Separation of host range from transformation functions of the hr-t gene of polyomavirus

Garcea, Robert L.; Talmage, David A.; Harmatz, Alan; Freund, Robert; Benjamin, Thomas L.

doi:10.1016/0042-6822(89)90271-7

Cited by 36 publications

(39 citation statements)

References 28 publications

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“…These results were supported by the complete lack of transformation by an MT mutant (Py-1387-T, C3T at position 1387) which lacks the ability to bind the plasma membrane by eliminating the last 37 aa of the carboxy terminus and therefore is not phosphorylated by the associated src kinase activity. However, 1387T is able to replicate to almost wild-type levels in culture, although this has been attributed to the ability of the truncated MT to substitute for the ST function (122,376).…”

Section: Activation Of the Src Familymentioning

confidence: 99%

“…The exact function (targets) of the tyrosine kinase activity of src is unknown, although src, fyn, and yes have been found in all cell types at approximately the same levels with terminally differentiated cells apparently having higher levels (63,341). One of the virus associated functions of src activation may be to phosphorylate the threonines found on VP1, one of the capsid proteins of Py, an apparent requirement for efficient viral encapsidation in vivo, although separable from the portions of MT required for transformation (122,199). In addition, besides using src to phosphorylate important signal transduction activating tyrosines on MT, Py may use the cell cycle progression and/or chemotaxis functions of src, although this relationship has yet to be determined.…”

Section: Activation Of the Src Familymentioning

confidence: 99%

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Natural Biology of Polyomavirus Middle T Antigen

Gottlieb

Villarreal

2001

Microbiol Mol Biol Rev

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“It has been commented by someone that ‘polyoma’ is an adjective composed of a prefix and suffix, with no root between—a meatless linguistic sandwich” (C. J. Dawe). The very name “polyomavirus” is a vague mantel: a name given before our understanding of these viral agents was clear but implying a clear tumor life-style, as noted by the late C. J. Dawe. However, polyomavirus are not by nature tumor-inducing agents. Since it is the purpose of this review to consider the natural function of middle T antigen (MT), encoded by one of the seemingly crucial transforming genes of polyomavirus, we will reconsider and redefine the virus and its MT gene in the context of its natural biology and function. This review was motivated by our recent in vivo analysis of MT function. Using intranasal inoculation of adult SCID mice, we have shown that polyomavirus can replicate with an MT lacking all functions associated with transformation to similar levels to wild-type virus. These observations, along with an almost indistinguishable replication of all MT mutants with respect to wild-type viruses in adult competent mice, illustrate that MT can have a play subtle role in acute replication and persistence. The most notable effect of MT mutants was in infections of newborns, indicating that polyomavirus may be highly adapted to replication in newborn lungs. It is from this context that our current understanding of this well-studied virus and gene is presented

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Section: Activation Of the Src Familymentioning

confidence: 99%

Section: Activation Of the Src Familymentioning

confidence: 99%

Natural Biology of Polyomavirus Middle T Antigen

Gottlieb

Villarreal

2001

Microbiol Mol Biol Rev

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“…Icosahedral viruses like adenovirus (70) and papillomavirus (22,58) harbor phosphorylated structural proteins, although the characteristics and roles of these phosphorylations have not been explored in depth. More information is available for polyomavirus (11,26,39), in which some phosphorylation sites have been mapped that play a function in viral assembly (4,25).…”

mentioning

confidence: 99%

Phosphorylation Status of the Parvovirus Minute Virus of Mice Particle: Mapping and Biological Relevance of the Major Phosphorylation Sites

