Nucleocytoplasmic shuttling of BEFV M protein-modulated by lamin A/C and chromosome maintenance region 1 through a transcription-, carrier- and energy-dependent pathway.

This study demonstrates for the first time that the matrix (M) protein of BEFV is a nuclear targeting protein that shuttles between the nucleus and the cytoplasm in a transcription-, carrier-, and energy-dependent manner. Experiments performed in both intact cells and digitonin-permeabilized cells revealed that M protein targets the nucleolus and requires carrier, cytosolic factors or energy input. By employing sequence and mutagenesis analyses, we have determined both nuclear localization signal (NLS) 6KKGKSK11 and nuclear export signal (NES) 98LIITSYL TI106 of M protein that are important for the nucleocytoplasmic shuttling of M protein. Furthermore, we found that both lamin A/C and chromosome maintenance region 1 (CRM-1) proteins could be coimmunoprecipitated and colocalized with the BEFV M protein. Knockdown of lamin A/C by shRNA and inhibition of CRM-1 by leptomycin B significantly reduced virus yield. Collectively, this study provides novel insights into nucleocytoplasmic shuttling of the BEFV M protein modulated by lamin A/C and CRM-1 and by a transcription- and carrier- and energy-dependent pathway.