title: The product of Kaposi's sarcoma-associated herpesvirus immediate early gene K4.2 regulates immunoglobulin secretion and calcium homeostasis by interacting with and inhibiting pERP1.
abstract: Chaperones are proteins that assist the noncovalent folding and assembly of macromolecular polypeptide chains, ultimately preventing the formation of nonfunctional or potentially toxic protein aggregates. Plasma cell-induced-endoplasmic reticulum (ER)-resident protein 1 (pERP1) is a cellular chaperone that is preferentially expressed in marginal-zone B cells and is highly upregulated during plasma cell differentiation. While initially identified as a dedicated factor for the assembly of secreted IgM, pERP1 has since been implicated in suppressing calcium mobilization, and its expression is misregulated in multiple tumors. A number of herpesvirus immediate early gene products play important roles in the regulation of viral gene expression and/or evasion of host immune responses. Here, we report that the Kaposi's sarcoma-associated herpesvirus (KSHV) immediate early viral gene K4.2 encodes an endoplasmic reticulum-localized protein that interacts with and inhibits pERP1. Consequently, K4.2 expression interfered with immunoglobulin secretion by delaying the kinetics of immunoglobulin assembly and also led to increased responsiveness of B-cell receptor signal transduction by enhancing phosphotyrosine signals and intracellular calcium fluxes. Furthermore, K4.2 expression also appeared to contribute to maximal lytic replication by enhancing viral glycoprotein expression levels and ultimately promoting infectious-virus production. Finally, immunohistochemistry analysis showed that pERP1 expression was readily detected in KSHV-positive cells from multicentric Castleman's disease (MCD) and Kaposi's sarcoma (KS) lesions, suggesting that pERP1 may have potential roles in the KSHV life cycle and malignancy. In conclusion, our data suggest that K4.2 participates in lytic replication by enhancing calcium flux and viral glycoprotein expression, but also by interfering with immunoglobulin assembly to potentially dampen the adaptive immune response.
authors.affiliation: Department of Molecular Microbiology and Immunology, University of Southern California, Los Angeles, Callifornia, USA.
authors.forename: Lai-Yee
authors.initials: LY
authors.lastname: Wong
authors.forename: Kevin
authors.initials: K
authors.lastname: Brulois
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Toth
authors.forename: Kyung-Soo
authors.initials: KS
authors.lastname: Inn
authors.forename: Sun-Hwa
authors.initials: SH
authors.lastname: Lee
authors.forename: Kathryn
authors.initials: K
authors.lastname: O'Brien
authors.forename: Hyera
authors.initials: H
authors.lastname: Lee
authors.forename: Shou-Jiang
authors.initials: SJ
authors.lastname: Gao
authors.forename: Ethel
authors.initials: E
authors.lastname: Cesarman
authors.forename: Armin
authors.initials: A
authors.lastname: Ensser
authors.forename: Jae U
authors.initials: JU
authors.lastname: Jung
mesh_terms: D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D005871:Castleman Disease / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D049109:Cell Proliferation; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D015967:Gene Expression Regulation, Viral; D017781:Genes, Immediate-Early / Q000502:physiology*; D019288:Herpesvirus 8, Human / Q000472:pathogenicity; D006706:Homeostasis; D006801:Humans; D007124:Immunoenzyme Techniques; D007136:Immunoglobulins / Q000276:immunology / Q000378:metabolism*; D047468:Immunoprecipitation; D018832:Molecular Chaperones / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012514:Sarcoma, Kaposi / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D020798:Two-Hybrid System Techniques; D014779:Virus Replication
chemical_list: D007136:Immunoglobulins; D018832:Molecular Chaperones; D012333:RNA, Messenger; D002118:Calcium