- Email: [email protected]
Adenoviral persistence
COMMENT
High-fives for FIV?
Adenoviral persistence
F
eline immunodeficiency virus (FIV) is a widespread lentivirus that causes an AIDS-like illness in cats but does not appear to infect humans, even after frequent cat bites. Poeschla et al. have recently reported experiments in which the FIV 59 long terminal repeat (LTR) U3 element was replaced by the human cytomegalovirus (CMV) immediate-early gene promoter, allowing productive FIV replication in human cells. They then used these CMV promoter–FIV vectors pseudotyped with vesicular stomatitis virus glycoprotein G (VSV-G) to transduce human cells, including nondividing cells. These results delineate a basis for species barriers to lentiviral transduction: i.e. until now, human cells were not infected because of ineffective FIV U3 promoter activity and a lack of receptors for FIV. This work suggests that appropriately engineered FIV might become an effective and potentially safe vector useful in human gene therapy. Poeschla, E.M., Wong-Staal, F. and Looney, D.J. (1998) Efficient transduction of nondividing human cells by feline immunodeficiency virus lentiviral vectors, Nat. Med. 4, 354–357
David E. Symer e-mail: [email protected]
Consistent conjugation
T
ransduction and transformation systems have been developed to move DNA experimentally among mycobacteria. These have their limitations, so the advent of another strategy is welcome. A conjugationlike process was described in mycobacteria almost 30 years ago. Now, this work has been revisited to confirm the occurrence of conjugation in Mycobacterium smegmatis, with the view to developing a new genetic tool. In M. smegmatis, extensive regions of the chromosome can be transferred and integrated into a recipient, possibly by a chromosomal oriT-like mechanism, similar to the Hfr (high frequency of recombination) system found
A
denoviruses have many different mechanisms by which they evade the immune response, but a new mechanism has recently been uncovered that may help to establish persistent infections. Two recent papers have documented the specific reduction in Fas surface expression on adenovirus-infected cells. The E3 10.4K/14.5K receptor internalization and degradation (RID) complex of adenovirus causes decreased surface expression of Fas by targeting it for internalization and degradation in a lysosomal compartment. Transcription and translation of the Fas-encoding gene in infected cells appears to be similar to that inuninfected cells. Internalization of Fas protects the infected cells from Fas-mediated apoptotic cell death, suggesting that it will protect infected cells from cytotoxic T lymphocyte (CTL) killing. Tollefson et al. have shown that
this is the case in a perforin-negative background but that, with normal CTL expressing perforin, there is no protection from killing. Fas is important during the decrease in activated lymphocytes once the immune response is no longer needed. Therefore, this novel mechanism may allow infected lymphocytes to grow without physiological checks and thus aid persistence of adenovirus in these cell types. Shisler, J. et al. (1997) The adenovirus E3-10.4K/14.5K complex mediates loss of cell surface Fas (CD95) and resistance to Fas-induced apoptosis, J. Virol. 71, 8299–8306 Tollefson, A.E. et al. (1998) Forced degradation of Fas inhibits apoptosis in adenovirus-infected cells, Nature 392, 726–730
Barbara Blacklaws e-mail: [email protected]
in Escherichia coli. These authors do suggest other mechanisms by which transfer may occur, such as by a cryptic plasmid or even a novel mechanism similar to that seen in the related Streptomyces and Nocardia spp. Apart from development into a genetic tool, this system permits further investigation of acquisition of antibiotic resistance among mycobacteria.
human CD4-protein G tail (38 aa) were produced. In both cases, VSV efficiently budded from cells, implying that specific information for virus budding is not carried by the VSV G tail. However, some form of tail is necessary, as a cytoplasmic domain of only one aa (compared with a domain containing the first nine aa of the G tail) did not drive efficient budding. Extensive passaging of the nonfunctional virus produced a revertant with a completely unrelated eight aa tail. To account for these findings, the authors propose that a nonspecific cytoplasmic tail fits into grooves formed by oligomers of the matrix or nucleocapsid protein. The only common feature of the functional tails is the presence of at least two basic aa, raising the possibility that ionic interactions of the G tail with an acidic pocket of the capsid drive efficient virus budding.
Parsons, L.M., Jankowski, C.S. and Derbyshire, K.M. (1998) Conjugal transfer of chromosomal DNA in Mycobacterium smegmatis, Mol. Microbiol. 28, 571–582
Schnell, M.J. et al. (1998) Requirement for a non-specific glycoprotein cytoplasmic domain sequence to drive efficient budding of vesicular stomatitis virus, EMBO J. 17, 1289–1296
Caroline Ash e-mail: [email protected]
Gary Whittaker e-mail: [email protected]
Groovy virus tails
I
n most cases, the budding of enveloped viruses requires the presence of envelope glycoproteins, sometimes with specific amino acids (aa) in their cytoplasmic tails. Schnell et al. have addressed the budding of vesicular stomatitis virus (VSV) using recombinant viruses. VSVs containing a wild-type glycoprotein (G) cytoplasmic tail (29 aa) or a
Copyright © 1998 Elsevier Science Ltd. All rights reserved. 0966 842X/98/$19.00 TRENDS
IN
MICROBIOLOGY
220
VOL. 6 NO. 6 JUNE 1998
High-fives for FIV?
