Bousse T, Takimoto T, Murti K G, Portner A
Department of Virology and Molecular Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Virology. 1997 May 26;232(1):44-52. doi: 10.1006/viro.1997.8524.
Interactions involved in the expression of parainfluenza glycoproteins were examined by expressing cDNA clones of the HN and F genes from human parainfluenza virus type-1 (hPIV1) or Sendai virus (SV) in recombinant Semliki Forest virus (recSFV) or vaccinia-T7 expression vectors. We found that expression of a cloned F protein gene of hPIV1 resulted in downregulation of the HN proteins of hPIV1 or SV. Compared to the amount of HN expressed in the absence of F, coexpression of HN and F led to about 70% reduction in HN. This reduction of HN was observed in both total cell lysates and in protein localized on the cell surface. In contrast to hPIV1 F, SV F did not suppress the expression of HN. Northern blot analysis indicated that similar levels of HN mRNA accumulated in the absence or presence of hPIV1 F. The reduction of HN protein expression by hPIV1 F was detectable after as little as a 10-min labeling period, suggesting that downregulation occurred at the level of translation or at an early stage of protein folding. In hPIV1-infected cells, the amount of F protein synthesized was only about 15% of that of HN, whereas SV F is expressed at high levels. When the level of F in hPIV1-infected cells was artificially increased by recSFV, HN expression was suppressed. The reduction of F protein production in hPIV1-infected cells was regulated at the level of transcription. Characterization of mRNAs produced in hPIV1-infected cells showed that only 20% of the hPIV1 F mRNAs were monocistronic transcripts; 80% were bicistronic M-F readthrough mRNAs. Because proteins are suggested to be synthesized from only the first cistron of bicistronic mRNA in paramyxovirus (T. C. Wong and A. Hirano (1987) J. Virol. 61, 584-589), production of F protein is likely suppressed by transcriptional regulation in hPIV1-infected cells. These results suggest that F is capable of downregulating the synthesis of HN, but that this is normally prevented in hPIV1-infected cells by suppression of F protein synthesis by transcriptional regulation.
通过在重组Semliki森林病毒（recSFV）或痘苗-T7表达载体中表达人1型副流感病毒（hPIV1）或仙台病毒（SV）的HN和F基因的cDNA克隆，研究了副流感病毒糖蛋白表达中涉及的相互作用。我们发现，hPIV1克隆F蛋白基因的表达导致hPIV1或SV的HN蛋白下调。与在无F情况下表达的HN量相比，HN和F的共表达导致HN减少约70%。在总细胞裂解物和细胞表面定位的蛋白中均观察到HN的这种减少。与hPIV1 F相反，SV F不抑制HN的表达。Northern印迹分析表明，在无或有hPIV1 F的情况下，积累的HN mRNA水平相似。hPIV1 F对HN蛋白表达的减少在仅10分钟的标记期后即可检测到，这表明下调发生在翻译水平或蛋白质折叠的早期阶段。在hPIV1感染的细胞中，合成的F蛋白量仅约为HN的15%，而SV F则高水平表达。当通过recSFV人为增加hPIV1感染细胞中F的水平时，HN表达受到抑制。hPIV1感染细胞中F蛋白产生的减少在转录水平受到调节。对hPIV1感染细胞中产生的mRNA的表征表明，只有20%的hPIV1 F mRNA是单顺反子转录本；80%是双顺反子M-F通读mRNA。因为在副粘病毒中，蛋白质被认为仅从双顺反子mRNA的第一个顺反子合成（T.C.Wong和A.Hirano（1987）J.Virol.61，584-589），所以在hPIV1感染的细胞中，F蛋白的产生可能通过转录调节受到抑制。这些结果表明，F能够下调HN的合成，但在hPIV1感染的细胞中，这通常通过转录调节抑制F蛋白合成来防止。
