Alternative splicing of the FGF antisense gene: differential subcellular localization in human tissues and esophageal adenocarcinoma

Abstract

Overexpression of FGF-2 is associated with tumor recurrence and reduced survival after surgical resection of esophageal cancer, and these risks are reduced in tumors co-expressing the FGF antisense (FGF-AS) RNA. The aim of this study was to characterize the expression of alternatively spliced FGF-AS transcripts and encoded nudix-motif proteins in normal human tissues and in esophageal adenocarcinoma, and to correlate their expression with clinicopathologic findings and outcome. Three alternatively spliced FGF-AS transcripts encoding GFG/NUDT6 isoforms with distinct N termini were detected in various human tissues including esophageal adenocarcinoma. Expression of each isoform as a fusion protein with enhanced green fluorescent protein revealed differential subcellular trafficking: hGFGa is localized to mitochondria by an N-terminal targeting sequence (MTS), whereas hGFGb and hGFGc were localized in the cytoplasm and nucleus. Mutation/deletion analysis confirmed that the predicted MTS was necessary and sufficient for mitochondrial compartmentalization. The predominant FGF-AS mRNA expressed in esophageal tumors was splice variant b. GFG immunoreactivity was detected in the cytoplasm of all esophageal adenocarcinomas and in 88% of tumor cell nuclei. Although we found a trend towards reduced disease-free survival in patients with FGF-2 overexpressing esophageal adenocarcinomas, significantly worse disease-free survival was noted among patients whose tumors did not also overexpress the FGF-AS b isoform (p = 0.03). Tetracycline-inducible FGF-AS b expression in stably transfected human Seg-1 esophageal adenocarcinoma cells resulted in a significant suppression of steady state FGF-2 mRNA content and cell proliferation. Our data implicate the FGF-AS b isoform in modulation of FGF-2 expression and clinical outcome in esophageal adenocarcinoma.

The disruption of the rod-derived cone viability gene leads to photoreceptor dysfunction and susceptibility to oxidative stress

“…This natural antisense of the Fgf2 gene is induced in many pathological conditions. 16 In the retina of the Nxnl1À/À mice at 3 months of age, the 22 and 22.5-kDa isoforms of FGF2 are more abundant in the total cell extract and the 18-kDa isoform of FGF2 is present at higher levels both in the total extract and in the nuclear fraction ( Figure 4a). By 12 months, the level of FGF2 is reduced (Figure 4b).…”

Inhibitory Actions of Anti-Müllerian Hormone (AMH) on Ovarian Primordial Follicle Assembly

“…A central regulatory factor in the gene network identified is the Nudt6 antisense transcript for the fibroblast growth factor 2 gene ( Fgf2 ) expression product. The Nudt6 is an embedded reverse transcript within the Fgf2 gene [53], [54] that has the capacity to inhibit the expression and action of FGF2 [55], [56]. This FGF2/NUDT6 relationship indicates a critical regulatory role in the gene network identified, Figure 6, to influence signal transduction processes and transcriptional regulation.…”

A potential proliferative gene, NUDT6, is down-regulated by green tea catechins at the posttranscriptional level

“…1A, right panel. Since we have recently reported that a major green tea catechin EGCG suppresses bFGF at the post translational level [7] and that the NUDT6 gene is an antisense of bFGF mRNA [11], we decided to further investigate NUDT6 in this study. NUDT6 belongs to the family of Nudix hydrolases but its function is not well known.…”

“…We previously reported that NAG-1 and ATF3 are induced by green tea catechins, and NR4A1 , ID1 , ID2 are known to play a role in tumorigenesis [29–31]. In contrast, the biological function of NUDT6 and its role in tumorigenesis have not been well elucidated [11]. To elucidate the biological function of NUDT6 in human colorectal cancer cells, we generated stable cell lines with V5/His tags.…”

“…The nudix superfamily is widespread among many species, and consists mainly of pyrophosphohydrolases that act upon substrates of general structure nucleoside diphosphates linked to another moiety, X, to yield NMP plus P×X [10]. Interestingly, NUDT6 is an antisense product of the bidirectional transcribed gene locus, 4q26, whose sense product is basic fibroblast growth factor (bFGF/FGF-2) [11]. As a consequence, Murphy et al have shown that NUDT6 regulates the expression of FGF-2 in mammalian cells because it is the antisense of FGF-2 [12].…”