CPSF30 at the Interface of Alternative Polyadenylation and Cellular Signaling in Plants

Abstract

Post-transcriptional processing, involving cleavage of precursor messenger RNA (pre mRNA), and further incorporation of poly(A) tail to the 3' end is a key step in the expression of genetic information. Alternative polyadenylation (APA) serves as an important check point for the regulation of gene expression. Recent studies have shown widespread prevalence of APA in diverse systems. A considerable amount of research has been done in characterizing different subunits of so-called Cleavage and Polyadenylation Specificity Factor (CPSF). In plants, CPSF30, an ortholog of the 30 kD subunit of mammalian CPSF is a key polyadenylation factor. CPSF30 in the model plant Arabidopsis thaliana was reported to possess unique biochemical properties. It was also demonstrated that poly(A) site choice in a vast majority of genes in Arabidopsis are CPSF30 dependent, suggesting a pivotal role of this gene in APA and subsequent regulation of gene expression. There are also indications of this gene being involved in oxidative stress and defense responses and in cellular signaling, suggesting a role of CPSF30 in connecting physiological processes and APA. This review will summarize the biochemical features of CPSF30, its role in regulating APA, and possible links with cellular signaling and stress response modules.

Keywords: CPSF30; alternative polyadenylation; cleavage and polyadenylation specificity factor (CPSF); mRNA 3' end formation; stress response.

Figure 1

Different types of alternative polyadenylation and their possible consequences on gene expression. A hypothetical gene with four exons is used for schematic representation of different kinds of APA. Exons, 5' UTRs and 3' UTRs are represented with green, black and brown boxes, respectively, while introns are depicted with black horizontal lines. Proximal and distal poly(A) sites are shown with black vertical lines.

Figure 2

Amino acid sequence alignment and domain architecture analysis of CPSF30. (A) Tree showing the results of alignments of the small CPSF30 polypeptide (corresponding to the 28 kD polypeptide encoded by the Arabidopsis At1g30460 locus) from diverse plant species, algae, and yeast. (B) Tree showing the results of alignments of the large CPSF30 polypeptides from diverse plant species (analogous polypeptides are not present in other eukaryotes). Amino acid sequences were obtained from databases as described [48], aligned with ClustalW, and trees were constructed using neighbor-joining statistical method in MEGA6 software [59]. (C) Comparison of domain architecture of CPSF30 in different organisms. Three conserved CCCH zinc finger motifs are depicted in green and white horizontal boxes. Additional CCCH zinc finger and CCHC zinc knuckle motifs in other organisms are shown in black and blue horizontal boxes, respectively. Plant specific N-terminal acidic domains, Pro-rich motifs, Gln-rich motifs, C-terminal PLPQG motifs and YTH domains are represented with gray, violet, yellow, red vertical boxes and brown horizontal boxes, respectively.

Figure 3

Model depicting possible links between environmental stresses, developmental cues, cellular signaling and AtCPSF30-regulated polyadenylation. Three conserved zinc finger domains of AtCPSF30 are shown with thick blue rectangles. Pertinent biochemical activities are represented as clouds and linked to the respective zinc finger motifs with black arrows. Stress and developmental cues can initiate cellular signaling transmitted through redox and/or calcium-calmodulin mediated signaling cascade, altering RNA binding and/or endonuclease activities of AtCPSF30. This leads to global changes in poly(A) site choice, resulting in numerous biochemical and molecular consequences (induction of protein quality control system, as well as alteration of mRNA stability, translatability and localization). These consequences contribute to the eventual physiological response.