In a recent study, we described a group of monoclonal antibodies that identify five high molecular mass proteins which associate with intermediate filaments in the cytoplasm and accumulate in nuclear foci as well. The proteins have been designated pNDCFs, proteins associated with nuclear dots and cytoplasmic filaments. Their expression in human B cells was upregulated by Epstein-Barr virus (EBV) infection or by exposure to anti-CD40 antibodies and IL4. Phenotypically representative (type I) Burkitt's lymphoma (BL) cell lines do not express pNDCFs or, if they do, the proteins accumulate preferentially in nuclear dots. Type III BL cell lines that have drifted to a more immunoblastic phenotype during in vitro passage and EBV-transformed lymphoblastoid cell lines (LCLs) of non-neoplastic origin express these proteins regularly at high levels. They are preferentially but not exclusively associated with vimentin filaments in the cytoplasm. Here we show that all five pNDCFs can be upregulated by expressing the EBV-encoded membrane protein LMP1 in type I BLs. Three of them could also be upregulated in the human keratinocyte cell line RHEK-1 by LMP1 transfection. This upregulation was paralleled by the LMP1-induced increase in vimentin expression in both cell types. One of the pNDCFs, detected by the MAb DM_4A6, accumulated in cap-like structures under the cell membrane that colocalized with membrane patches of LMP1, in addition to its localization in nuclear dots and in association with cytoplasmic vimentin filaments.


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