Characterisation of the Interaction Between A Subset of Ribosomal Protein and their Putative Co-Acting Factors in Nasopharyngeal Carcinoma

Ng, Kher Lee (2020) Characterisation of the Interaction Between A Subset of Ribosomal Protein and their Putative Co-Acting Factors in Nasopharyngeal Carcinoma. PhD thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Ribosomal proteins (RPs) are a family of proteins that, together with rRNAs, constitute the ribosomal subunits involved in protein biosynthesis. As it was traditionally believed to only play a role in ribosomal biogenesis, RPs have remained largely unexplored until studies from the past few decades revealed the extra-ribosomal roles of RPs, particularly in the tumorigenesis of various cancers. Relative to other well-studied cancers such as breast, lung and colorectal carcinomas, RP research on nasopharyngeal carcinoma (NPC), in particular, received a lesser extent of global attention and interest due to its exclusive geographical and racial affiliation. To date, the expression of only a handful of RPs had been implicated in NPC progression and none of those reported were functionally investigated. Therefore, this study aims to characterise the interaction of a subset of ribosomal proteins and their putative co-acting factor in NPC cells. Differential expression of eight RP genes (uS4 (S9), eS8 (S8), eS31 (S27a), eL6 (L6), uL14 (L23), eL18 (L18), eL24 (L24), eL30 (L30)) and three possible target proteins (NPM1, BTF3 and UBA52) was determine in six different NPC cell lines (HONE-1, SUNE-1, HK1, TW01, TW04 and C666-1) compared to an immortalized nasopharyngeal epithelial cell line (NP69). Of the eight RP genes, four RPs (uS4 (S9), eS8 (S8), eS31 (S27a) and uL14 (L23)) and a potential binding partner, NPM1, were significantly dysregulated in their transcript and protein levels in NPC cell lines. On the other hand, this study also demonstrated the insignificant correlation in terms of the expression levels of eL6 (L6), eL18 (L18), eL24 (L24), eL30 (L30), BTF3, and UBA52, in the progression of NPC. Additionally, sequence analyses revealed missense mutations on uS4 (S9) and uL14 (L23). Subsequent in vitro and in vivo protein-protein interaction assay demonstrated the direct association of uS4 (S9) and uL14 (L23) to NPM1. The central domain of uS4 (S9) was able to interact with the N- and C-terminal domains of NPM1, while the centre motif of uL14 (L23) interacted with the N-terminal oligomerization domain of NPM1. Both RPs were identified as positive regulators of MDM2 by sequestering NPM1, while uL14 (L23) also played a dual-role as negative regulator of NPM1. Overall, this study has revealed the over-expression of uS4 (S9) and uL14 (L23) in NPC cells induced the translocation of NPM1 from the nucleolus to the nucleoplasm and cytoplasm, which in turn, transactivated MDM2 and its associated effector pathways in promoting tumorigenicity of NPC.

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