Clusterin (CLU), a multifunctional chaperonic glycoprotein associated with diverse cellular functions has been shown to act as an oncogene or tumour suppressor gene in different cancers, implying a dual role in tumorigenesis. Here, we investigated the expression of CLU isoforms, their subcellular localization and functional significance in oral cancer cells. Significant downregulation of secretory CLU (sCLU) transcripts was observed in oral cancer cell lines and tumours versus normal cells while the nuclear CLU (nCLU) transcripts were undetectable. We demonstrated for the first time the nucleolar localization of sCLU, its response to different nucleolar stresses and association with cajal bodies post nucleolar stress. Functionally, knockdown of CLU revealed its negative association with ribosome biogenesis implying a possible tumour suppressor like role in oral cancers. Further, loss of sCLU in these cells also resulted in altered nuclear morphology and shrunken tubulin filaments. In addition, the levels of nucleolar Nucleophosmin 1(NPM1) and Fibrillarin, known to regulate nuclear morphology were downregulated indicating a possible role of sCLU in their stabilization. Further, an in silico docking approach to gain insights into the interaction of sCLU with nucleolar proteins NPM1, Fibrillarin, UBF and Nucleolin, revealed the involvement of a conserved region comprising of amino acid residues 140‐155 of sCLU β‐chain, specifically via the Phe152 residue in hydrophobic interactions with these client nucleolar proteins indicating a possible stabilizing or regulatory role of sCLU.

中文翻译：

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Clusterin的新核仁定位及其在人类口腔癌中的相关功能：体外和计算机分析

簇蛋白（CLU）是一种与多种细胞功能相关的多功能伴侣糖蛋白，已被证明在不同的癌症中起癌基因或抑癌基因的作用，这暗示着其在肿瘤发生中的双重作用。在这里，我们调查了口腔癌细胞中CLU亚型的表达，亚细胞定位和功能意义。在口腔癌细胞系和肿瘤与正常细胞中观察到分泌性CLU（sCLU）转录物显着下调，而无法检测到核CLU（nCLU）转录物。我们首次证明了sCLU的核仁定位，其对不同核仁应力的反应以及与核仁胁迫后的唾液体的关联。在功能上 CLU基因敲低表明其与核糖体生物发生负相关，这暗示可能在口腔癌中发挥类似抑癌作用。此外，这些细胞中sCLU的丢失还导致改变的核形态和收缩的微管蛋白丝。另外，已知调节核形态的核仁Nucleophosmin 1（NPM1）和原纤维蛋白的水平被下调，表明sCLU在其稳定中可能发挥作用。此外，通过计算机对接方法深入了解sCLU与核仁蛋白NPM1，原纤维蛋白，UBF和Nucleolin的相互作用，揭示了一个保守区域的参与，该保守区域包含sCLUβ链的氨基酸残基140-155，