C-Mannosylation of Human RNase 2 Is an Intracellular Process Performed by a Variety of Cultured Cells

Krieg, Joachim; Gläsner, Wolfgang; Vicentini, Anna M.; Doucey, Marie‐Agnès; Löffler, Andreas; Heß, Daniel; Hofsteenge, Jan

doi:10.1074/jbc.272.42.26687

Cited by 74 publications

(68 citation statements)

References 28 publications

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“…This is in contrast to the situation in yeast where the factor disappears within 1 ± 2 h of rapamycin treatment (Berset et al, 1998). Another potential mechanism by which cycloheximide might destabilize eIF4G is by promoting the phosphorylation of the 4E-BPs via activation of the mTOR/p70 S6 kinase signalling pathway (Krieg et al, 1988;Brunn et al, 1997;Fadden et al, 1997;Lawrence and Abraham, 1997). This would have the e ect of dissociating eIF4E from the 4E-BPs and favouring its association with eIF4G (Graves et al, 1995;Von Manteu el et al, 1996;Brunn et al, 1997), thus potentially altering the conformation of the latter (Ohlmann et al, 1997).…”

Section: Discussionmentioning

confidence: 95%

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

1998

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We have investigated the e ect of inducing apoptosis in BJAB and Jurkat cells on the cellular content of several polypeptide chain initiation factors. Serum deprivation results in inhibition of protein synthesis and induction of apoptosis in BJAB cells; at early times, there is selective degradation of polypeptide initiation factor eIF4G but no major losses of other key initiation factors. The disappearance of full length eIF4G is accompanied by the appearance of smaller forms of the protein, including a major product of approximately 76 kDa. Apoptosis induced by cycloheximide results in similar e ects. Both total cytoplasmic eIF4G and eIF4G associated with eIF4E are degraded with a half-life of 2 ± 4 h under these conditions. Treatment of serum-starved or cycloheximide-treated cells with Z-VAD.FMK or Z-DEVD.FMK, which inhibit caspases required for apoptosis, protects eIF4G from degradation and blocks the appearance of the ca. 76 kDa product. Exposure of BJAB cells to rapamycin rapidly inhibits protein synthesis but does not lead to acute degradation of eIF4G. In both BJAB and Jurkat cells induction of apoptosis with anti-Fas antibody or etoposide also results in the selective loss of eIF4G, which is inhibitable by Z-VAD.FMK. These data suggest that eIF4G is selectively targeted for cleavage as cells undergo apoptosis and is a substrate for proteases activated during this process.

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Section: Discussionmentioning

confidence: 95%

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

1998

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“…Digests were fractionated by C 8 reversed phase LC-ESIMS as described (10). If necessary final purification was achieved by LC-ESIMS, using 25 mM NH 4 acetate, pH 6.0, containing 2 or 80% CH 3 CN, as buffers A and B, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…The enzyme uses dolichylphosphate mannose as the sugar donor, and its activity has been found in mammals, birds, amphibians, and fish. Furthermore, it could also be detected in most mouse organs that were examined (10,11). In addition to the widespread distribution of the C-mannosyltransferase, its recognition motif, WXXW, has been found in over 300 secreted mammalian proteins (9).…”

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confidence: 95%

The Four Terminal Components of the Complement System AreC-Mannosylated on Multiple Tryptophan Residues

Hofsteenge¹,

Blommers²,

Heß³

et al. 1999

Journal of Biological Chemistry

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100

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C-Mannosylation is a unique form of protein glycosylation, involving the C-glycosidic attachment of a mannosyl residue to the indole moiety of Trp. In the two examples found so far, human RNase 2 and interleukin-12, only the first Trp in the recognition motif WXXW is specifically C-mannosylated. To establish the generality of protein C-mannosylation, and to learn more about its mechanism, the terminal components of the human complement system (C6, C7, C8,and C9), which contain multiple and complex recognition motifs, were examined. Together with C5b they form the cytolytic agent, the membrane attack complex. These are the first proteins that are C-mannosylated on more than one Trp residue as follows: six in C6, four in C7, C8␣, and C8␤, and two in C9. Thus, from the 113 Trp residues in the complete membrane attack complex, 50 were found to undergo C-mannosylation. The other important finding is that in C6, C7, C8, and C9 Trp residues without a second Trp (or another aromatic residue) at the ؉3 position can be C-mannosylated. This shows that they must contain an additional C-mannosylation signal. Whether this is encoded in the primary or tertiary structure is presently unknown. Finally, all modified Trp residues are part of the highly conserved core of the thrombospondin type 1 repeats present in these proteins. Since this module has been found in a large number of other proteins, the results suggest further candidates for C-mannosylation.

