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At least 19 recordsLinked to original sources

PubMed2003

Identification of an additional interaction domain in transmembrane domains 11 and 12 that supports oligomer formation in the human serotonin transporter.

Na+/Cl--dependent neurotransmitter transporters form constitutive oligomers. The topological arrangement is not known, but a leucine heptad repeat in transmembrane domain (TM) 2 and a glycophorin-like motif in TM6 have been proposed to stabilize the oligomer. To determine the topology, we generated versions of the human serotonin transporter (hSERT) that carried cyan or yellow fluorescent proteins at their amino and/or carboxyl terminus. Appropriate pairs were coexpressed to measure fluorescence resonance energy transfer (FRET). Donor photobleaching FRET microscopy was employed to deduce the following arrangement: within the monomer, the amino and carboxyl termini are in close vicinity. In addition, in the oligomer, the carboxyl termini are closer to each other than the amino termini. Hence, a separate interaction domain (i.e. distinct from TM2 and TM6) must reside in the carboxyl-terminal half of hSERT. This was confirmed by expressing the amino- and carboxyl-terminal halves of hSERT. These were retained intracellularly; they also retained the coexpressed full-length transporter by forming export-deficient oligomers and, when cotransfected in all possible combinations, supported FRET. Hence, both the carboxyl and amino termini contain elements that drive oligomerization. By employing fragments comprising two neighboring TM helices, we unequivocally identified TM11/12 as a new contact site by donor photobleaching FRET and beta-lactamase protein fragment complementation assay. TM1/2 was also found to self-associate. Thus, oligomerization of hSERT involves at least two discontinuous interfaces. The currently identified interaction sites drive homophilic interactions. This is consistent with assembly of SERT oligomers in an array-like structure containing multimers of dimers.

Amino Acid Motifs↗

PubMed2004

Restoration of transport activity by co-expression of human reduced folate carrier half-molecules in transport-impaired K562 cells: localization of a substrate binding domain to transmembrane domains 7-12.

Reduced folates such as 5-methyl tetrahydrofolate and classical antifolates such as methotrexate are actively transported into mammalian cells by the reduced folate carrier (RFC). RFC is characterized by 12 stretches of mostly hydrophobic, alpha-helix-promoting amino acids, internally oriented N and C termini, and a large central linker connecting transmembrane domains (TMDs) 1-6 and 7-12. Previous studies showed that deletion of the majority of the central loop domain between TMDs 6 and 7 abolished transport, but this segment could be replaced with mostly non-homologous sequence from the SLC19A2 thiamine transporter to restore transport function. In this report, we expressed RFC from separate TMD1-6 and TMD7-12 RFC half-molecule constructs, each with a unique epitope tag, in RFC-null K562 cells to restore transport activity. Restored transport exhibited characteristic transport kinetics for methotrexate, a capacity for trans-stimulation by pretreatment with leucovorin, and inhibition by N-hydroxysuccinimide methotrexate, a documented affinity inhibitor of RFC. The TMD1-6 half-molecule migrated on SDS gels as a 38-58 kDa glycosylated species and was converted to 27 kDa by N-glycosidase F or tunicamycin treatments. The 40 kDa TMD7-12 half-molecule was unaffected by these treatments. Using transfected cells expressing both TMDs 1-6 and TMDs 7-12 as separate polypeptides, the TMD7-12 half-molecule was covalently radiolabeled with N-hydroxysuccinimide [(3)H]methotrexate. No radioactivity was incorporated into the TMD1-6 half-molecule. Digestion with endoproteinase GluC decreased the size of the radiolabeled 40 kDa TMD7-12 polypeptide to approximately 20 kDa. Our results demonstrate that a functional RFC can be reconstituted with RFC half-molecules and localize a critical substrate binding domain to within TMDs 7-12.

Amino Acid Sequence↗

PubMed2006

Chimeras of the ABC drug transporter Cdr1p reveal functional indispensability of transmembrane domains and nucleotide-binding domains, but transmembrane segment 12 is replaceable with the corresponding homologous region of the non-drug transporter Cdr3p.

