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S J Morley

Publications and source records attributed to S J Morley.

At least 19 recordsLinked to original sources
PubMed2001

Proteasome inhibitors and immunosuppressive drugs promote the cleavage of eIF4GI and eIF4GII by caspase-8-independent mechanisms in Jurkat T cell lines.

Previously, we have shown that translation eukaryotic initiation factor (eIF) 4GI is cleaved during anti-Fas-mediated apoptosis. Here, we have investigated the effects of the proteasome inhibitors, MG132 and lactacystin, and the immunosuppressants, 2-amino-2[2-(4-octylphenyl)ethyl]-1,3,propane diol (FTY720) and cyclosporin A, on the integrity of eIF4GI and eIF4GII in T cells. Using wild-type Jurkat T cells, we show that the proteasome inhibitors MG132 and lactacystin promote the cleavage of eIF4G, activate caspase-8 and caspase-3-like activities and decrease cell viability. Furthermore, MG132 also promotes the cleavage of eIF4G and the activation of caspase-3-like activity in a caspase-8-deficient Jurkat cell line which is resistant to anti-Fas-mediated apoptosis. Using specific anti-peptide antisera, we show that both eIF4GI and eIF4GII are cleaved in either cell line in response to MG132 and lactacystin. In response to such treatments, we demonstrate that the fragments of eIF4GI generated include those previously observed with anti-Fas antiserum together with a novel product which lacks the ability to interact with eIF4E. In contrast, cells treated with the immunosuppressants FTY720 and cyclosporin A appear to contain only the novel cleavage fragment of eIF4GI and to lack those characteristic of cells treated with anti-Fas antiserum. These data suggest that caspase-8 activation is not required for apoptosis and eIF4G cleavage mediated by proteasome inhibitors and immunosuppressants in human T cells.

Acetylcysteine↗
PubMed2001

Truncated initiation factor eIF4G lacking an eIF4E binding site can support capped mRNA translation.

Picornavirus proteases cleave translation initiation factor eIF4G into a C-terminal two-thirds fragment (hereafter named p100) and an N-terminal one-third fragment, which interacts with the cap-binding factor eIF4E. As the timing of this cleavage correlates broadly with the shut-off of host cell protein synthesis in infected cells, a very widespread presumption has been that p100 cannot support capped mRNA translation. Through the use of an eIF4G-depleted reticulocyte lysate system, we show that this presumption is incorrect. Moreover, recombinant p100 can also reverse the inhibition of capped mRNA translation caused either by m7GpppG cap analogue, by 4E-BP1, which sequesters eIF4E and thus blocks its association with eIF4G, or by cleavage of endogenous eIF4G by picornavirus proteases. The concentration of p100 required for maximum translation of capped mRNAs is approximately 4-fold higher than the endogenous eIF4G concentration in reticulocyte lysates. Our results imply that picornavirus-induced shut-off is not due to an intrinsic inability of p100 to support capped mRNA translation, but to the viral RNA outcompeting host cell mRNA for the limiting concentration of p100.

Animals↗
PubMed2001

Disruption of the interaction of mammalian protein synthesis eukaryotic initiation factor 4B with the poly(A)-binding protein by caspase- and viral protease-mediated cleavages.

Eukaryotic initiation factor (eIF) 4B interacts with several components of the initiation pathway and is targeted for cleavage during apoptosis. In a cell-free system, cleavage of eIF4B by caspase-3 coincides with a general inhibition of protein synthetic activity. Affinity chromatography demonstrates that mammalian eIF4B interacts with the poly(A)-binding protein and that a region consisting of the N-terminal 80 amino acids of eIF4B is both necessary and sufficient for such binding. This interaction is lost when eIF4B is cleaved by caspase-3, which removes the N-terminal 45 amino acids. Similarly, the association of eIF4B with the poly(A)-binding protein in vivo is reduced when cells are induced to undergo apoptosis. Cleavage of the poly(A)-binding protein itself, using human rhinovirus 3C protease, also eliminates the interaction with eIF4B. Thus, disruption of the association between mammalian eIF4B and the poly(A)-binding protein can occur during both apoptosis and picornaviral infection and is likely to contribute to the inhibition of translation observed under these conditions.

3C Viral Proteases↗
PubMed2001

Behavioral treatment for chronic low back pain: a systematic review within the framework of the Cochrane Back Review Group.

