The Bcl-2 protein family and its role in the development of neoplastic disease

Programmed cell death is the physiological process responsible for shaping organs during embryogenesis, maintaining tissue homeostasis and allowing controlled deletion of potentially harmful cells within the adult organism. The genetics of apoptosis are well conserved in all metazoans and although the evolution of humans and worms separated more than 600 million years ago, basic signaling concepts in apoptosis are highly related in both species. More crucial to humans than worms is the fact that abnormalities in cell death control can contribute to the development of cancer. While C.elegans can easily survive with additional somatic cells that should normally be deleted during development humans may suffer pathological consequences, ranging from tumorigenesis to autoimmunity, as a result of mutations in cell death regulatory genes. Despite the high degree of evolutionary conservation in cell death control, apoptosis signaling in mammals is much more complex than in C.elegans. In mammalian cells, programmed cell death can be induced either by ligand-mediated activation of certain members of the tumor necrosis factor receptor family--so-called 'death receptors'--such as Fas (CD95/Apo-1) and TRAIL or it can be induced in a cell autonomous manner in response to certain stress signals by pro-apoptotic members of the Bcl-2 family. In this review, we focus on general concepts of how the Bcl-2 protein family regulates cell death and how deregulation of this 'intrinsic' apoptotic signaling pathway impinges on the pathogenesis of malignant disease, the major cause of death in the aging population.     

Soluble transferrin receptor and zinc protoporphyrin – competitors or efficient partners?

OBJECTIVES: Soluble transferrin receptor (sTfR) and zinc protoporphyrin (ZPP) are both parameters of iron deficient erythropoiesis (IDE), the sTfR measurement is commonly regarded to be the more sensitive test. sTfR also reflects erythropoietic activity, it is increased in enhanced erythropoiesis. METHODS: We investigated the diagnostic accuracy of sTfR in assessment of iron deficiency (ID) and compared it with ZPP. The study was performed on 174 subjects, in which ID has been precisely staged. RESULTS: Individuals without ID and patients with storage iron depletion only, had normal sTfR values. Patients classified as IDE and patients with iron deficiency anemia had significantly increased sTfR. There was a good correlation between sTfR and hemoglobin (r = -0.86; P < 0.0001) and between sTfR and ZPP (r = 0.86; P < 0.0001). When diagnosing ID, ZPP was the more sensitive test. In mildly developed IDE associated with ZPP-ratios between 40 and 70 micromol/mol heme, the sTfR concentration was elevated in only 25% of the cases. Reliably elevated sTfR values were observed only in more advanced IDE, associated with ZPP > 70 mumol/mol heme. CONCLUSIONS: ZPP is not inferior to sTfR when diagnosing IDE. Given the good correlation between sTfR and ZPP and because ZPP is uninfluenced by the erythropoietic activity, sTfR and ZPP are not competitors, rather efficient partners in diagnosing anemias. By measuring ZPP and sTfR simultaneously, the diagnostic uncertainty inherent in each of them individually can be eliminated. In particular, the simultaneous determination of ZPP and sTfR enhances the diagnostic power of sTfR in assessment of the erythropoietic activity.     

Virus-induced over-expression of protein phosphatase 2A inhibits insulin signalling in chronic hepatitis C

BACKGROUND/AIMS: Hepatitis C virus (HCV) infection disturbs glucose and lipid metabolism contributing to the development of liver steatosis, insulin resistance and type 2 diabetes mellitus. On the other hand, insulin resistance and steatosis have been found to be associated with increased rates of fibrosis progression and lower rates of response to interferon therapy in chronic hepatitis C (CHC). The molecular mechanisms contributing to insulin resistance in CHC are not well understood. We have shown previously that protein phosphatase 2A (PP2A) is over-expressed in biopsies from patients with CHC. In this study, we tested if PP2A over-expression leads to insulin resistance. METHODS: We studied insulin signalling in cell lines that allow the regulated over-expression of HCV proteins and of the PP2A catalytic subunit (PP2Ac). Insulin signalling and PP2Ac expression were also studied in HCV transgenic mice and in liver biopsies from patients with CHC. RESULTS: Over-expression of PP2Ac in cells inhibited insulin signalling by dephosphorylation of PKB/Akt. PP2Ac over-expression and impaired insulin signalling were found in the liver of HCV transgenic mice and in liver biopsies of patients with CHC. CONCLUSIONS: HCV-induced over-expression of PP2A in the liver contributes to the pathogenesis of insulin resistance in patients with CHC.     

Functional Characterization of Novel Mutations Affecting Survivin (BIRC5)‐Mediated Therapy Resistance in Head and Neck Cancer Patients

Survivin (BIRC5) is an acknowledged cancer therapy‐resistance factor and overexpressed in head and neck squamous cell carcinomas (HNSCC). Driven by its nuclear export signal (NES), Survivin shuttles between the nucleus and the cytoplasm, and is detectable in both cellular compartments in tumor biopsies. Although predominantly nuclear Survivin is considered a favorable prognostic disease marker for HNSCC patients, the underlying molecular mechanisms are not resolved. Hence, we performed immunohistochemical and mutational analyses using laser capture microdissection on HNSCC biopsies from patients displaying high levels of nuclear Survivin. We found somatic BIRC5 mutations, c.278T>C (p.Phe93Ser), c.292C>T (p.Leu98Phe), and c.288A>G (silent), in tumor cells, but not in corresponding normal tissues. Comprehensive functional characterization of the Survivin mutants by ectopic expression and microinjection experiments revealed that p.Phe93Ser, but not p.Leu98Phe inactivated Survivin's NES, resulted in a predominantly nuclear protein, and attenuated Survivin's dual cytoprotective activity against chemoradiation‐induced apoptosis. Notably, in xenotransplantation studies, HNSCC cells containing the p.Phe93Ser mutation responded significantly better to cisplatin‐based chemotherapy. Collectively, our results underline the disease relevance of Survivin's nucleocytoplasmic transport, and provide first evidence that genetic inactivation of Survivin's NES may account for predominantly nuclear Survivin and increased therapy response in cancer patients.