The molecular basis of the broad substrate recognition and the transport of substrates by Cdr1p, a major drug efflux protein of Candida albicans, is not well understood. To investigate the role of transmembrane domains and nucleotide-binding domains (NBDs) of Cdr1p in drug transport, two sets of protein chimeras were constructed: one set between homologous regions of Cdr1p and the non-drug transporter Cdr3p, and another set consisting of Cdr1p variants comprising either two N- or two C-terminal NBDs of Cdr1p. The replacement of either the N- or the C-terminal half of Cdr1p by the homologous segments of Cdr3p resulted in non-functional recombinant strains expressing chimeric proteins. The results suggest that the chimeric protein could not reach the plasma membrane, probably because of misfolding and subsequent cellular trafficking problems, or the rapid degradation of the chimeras. As an exception, the replacement of transmembrane segment 12 (TMS12) of Cdr1p by the corresponding region of Cdr3p resulted in a functional chimera which displayed unaltered affinity for all the tested substrates. The variant protein comprising either two N-terminal or two C-terminal NBDs of Cdr1p also resulted in non-functional recombinant strains. However, the N-terminal NBD variant, which also showed poor cell surface localization, could be rescued to cell surface, if cells were grown in the presence of drug substrates. The rescued chimera remained non-functional, as was evident from impaired ATPase and efflux activities. Taken together, the results suggest that the two NBDs of Cdr1p are asymmetric and non-exchangeable and that the drug efflux by Cdr1p involves complex interactions between the two halves of the protein.

Adenosine Triphosphatases↗

PubMed2002

The extracellular N-terminal domain and transmembrane domains 1 and 2 mediate oligomerization of a yeast G protein-coupled receptor.

G protein-coupled receptors (GPCRs) can form homodimers/oligomers and/or heterodimers/oligomers. The mechanisms used to form specific GPCR oligomers are poorly understood because the domains that mediate such interactions and the step(s) in the secretory pathway where oligomerization occurs have not been well characterized. Here we have used subcellular fractionation and fluorescence resonance energy transfer (FRET) experiments to show that oligomerization of a GPCR (alpha-factor receptor; STE2 gene product) of the yeast Saccharomyces cerevisiae occurs in the endoplasmic reticulum. To identify domains of this receptor that mediate oligomerization, we used FRET and endocytosis assays of oligomerization in vivo to analyze receptor deletion mutants. A mutant lacking the N-terminal extracellular domain and transmembrane (TM) domain 1 was expressed at the cell surface but did not self-associate. In contrast, a receptor fragment containing only the N-terminal extracellular domain and TM1 could self-associate and heterodimerize with wild type receptors. Analysis of other mutants suggested that oligomerization is facilitated by the N-terminal extracellular domain and TM2. Therefore, the N-terminal extracellular domain, TM1, and TM2 appear to stabilize alpha-factor receptor oligomers. These domains may form an interface in contact or domain-swapped oligomers. Similar domains may mediate dimerization of certain mammalian GPCRs.

Cell Membrane↗

PubMed1992

Substitution of the insulin receptor transmembrane domain with the c-neu/erbB2 transmembrane domain constitutively activates the insulin receptor kinase in vitro.

To examine the role of the transmembrane domain (TM) of the insulin receptor in insulin-induced receptor kinase activation, we prepared four mutated insulin receptors: 1) a Val938----Asp substitution (IR/TMv----D), 2) insertion of a 3-amino acid repeat (Val938-Phe939-Leu940) (IR/TM+3), or the entire TM was replaced by the corresponding domain of either the 3) platelet-derived growth factor (PDGF) receptor (IR/TMPDGFR) or 4) c-neu/erbB2 proto-oncogene product (IR/TMc-neu). Each mutant receptor was stably expressed in Chinese hamster ovary cells, assessed by fluorescence-activated cell sorting, insulin binding, and biosynthetic labeling. All mutant receptors exhibited normal affinity for insulin. Pulse-chase experiments showed that each proreceptor was processed into alpha- and beta-subunits, although the rate of IR/TMV----D conversion was reduced approximately 3-fold. With IR/TMPDGFR, IR/TMV----D, and IR/TM+3 basal and insulin-stimulated levels of autophosphorylation and tyrosine kinase activation were normal, both in wheat germ agglutinin (WGA)-purified receptor preparations and intact cells. By contrast, following WGA purification or isolation of crude membranes, IR/TMc-neu was a constitutively active autokinase and substrate kinase in vitro. However, in intact cells insulin-stimulated autophosphorylation and kinase activity appeared normal. We conclude that although there is considerable latitude in acceptable structure, residues within the insulin receptor transmembrane domain can play a functional role in regulation of insulin receptor tyrosine kinase activity.

