Biomedical subjects

Svetlana Avdulov

Publications and source records attributed to Svetlana Avdulov.

5 recordsLinked to original sources

PubMed2006

Repression of cap-dependent translation attenuates the transformed phenotype in non-small cell lung cancer both in vitro and in vivo.

Aberrant hyperactivation of the cap-dependent protein synthesis apparatus has been documented in a wide range of solid tumors, including epithelial carcinomas, but causal linkage has only been established in breast carcinoma. In this report, we sought to determine if targeted disruption of deregulated cap-dependent translation abrogates tumorigenicity and enhances cell death in non-small cell lung cancer (NSCLC). NSCLC cell lines were stably transfected with either wild-type 4E-BP1 (HA-4E-BP1) or the dominant-active mutant 4E-BP1(A37/A46) (HA-TTAA). Transfected NSCLC cells with enhanced translational repression showed pronounced cell death following treatment with gemcitabine. In addition, transfected HA-TTAA and HA-4E-BP1wt proteins suppressed growth in a cloning efficiency assay. NSCLC cells transduced with HA-TTAA also show decreased tumorigenicity in xenograft models. Xenograft tumors expressing HA-TTAA were significantly smaller than control tumors. This work shows that hyperactivation of the translational machinery is necessary for maintenance of the malignant phenotype in NSCLC, identifies the molecular strategy used to activate translation, and supports the development of lung cancer therapies that directly target the cap-dependent translation initiation complex.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Translation initiation factor 4E blocks endoplasmic reticulum-mediated apoptosis.

Eukaryotic translation initiation factor 4E (eIF4E) is the mRNA cap-binding protein required for translation of cellular mRNAs utilizing the 5' cap structure. The rate-limiting factor for mRNA recruitment to ribosomes, eIF4E is a major target for regulation of translation by growth factors, hormones, and other extracellular stimuli. When overexpressed, eIF4E exerts profound effects on cell growth and survival, leading to suppression of oncogene-dependent apoptosis, causing malignant transformation and conferring tumors with multiple drug resistance. We found previously that overexpressed eIF4E interdicts the apoptotic pathway induced by growth factor withdrawal and cytotoxic drugs by selectively activating the expression of Bcl-X(L), thus preventing mitochondrial release of cytochrome c. In this study, we examined the impact of ectopic eIF4E expression on apoptosis mediated by the endoplasmic reticulum (ER). Here we show that eIF4E rescued cells from the ER stressors brefeldin A, tunicamycin, thapsigargin, and the Ca(2+) ionophore A23187. In addition, we found that cells rescued from Ca(2+) ionophore-triggered apoptosis did not release calcium from their ER nor did they translocate caspase-12 from the ER to the cytoplasm. These data lend strong support to the concept that eIF4E functions as a pleiotropic regulator of cell viability and that integration of critical organelle-mediated checkpoints for apoptosis can be controlled by the cap-dependent translation apparatus.

3T3 Cells↗

PubMed2004

Activation of translation complex eIF4F is essential for the genesis and maintenance of the malignant phenotype in human mammary epithelial cells.

Common human malignancies acquire derangements of the translation initiation complex, eIF4F, but their functional significance is unknown. Hypophosphorylated 4E-BP proteins negatively regulate eIF4F assembly by sequestering its mRNA cap binding component eIF4E, whereas hyperphosphorylation abrogates this function. We found that breast carcinoma cells harbor increases in the eIF4F constituent eIF4GI and hyperphosphorylation of 4E-BP1 which are two alterations that activate eIF4F assembly. Ectopic expression of eIF4E in human mammary epithelial cells enabled clonal expansion and anchorage-independent growth. Transfer of 4E-BP1 phosphorylation site mutants into breast carcinoma cells suppressed their tumorigenicity, whereas loss of these 4E-BP1 phosphorylation site mutants accompanied spontaneous reversion to a malignant phenotype. Thus, eIF4F activation is an essential component of the malignant phenotype in breast carcinoma.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Translation factor eIF4E rescues cells from Myc-dependent apoptosis by inhibiting cytochrome c release.

Eukaryotic translation initiation factor 4E (eIF4E) markedly reduces cellular susceptibility to apoptosis. However, the mechanism by which the translation apparatus operates on the cellular apoptotic machinery remains uncertain. Here we show that eIF4E-mediated rescue from Myc-dependent apoptosis is accompanied by inhibition of mitochondrial cytochrome c release. Experiments achieving gain and loss of function demonstrate that eIF4E-mediated rescue is governed by pretranslational and translational activation of bcl-x as well as by additional intermediates acting directly on, or upstream of, the mitochondria. Thus, our data trace a pathway controlling apoptotic susceptibility that begins with the activity state of the protein synthesis machinery and leads to interdiction of the apoptotic program at the mitochondrial checkpoint.

Animals↗

PubMed2002

Translational control of cell fate: availability of phosphorylation sites on translational repressor 4E-BP1 governs its proapoptotic potency.

Translational control has been recently added to well-recognized genomic, transcriptional, and posttranslational mechanisms regulating apoptosis. We previously found that overexpressed eukaryotic initiation factor 4E (eIF4E) rescues cells from apoptosis, while ectopic expression of wild-type eIF4E-binding protein 1 (4E-BP1), the most abundant member of the 4E-BP family of eIF4E repressor proteins, activates apoptosis--but only in transformed cells. To test the possibility that nontransformed cells require less cap-dependent translation to suppress apoptosis than do their transformed counterparts, we intensified the level of translational repression in nontransformed fibroblasts. Here, we show that inhibition of 4E-BP1 phosphorylation by rapamycin triggers apoptosis in cells ectopically expressing wild-type 4E-BP1 and that expression of 4E-BP1 phosphorylation site mutants potently activates apoptosis in a phosphorylation site-specific manner. In general, proapoptotic potency paralleled repression of cap-dependent translation. However, this relationship was not a simple monotone. As repression of cap-dependent translation intensified, apoptosis increased to a maximum value. Further repression resulted in less apoptosis--a state associated with activation of translation through internal ribosomal entry sites. These findings show: that phosphorylation events govern the proapoptotic potency of 4E-BP1, that 4E-BP1 is proapoptotic in normal as well as transformed fibroblasts, and that malignant transformation is associated with a higher requirement for cap-dependent translation to inhibit apoptosis. Our results suggest that 4E-BP1-mediated control of apoptosis occurs through qualitative rather than quantitative changes in protein synthesis, mediated by a dynamic interplay between cap-dependent and cap-independent processes.

Adaptor Proteins, Signal Transducing↗