A feedback mechanism between PLD and deadenylase PARN for the shortening of eukaryotic poly(A) mRNA tails that is deregulated in cancer cells.

Taylor E Miller,Julian Gomez-Cambronero

doi:10.1242/bio.021261

Taylor E Miller, Julian Gomez-Cambronero

Open Access

https://doi.org/10.1242/bio.021261

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Abstract

ABSTRACTThe removal of mRNA transcript poly(A) tails by 3′→5′ exonucleases is the rate-limiting step in mRNA decay in eukaryotes. Known cellular deadenylases are the CCR4-NOT and PAN complexes, and poly(A)-specific ribonuclease (PARN). The physiological roles and regulation for PARN is beginning to be elucidated. Since phospholipase D (PLD2 isoform) gene expression is upregulated in breast cancer cells and PARN is downregulated, we examined whether a signaling connection existed between these two enzymes. Silencing PARN with siRNA led to an increase in PLD2 protein, whereas overexpression of PARN had the opposite effect. Overexpression of PLD2, however, led to an increase in PARN expression. Thus, PARN downregulates PLD2 whereas PLD2 upregulates PARN. Co-expression of both PARN and PLD2 mimicked this pattern in non-cancerous cells (COS-7 fibroblasts) but, surprisingly, not in breast cancer MCF-7 cells, where PARN switches from inhibition to activation of PLD2 gene and protein expression. Between 30 and 300 nM phosphatidic acid (PA), the product of PLD enzymatic reaction, added exogenously to culture cells had a stabilizing role of both PARN and PLD2 mRNA decay. Lastly, by immunofluorescence microscopy, we observed an intracellular co-localization of PA-loaded vesicles (0.1-1 nm) and PARN. In summary, we report for the first time the involvement of a phospholipase (PLD2) and PA in mediating PARN-induced eukaryotic mRNA decay and the crosstalk between the two enzymes that is deregulated in breast cancer cells.

Highlights

The shortening of eukaryotic poly (A) mRNA tails is a key way to repress mRNA translation and to induce transcript turnover
Differential expression of poly(A)specific ribonuclease (PARN) and phospholipase D2 (PLD2) in breast cancer cells compared to non-cancerous cells A molecular connection between poly(A) deadenylases and Phospholipase D (PLD) has not been investigated to date
Using the Finak Breast dataset from the ONCOMINE cancer microarray database (Finak et al, 2008), we determined that PARN was downregulated in invasive breast carcinoma compared to adjacent non-cancerous breast stroma (Fig. 1A), while gene expression of PLD2 was significantly upregulated in the same dataset (Fig. 1B)

Summary

Introduction

The shortening of eukaryotic poly (A) mRNA tails is a key way to repress mRNA translation and to induce transcript turnover. Deadenylation is a principal strategy employed by cells to control mRNA stability and gene expression involved in basic cellular functions, such as development and cell differentiation, as well as in pathological conditions, such as chronic inflammation, cancer and an abnormal DNA damage response A third deadenylase, poly(A)-specific ribonuclease (PARN), which is a member of the RNase D exonuclease family and degrades poly (A) from the 3′ end (Mian, 1997; Moser et al, 1997; Körner et al, 1998), is lesser known in terms of its own specific functional roles and regulation in vivo

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