Amino Acid Sequence↗

PubMed1995

Quantitative approaches to utilizing mutational analysis and disulfide crosslinking for modeling a transmembrane domain.

The transmembrane domain of chemoreceptor Trg from Escherichia coli contains four transmembrane segments in its native homodimer, two from each subunit. We had previously used mutational analysis and sulfhydryl cross-linking between introduced cysteines to obtain data relevant to the three-dimensional organization of this domain. In the current study we used Fourier analysis to assess these data quantitatively for periodicity along the sequences of the segments. The analyses provided a strong indication of alpha-helical periodicity in the first transmembrane segment and a substantial indication of that periodicity for the second segment. On this basis, we considered both segments as idealized alpha-helices and proceeded to model the transmembrane domain as a unit of four helices. For this modeling, we calculated helical crosslinking moments, parameters analogous to helical hydrophobic moments, as a quantitative way of condensing and utilizing a large body of crosslinking data. Crosslinking moments were used to define the relative separation and orientation of helical pairs, thus creating a quantitatively derived model for the transmembrane domain of Trg. Utilization of Fourier transforms to provide a quantitative indication of periodicity in data from analyses of transmembrane segments, in combination with helical crosslinking moments to position helical pairs should be useful in modeling other transmembrane domains.

Amino Acid Sequence↗

PubMed1997

Interaction of influenza virus haemagglutinin with sphingolipid-cholesterol membrane domains via its transmembrane domain.

Sphingolipid-cholesterol rafts are microdomains in biological membranes with liquid-ordered phase properties which are implicated in membrane traffic and signalling events. We have used influenza virus haemagglutinin (HA) as a model protein to analyse the interaction of transmembrane proteins with these microdomains. Here we demonstrate that raft association is an intrinsic property encoded in the protein. Mutant HA molecules with foreign transmembrane domain (TMD) sequences lose their ability to associate with the lipid microdomains, and mutations in the HA TMD reveal a requirement for hydrophobic residues in contact with the exoplasmic leaflet of the membrane. We also provide experimental evidence that cholesterol is critically required for association of proteins with lipid rafts. Our data suggest that the binding to specific membrane domains can be encoded in transmembrane proteins and that this information will be used for polarized sorting and signal transduction processes.

Amino Acid Sequence↗

PubMed1991

Lipid association, but not the transmembrane domain, is required for tissue factor activity. Substitution of the transmembrane domain with a phosphatidylinositol anchor.

Full-length tissue factor (263 rTF) and three truncated forms have been expressed in human kidney 293 cells; 1) 243 rTF, which lacks the cytoplasmic tail, is fully functional in the chromogenic assay and has a specific activity comparable with that of the full-length molecule, 263 rTF; 2) 219 rTF, which lacks both the transmembrane and cytoplasmic domains, is not functional; 3) the third variant, referred to as TF-PI, is a fusion protein containing the extracellular domain of TF (amino acids 1-219) fused to the last 37 amino acids of decay-accelerating factor which contain a signal for attachment of a phosphatidylinositol membrane anchor (PI). TF-PI is a membrane-bound protein expressed on the cell surface. The PI anchor restores TF activity lost when the transmembrane domain is deleted from the 219 rTF variant. The ability of the PI anchor to restore activity to 219 rTF clearly demonstrates that while the transmembrane domain is not required for TF activity, lipid association is required.

Amino Acid Sequence↗

PubMed1998

High affinity IgG binding by FcgammaRI (CD64) is modulated by two distinct IgSF domains and the transmembrane domain of the receptor.

The high affinity IgG receptor, FcgammaRI, is comprised of three immunoglobulin superfamily (IgSF) domains (EC1, EC2 and EC3), a single transmembrane spanning region, and a short cytoplasmic tail. We have shown a role for three separate domains of FcgammaRI in the high affinity binding of IgG. Affinity measurements of chimeric FcgammaRs in which EC1 and EC2 of FcgammaRI have been replaced with the homologous EC1 and/or EC2 domains of the low affinity IgG receptor, FcgammaRII indicate that both EC2 and EC3 are essential for high affinity binding of monomeric IgG. Identification of EC3 from FcgammaRI as the binding site for the monoclonal antibody 10.1, which blocks IgG binding, provides further evidence for the role of this domain in binding. In addition, we have found that the affinity of FcgammaRI is increased threefold when co-expressed with its accessory molecule, gamma-chain. Affinity measurements of further chimeras indicates that the transmembrane domain of FcgammaRI has a negative influence upon the affinity of the receptor. To account for these observations, we propose that receptor dimerization is required for maximal affinity of FcgammaRI. Dimerization may serve as the mechanism by which IgG binding triggers several FcgammaRI-mediated events.

