ZFP36L1 plays an ambiguous role in the regulation of cell expansion and negatively regulates CDKN1A in chronic myeloid leukemia cells.

The mRNA-destabilizing proteins ZFP36L1 and ZFP36L2 are described as mediators of quiescence and play a pivotal role in hematopoietic malignancies. Both genes are mainly classified as tumor suppressor genes as they posttranscriptionally downregulate the expression of oncogenes and contribute to cellular quiescence. Here, we analyzed the role of ZFP36L1 and ZFP36L2 in chronic myeloid leukemia (CML). We found ZFP36L1 and ZFP36L2 expression to be deregulated in patients with CML. By use of in vitro models of tyrosine kinase inhibitor resistance, an increase in ZFP36L1 and ZFP36L2 expression was detected during the development of imatinib resistance. CRISPR/Cas9-derived knockout of ZFP36L1, but not of ZFP36L2, in imatinib-sensitive cells led to decreased proliferation rates in response to tyrosine kinase inhibitor treatment. This effect was also observed in untreated ZFP36L1 knockout cells, albeit to a lower extent. Genomewide gene expression analyses of ZFP36L1 knockout cells revealed differential expression of cell cycle regulators, in particular upregulation of the cell cycle inhibitor CDKN1A. In addition, the 3' untranslated region of CDKN1A was proven to be a direct target of ZFP36L1. This indicates that tumor suppressor genes can also be targeted by ZFP36L1. Hence, ZFP36L1 cannot unambiguously be regarded as a tumor suppressor gene.

Overexpression of microRNA-129-5p in glioblastoma inhibits cell proliferation, migration, and colony-forming ability by targeting ZFP36L1.

Glioblastoma multiforme (GBM) is a highly invasive cancer with a high recurrence rate. The prognosis of GBM patients remains poor, even after standard surgical resection combined with chemoradiotherapy. Thus, there is an urgent need for new therapeutic targets in GBM. In recent years, microRNAs have received considerable attention due to their important role in tumor development and progression. In this study, we investigated the role of miR-129-5p and miR-129-5p/ZFP36L1 axis in GBM tumorigenesis. Analysis of GSE103228 microarray data from the GEO database showed that miR-129-5p was significantly downregulated in GBM vs. normal brain tissues. Quantitative reverse transcription PCR analysis of miR-129-5p expression in seven GBM cell lines (LN229, A172, U87, T98G, U251, H4, and LN118) vs. normal human astrocytes (NHA) showed miR-129-5p was significantly downregulated in GBM cells. Overexpression of miR-129-5p in LN229 and A172 cells significantly suppressed cell proliferation, migration, invasion, and colony-forming ability. Target Scan analysis identified ZFP36L1 as the target of miR-129-5p. UALCAN dataset analysis found that ZFP36L1 was significantly upregulated in GBM vs. normal brain tissues, and high ZFP36L1 expression was positively associated with poor survival of GBM patients. Western blot analysis demonstrated that ZFP36L1 was significantly upregulated in seven GBM cell lines vs. NHA. Overexpression of miR-129-5p in LN229 and A172 cells significantly inhibited ZFP36L1 mRNA and protein expression, while overexpression of ZFP36L1 in LN229 and A172 cells reversed miR-129-5p-mediated inhibition on GBM tumorigenesis. Our results revealed an important role of miR-129-5p in the negative regulation of ZFP36L1 expression in GBM, suggesting new candidates for targeted therapy in GBM patients.

Brf1 loss and not overexpression disrupts tissues homeostasis in the intestine, liver and pancreas.

RNA polymerase III (Pol-III) transcribes tRNAs and other small RNAs essential for protein synthesis and cell growth. Pol-III is deregulated during carcinogenesis; however, its role in vivo has not been studied. To address this issue, we manipulated levels of Brf1, a Pol-III transcription factor that is essential for recruitment of Pol-III holoenzyme at tRNA genes in vivo. Knockout of Brf1 led to embryonic lethality at blastocyst stage. In contrast, heterozygous Brf1 mice were viable, fertile and of a normal size. Conditional deletion of Brf1 in gastrointestinal epithelial tissues, intestine, liver and pancreas, was incompatible with organ homeostasis. Deletion of Brf1 in adult intestine and liver induced apoptosis. However, Brf1 heterozygosity neither had gross effects in these epithelia nor did it modify tumorigenesis in the intestine or pancreas. Overexpression of BRF1 rescued the phenotypes of Brf1 deletion in intestine and liver but was unable to initiate tumorigenesis. Thus, Brf1 and Pol-III activity are absolutely essential for normal homeostasis during development and in adult epithelia. However, Brf1 overexpression or heterozygosity are unable to modify tumorigenesis, suggesting a permissive, but not driving role for Brf1 in the development of epithelial cancers of the pancreas and gut.