STUDY DESIGN: A systematic review of randomized controlled trials. SUMMARY OF BACKGROUND DATA: The treatment of chronic low back pain is not primarily focused on removing an underlying organic disease but at the reduction of disability through the modification of environmental contingencies and cognitive processes. Behavioral interventions are commonly used in the treatment of chronic (disabling) low back pain. OBJECTIVES: To determine whether behavioral therapy is more effective than reference treatments for chronic nonspecific low back pain and which type of behavioral treatment is most effective. METHODS: The authors searched the Medline and PsychLit databases and the Cochrane Controlled Trials Register up to April 1999, and Embase up to September 1999. Also screened were references of identified randomized trials and relevant systematic reviews. Methodologic quality assessment and data extraction were performed independently by two reviewers. The magnitude of effect was assessed by computing a pooled effect size for each domain (i.e., behavioral outcomes, overall improvement, back pain-specific and generic functional status, return to work, and pain intensity) using the random effects model. RESULTS: Only six (25%) studies were high quality. There is strong evidence (level 1) that behavioral treatment has a moderate positive effect on pain intensity (pooled effect size 0.62; 95% confidence interval [CI] 0.25, 0.98), and small positive effects on generic functional status (pooled effect size 0.35; 95% CI: -0.04, 0.74) and behavioral outcomes (pooled effect size 0.40; 95% CI: 0.10, 0.70) of patients with chronic low back pain when compared with waiting-list controls or no treatment. There is moderate evidence (level 2) that a addition of behavioral component to a usual treatment program for chronic low backpain has no positive short-term effect on generic functional status (pooled effect size 0.31; 95% CI: -0.01, 0.64), pain intensity (pooled effect size 0.03; 95% CI:-0.30, 0.36), and behavioral outcomes (pooled effect size 0.19; 95% CI: -0.08, 0.45). CONCLUSIONS: Behavioral treatment seems to be an effective treatment for patients with chronic low back pain,but it is still unknown what type of patients benefit most from what type of behavioral treatment.

Chronic Disease↗
PubMed2001

Phosphorylation of eukaryotic initiation factor 4E (eIF4E) at Ser209 is not required for protein synthesis in vitro and in vivo.

Eukaryotic translation initiation factor 4E (eIF4E) is essential for efficient translation of the vast majority of capped cellular mRNAs; it binds the 5'-methylated guanosine cap of mRNA and serves as a nucleation point for the assembly of the 48S preinitiation complex. eIF4E is phosphorylated in vivo at residue 209 of the human sequence. The phosphorylated form is often regarded as the active state of the protein, with ribosome-associated eIF4E enriched for the phosphorylated form and increased phosphorylation often correlated with upregulation of rates of protein synthesis. However, the only reported measured effect attributable to phosphorylation at the physiological site has been a relatively small increase in the affinity of eIF4E for the mRNA m7GTP cap structure. Here, we provide data to suggest that phosphorylation of eIF4E at Ser209 is not required for translation. eIF4E that is modified such that it cannot be phosphorylated (Ser209-->Ala), is unimpaired in its ability to restore translation to an eIF4E-dependent in vitro translation system. In addition, both the wild-type and mutant forms of eIF4E interact equally well with eIF4G, with the phosphorylation of eIF4E not required to effect the change in conformation of eIF4G that is required for efficient cleavage of eIF4G by L-protease. Furthermore, we show that wild-type and phosphorylation-site variants of eIF4E protein are equally able to rescue the lethal phenotype of eIF4E deletion in S. cerevisiae.

Animals↗
PubMed2001

Activity of the hepatitis A virus IRES requires association between the cap-binding translation initiation factor (eIF4E) and eIF4G.

The question of whether translation initiation factor eIF4E and the complete eIF4G polypeptide are required for initiation dependent on the IRES (internal ribosome entry site) of hepatitis A virus (HAV) has been examined using in vitro translation in standard and eIF4G-depleted rabbit reticulocyte lysates. In agreement with previous publications, the HAV IRES is unique among all picornavirus IRESs in that it was inhibited if translation initiation factor eIF4G was cleaved by foot-and-mouth disease L-proteases. In addition, the HAV IRES was inhibited by addition of eIF4E-binding protein 1, which binds tightly to eIF4E and sequesters it, thus preventing its association with eIF4G. The HAV IRES was also inhibited by addition of m(7)GpppG cap analogue, irrespective of whether the RNA tested was capped or not. Thus, initiation on the HAV IRES requires that eIF4E be associated with eIF4G and that the cap-binding pocket of eIF4E be empty and unoccupied. This suggests two alternative models: (i) initiation requires a direct interaction between an internal site in the IRES and eIF4E/4G, an interaction which involves the cap-binding pocket of eIF4E in addition to any direct eIF4G-RNA interactions; or (ii) it requires eIF4G in a particular conformation which can be attained only if eIF4E is bound to it, with the cap-binding pocket of the eIF4E unoccupied.