Amino Acid Substitution↗

PubMed1998

Targeting to the endoplasmic reticulum in yeast cells by determinants present in transmembrane domains.

The transmembrane domains (TMDs) of many type I integral membrane proteins contain determinants that cause localization in the endoplasmic reticulum (ER) in mammalian cells by an unknown mechanism. Here we show that the yeast ER localization machinery recognizes determinants in TMDs that are very similar to those identified previously in mammalian cells. These determinants are recognized in post-ER compartments and recycled back to the ER, thus acting as ER retrieval signals. Moreover determinants in TMDs are inefficiently sorted in several previously characterized yeast mutants with defects in the ER retrieval machinery. Similar ER retrieval signals are also recognized in the TMDs of polytopic integral membrane proteins, apparently by the same sorting machinery. The isolation of new mutants defective in sorting of membrane determinants might provide a better understanding of the molecular mechanisms involved in this process.

Amino Acid Sequence↗

PubMed2006

A DNA vaccine that encodes rabies virus glycoprotein lacking transmembrane domain enhances antibody response but not protection.

Rabies virus (RV) glycoprotein (gp) consists of three domains: cytoplasmic, transmembrane and ectodomain. It occurs in a complete, membrane-bound form within the infected cell, but it is released from them in a deleted, secreted form lacking the transmembrane domain. This study was performed to test the importance of the transmembrane domain for the capability of the RV gp gene, introduced into mice via a recombinant plasmid (DNA vaccine), to induce immune response and protection against challenge. Although the antibody response to the secreted form of gp was higher than that to complete gp, the protective efficacy of the respective DNA vaccine against challenge was not better than that of the DNA vaccine inducing complete gp. This indicates that the transmembrane domain of RV gp is important for generating protection against rabies and should be present in RV DNA vaccines.

Animals↗

PubMed1998

High affinity recognition of serotonin transporter antagonists defined by species-scanning mutagenesis. An aromatic residue in transmembrane domain I dictates species-selective recognition of citalopram and mazindol.

Human and Drosophila melanogaster serotonin (5-HT) transporters (SERTs) exhibit similar 5-HT transport kinetics and can be distinguished pharmacologically by many, but not all, biogenic amine transporter antagonists. By using human and Drosophila SERT chimeras, major determinants of potencies of two transporter antagonists, mazindol and citalopram, were tracked to the amino-terminal domains encompassing transmembrane domains I and II. Species-scanning mutagenesis, whereby amino acid substitutions are made switching residues from one species to another, was employed on the eight amino acids that differ between human and Drosophila SERTs in this region, and antagonist potencies were reassessed in 5-HT uptake assays. A single mutation in transmembrane domain I of human SERT, Y95F, shifted both citalopram and mazindol to Drosophila SERT-like potencies. Strikingly, these potency changes were in opposite directions suggesting Tyr95 contributes both positive and negative determinants of antagonist potency. To gain insight into how the Y95F mutant might influence mazindol potency, we determined how structural variants of mazindol responded to the mutation. Our studies demonstrate the importance of the hydroxyl group on the heterocyclic nucleus of mazindol for maintaining species-selective recognition of mazindol and suggest that transmembrane domain I participates in the formation of antagonist-binding sites for amine transporters.

Animals↗

PubMed1999

Five-transmembrane domains appear sufficient for a G protein-coupled receptor: functional five-transmembrane domain chemokine receptors.

The putative seven-transmembrane (TM) domains have been the structural hallmark for the superfamily of heterotrimeric G protein-coupled receptors (GPCRs) that regulate a variety of cellular functions by mediating a large number of extracellular signals. Five-TM GPCR mutants of chemokine receptor CCR5 and CXCR4, the N-terminal segment of which connected directly to TM3 as a result of a deletion of TM1-2 and the first intracellular and extracellular loops, have been obtained in this study. Laser confocal microscopy and flow cytometry analysis revealed that these five-TM mutant GPCRs were expressed stably on the cell surface after transfection into human embryonic kidney 293 cells. The five-TM CCR5 and CXCR4 functioned as normal chemokine receptors in mediating chemokine-stimulated chemotaxis, Ca2+ influx, and activation of pertussis toxin-sensitive G proteins. Like the wild-type GPCRs, the five-TM mutant receptors also underwent agonist-dependent internalization and desensitization and were subjected to regulation by GPCR kinases and arrestins. Our study indicates that five-TM domains, at least in the case of CCR5 and CXCR4, appear to meet the minimum structural requirements for a functional GPCR and suggests possible existence of functional five-TM GPCRs in nature during evolution.

