Novel nucleolar localization of clusterin and its associated functions in human oral cancers: An in vitro and in silico analysis

Abstract

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. Significance of the study This is the first study to demonstrate the nucleolar localization of sCLU and its associated functions in oral cancer cells. Downregulation of sCLU in oral cancer tissues and cell lines, and its negative association with ribogenesis suggest its tumour suppressor like role in oral cancers. The possible role of sCLU in stabilization or regulation of different nucleolar proteins thereby impacting their functions is also implicated.

A pan-cancer analysis reveals role of clusterin (CLU) in carcinogenesis and prognosis of human tumors

“…The most frequent type of OSCC, TSCC, is characterized by aggressive biological activity and poor survival ( Sano and Myers, 2007 ; Karatas et al, 2017 ). Recent studies have suggested a significant interaction between CLU and OSCC ( Kadam et al, 2021 ). This study aimed to examine the function of CLU gene, which was retrieved from the tongue squamous carcinoma dataset, in OSCC, HNSC, and diverse human cancers.…”

“…We conclude that CLU is expressed lower in most cancers than non-tumor tissues. CLU has been reported to have tumor suppressor activity in prostate, lung, and oral cancers, and low expression of CLU is associated with worse prognosis and genetic instability ( Panico et al, 2009 ; Rizzi and Bettuzzi, 2009 ; Kadam et al, 2021 ). This finding is in agreement with the results of the present study.…”

“…s CLU is downregulated in oral cancer cell lines and tissues and exhibits tumor-suppressor-like actions ( Kadam et al, 2021 ). Moreover, a series of studies revealed that CLU plays a crucial role in the lung ( Panico et al, 2009 ), prostate ( Rizzi and Bettuzzi, 2009 ), breast ( Redondo et al, 2009 ), ovarian ( Hoter and Naim, 2019 ), and colon cancers ( Mazzarelli et al, 2009 ).…”

Clusterin and Its Isoforms in Oral Squamous Cell Carcinoma and Their Potential as Biomarkers: A Comprehensive Review

“…In the literature, various transcript variants of CLU have been documented that arise from alternative splicing, with the secretory and nuclear isoforms being the most prevalent. Several studies have reported the involvement of CLU and its isoforms in various cancers, demonstrating their dual role in promoting and suppressing cancer cells [12]. The dysregulated expression of CLU and its correlation with tumorigenesis, along with potential clinical implications, have been extensively documented in multiple types of cancer, including lung cancer, prostate cancer, and breast cancer [13][14][15].…”

Clusterin negatively modulates mechanical stress-mediated ligamentum flavum hypertrophy through TGF-β1 signaling

“…Two isoforms are encoded by the CLU gene: a truncated nuclear form and a conventional omnipresent secretory heterodimeric disulfide-linked glycoprotein 14 . CLU is highly expressed in patients with diabetes 15 , atherosclerosis 16 , and tumorigenesis 17 . The role of CLU in LFH has not been fully explored.…”