The Notch signaling pathway mediates cell fate decisions1,2 and is tumor suppressive or oncogenic depending on the context2,3. During lung development, Notch pathway activation inhibits the differentiation of precursor cells to a neuroendocrine (NE) fate4–6. In small cell lung cancer (SCLC), an aggressive NE lung cancer7, loss-of-function NOTCH mutations and the inhibitory effects of ectopic Notch activation indicate that Notch signaling is tumor suppressive8,9. Here, we show that Notch signaling can be both tumor suppressive and pro-tumorigenic in SCLC. Endogenous activation of the Notch pathway results in a NE to non-NE fate switch in 10-50% of tumor cells in a mouse model of SCLC and in human tumors. This switch is mediated in part by Rest/Nrsf, a transcriptional repressor that inhibits NE gene expression. Non-NE Notch-active SCLC cells are slow growing, consistent with a tumor suppressive role for Notch, but these cells are also relatively chemoresistant and provide trophic support to NE tumor cells, consistent with a pro-tumorigenic role. Importantly, Notch blockade in combination with chemotherapy suppresses tumor growth and delays relapse. Thus, SCLC tumors generate their own microenvironment via activation of Notch signaling in a subset of tumor cells, and the presence of these cells may serve as a biomarker for the use of Notch pathway inhibitors in combination with chemotherapy in select SCLC patients.

Heart attacks caused by occlusion of coronary arteries are often treated by mechanical or enzymatic removal of the occlusion and reperfusion of the ischemic heart. It is now recognized that reperfusion per se contributes to myocardial damage, and there is a great interest in identifying the molecular basis of this damage. We recently showed that inhibiting protein kinase C␦ (PKC␦) protects the heart from ischemia and reperfusion-induced damage. Here, we demonstrate that PKC␦ activity and mitochondrial translocation at the onset of reperfusion mediates apoptosis by facilitating the accumulation and dephosphorylation of the pro-apoptotic BAD (Bcl-2-associated death promoter), dephosphorylation of Akt, cytochrome c release, PARP (poly(ADPribose) polymerase) cleavage, and DNA laddering. Our data suggest that PKC␦ activation has a critical proapoptotic role in cardiac responses following ischemia and reperfusion.

Abstract-Cardiac ischemia and reperfusion are associated with loss in the activity of the mitochondrial enzyme pyruvate dehydrogenase (PDH). Pharmacological stimulation of PDH activity improves recovery in contractile function during reperfusion. Signaling mechanisms that control inhibition and reactivation of PDH during reperfusion were therefore investigated. Using an isolated rat heart model, we observed ischemia-induced PDH inhibition with only partial recovery evident on reperfusion. Translocation of the redox-sensitive ␦-isoform of protein kinase C (PKC) to the mitochondria occurred during reperfusion. Key Words: pyruvate dehydrogenase Ⅲ ␦PKC Ⅲ pyruvate dehydrogenase kinase Ⅲ free radicals Ⅲ mitochondria Ⅲ ischemia/reperfusion P yruvate dehydrogenase (PDH) is responsible for the conversion of pyruvate derived from glycolysis to acetylCoA for Krebs cycle activity. Enzyme activity is regulated, in part, by phosphorylation-and dephosphorylation-dependent inhibition and activation, respectively. 1,2 Phosphorylation is catalyzed by 4 PDH-associated pyruvate dehydrogenase kinases (PDK1-4) that exhibit tissue-specific expression patterns and differences in specific activity toward 3 phosphorylation sites on the E1␣ subunit of PDH. The PDH complex also contains 2 pyruvate dehydrogenase phosphatases (PDP 1 and PDP 2) responsible for reactivation of PDH. 2-4 PDH therefore represents a highly regulated and critical site for the control of glycolytic flux and ATP production.Cardiac ischemia/reperfusion is associated with alterations in metabolism that, depending on the severity of the ischemic insult, can progress to irreparable myocardial damage. 5 Although PDH activity in myocardial tissue has been reported to decline during flow-induced ischemia, 6 this is not universally observed. [7][8][9] The effects of reperfusion also exhibit considerable variability, with the majority of studies demonstrating a decrease in PDH activity. [7][8][9] Despite the disparity in evidence regarding PDH activity, cardiac efficiency and recovery of contractile function in postischemic hearts can be improved by pharmacological stimulation of PDH 8,10 -16 or infusion of pyruvate. [17][18][19][20][21][22][23] Identification of factors that regulate PDH activity during ischemia/reperfusion may therefore enhance the potential for therapeutic intervention.Reperfusion of ischemic myocardium is associated with enhanced free radical generation. 5,24 Pro-oxidants have been shown to regulate protein function either directly or indirectly through the modulation of other regulatory molecules. [25][26][27] One such example is the novel ␦-isoform of PKC. Exposure of purified ␦PKC to the thiol-specific oxidant diamide and glutathione (GSH) at concentrations that induce inactivation of other PKC isozymes results in ␦PKC activation. 28 Additionally, treatment of various cell types with H 2 O 2 , glutathione depleting agents, or the general PKC activator PMA results in tyrosine phosphorylation and/or activation and translocation of ␦PKC to the mitochondri...