PUF: A potential repressor of oncogenes.

Abstract

e15095 Background: RNA-binding proteins (RBPs) play a crucial role in orchestrating the function of RNAs. The regulation of RBPs is critical in various biological processes, including tumorigenesis. The PUF (Pumilio/FBF) RBPs are of particular interest due to their function in stem cells and tumor-initiating cells. Its has been shown that PUF proteins inhibit the translation of target genes by binding to a regulatory element (PBE) in the 3’ untranslated regions (3’UTRs) of their target mRNA. PUF proteins are required to maintain normal stem cells and potentially inhibit the formation of tumor-initiating cells by repressing the expression of oncogenes. Bioinformatics analysis has identified many oncogenes as potential targets of PUF, and pilot studies have confirmed that ERK, p38, JAK2, RUNX2, and RET mRNAs specifically interact with PUF protein. The objective of this study is to investigate the function of human PUF proteins in the initiation and progression of cancer cells. Methods: In worms (C. elegans), 100 % PUF mutants form tumors. Bioinformatics were performed to identify PUF target genes, it specifically binds UGUAnAUA sequences on target mRNA 3'UTRs. Yeast three-hybrid assay were performed to test the physical interaction between PUF protein and its target mRNA. The novel function of human PUF proteins in the initiation and progression of cancer cells was investigated using CRISPR/Cas9 knockout cancer cell lines and western Blot/IHC was done to determine their expression. Results: The results of the study showed that PUF proteins play a crucial role in inhibiting the formation of tumor-initiating cells. Loss of PUF function and activation of ERK signaling were found to promote the formation of these cells. Bioinformatics analysis revealed that many oncogenes are potential targets for PUF repression. The study also demonstrated that PUF represses the expression of ERK and p38 mRNAs via their 3’UTRs. These findings suggest that PUF may have therapeutic potential as a target for cancer treatment. Conclusions: In worms and human cells, normal PUF proteins promote the cell proliferation of stem cells, however, stem cells begin to differentiate, PUF proteins are required to complete differentiation. Therefore, in the differentiating cells, PUF mutation cannot complete differentiation, instead, return to undifferentiating cells, resulting in tumors. Bioinformatics and biochemical analyses revealed that many PUF repressing targets (~ > 30%) are oncogene and some labs including us found that PUF knockdown enhanced oncogene expression. PUF can be a potential biomarker, as low PUF expression may initiate tumors. Therapeutically, conditional PUF expression in tumor-initiating cells may suppress tumor progression by suppressing oncogene.