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.

No abstract

There is increasing evidence that cell cycle transit is potentially lethal, with survival depending on the activation of metabolic pathways which block apoptosis. However, the identities of those pathways coupling cell cycle transit to survival remain undefined. Here we show that the eukaryotic translation initiation factor 4E (eIF4E) can mediate both proliferative and survival signaling. Overexpression of eIF4E completely substituted for serum or individual growth factors in preserving the viability of established NIH 3T3 fibroblasts. An eIF4E mutant (Ser-53 changed to Ala) defective in mediating its growth-factor-regulated functions was also defective in its survival signaling. Survival signaling by enforced expression of eIF4E did not result from autocrine release of survival factors, nor did it lead to increased expression of the apoptosis antagonists Bcl-2 and Bcl-X L . In addition, the execution apparatus of the apoptotic response in eIF4E-overexpressing cells was found to be intact. Increased expression of eIF4E was sufficient to inhibit apoptosis in serum-restricted primary fibroblasts with enforced expression of Myc. In contrast, activation of Ha-Ras, which is required for eIF4E proliferative signaling, did not suppress Myc-induced apoptosis. These data suggest that the eIF4E-activated pathways leading to survival and cell cycle progression are distinct. This dual signaling of proliferation and survival might be the basis for the potency of eIF4E as an inducer of neoplastic transformation.Normal diploid fibroblasts deprived of serum or polypeptide growth factors exit the cell cycle and persist in a quiescent state. When quiescent cells are stimulated to enter the cell cycle by viral oncogenes (31) or by enforced expression of cellular growth-promoting proteins such as c-Myc (2, 8; reviewed in reference 38), E2F (1, 17, 68), or cyclin A (18, 35), they do not progress toward mitosis but undergo programmed cell death. Similarly, the relaxation of negative growth control that occurs during preneoplastic progression of fibroblasts toward immortalization (42, 62) or by decreased retinoblastoma protein expression (1, 57) leads to apoptosis in response to growth factor withdrawal. Along these lines, peptide growth factors such as platelet-derived growth factor (PDGF) and epidermal growth factor can signal both cell cycle entry and apoptosis in fibroblasts deprived of progression-type growth factors (24). These findings support the idea that cell cycle transit is a potentially lethal condition unless specific rescue factors prevent this fate (20,43,44). Therefore, a mitogenic stimulus must coordinately activate metabolic pathways directing both proliferation and survival in order to result in cell division without death. While recent advances in our understanding of the cell division cycle reveal how cells integrate proliferative signals with the cell cycle machinery, the molecular mechanisms and regulatory pathways involved in growth factor survival signaling remain uncertain.The quiescent state is characterize...

Pathologic redirection of translational control by constitutive activation of eukaryotic translation initiation factor 4F

Repair after acute lung injury requires elimination of granulation tissue from the alveolar airspace. We hypothesized that during lung repair, signals capable of inducing the death of the two principal cellular elements of granulation tissue, fibroblasts and endothelial cells, would be present at the air-lung interface. Bronchoalveolar lavage fluid obtained from patients during lung repair induced both fibroblast and endothelial cell death, while fluid obtained at the time of injury or from patient controls did not. The mode of cell death for endothelial cells was apoptosis. Fibroblast death, while morphologically distinct from necrosis, also differed from typical apoptosis. Only proliferating cells were susceptible to the bioactivities in lavage fluid, which were trypsin sensitive and lipid insoluble. Histological examination of lung tissue from patients after lung injury revealed evidence of apoptotic cells within airspace granulation tissue. Our results suggest that cell death induced by peptide(s) present at the air-lung interface may participate in the remodeling process that accompanies tissue repair after injury. (J. Clin. Invest. 1993. 92:388-397.)