Maroto

Ramírez

Almendral

2000

J Virol

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The core of the VP-1 and VP-2 proteins forming the T‫1؍‬ icosahedral capsid of the prototype strain of the parvovirus minute virus of mice (MVMp) share amino acids sequence and a common three-dimensional structure; however, the roles of these polypeptides in the virus infection cycle differ. To gain insights into this paradox, the nature, distribution, and biological significance of MVMp particle phosphorylation was investigated. The VP-1 and VP-2 proteins isolated from purified empty capsids and from virions containing DNA harbored phosphoserine and phosphothreonine amino acids, which in two-dimensional tryptic analysis resulted in complex patterns reproducibly composed by more than 15 unevenly phosphorylated peptides. Whereas secondary protease digestions and comigration of most weak peptides in the fingerprints revealed common phosphorylation sites in the VP-1 and VP-2 subunits assembled in capsids, the major tryptic phosphopeptides were remarkably characteristic of either polypeptide. The VP-2-specific peptide named B, containing the bulk of the 32 P label of the MVMp particle in the form of phosphoserine, was mapped to the structurally unordered N-terminal domain of this polypeptide. Mutations in any or all four serine residues present in peptide B showed that the VP-2 N-terminal domain is phosphorylated at multiple sites, even though none of them was essential for capsid assembly or virus formation. Chromatographic analysis of purified wild-type (wt) and mutant peptide B digested with a panel of specific proteases allowed us to identify the VP-2 residues Ser-2, Ser-6, and Ser-10 as the main phosphate acceptors for MVMp capsid during the natural viral infection. Phosphorylation at VP-2 N-terminal serines was not necessary for the externalization of this domain outside of the capsid shell in particles containing DNA. However, the plaque-forming capacity and plaque size of VP-2 N-terminal phosphorylation mutants were severely reduced, with the evolutionarily conserved Ser-2 determining most of the phenotypic effect. In addition, the phosphorylated amino acids were not required for infection initiation or for nuclear translocation of the expressed structural proteins, and thus a role at a late stage of MVMp life cycle is proposed. This study illustrates the complexity of posttranslational modification of icosahedral viral capsids and underscores phosphorylation as a versatile mechanism to modulate the biological functions of their protein subunits.The functions of viral capsids include making contact with cellular receptors on the target cells of the host, intracellular trafficking of the nucleic acid inward to the replication site and outward to the cellular surface, and preservation of vital functions in the environment. Large viruses may code for polypeptides with specific functions for each of these steps, but small viruses must use determinants of a few amino acids to accomplish these life cycle needs. The 20-nm-diameter nonenveloped capsid of the Parvoviridae family (60) offers a well-defined model for f...

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“…Large T is central to virus production as the initiator of viral DNA replication (20). Middle T and small T also play important roles in different aspects of polyomavirus infection (21,23,55). Defects in viral DNA replication and transcription, as well as defects in viral assembly, have been observed in different mutants of middle T and small T (1,7,8,22,38).…”

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confidence: 99%

Genetic Analysis of the Polyomavirus DnaJ Domain

Whalen

Jesus

Kean

et al. 2005

J Virol

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Polyomavirus T antigens share a common N-terminal sequence that comprises a DnaJ domain. DnaJ domains activate DnaK molecular chaperones. The functions of J domains have primarily been tested by mutation of their conserved HPD residues. Here, we report detailed mutagenesis of the polyomavirus J domain in both large T (63 mutants) and middle T (51 mutants) backgrounds. As expected, some J mutants were defective in binding DnaK (Hsc70); other mutants retained the ability to bind Hsc70 but were defective in stimulating its ATPase activity. Moreover, the J domain behaves differently in large T and middle T. A given mutation was twice as likely to render large T unstable as it was to affect middle T stability. This apparently arose from middle T's ability to bind stabilizing proteins such as protein phosphatase 2A (PP2A), since introduction of a second mutation preventing PP2A binding rendered some middle T J-domain mutants unstable. In large T, the HPD residues are critical for Rb-dependent effects on the host cell. Residues Q32, A33, Y34, H49, M52, and N56 within helix 2 and helix 3 of the large T J domain were also found to be required for Rb-dependent transactivation. Cyclin A promoter assays showed that J domain function also contributes to large T transactivation that is independent of Rb. Single point mutations in middle T were generally without effect. However, residue Q37 is critical for middle T's ability to form active signaling complexes. The Q37A middle T mutant was defective in association with pp60 c-src and in transformation.Polyomavirus T antigens function both in replication of the virus and in transformation of the host cell. Large T is central to virus production as the initiator of viral DNA replication (20). Middle T and small T also play important roles in different aspects of polyomavirus infection (21,23,55). Defects in viral DNA replication and transcription, as well as defects in viral assembly, have been observed in different mutants of middle T and small T (1,7,8,22,38). Each of the viral early proteins also contributes to regulation of host cell function. Large T is able to immortalize primary cells (44), to block differentiation (37), and to provoke apoptosis (18, 48). These activities are mediated via association with the retinoblastoma susceptibility (Rb) family of tumor suppressors. Middle T, the major transforming protein, works through activation of cellular signaling pathways that are regulated by src-family tyrosine phosphorylation (15). Small T is able to promote cell cycle progression via association with protein phosphatase 2A (PP2A) (39).All three T antigens are produced by differential splicing of common primary transcripts (56). As a result, they have the identical N-terminal sequence of 79 amino acids that encompasses a DnaJ domain. DnaJ domains, consisting of approximately 70 amino acids, have a helical structure in which a conserved HPD motif is found between helix 2 and helix 3 (2, 13, 32, 43, 54). DnaJ domains, found in a broad range of proteins, function to stimulate ...

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Separation of host range from transformation functions of the hr-t gene of polyomavirus

Cited by 36 publications

References 28 publications

Natural Biology of Polyomavirus Middle T Antigen

Natural Biology of Polyomavirus Middle T Antigen

Phosphorylation Status of the Parvovirus Minute Virus of Mice Particle: Mapping and Biological Relevance of the Major Phosphorylation Sites

Genetic Analysis of the Polyomavirus DnaJ Domain

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