1-Methyl-3-isobutylxanthine↗

PubMed1995

Sorting of yeast alpha 1,3 mannosyltransferase is mediated by a lumenal domain interaction, and a transmembrane domain signal that can confer clathrin-dependent Golgi localization to a secreted protein.

alpha 1,3 mannosyltransferase (Mnn1p) is a type II integral membrane protein that is localized to the yeast Golgi complex. We have examined the signals within Mnn1p that mediate Golgi localization by expression of fusion proteins comprised of Mnn1p and the secreted protein invertase. The N-terminal transmembrane domain (TMD) of Mnn1p is sufficient to localize invertase to the Golgi complex by a mechanism that is not saturable by approximately 15-20 fold overexpression. Furthermore, the TMD-mediated localization mechanism is clathrin dependent, as an invertase fusion protein bearing only the Mnn1p TMD is mislocalized to the plasma membrane of a clathrin heavy chain mutant. The Mnn1-invertase fusion proteins are not retained in the Golgi complex as efficiently as Mnn1p, suggesting that other signals may be present in the wild-type protein. Indeed, the Mnn1p lumenal domain (Mnn1-s) is also localized to the Golgi complex when expressed as a functional, soluble protein by exchanging its TMD for a cleavable signal sequence. In contrast to the Mnn1-invertase fusion proteins, overexpression of Mnn1-s saturates its retention mechanism, and results in the partial secretion of this protein. These data indicate that Mnn1p has separable Golgi localization signals within both its transmembrane and lumenal domains.

Amino Acid Sequence↗

PubMed2006

Activation of platelet alphaIIbbeta3 by an exogenous peptide corresponding to the transmembrane domain of alphaIIb.

A transmembrane domain heterodimer, acting in concert with a membrane-proximal cytoplasmic domain clasp, is thought to maintain integrins in a low affinity state. To test whether helix-helix interactions between the alphaIIb and beta3 transmembrane domains regulate the activity of integrin alphaIIbbeta3, we synthesized a soluble peptide corresponding to the alphaIIb transmembrane domain, designated alphaIIb-TM, and we studied its ability to affect alphaIIbbeta3 activity in human platelets. alphaIIb-TM was alpha-helical in detergent micelles and phospholipid vesicles, readily inserted into membrane bilayers, bound to intact purified alphaIIbbeta3, and specifically associated with the transmembrane domain of alphaIIb, rather than the transmembrane domains of beta3, alpha2, and beta1, other integrin subunits present in platelets. When added to suspensions of gel-filtered platelets, alphaIIb-TM rapidly induced platelet aggregation that was not inhibited by preincubating platelets with the prostaglandin E(1) or the ADP scavenger apyrase but was prevented by the divalent cation chelator EDTA. Furthermore, alphaIIb-TM induced fibrinogen binding to platelets but not the binding of osteopontin, a specific ligand for platelet alphavbeta3. The peptide also induced fibrinogen binding to recombinant alphaIIbbeta3 expressed by Chinese hamster ovary cells, confirming that its effect was independent of platelet signal transduction. Finally, transmission electron microscopy of purified alphaIIbbeta3 revealed that alphaIIb-TM shifted the integrin from a closed configuration with its stalks touching to an open configuration with separated stalks. These observations demonstrate that transmembrane domain interactions regulate integrin function in situ and that it is possible to target intra-membranous protein-protein interactions in a way that can have functional consequences.

Animals↗

PubMed2002

Extracellular domains, transmembrane segments, and intracellular domains interact to determine the cation selectivity of Na,K- and gastric H,K-ATPase.