5' Untranslated Regions↗
PubMed2001

Interaction of eukaryotic translation initiation factor 4G with the nuclear cap-binding complex provides a link between nuclear and cytoplasmic functions of the m(7) guanosine cap.

In eukaryotes the majority of mRNAs have an m(7)G cap that is added cotranscriptionally and that plays an important role in many aspects of mRNA metabolism. The nuclear cap-binding complex (CBC; consisting of CBP20 and CBP80) mediates the stimulatory functions of the cap in pre-mRNA splicing, 3' end formation, and U snRNA export. As little is known about how nuclear CBC mediates the effects of the cap in higher eukaryotes, we have characterized proteins that interact with CBC in HeLa cell nuclear extracts as potential mediators of its function. Using cross-linking and coimmunoprecipitation, we show that eukaryotic translation initiation factor 4G (eIF4G), in addition to its function in the cytoplasm, is a nuclear CBC-interacting protein. We demonstrate that eIF4G interacts with CBC in vitro and that, in addition to its cytoplasmic localization, there is a significant nuclear pool of eIF4G in mammalian cells in vivo. Immunoprecipitation experiments suggest that, in contrast to the cytoplasmic pool, much of the nuclear eIF4G is not associated with eIF4E (translation cap binding protein of eIF4F) but is associated with CBC. While eIF4G stably associates with spliceosomes in vitro and shows close association with spliceosomal snRNPs and splicing factors in vivo, depletion studies show that it does not participate directly in the splicing reaction. Taken together the data indicate that nuclear eIF4G may be recruited to pre-mRNAs via its interaction with CBC and accompanies the mRNA to the cytoplasm, facilitating the switching of CBC for eIF4F. This may provide a mechanism to couple nuclear and cytoplasmic functions of the mRNA cap structure.

3T3 Cells↗
PubMed2001

Utilizing the peptidyl-prolyl cis-trans isomerase pin1 as a probe of its phosphorylated target proteins. Examples of binding to nuclear proteins in a human kidney cell line and to tau in Alzheimer's diseased brain.

The human parvulin Pin1 is a member of the peptidyl-prolyl cis-trans isomerase group of proteins, which modulate the assembly, folding, activity, and transport of essential cellular proteins. Pin1 is a mitotic regulator interacting with a range of proteins that are phosphorylated before cell division. In addition, an involvement of Pin1 in the tau-related neurodegenerative brain disorders has recently been shown. In this context, Pin1 becomes depleted from the nucleus in Alzheimer's disease (AD) neurons when it is redirected to the large amounts of hyperphosphorylated tau associated with the neurofibrillary tangles. This depletion from the nucleus may ultimately contribute to neuron cell death. Recently we have devised a novel methodology in which exogenous Pin1 is used as a TEM probe for its target proteins. Here we extend this methodology to provide further evidence that Pin1 binds at enhanced levels to mitotic nuclear proteins and to hyperphosphorylated tau in AD brain. We suggest that exogenous Pin1 labeling can be used to elucidate the phosphorylation status of its target proteins in general and could specifically provide important insights into the development of tau-related neurodegenerative brain disorders.

Alzheimer Disease↗
PubMed2000

Behavioral treatment for chronic low back pain: a systematic review within the framework of the Cochrane Back Review Group.

