Nucleolar Localization of Mouse Mammary Tumor Virus Proteins in T-Cell Lymphomas

Hoch-Marchaim, Hagit; Hasson, Tsuri; Rorman, Efrat; Cohen, S.; Hochman, Jacob

doi:10.1006/viro.1997.8997

Cited by 13 publications

(19 citation statements)

References 21 publications

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“…Although a variety of viral proteins are translocated into the nucleolus following viral infection (33), we were the first to show that the signal peptide of MMTV-Env precursor is also localized to this compartment (16,17). It turns out that this is not an isolated case, as it was recently shown that the leader sequence of HERV-K is also localized in the nucleolus (22).…”

Section: Discussionmentioning

confidence: 73%

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The Signal Peptide of Mouse Mammary Tumor Virus-Env: A Phosphoprotein Tumor Modulator

Feldman

Roniger

Bar-Sinai

et al. 2012

Molecular Cancer Research

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Mouse mammary tumor virus (MMTV) is associated primarily with mammary carcinomas and lymphomas. The signal peptide of the MMTV envelope precursor is uniquely targeted to nucleoli of cells that harbor the virus, where it can function as a nuclear export factor for intron-containing transcripts. Antibodies to this signal peptide, which we refer to as p14, were previously shown to label nucleoli in a subset of human breast cancers. To look for additional cellular functions of p14, different mutants were ectopically expressed in the MCF-7 human breast cancer cell line. This approach identified motifs responsible for its nucleolar targeting, nucleocytoplasmic shuttling, target protein (B23, nucleophosmin) binding, and phosphorylation at serine 18 and 65 both in situ and in vitro. To test the role of these phosphorylation sites, we carried out in vivo tumorigenesis studies in severe combined immunodeficient mice. The findings show that the p14-Ser65Ala mutation is associated with impaired tumorigenicity, whereas the p14-Ser18Ala mutation is associated with enhanced tumorigenicity. Microarray analysis suggests that phosphorylation at serine 18 or at serine 65 is associated with transcriptional regulation of the L5 nucleolar ribosomal protein (a p14 target) and the Erb-B signal transduction pathway. Taken together, these results show that the phosphorylation status of p14 determines whether it functions as a pro-oncogenic or antioncogenic modulator.

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Section: Discussionmentioning

confidence: 73%

“…Previously, we showed that the signal peptide (98 Nterminal amino acids) of the Env-precursor protein of MMTV is localized in nucleoli of murine T-cell lymphomas that harbor the virus (16,17). This peptide was initially named MMTV-p14 (p14, for short) because of its electrophoretic mobility.…”

Section: Introductionmentioning

confidence: 99%

The Signal Peptide of Mouse Mammary Tumor Virus-Env: A Phosphoprotein Tumor Modulator

Feldman

Roniger

Bar-Sinai

et al. 2012

Molecular Cancer Research

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“…The best-documented association of MMTV with non-mammary tumors is with T cell lymphomas (1,2). Previously, we have shown that the leader peptide of the Env-precursor of MMTV is translocated from the cytoplasm to the nucleoli of murine T cell lymphomas (3,4). This protein, designated p14 based on Western blotting analysis, corresponds to the first 97 NH 2 -terminal amino acids of the MMTV 73 kDa Env-precursor, terminating just before the beginning of gp52 (ref.…”

Section: Introductionmentioning

confidence: 99%

“…The mass of this protein determined by mass spectrometry is 11 kDa. p14 has been identified and characterized using a monoclonal antibody (M-66) generated against a cell surface epitope of T-25-Adh cells (3). T-25-Adh are nontumorigenic, immunogenic (substrate-adherent) cell variants derived from highly tumorigenic (suspension-borne) T-25 cells (5,6).…”

Section: Introductionmentioning

confidence: 99%

Mouse Mammary Tumor Virus Env–Derived Peptide Associates with Nucleolar Targets in Lymphoma, Mammary Carcinoma, and Human Breast Cancer

et al. 2005

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We have previously shown that the leader peptide (p14) of the Env-precursor of mouse mammary tumor virus is translocated into the nucleoli of murine T cell lymphomas that harbor this virus. Using a polyclonal antibody against recombinant p14, we show here that p14 is also localized to the nucleoli of murine mammary carcinomas and some human breast cancer samples. Affinity purification studies define a number of proteins, mostly nucleolar, that bind p14. Taken together, these findings point towards a more general involvement of p14 in lymphomagenesis and mammary carcinogenesis. (Cancer Res 2005; 65(16): 7223-30)

