The interaction between the measles virus nucleoprotein and the Interferon Regulator Factor 3 relies on a specific cellular environment.
BACKGROUND
The genome of measles virus consists of a non-segmented single-stranded RNA molecule of negative polarity, which is encapsidated by the viral nucleoprotein (N) within a helical nucleocapsid. The N protein possesses an intrinsically disordered C-terminal domain (aa 401-525, N(TAIL)) that is exposed at the surface of the viral nucleopcapsid. Thanks to its flexible nature, N(TAIL) interacts with several viral and cellular partners. Among these latter, the Interferon Regulator Factor 3 (IRF-3) has been reported to interact with N, with the interaction having been mapped to the regulatory domain of IRF-3 and to N(TAIL). This interaction was described to lead to the phosphorylation-dependent activation of IRF-3, and to the ensuing activation of the pro-immune cytokine RANTES gene.


RESULTS
After confirming the reciprocal ability of IRF-3 and N to be co-immunoprecipitated in 293T cells, we thoroughly investigated the N(TAIL)-IRF-3 interaction using a recombinant, monomeric form of the regulatory domain of IRF-3. Using a large panel of spectroscopic approaches, including circular dichroism, fluorescence spectroscopy, nuclear magnetic resonance and electron paramagnetic resonance spectroscopy, we failed to detect any direct interaction between IRF-3 and either full-length N or NTAIL under conditions where these latter interact with the C-terminal X domain of the viral phosphoprotein. Furthermore, such interaction was neither detected in E. coli nor in a yeast two hybrid assay.


CONCLUSIONS
Altogether, these data support the requirement for a specific cellular environment, such as that provided by 293T human cells, for the N(TAIL)-IRF-3 interaction to occur. This dependence from a specific cellular context likely reflects the requirement for a human or mammalian cellular co-factor.
Colombo
Matteo
M
Architecture et Fonction des Macromolécules Biologiques, UMR 6098 CNRS et Universités Aix-Marseille I et II, 163 Avenue de Luminy, Case 932, 13288 Marseille Cedex 09, France. Matteo.Colombo@unimi.it
Bourhis
Jean-Marie
JM
Chamontin
Celia
C
Soriano
Carine
C
Villet
Stéphanie
S
Costanzo
Stéphanie
S
Couturier
Marie
M
Belle
Valérie
V
Fournel
André
A
Darbon
Hervé
H
Gerlier
Denis
D
Longhi
Sonia
S
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D002460:Cell Line; D006801:Humans; D050838:Interferon Regulatory Factor-3 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008457:Measles / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D008459:Measles virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D019590:Nucleocapsid Proteins; D009698:Nucleoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020798:Two-Hybrid System Techniques; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D050838:Interferon Regulatory Factor-3; D019590:Nucleocapsid Proteins; D009698:Nucleoproteins; D014764:Viral Proteins; C058314:nucleoprotein, Measles virus