STUDY DESIGN: A systematic review of randomized controlled trials. SUMMARY OF BACKGROUND DATA: The treatment of chronic low back pain is not primarily focused on removing an underlying organic disease but at the reduction of disability through the modification of environmental contingencies and cognitive processes. Behavioral interventions are commonly used in the treatment of chronic (disabling) low back pain. OBJECTIVES: To determine whether behavioral therapy is more effective than reference treatments for chronic nonspecific low back pain and which type of behavioral treatment is most effective. METHODS: The authors searched the Medline and PsychLit databases and the Cochrane Controlled Trials Register up to April 1999, and Embase up to September 1999. Also screened were references of identified randomized trials and relevant systematic reviews. Methodologic quality assessment and data extraction were performed independently by two reviewers. The magnitude of effect was assessed by computing a pooled effect size for each domain (i.e., behavioral outcomes, overall improvement, back pain-specific and generic functional status, return to work, and pain intensity) using the random effects model. RESULTS: Only six (25%) studies were high quality. There is strong evidence (level 1) that behavioral treatment has a moderate positive effect on pain intensity (pooled effect size 0.62; 95% confidence interval [CI] 0. 25, 0.98), and small positive effects on generic functional status (pooled effect size 0.35; 95% CI: 0.04, 0.74) and behavioral outcomes (pooled effect size 0.40; 95% CI: 0.10, 0.70) of patients with chronic low back pain when compared with waiting-list controls or no treatment. There is moderate evidence (level 2) that a addition of behavioral component to a usual treatment program for chronic low backpain has no positive short-term effect on generic functional status (pooled effect size 0.31; 95% CI: 0.01, 0.64), pain intensity (pooled effect size 0.03; 95% CI: 0.30,0.36), and behavioral outcomes (pooled effect size 0.19; 95% CI: 0.08, 0.45). CONCLUSIONS: Behavioral treatment seems to be an effective treatment for patients with chronic low back pain,but it is still unknown what type of patients benefit most from what type of behavioral treatment.

Analgesics↗
PubMed2000

The role of 5'-leader length, secondary structure and PABP concentration on cap and poly(A) tail function during translation in Xenopus oocytes.

The 5'-cap structure and poly(A) tail of eukaryotic mRNAs function synergistically to promote translation initiation through a physical interaction between the proteins that bind to these regulatory elements. In this study, we have examined the effect of leader length and the presence of secondary structure on the translational competence and the function of the cap and poly(A) tail for mRNAs microinjected into Xenopus oocytes. Increasing the length of the 5'-leader from 17 to 144 nt resulted in a 2- to 4-fold increase in expression from an mRNA containing an unstructured leader but increased expression up to 20-fold for an mRNA containing 5'-proximal structure. Consequently, the presence of secondary structure was less inhibitory for those mRNAs with a longer 5'-leader. Co-injection of poly(A)-binding protein (PABP) mRNA increased the function of the cap and poly(A) tail in promoting translation from poly(A)(+) but not poly(A)(-) mRNAs, particularly for mRNAs containing secondary structure. In the absence of an internal ribosome entry site, expression from the distal cistron of a dicistronic mRNA increased as a function of the length of the intercistronic region and the concentration of PABP. The inhibitory effect of intercistronic located secondary structure on translation was position-dependent. Indeed, the effect of secondary structure was abolished if positioned 134 nt upstream of the distal cistron. These data suggest that the length of a leader, the presence of secondary structure and the concentration of PABP determine the extent to which the cap and poly(A) tail regulate translation.

5' Untranslated Regions↗
PubMed2000

Differential requirements for caspase-8 activity in the mechanism of phosphorylation of eIF2alpha, cleavage of eIF4GI and signaling events associated with the inhibition of protein synthesis in apoptotic Jurkat T cells.

Previously we have reported that induction of apoptosis in Jurkat cells results in an inhibition of overall protein synthesis with the selective and rapid cleavage of eukaryotic initiation factor (eIF) 4GI. For the cleavage of eIF4GI, caspase-3 activity is both necessary and sufficient in vivo, in a process which does not require signaling through the p38 MAP kinase pathway. We now show that activation of the Fas/CD95 receptor promotes an early, transient increase in the level of eIF2alpha phosphorylation, which is temporally correlated with the onset of the inhibition of translation. This is associated with a modest increase in the autophosphorylation of the protein kinase activated by double-stranded RNA. Using a Jurkat cell line that is deficient in caspase-8 and resistant to anti-Fas-induced apoptosis, we show that whilst the cleavage of eIF4GI is caspase-8-dependent, the enhancement of eIF2alpha phosphorylation does not require caspase-8 activity and occurs prior to the cleavage of eIF4GI. In addition, activation of the Fas/CD95 receptor results in the caspase-8-dependent dephosphorylation and degradation of p70(S6K), the enhanced binding of 4E-BP1 to eIF4E, and, at later times, the cleavage of eIF2alpha. These data suggest that apoptosis impinges upon the activity of several polypeptides which are central to the regulation of protein synthesis and that multiple signaling pathways are involved in vivo.

