DAP-5, a Novel Homolog of Eukaryotic Translation Initiation Factor 4G Isolated as a Putative Modulator of Gamma Interferon-Induced Programmed Cell Death

Abstract

A functional approach to gene cloning was applied to HeLa cells in an attempt to isolate cDNA fragments which convey resistance to gamma interferon (IFN-␥)-induced programmed cell death. One of the rescued cDNAs, described in this work, was a fragment of a novel gene, named DAP-5. Analysis of a DAP-5 full-length cDNA clone revealed that it codes for a 97-kDa protein that is highly homologous to eukaryotic translation initiation factor 4G (eIF4G, also known as p220). According to its deduced amino acid sequence, this novel protein lacks the N-terminal region of eIF4G responsible for association with the cap binding protein eIF4E. The N-terminal part of DAP-5 has 39% identity and 63% similarity to the central region of mammalian p220. Its C-terminal part is less homologous to the corresponding region of p220, suggesting that it may possess unique functional properties. The rescued DAP-5 cDNA fragment which conveyed resistance to IFN-␥-induced cell death was expressed from the vector in the sense orientation. Intriguingly, it comprised part of the coding region which corresponds to the less conserved C-terminal part of DAP-5 and directed the synthesis of a 28-kDa miniprotein. The miniprotein exerted a dual effect on HeLa cells. Low levels of expression protected the cells from IFN-␥-induced programmed cell death, while high levels of expression were not compatible with continuous cell growth. The relevance of DAP-5 protein to possible changes in a cell's translational machinery during programmed cell death and growth arrest is discussed.

Degradation of eukaryotic polypeptide chain initiation factor (eIF) 4G in response to induction of apoptosis in human lymphoma cell lines

“…Over-expression of the factor has been reported to cause malignant transformation (Fukuchi-Shimogori et al, 1997). Intriguingly, a fragment of a gene that encodes a mammalian homologue of the C-terminal part of eIF4G, variously called p97, DAP-5 or NAT1 Levy-Strumpf et al, 1997;Yamanaka et al, 1997), has been reported to protect HeLa cells against interferong-induced apoptosis. The functional relationship, if any, of p97/DAP-5/NAT1 to the ca.…”

DAP5 and IRES-mediated translation during programmed cell death

“…DAP5/ p97/NAT1) stem from the fact that the gene was identified and cloned simultaneously by four independent groups. [60][61][62][63] In our laboratory, DAP5 was isolated as a positive mediator of IFN-g-induced cell death. 64 It was rescued in a genetic screen, which was based on knocking down RNA expression by transfection with antisense cDNA libraries followed by positive growth selection.…”

“…Independently, expression of an antisense cDNA fragment of DAP5 was also found to exert similar death-protective effects, further establishing the role of DAP5 as a positive mediator of cell death in the IFN-g system, which represents a slow type of cell death. 61 In parallel, Sonenberg and colleagues cloned DAP5/p97 in an effort to identify novel homologs of the eukaryotic translation initiation factor eIF4GI. 60 In addition, Shaughnessy et al, cloned the mouse DAP5 gene based on its physical linkage to a common retroviral integration site found in myeloid leukemia of BXH2 mice.…”

“…Its mRNA possesses a relatively long 5 0 UTR and a single ORF starting at a GUG initiation codon, which resides within the consensus sequence for non-AUG initiators. [60][61][62][63] The homology to eIF4G 65,66 was restricted to the central segment of eIF4GI/II, which corresponds to the region that binds to eIF4A and eIF3, necessary elements of the translation initiation complex. Interestingly, the N-terminal part of eIF4GI/GII, which mediates the interaction with the mRNA cap structure by direct binding to eIF4E, is completely missing from DAP5 protein (Figure 1).…”

“…Consistent with the structural predictions, it was shown by a few strategies that DAP5/p97/NAT1 indeed binds eIF3 and eIF4A, but fails to bind eIF4E, which is essential for mediating cap-dependent translation. 60,61,63,[65][66][67][68] In this respect, DAP5 resembles the cleaved version of eIF4GI/GII that arises upon picornavirus infection. This structural resemblance raised the possibility that DAP5, like the virally cleaved eIF4GI/II that lost the capbinding features, may maintain the capability to mediate IRES-driven translation under stress conditions.…”