Adenoviral persistence
F
eline immunodeficiency virus (FIV) is a widespread lentivirus that causes an AIDS-like illness in cats but does not appear to infect humans, even after frequent cat bites. Poeschla et al. have recently reported experiments in which the FIV 59 long terminal repeat (LTR) U3 element was replaced by the human cytomegalovirus (CMV) immediate-early gene promoter, allowing productive FIV replication in human cells. They then used these CMV promoter–FIV vectors pseudotyped with vesicular stomatitis virus glycoprotein G (VSV-G) to transduce human cells, including nondividing cells. These results delineate a basis for species barriers to lentiviral transduction: i.e. until now, human cells were not infected because of ineffective FIV U3 promoter activity and a lack of receptors for FIV. This work suggests that appropriately engineered FIV might become an effective and potentially safe vector useful in human gene therapy. Poeschla, E.M., Wong-Staal, F. and Looney, D.J. (1998) Efficient transduction of nondividing human cells by feline immunodeficiency virus lentiviral vectors, Nat. Med. 4, 354–357
David E. Symer e-mail: [email protected]
Consistent conjugation
T
ransduction and transformation systems have been developed to move DNA experimentally among mycobacteria. These have their limitations, so the advent of another strategy is welcome. A conjugationlike process was described in mycobacteria almost 30 years ago. Now, this work has been revisited to confirm the occurrence of conjugation in Mycobacterium smegmatis, with the view to developing a new genetic tool. In M. smegmatis, extensive regions of the chromosome can be transferred and integrated into a recipient, possibly by a chromosomal oriT-like mechanism, similar to the Hfr (high frequency of recombination) system found
A
denoviruses have many different mechanisms by which they evade the immune response, but a new mechanism has recently been uncovered that may help to establish persistent infections. Two recent papers have documented the specific reduction in Fas surface expression on adenovirus-infected cells. The E3 10.4K/14.5K receptor internalization and degradation (RID) complex of adenovirus causes decreased surface expression of Fas by targeting it for internalization and degradation in a lysosomal compartment. Transcription and translation of the Fas-encoding gene in infected cells appears to be similar to that inuninfected cells. Internalization of Fas protects the infected cells from Fas-mediated apoptotic cell death, suggesting that it will protect infected cells from cytotoxic T lymphocyte (CTL) killing. Tollefson et al. have shown that
this is the case in a perforin-negative background but that, with normal CTL expressing perforin, there is no protection from killing. Fas is important during the decrease in activated lymphocytes once the immune response is no longer needed. Therefore, this novel mechanism may allow infected lymphocytes to grow without physiological checks and thus aid persistence of adenovirus in these cell types. Shisler, J. et al. (1997) The adenovirus E3-10.4K/14.5K complex mediates loss of cell surface Fas (CD95) and resistance to Fas-induced apoptosis, J. Virol. 71, 8299–8306 Tollefson, A.E. et al. (1998) Forced degradation of Fas inhibits apoptosis in adenovirus-infected cells, Nature 392, 726–730
Barbara Blacklaws e-mail: [email protected]
in Escherichia coli. These authors do suggest other mechanisms by which transfer may occur, such as by a cryptic plasmid or even a novel mechanism similar to that seen in the related Streptomyces and Nocardia spp. Apart from development into a genetic tool, this system permits further investigation of acquisition of antibiotic resistance among mycobacteria.
human CD4-protein G tail (38 aa) were produced. In both cases, VSV efficiently budded from cells, implying that specific information for virus budding is not carried by the VSV G tail. However, some form of tail is necessary, as a cytoplasmic domain of only one aa (compared with a domain containing the first nine aa of the G tail) did not drive efficient budding. Extensive passaging of the nonfunctional virus produced a revertant with a completely unrelated eight aa tail. To account for these findings, the authors propose that a nonspecific cytoplasmic tail fits into grooves formed by oligomers of the matrix or nucleocapsid protein. The only common feature of the functional tails is the presence of at least two basic aa, raising the possibility that ionic interactions of the G tail with an acidic pocket of the capsid drive efficient virus budding.
Parsons, L.M., Jankowski, C.S. and Derbyshire, K.M. (1998) Conjugal transfer of chromosomal DNA in Mycobacterium smegmatis, Mol. Microbiol. 28, 571–582
Schnell, M.J. et al. (1998) Requirement for a non-specific glycoprotein cytoplasmic domain sequence to drive efficient budding of vesicular stomatitis virus, EMBO J. 17, 1289–1296
Caroline Ash e-mail: [email protected]
Gary Whittaker e-mail: [email protected]
Groovy virus tails
I
n most cases, the budding of enveloped viruses requires the presence of envelope glycoproteins, sometimes with specific amino acids (aa) in their cytoplasmic tails. Schnell et al. have addressed the budding of vesicular stomatitis virus (VSV) using recombinant viruses. VSVs containing a wild-type glycoprotein (G) cytoplasmic tail (29 aa) or a
Copyright © 1998 Elsevier Science Ltd. All rights reserved. 0966 842X/98/$19.00 TRENDS
IN
MICROBIOLOGY
220
VOL. 6 NO. 6 JUNE 1998