Apoptosis↗
PubMed2000

Behavioural treatment for chronic low back pain.

BACKGROUND: The treatment of chronic low back pain is not primarily focused on removing an underlying organic pathology, but at the reduction of disability through the modification of environmental contingencies and cognitive processes. Behavioural interventions are commonly used in the treatment of chronic (disabling) low back pain. OBJECTIVES: The objective of this systematic review was to determine if behavioural therapy is more effective than reference treatments for chronic non-specific low back pain, and which type of behavioural treatment is most effective. SEARCH STRATEGY: We searched the Medline, PsycLit databases, and the Cochrane Controlled Trials Register up to April 1999, Embase up to September 1999. We also screened references of identified randomised trials and relevant systematic reviews. SELECTION CRITERIA: Only randomised trials on any type of behavioural treatment for non-specific chronic low back pain were included. DATA COLLECTION AND ANALYSIS: Methodological quality assessment and data extraction was done by two reviewers independently. The magnitude of effect was assessed by computing a pooled effect size for each domain (i.e., behavioural outcomes, overall improvement, back pain specific and generic functional status, return to work, and pain intensity) using the random effects model. MAIN RESULTS: Only 6 studies (25%) were high quality. There is strong evidence (level 1) that behavioural treatment has a moderate positive effect on pain intensity (pooled effect size 0.62; 95% CI 0.25, 0.98), and small positive effects on generic functional status (pooled effect size 0.35; 95% CI -0.04, 0.74) and behavioural outcomes (pooled effect size 0.40; 95% CI 0.10, 0.70) of chronic low back pain patients when compared to waiting list controls or no treatment. There is moderate evidence (level 2) that an additional behavioural component to a usual treatment program for chronic low back pain has no positive short-term effect on generic functional status (pooled effect size 0.31; 95% CI - 0.01, 0.64), pain intensity (pooled effect size 0.03; 95% CI - 0.30, 0. 36) and behavioural outcomes (pooled effect size 0.19; 95% CI - 0.08, 0.45). REVIEWER'S CONCLUSIONS: Behavioural treatment seems to be an effective treatment for chronic low back pain patients, but it is still unknown what type of patients benefit most from what type of behavioural treatment.

Behavior Therapy↗
PubMed2000

Translation initiation factor modifications and the regulation of protein synthesis in apoptotic cells.

The rate of protein synthesis is rapidly down-regulated in mammalian cells following the induction of apoptosis. Inhibition occurs at the level of polypeptide chain initiation and is accompanied by the phosphorylation of the alpha subunit of initiation factor eIF2 and the caspase-dependent cleavage of initiation factors eIF4G, eIF4B, eIF2alpha and the p35 subunit of eIF3. Proteolytic cleavage of these proteins yields characteristic products which may exert regulatory effects on the translational machinery. Inhibition of caspase activity protects protein synthesis from long-term inhibition in cells treated with some, but not all, inducers of apoptosis. This review describes the initiation factor modifications and the possible signalling pathways by which translation may be regulated during apoptosis. We discuss the significance of the initiation factor cleavages and other changes for protein synthesis, and the implications of these events for our understanding of the cellular changes associated with apoptosis.

Animals↗
PubMed2000

Cleavage of polypeptide chain initiation factor eIF4GI during apoptosis in lymphoma cells: characterisation of an internal fragment generated by caspase-3-mediated cleavage.

Polypeptide chain initiation factor eIF4GI undergoes caspase-mediated degradation during apoptosis to give characteristic fragments. The most prominent of these has an estimated mass of approximately 76 kDa (Middle-Fragment of Apoptotic cleavage of eIF4G; M-FAG). Subcellular fractionation of the BJAB lymphoma cell line after induction of apoptosis indicates that M-FAG occurs in both ribosome-bound and soluble forms. Affinity chromatography on m7GTP-Sepharose shows that M-FAG retains the ability of eIF4GI to associate with both the mRNA cap-binding protein eIF4E and initiation factor eIF4A and that the ribosome-bound form of M-FAG is also present as a complex with eIF4E and eIF4A. These data suggest that the binding sites for eIF4E, eIF4A and eIF3 on eIF4GI are retained in the caspase-generated fragment. M-FAG is also a substrate for cleavage by the Foot-and-Mouth-Disease Virus-encoded L protease. These properties, together with the pattern of recognition by a panel of antibodies, define the origin of the apoptotic cleavage fragment. N-terminal sequencing of the products of caspase-3-mediated eIF4GI cleavage has identified the major cleavage sites. The pattern of eIF4GI degradation and the possible roles of the individual cleavage products in cells undergoing apoptosis are discussed.