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“…Previous data indicated that generation of full-length Rem or SP might be dependent on the cell line used for expression (2,11,12). Whole-cell extracts from mouse mammary tumor cells (GR-B2) expressing GR-strain MMTV were subjected to Western blotting with antibody prepared against the NLS/RNA-binding domain within the SP.…”

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confidence: 99%

Retroviral Rem protein requires processing by signal peptidase and retrotranslocation for nuclear function

Byun

Halani²,

Mertz³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

114

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Mouse mammary tumor virus (MMTV) is a complex murine retrovirus that encodes an HIV Rev-like export protein, Rem, from a doubly spliced version of envelope (Env) mRNA. Previously, the Nterminal 98-amino acid sequence of Rem, which is identical to Env signal peptide (SP), and full-length Rem were shown to be functional in a reporter assay that measures a postexport function. Here we show that MMTV-infected cells or cells transfected with rem or env cDNAs express SP, which is the active component in the reporter assay. Uncleaved Rem was partially glycosylated, but mutations in both glycosylation sites within the C terminus prevented Rem function. Mutations that reduced Rem or Env cleavage by signal peptidase greatly reduced SP levels and functional activity in the reporter assay and allowed accumulation of the uncleaved protein. Fluorescence microscopy revealed that GFP-tagged cleavagesite mutants are unstable and lack fluorescence compared with wild-type Rem, suggesting improper folding. Proteasome inhibitors allowed accumulation of uncleaved Rem relative to SP and increased reporter activity, consistent with SP retrotranslocation and proteasome escape before nuclear entry. Expression of a dominant-negative p97 ATPase did not alter levels of unprocessed Rem and SP but decreased reporter activity, suggesting p97-facilitated retrotranslocation of SP. Our results provide an example of a SP that is processed by signal peptidase and retrotranslocated to allow nuclear localization and function. mouse mammary tumor virus | retrotranslocation | retrovirus | signal peptide | ERAD M ouse mammary tumor virus (MMTV) has provided many insights into cell and cancer biology. MMTV is a complex mouse retrovirus with regulatory features similar to those found in human complex retroviruses, such as HIV and human T-cell leukemia virus (HTLV) (1). These features include the ability to manipulate the immune system and to produce a doubly spliced mRNA encoding a protein (Rem) functionally similar to HIV Rev (1, 2). Rem mRNA is translated in the same reading frame as the MMTV envelope (env) gene but has a deletion of internal sequences encoding the surface (SU) and transmembrane (TM) proteins (1, 2) (Fig. 1A).MMTV Rem is a 301-amino acid protein that regulates expression and export of full-length viral RNA from the nucleus to the cytoplasm using the Crm1 export pathway (1, 2). The Rem protein contains several Rev-like motifs, including a nuclear localization signal (NLS), a nucleolar localization sequence, an arginine-rich RNA-binding motif, and a leucine-rich nuclear export sequence (Fig. 1A). These motifs map to the N-terminal 98 amino acids, which are identical in sequence to the signal peptide (SP) of the MMTV Env protein (1, 2). Similar to HIV Rev or HTLV-1 Rex (3, 4), GFP fusions to Rem or the SP are localized to nucleoli. Both GFPRem and GFP-SP fusions are functional in a reporter assay that measures a postexport function (e.g., translation) (5). Rem-dependent reporter activity requires the NLS as well as the presence of a Rem-re...

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Nucleolar Localization of Mouse Mammary Tumor Virus Proteins in T-Cell Lymphomas

Cited by 13 publications

References 21 publications

The Signal Peptide of Mouse Mammary Tumor Virus-Env: A Phosphoprotein Tumor Modulator

The Signal Peptide of Mouse Mammary Tumor Virus-Env: A Phosphoprotein Tumor Modulator

Mouse Mammary Tumor Virus Env–Derived Peptide Associates with Nucleolar Targets in Lymphoma, Mammary Carcinoma, and Human Breast Cancer

Retroviral Rem protein requires processing by signal peptidase and retrotranslocation for nuclear function

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