title: Pericentriolar Targeting of the Mouse Mammary Tumor Virus GAG Protein.
abstract: The Gag protein of the mouse mammary tumor virus (MMTV) is the chief determinant of subcellular targeting. Electron microscopy studies show that MMTV Gag forms capsids within the cytoplasm and assembles as immature particles with MMTV RNA and the Y box binding protein-1, required for centrosome maturation. Other betaretroviruses, such as Mason-Pfizer monkey retrovirus (M-PMV), assemble adjacent to the pericentriolar region because of a cytoplasmic targeting and retention signal in the Matrix protein. Previous studies suggest that the MMTV Matrix protein may also harbor a similar cytoplasmic targeting and retention signal. Herein, we show that a substantial fraction of MMTV Gag localizes to the pericentriolar region. This was observed in HEK293T, HeLa human cell lines and the mouse derived NMuMG mammary gland cells. Moreover, MMTV capsids were observed adjacent to centrioles when expressed from plasmids encoding either MMTV Gag alone, Gag-Pro-Pol or full-length virus. We found that the cytoplasmic targeting and retention signal in the MMTV Matrix protein was sufficient for pericentriolar targeting, whereas mutation of the glutamine to alanine at position 56 (D56/A) resulted in plasma membrane localization, similar to previous observations from mutational studies of M-PMV Gag. Furthermore, transmission electron microscopy studies showed that MMTV capsids accumulate around centrioles suggesting that, similar to M-PMV, the pericentriolar region may be a site for MMTV assembly. Together, the data imply that MMTV Gag targets the pericentriolar region as a result of the MMTV cytoplasmic targeting and retention signal, possibly aided by the Y box protein-1 required for the assembly of centrosomal microtubules.
authors.affiliation: Division of Gastroenterology, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Guangzhi
authors.initials: G
authors.lastname: Zhang
authors.affiliation: Division of Gastroenterology, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Sharon
authors.affiliation: Division of Gastroenterology, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Juan
authors.initials: J
authors.lastname: Jovel
authors.affiliation: Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Lei
authors.initials: L
authors.lastname: Liu
authors.affiliation: Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Eytan
authors.initials: E
authors.lastname: Wine
authors.affiliation: Department of Cell Biology, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Nasser
authors.initials: N
authors.lastname: Tahbaz
authors.affiliation: Research Institute for Virology and Biomedicine, University of Veterinary Medicine Vienna, Vienna, A-1210, Austria.
authors.forename: Stanislav
authors.initials: S
authors.lastname: Indik
authors.affiliation: Division of Gastroenterology, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Andrew
authors.initials: A
authors.lastname: Mason
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D002213:Capsid / Q000648:ultrastructure; D002502:Centrioles / Q000378:metabolism*; D015683:Gene Products, gag / Q000737:chemistry / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008324:Mammary Tumor Virus, Mouse / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics
chemical_list: D020121:5' Untranslated Regions; D015683:Gene Products, gag; D049452:Green Fluorescent Proteins