title: Characterization of functional domains in the Merkel cell polyoma virus Large T antigen.
abstract: Merkel cell polyomavirus (MCPyV)--positive Merkel cell carcinoma (MCC) tumor cell growth is dependent on the expression of a viral Large T antigen (LT) with an intact retinoblastoma protein (RB)-binding site. This RB-binding domain in MCPyV-LT is--in contrast to other polyomavirus LTs (e.g., SV40)--embedded between two large MCPyV unique regions (MUR1 and MUR2). To identify elements of the MCPyV-LT necessary for tumor cell growth, we analyzed the rescue activity of LT variants following knockdown of the endogenous LT in MCC cells. These experiments demonstrate that nuclear localization is essential for LT function, but that a motif previously described to be a nuclear localization sequence is neither required for nuclear accumulation of truncated MCPyV-LT nor for promotion of MCC cell proliferation. Furthermore, large parts of the MURs distal to the RB binding domain as well as ALTO--a second protein encoded by an alternative reading frame in the MCPyV-LT mRNA--are completely dispensable for MCPyV-driven tumor cell proliferation. Notably, even MCPyV-LTs in which the entire MURs have been removed are still able to promote MCC cellular growth although rescue activity is reduced which may be due to MUR1 being required for stable LT expression in MCC cells. Finally, we provide evidence implying that--while binding to Vam6p is not essential--HSC-70 interaction is significantly involved in mediating MCPyV-LT function in MCC cells including growth promotion and induction of E2F target genes.
authors.affiliation: Department of Dermatology, University Hospital, Würzburg, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Houben
authors.forename: Sabrina
authors.initials: S
authors.lastname: Angermeyer
authors.forename: Sebastian
authors.initials: S
authors.lastname: Haferkamp
authors.forename: Annemarie
authors.initials: A
authors.lastname: Aue
authors.forename: Matthias
authors.initials: M
authors.lastname: Goebeler
authors.forename: David
authors.initials: D
authors.lastname: Schrama
authors.forename: Sonja
authors.initials: S
authors.lastname: Hesbacher
mesh_terms: D020816:Amino Acid Motifs; D000957:Antigens, Viral, Tumor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017209:Apoptosis; D015153:Blotting, Western; D015266:Carcinoma, Merkel Cell / Q000378:metabolism* / Q000473:pathology / Q000821:virology; D049109:Cell Proliferation; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D007124:Immunoenzyme Techniques; D059965:Merkel cell polyomavirus / Q000502:physiology*; D027601:Polyomavirus Infections / Q000378:metabolism* / Q000473:pathology / Q000821:virology; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured; D014412:Tumor Virus Infections / Q000378:metabolism* / Q000473:pathology / Q000821:virology
chemical_list: D000957:Antigens, Viral, Tumor; D012333:RNA, Messenger; D034741:RNA, Small Interfering
keywords: Large T antigen; Merkel cell carcinoma; polyomavirus