Transport of the Murine Mx Protein into the Nucleus Is Dependent on a Basic Carboxy-Terminal Sequence

Abstract

Cytoplasmic microinjection of murine Mx mRNA synthesized in vitro or nuclear microinjection of Mx cDNA under the control of a constitutive promoter into murine Mx- cells led to the accumulation of Mx protein in the nucleus and inhibited the replication of influenza virus but not of vesicular stomatitis virus (VSV). Similar results were also found with dog, rat, chicken, and monkey cells. A human lung fibroblast cell line (A549) was exceptional in that Mx protein was located predominantly in the cytoplasm and showed antiviral activity. Truncation of the 19 last residues of murine Mx protein almost completely abolished accumulation of Mx protein in the nucleus; however the activity against influenza virus was at least partially retained. The truncated region contains a segment rich in basic amino acids, similar to that reported for several nuclear location signals.

Mx Proteins: Antiviral Gatekeepers That Restrain the Uninvited

“…1A). The C terminus of rodent Mx1 protein is unique in that it contains a functional nuclear localization signal (NLS) (amino acids 606 to 615) (70,71). Mouse Mx1 accumulates in the nuclei of most cell types tested, and this localization is important for its antiviral activity (70,72).…”

Role of GTPase activity of murine Mx1 protein in nuclear localization and anti-influenza virus activity

“…Biochemical analysis indicated that Mxl is a GTP-binding protein with GTPase activity (Nakayama et al, 1991(Nakayama et al, , 1992Mel6n et al, 1994) and that Mxl forms self-assemblies (Nakayama et al, 1993). The functional domains of Mxl involved in GTPbinding, GTP hydrolysis, self-assembly, di-and trimerization, and nuclear localization have been mapped (Noteborn et al, 1987;Nakayama et al, 1991Nakayama et al, , 1992Nakayama et al, , 1993MelOn et al, 1992MelOn et al, , 1994. Mutant analysis indicated that nuclear localization, GTP binding and GTPase activities, and dimer or trimer formation are essential for its anti-influenza virus activity (Ztircher et al, 1992;Garber et al, 1993;Pitossi et al, 1993 The fragments containing Mxl and its mutant cDNA, S50I, were cloned from pTrpA12Mx and pS50I (Nakayama et al, 1991), respectively, into the expression vector pCB6 (obtained from Dr M. Roth, University of Texas, Tex., USA, with permission from Dr M. Stinski, University of Iowa, Iowa, USA) between BglII and HindIII to create pCBMxl and pCBS50I, respectively.…”

Differential expression of two Carassius auratus Mx genes in cultured CAB cells induced by grass carp hemorrhage virus and interferon

“…1). It is known that human MxA and mouse Mx2 are localized in the cytoplasm (Leong et al 1998), and that nuclear retention requires a nuclear localization signal (NLS) motif, characterized by a short stretch of positively charged residues (K/L) near the carboxylic acid terminus of a protein (Noteborn et al 1987). Crucian carp Mx proteins bear a slightly greater identity both to MxA and to Mx2, compared with their counterparts MxB in human and Mx1 in mouse, respectively (Table 2), and they both do not contain a NLS (Fig.…”