Apoptosis↗
PubMed2000

Changes in integrity and association of eukaryotic protein synthesis initiation factors during apoptosis.

Induction of apoptosis results in inhibition of the rate of overall protein synthesis in a variety of cell types. We have shown previously that polypeptide chain initiation factor eIF4GI is rapidly cleaved by caspase-3, whereas other components of the eIF4F complex are much more stable during apoptosis in BJAB and Jurkat cells. We have now extended our analysis to other factors involved in the initiation of protein synthesis and we report here that eIF4B, the p35 subunit of eIF3, and minor proportions of the alpha subunit of eIF2 and the eIF4E-binding protein 4E-BP1 are also cleaved to give rise to discrete fragments. These cleavages occur with delayed kinetics relative to that seen for eIF4GI, and eIF2beta and eIF2gamma levels also decrease at a relatively late stage of apoptosis. In contrast, the second form of eIF4G described recently, eIF4GII, is cleaved as rapidly as eIF4GI under the same conditions. Purified recombinant caspase-3 is able to degrade eIF4B and eIF3(p35) in vitro, producing fragments of the same sizes as those seen in intact cells. Induction of apoptosis also results in a biphasic change in the association of 4E-BP1 with eIF4E. Thus the progress of apoptosis is characterized by a complex programme of changes in several initiation factors, including the specific fragmentation or complete degradation of some and alterations in the association status of others. These events are likely to contribute to the inhibition of protein synthesis seen under these conditions.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Cellular stress in xenopus kidney cells enhances the phosphorylation of eukaryotic translation initiation factor (eIF)4E and the association of eIF4F with poly(A)-binding protein.

Eukaryotic initiation factor (eIF) 4E binds to the 5'-cap structure of eukaryotic mRNA and has a central role in the control of cell proliferation. We have shown previously that the stimulation of cultured Xenopus kidney cells with serum resulted in the activation of protein synthesis, enhanced phosphorylation of eIF4E and increased binding of the adapter protein, eIF4G, and poly(A)-binding protein (PABP) to eIF4E to form the functional initiation factor complex, eIF4F/PABP. We now show that cellular stresses such as arsenite, anisomycin and heat shock also result in increased phosphorylation of eIF4E, eIF4F complex formation and the association of PABP with eIF4G, in conditions under which the rate of protein synthesis is severely inhibited. In contrast with reported effects on mammalian cells, the stress-induced increase in eIF4F complex formation occurs in the absence of changes in the association of eIF4E with its binding proteins 4E-BP1 or 4E-BP2. The stress-induced changes in eIF4E phosphorylation were totally abrogated by the p38 mitogen-activated protein (MAP) kinase inhibitor SB203580, and were partly inhibited by the phosphoinositide 3-kinase inhibitor LY294002 and the mammalian target of rapamycin (mTOR) inhibitor rapamycin. However, eIF4E phosphorylation was unaffected by extracellular signal-regulated protein kinase (MAP kinase) inhibitor PD98059. These results indicate that cellular stresses activate multiple signalling pathways that converge at the level of eIF4F complex formation to influence the interactions between eIF4E, eIF4G and PABP.

Animals↗
PubMed1999

Caspase-3 is necessary and sufficient for cleavage of protein synthesis eukaryotic initiation factor 4G during apoptosis.

Induction of apoptosis BJAB cells is accompanied by the rapid cleavage of protein synthesis eukaryotic initiation factor 4G and the appearance of a fragment of approximately 76 kDa. Inhibition of apoptotic proteases (caspases) has previously been shown to prevent the cleavage of eukaryotic initiation factor 4G. In MCF-7 breast carcinoma cells, which are deficient in caspase-3, eukaryotic initiation factor 4G is not cleaved but in vivo expression of caspase-3 restores eukaryotic initiation factor 4G cleavage following induction of apoptosis. Recombinant caspase-3 can also cleave eukaryotic initiation factor 4G to yield the 76 kDa fragment both in cell extracts and when the eukaryotic initiation factor 4G is presented in a purified eukaryotic initiation factor 4F complex. These results indicate that caspase-3 activity is necessary and sufficient for eukaryotic initiation factor 4G degradation.

Apoptosis↗