o-Phenanthroline br Abbreviations CPE core polyadenylation e
Abbreviations: CPE, core polyadenylation elements; mRNAs, messenger RNAs; PAS, polyadenylation signal; CS, cleavage site; CPGs, cancer predisposition genes; miRNAs, microRNAs; NCBI, National Center for Biotechnology Information; nt, nucleotides; CPSF, polyadenylation specificity factor; CstF, cleavage stimulatory factor; CFI/CFII, cleavage factors I and II; PAP, poly(A) polymerase; APA, alternative polyadenylation; 3′UTR, 3′ untranslated region; HCS, hereditary cancer syndromes; ONC, oncogene; TSG, tumor suppressor gene; bp, o-Phenanthroline pairs
Corresponding author at: Laboratório de Medicina Genômica, Serviço de Pesquisa Experimental, Hospital de Clínicas de Porto Alegre, Ramiro Barcelos, 2350, 90035-903 Porto Alegre, Rio Grande do Sul, Brazil.
E-mail address: [email protected] (I.A. Vieira).
(3) a less well-conserved G-U-rich sequence 14–70 nt downstream of the PAS (Proudfoot and Brownlee, 1976; Gil and Proudfoot, 1987; Chen et al., 1995; Legendre and Gautheret, 2003; Matoulkova et al., 2012). There are five major trans-acting protein factors that constitute the ma-chinery involved in this process: cleavage and polyadenylation specificity factor (CPSF), cleavage stimulatory factor (CstF), cleavage factors I and II (CFI and CFII), and poly(A) polymerase (PAP) (Zhao et al., 1999; Millevoi and Vagner, 2010; Ryan et al., 2004). The first one recognizes the AAUAAA sequence and CstF binds to the G-U-rich sequence, while CFI and CFII cleave RNA at the CS and generate a 3′ end for PAP to perform polyadenylation (Keller et al., 1991; MacDonald et al., 1994; Proudfoot, 2011). Moreover, alternative polyadenylation (APA), defined as the use of more than one functional PAS/CS, occurs in at least 50% of human genes, allowing a single gene to encode multiple mRNA transcripts with variable 3′ untranslated regions (3′UTR) (Tian et al., 2005; Lutz, 2008).
The known regulatory role of polyadenylation in mRNA localization, stability, and translation, as well as the emerging link between deleter-ious variants located in CPE and human disease underscore the need to fully characterize them (Zhao et al., 1999; Chen et al., 2006). Alterations in CPE and neighboring sequences in the 3′UTR disrupt the cleavage and polyadenylation steps, resulting in several human pathologies (Chen et al., 2006; Michalova et al., 2013; Hollerer et al., 2014). Recently, functional CPE-related germline variants were reported in cancer pre-disposition genes (CPGs) and were associated with hereditary cancer syndromes (HCS). For example, the single nucleotide polymorphism (SNP) rs78378222 changes the constitutive PAS of the tumor suppressor gene TP53 (Stacey et al., 2011) and has been linked with a Li-Fraumeni-like syndrome phenotype (Macedo et al., 2016). Another functional variant (duplication of 20 base pairs) located upstream of the MSH6 PAS (a DNA-repair gene) was identified in two patients fulfilling clinical criteria for Lynch syndrome (Decorsière et al., 2012). MicroRNAs (miRNAs) are endogenous, single-stranded, small non-coding RNAs (18–25 nt) that post-transcriptionally regulate gene ex-pression through mRNA degradation and/or translation repression. In addition to CPE sequences, miRNA binding sites represent another class of elements predominantly located in the 3′UTR of mRNAs (Ambros, 2004; Bartel, 2004). Remarkable studies showed that miRNA mutations or altered expression levels correlate with various human cancers, and indicate that some miRNAs can function as tumor suppressors and/or oncogenes (Calin et al., 2002; Takamizawa et al., 2004; Cimmino et al., 2005; Esquela-Kerscher and Slack, 2006). The deletion or down-regulation of a miRNA that has a tumor suppressor role, by modulating the expression of oncogenes, leads to inappropriate amounts of the miRNA-target oncoproteins. The overall outcome might involve in-creased cellular proliferation, ultimately contributing to carcinogenesis. Additionally, oncogenic miRNA amplification or overexpression can reduce or eliminate the expression of a miRNA-target tumor-suppressor gene, resulting in an abnormal cellular proliferation and potentially, tumor formation (Esquela-Kerscher and Slack, 2006).