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“…Because the initial discovery that liver-derived rpS6 was phosphorylated (11), mitogenic stimulation of cells was found to correlate with phosphorylation of rpS6 on serines, which suggested that rpS6 may control mRNA translation in dividing cells (12). rpS6 phosphorylation sites have been mapped to five clustered residues that are conserved in metazoans, consisting of Ser 235 , Ser 236 , Ser 240 , Ser 244 , and Ser 247 , located at the C-terminal part of the protein (13). Two classes of protein kinases were found to phosphorylate rpS6 in vitro, the S6K1/2 and the p90 ribosomal S6 kinase (RSK) family of serine/threonine kinases (reviewed in Refs.…”

mentioning

confidence: 99%

RAS/ERK Signaling Promotes Site-specific Ribosomal Protein S6 Phosphorylation via RSK and Stimulates Cap-dependent Translation

Roux

Shahbazian

et al. 2007

Journal of Biological Chemistry

638

618

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Converging signals from the mammalian target of rapamycin (mTOR) and phosphoinositide 3-kinase (PI3K) pathways are well established to modulate translation initiation. Less is known regarding the molecular basis of protein synthesis regulated by other inputs, such as agonists of the Ras/extracellular signal-regulated kinase (ERK) signaling cascade. Ribosomal protein (rp) S6 is a component of the 40S ribosomal subunit that becomes phosphorylated at several serine residues upon mitogen stimulation, but the exact molecular mechanisms regulating its phosphorylation and the function of phosphorylated rpS6 is poorly understood. Here, we provide evidence that activation of the p90 ribosomal S6 kinases (RSKs) by serum, growth factors, tumor promoting phorbol esters, and oncogenic Ras is required for rpS6 phosphorylation downstream of the Ras/ERK signaling cascade. We demonstrate that while ribosomal S6 kinase 1 (S6K1) phosphorylates rpS6 at all sites, RSK exclusively phosphorylates rpS6 at Ser 235/236 in vitro and in vivo using an mTORindependent mechanism. Mutation of rpS6 at Ser 235/236 reveals that phosphorylation of these sites promotes its recruitment to the 7-methylguanosine cap complex, suggesting that Ras/ERK signaling regulates assembly of the translation preinitiation complex. These data demonstrate that RSK provides an mTORindependent pathway linking the Ras/ERK signaling cascade to the translational machinery.In eukaryotic cells, the main rate-limiting step of translation is initiation, which is controlled by an array of proteins that respond to signaling cascades activated by extracellular signals (reviewed in Refs. 1-3). The mammalian target of rapamycin, mTOR, 4 is a conserved serine/threonine kinase that integrates signals from nutrients, energy sufficiency, and growth factors to regulate mammalian cell growth (reviewed in Refs. 4, 5-8).Under conditions of nutrient and energy sufficiency and insulin or mitogen stimulation, mTOR stimulates two important translational regulators, the ribosomal S6 kinases (S6K1 and S6K2) and the eukaryotic initiation factor 4E (eIF4E). eIF4E is crucial for ribosome recruitment as it binds to the 7-methylguanosine cap structure (m7GpppN, where N is any nucleotide) at the 5Ј-end of nearly all transcribed mRNAs to initiate cap-dependent translation (reviewed in Ref. 7). When mTOR is active, eIF4E nucleates the assembly of the translation preinitiation complex through recruitment of numerous initiation factors, resulting in association of the ribosomal subunits to the mRNA. S6K1 and S6K2 are serine/threonine kinases directly stimulated by mTOR which in turn, phosphorylate substrates involved in cell and body size (5, 6). S6K1 phosphorylates several substrates located in the cytoplasm and the nucleus, including the ribosomal protein (rp) S6 (reviewed in Ref. 9).Ribosomal protein S6 is one of 33 proteins that comprise the 40 S ribosomal subunit and represents the most extensively studied substrate of S6K1 (10). Because the initial discovery that liver-derived rpS6 was phosphoryla...

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C-Mannosylation of Human RNase 2 Is an Intracellular Process Performed by a Variety of Cultured Cells

Cited by 74 publications

References 28 publications

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

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

The Four Terminal Components of the Complement System AreC-Mannosylated on Multiple Tryptophan Residues

RAS/ERK Signaling Promotes Site-specific Ribosomal Protein S6 Phosphorylation via RSK and Stimulates Cap-dependent Translation

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