Dmp1 (Dmtf1) is activated by oncogenic Ras-Raf signaling and induces cell-cycle arrest in an Arf, p53-dependent fashion. The survival of K-ras(LA) mice was shortened by approximately 15 weeks in both Dmp1(+/-) and Dmp1(-/-) backgrounds, the lung tumors of which showed significantly decreased frequency of p53 mutations compared to Dmp1(+/+). Approximately 40% of K-ras(LA) lung tumors from Dmp1(+/+) mice lost one allele of the Dmp1 gene, suggesting the primary involvement of Dmp1 in K-ras-induced tumorigenesis. Loss of heterozygosity (LOH) of the hDMP1 gene was detectable in approximately 35% of human lung carcinomas, which was found in mutually exclusive fashion with LOH of INK4a/ARF or that of P53. Thus, DMP1 is a pivotal tumor suppressor for both human and murine lung cancers.

SUMMARY Chronic hypoxia in the presence of high glucose leads to progressive acidosis of cardiac myocytes in culture. The condition parallels myocardial ischemia in vivo, where ischemic tissue becomes rapidly hypoxic and acidotic. Cardiac myocytes are resistant to chronic hypoxia at neutral pH but undergo extensive death when the extracellular pH (pH[o]) drops below 6.5. A microarray analysis of 20 000 genes (cDNAs and expressed sequence tags)screened with cDNAs from aerobic and hypoxic cardiac myocytes identified>100 genes that were induced by >2-fold and ∼20 genes that were induced by >5-fold. One of the most strongly induced transcripts was identified as the gene encoding the pro-apoptotic Bcl-2 family member BNIP3. Northern and western blot analyses confirmed that BNIP3 was induced by 12-fold(mRNA) and 6-fold (protein) during 24 h of hypoxia. BNIP3 protein, but not the mRNA, accumulated 3.5-fold more rapidly under hypoxia–acidosis. Cell fractionation experiments indicated that BNIP3 was loosely bound to mitochondria under conditions of neutral hypoxia but was translocated into the membrane when the myocytes were acidotic. Translocation of BNIP3 coincided with opening of the mitochondrial permeability pore (MPTP). Paradoxically,mitochondrial pore opening did not promote caspase activation, and broad-range caspase inhibitors do not block this cell death pathway. The pathway was blocked by antisense BNIP3 oligonucleotides and MPTP inhibitors. Therefore,cardiac myocyte death during hypoxia–acidosis involves two distinct steps: (1) hypoxia activates transcription of the death-promoting BNIP3 gene through a hypoxia-inducible factor-1 (HIF-1) site in the promoter and (2) acidosis activates BNIP3 by promoting membrane translocation. This is an atypical programmed death pathway involving a combination of the features of apoptosis and necrosis. In this article, we will review the evidence for this unique pathway of cell death and discuss its relevance to ischemic heart disease. The article also contains new evidence that chronic hypoxia at neutral pH does not promote apoptosis or activate caspases in neonatal cardiac myocytes.

Summary The transcription factor Dmp1 is a Ras/HER2-activated haplo-insufficient tumor suppressor that activates the Arf/p53 pathway of cell cycle arrest. Recent evidence suggests that Dmp1 may activate p53 independently of Arf in certain cell types. Here we report findings supporting this concept with the definition an Arf-independent function for Dmp1 in tumor suppression. We found that Dmp1 and p53 can interact directly in mammalian cells via the carboxyl-terminus of p53 and the DNA-binding domain of Dmp1. Expression of Dmp1 antagonized ubiquitination of p53 by Mdm2 and promoted nuclear localization of p53. Dmp1-p53 binding significantly increased the level of p53, independent of Dmp1’s DNA-binding activity. Mechanistically, p53 target genes were activated synergistically by co-expression of Dmp1 and p53 in p53−/−; Arf−/−cells and genotoxic responses of these genes were hampered more dramatically in Dmp1−/− and p53−/− cells than in Arf−/− cells. Together, our findings identify a robust new mechanism of p53 activation mediated through by direct physical interaction between Dmp1 and p53.

C-Jun N-terminal kinase (JNK) is part of the mitogen-activated protein kinase (MAPK) family of signaling pathways that are induced in response to extracellular stimuli. JNK is primarily a stress-response pathway and can be activated by proinflammatory cytokines and growth factors coupled to membrane receptors or through non-receptor pathways by stimuli such as heat shock, UV irradiation, protein synthesis inhibitors, and conditions that elevate the levels of reactive oxygen intermediates (ROI). The molecular initiators of MAPKs by non-receptor stimuli have not been described. Ischemia followed by reperfusion or hypoxia with reoxygenation represents a condition of high oxidative stress where JNK activation is associated with elevated ROI. We show here that the activation of JNK by this condition is initiated in the mitochondria and requires coupled electron transport, ROI generation, and calcium flux. These signals cause the selective, sequential activation of the calcium-dependent, proline-rich kinase Pyk2 and the small GTP binding factors Rac-1 and Cdc42. Interruption of these interactions with inactivated dominant negative mutant proteins, blocking calcium flux, or inhibiting electron transport through mitochondrial complexes II, III, or IV prevents JNK activation and results in a proapoptotic phenotype that is characteristic of JNK inhibition in this model of ischemia-reperfusion. The signaling pathway is unique for the reoxygenation stimulus and provides a framework for other non-receptor-mediated pathways of MAPK activation.

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