage signal to the tumor suppressor p53 to induce cell cycle arrest, apoptosis or senescence. Although many functions of the individual kinases have been identified, it remains unclear how they act in concert to ensure faithful processing of the damage signal. Using specific inhibitors and quantitative analysis at the single cell level, we systematically characterize the contribution of each kinase for regulating p53 activity. Our results reveal a new regulatory interplay, where loss of DNA-PKcs function leads to hyper-activation of ATM and amplification of the p53 response, sensitizing cells for damage-induced senescence. This interplay determines the outcome of treatments regimens combining irradiation with DNA-PKcs inhibitors in a p53-dependent manner

Cell-specific responses to the cytokine TGFβ are determined by variability in protein levels

The cytokine TGFβ provides important information during embryonic development, adult tissue homeostasis, and regeneration. Alterations in the cellular response to TGFβ are involved in severe human diseases. To understand how cells encode the extracellular input and transmit its information to elicit appropriate responses, we acquired quantitative time-resolved measurements of pathway activation at the single-cell level. We established dynamic time warping to quantitatively compare signaling dynamics of thousands of individual cells and described heterogeneous single-cell responses by mathematical modeling. Our combined experimental and theoretical study revealed that the response to a given dose of TGFβ is determined cell specifically by the levels of defined signaling proteins. This heterogeneity in signaling protein expression leads to decomposition of cells into classes with qualitatively distinct signaling dynamics and phenotypic outcome. Negative feedback regulators promote heterogeneous signaling, as a SMAD7 knock-out specifically affected the signal duration in a subpopulation of cells. Taken together, we propose a quantitative framework that allows predicting and testing sources of cellular signaling heterogeneity

Impaired myocardial development resulting in neonatal cardiac hypoplasia alters postnatal growth and stress response in the heart

AIMS: Fetal growth has been proposed to influence cardiovascular health in adulthood, a process referred to as fetal programming. Indeed, intrauterine growth restriction in animal models alters heart size and cardiomyocyte number in the perinatal period, yet the consequences for the adult or challenged heart are largely unknown. The aim of this study was to elucidate postnatal myocardial growth pattern, left ventricular function and stress response in the adult heart after neonatal cardiac hypoplasia in mice. METHODS AND RESULTS: Utilizing a new mouse model of impaired cardiac development leading to fully functional but hypoplastic hearts at birth, we show that myocardial mass is normalized until early adulthood by accelerated physiological cardiomyocyte hypertrophy. Compensatory hypertrophy, however, cannot be maintained upon ageing resulting in reduced organ size without maladaptive myocardial remodeling. Angiotensin II stress revealed aberrant cardiomyocyte growth kinetics in adult hearts after neonatal hypoplasia when compared to normally developed controls, characterized by reversible overshooting hypertrophy. This exaggerated growth mainly depends on STAT3, whose inhibition during Angiotensin II treatment reduces left ventricular mass in both groups but causes contractile dysfunction in developmentally impaired hearts only. Whereas JAK/STAT3 inhibition reduces cardiomyocyte cross sectional area in the latter, it prevents fibrosis in control hearts, indicating fundamentally different mechanisms of action. CONCLUSIONS: Impaired prenatal development leading to neonatal cardiac hypoplasia alters postnatal cardiac growth and stress response in vivo, thereby linking fetal programming to organ size control in the heart