The chemotherapeutic Doxorubicin (DOX) has significantly increased survival rates of pediatric and adult cancer patients. However, 10 % of pediatric cancer survivors will 10-20 years later develop severe Dilated Cardiomyopathy (DCM) and the exact molecular mechanisms of disease progression after this long latency time remain puzzling. We here revisit the hypothesis that elevated apoptosis signaling or its increased likelihood after DOX exposure can lead to an impairment of cardiac function and cause a cardiac dilation. Based on recent literature evidences, we first argue why even little detectable apoptosis may be sufficient to cause a dilated phenotype. We then review findings suggesting that mature cardiomyocytes are protected against DOX-induced apoptosis downstream, but not upstream to Mitochondrial Outer Membrane Permeabilisation (MOMP). This lack of prevention of MOMP-induction then is proposed to alter the metabolic phenotype, induce hypertrophic remodeling and lead to functional cardiac impairment even in absence of cardiomyocyte apoptosis. We further discuss findings that DOX exposure can lead to increased sensitivity to further cardiomyocyte apoptosis, which may cause a gradual loss in cardiomyocytes over time and a compensatory hypertrophic remodeling after treatment, potentially explaining the long lag time in disease onset. We finally note similarities between DOX-exposed cardiomyocytes and apoptosisprimed cancer cells and propose computational systems biology as tool to predict patient individual DOX doses. In conclusion, combining recent findings in rodent hearts and cardiomyocytes exposed to DOX with insights from apoptosis signal transduction allowed us to obtain a molecularly deeper insight in this delayed and still enigmatic pathology of DCM. Key messages1. Differentiated cardiomyocyte are protected to post but not pre-MOMP apoptosis 2. MOMP-induction can lead to cardiac hypertrophy and metabolic remodeling after DOX 3. DOX-exposed cardiomyocytes may be more sensitive to apoptosis over life time 4. DOX-exposed cardiomyocytes show similarities to apoptosis-primed cancer cells

The KRAS GTPase plays a fundamental role in transducing signals from plasma membrane growth factor receptors to downstream signalling pathways controlling cell proliferation, survival and migration. Activating KRAS mutations are found in 20% of all cancers and in up to 40% of colorectal cancers, where they contribute to dysregulation of cell processes underlying oncogenic transformation. Multiple KRAS-regulated cell functions are also influenced by changes in intracellular Ca levels that are concurrently modified by receptor signalling pathways. Suppression of intracellular Ca release mechanisms can confer a survival advantage in cancer cells, and changes in Ca entry across the plasma membrane modulate cell migration and proliferation. However, inconsistent remodelling of Ca influx and its signalling role has been reported in studies of transformed cells. To isolate the interaction between altered Ca handling and mutated KRAS in colorectal cancer, we have previously employed isogenic cell line pairs, differing by the presence of an oncogenic KRAS allele (encoding KRAS), and have shown that reduced Ca release from the ER and mitochondrial Ca uptake contributes to the survival advantage conferred by oncogenic KRAS. Here we show in the same cell lines, that Store-Operated Ca Entry (SOCE) and its underlying current, I are under the influence of KRAS. Specifically, deletion of the oncogenic KRAS allele resulted in enhanced STIM1 expression and greater Ca influx. Consistent with the role of KRAS in the activation of the ERK pathway, MEK inhibition in cells with KRAS resulted in increased STIM1 expression. Further, ectopic expression of STIM1 in HCT 116 cells (which express KRAS) rescued SOCE, demonstrating a fundamental role of STIM1 in suppression of Ca entry downstream of KRAS. These results add to the understanding of how ERK controls cancer cell physiology and highlight STIM1 as an important biomarker in cancerogenesis.

The rat cardiomyoblast cell line H9C2 has emerged as a valuable tool for studying cardiac development, mechanisms of disease and toxicology. We present here a rigorous proteomic analysis that monitored the changes in protein expression during differentiation of H9C2 cells into cardiomyocyte-like cells over time. Quantitative mass spectrometry followed by gene ontology (GO) enrichment analysis revealed that early changes in H9C2 differentiation are related to protein pathways of cardiac muscle morphogenesis and sphingolipid synthesis. These changes in the proteome were followed later in the differentiation time-course by alterations in the expression of proteins involved in cation transport and beta-oxidation.