We have previously reported that three residues of the fourth transmembrane segment (TM4) of the Na,K- and gastric H,K-ATPase alpha-subunits appear to play a major role in the distinct cation selectivities of these pumps [Mense, M., et al. (2000) J. Biol. Chem. 275, 1749-1756]. Substituting these three residues in the Na,K-ATPase sequence with their H,K-ATPase counterparts (L319F, N326Y, T340S) and replacing the TM3-TM4 ectodomain sequence with that of the H,K-ATPase alpha-subunit result in a pump that exhibits 50% of its maximal ATPase activity in the absence of Na(+) when the assay is performed at pH 6.0. This effect is not seen when the ectodomain alone is replaced. To gain more insight into the contributions of the three residues to establishing the selectivity of these pumps for Na(+) ions versus protons, we generated Na,K-ATPase constructs in which these residues are replaced by their H,K-ATPase counterparts either singly or in combinations. Surprisingly, none of the point mutants nor even the triple mutant was able to hydrolyze ATP at pH 6.0 at a rate greater than 20% of their respective V(max)s. For the point mutants L319F and N326Y, protons seem to competitively inhibit ATP hydrolysis at pH 6.0, based on the low apparent affinity for Na(+) ions at pH 6.0 compared to pH 7.5. It would appear, therefore, that the cation selectivity of Na,K- and H,K-ATPase is generated through a cooperative effort between residues of transmembrane segments and the flanking loops that connect these transmembrane domains. This view is further supported by homology modeling of the Na,K-ATPase based on the crystal structure of the SERCA pump.

Animals↗

PubMed1998

A functional GTPase domain, but not its transmembrane domain, is required for function of the SRP receptor beta-subunit.

The signal recognition particle and its receptor (SR) target nascent secretory proteins to the ER. SR is a heterodimeric ER membrane protein whose subunits, SRalpha and SRbeta, are both members of the GTPase superfamily. Here we characterize a 27-kD protein in Saccharomyces cerevisiae (encoded by SRP102) as a homologue of mammalian SRbeta. This notion is supported (a) by Srp102p's sequence similarity to SRbeta; (b) by its disposition as an ER membrane protein; (c) by its interaction with Srp101p, the yeast SRalpha homologue; and (d) by its role in SRP-dependent protein targeting in vivo. The GTP-binding site in Srp102p is surprisingly insensitive to single amino acid substitutions that inactivate other GTPases. Multiple mutations in the GTP-binding site, however, inactivate Srp102p. Loss of activity parallels a loss of affinity between Srp102p and Srp101p, indicating that the interaction between SR subunits is important for function. Deleting the transmembrane domain of Srp102p, the only known membrane anchor in SR, renders SR soluble in the cytosol, which unexpectedly does not significantly impair SR function. This result suggests that SR functions as a regulatory switch that needs to associate with the ER membrane only transiently through interactions with other components.

Amino Acid Sequence↗

PubMed2002

Frequent deletion of Fas gene sequences encoding death and transmembrane domains in nasal natural killer/T-cell lymphoma.

Nasal natural killer (NK)/T-cell lymphoma (NL) frequently co-expresses Fas (Apo-1/CD95) and Fas ligand (FasL), but the tumor cells seldom undergo apoptosis. To determine the reason for failure of apoptosis, we examined Fas mRNA expression in 23 NL cases by reverse transcriptase-polymerase chain reaction and sequenced the entire coding region of the Fas gene in 15 of these cases for which the full-length Fas cDNA could be amplified. The reverse transcriptase-polymerase chain reaction analysis revealed that all of the 23 cases expressed Fas mRNA and the sequencing results showed that in addition to the commonly expressed wild-type Fas mRNA and four alternative splice variants detected in 7 cases, mutant Fas transcripts were present in 9 of the 15 (60%) cases sequenced. With confirmation of some Fas mutations at the gene level, 12 deletions in nine cases and one insertion in one case were eventually identified. To rule out any potential polymerase chain reaction artifacts, the same protocol was used to examine 10 reactive tonsils as a control. No aberrant transcripts associated with deletions were detected in these tonsils except for three alternative splice variants. All of the deletion variants detected in NL contained N-terminal preligand assembly domain but not C-terminal death domain and/or transmembrane domain. Co-detection of the wild-type allele and the mutated Fas alleles without the death domain suggested that a dominant-negative mechanism could block the apoptosis signaling. Moreover, loss of the transmembrane domain could protect the tumor cells from apo-ptosis by producing a soluble form of the Fas receptor. The actuarial 3-year survivals leveled off at 15% for patients carrying the Fas mutations and/or splice variants in the lesions and 49% for those carrying the wild type only, but the difference did not reach statistical significance on the univariate analysis (P = 0.396). Taken together, the findings in this study suggest that frequent Fas gene mutations in NL can result in resistance to apoptosis and may contribute to the pathogenesis of NL by adding to the tumor immune privilege.

Adolescent↗