Novel diagnosis and therapy for hepatoma targeting HBV-related carcinogenesis through alternative splicing of FIR (PUF60)/FIRΔexon2

Abstract

Aim: Disturbed alternative splicing of far upstream element-binding protein-interacting repressor (FIR) was found to be unable to repress c-Myc transcription and so it might be important for suppressing tumor development. FIR is a splicing variant of poly (U)-binding-splicing factor (PUF60), and forms complex with other splicing factors. FIR/PUF60 is a splicing factor of U2 small nuclear ribonucleoprotein auxiliary factor family, Thus FIR/PUF60 is a multifunctional protein. The expression of exon2-lacking splicing variant of FIR, FIRΔexon2, is elevated in many cancer tissues and promotes tumor development by disabling FIR-repression to sustain c-Myc activation. FIRΔexon2, as a dominant negative of FIR, opposed apoptosis in cancer cells. FIR/FIRΔexon2 interacts with degron pocket of F-box and W (Typ) D (Asp) repeat domain-containing 7 and inhibits proteolysis of substrates proteins. Recently, FIR/PUF60 was identified as a versatile regulator of transcriptional and post-transcriptional steps in expression of hepatitis B virus (HBV) pregenomic RNA (pgRNA) expression. Methods: Small molecular chemical compounds against FIR and FIRΔexon2 were screened among 2,3275 chemicals by natural product depository array (RIKEN, Wako, Saitama, Japan). Results: Nine chemicals against FIR and four chemicals against FIRΔexon2 were identified as candidates of interacting chemicals. Interestingly, BK697 contains WD-like structure. Among them, BK697 against FIRΔexon2 inhibited hepatoma cell growth. Conclusion: Therefore, FIR (PUF60)/FIRΔexon2 is multifunctional and applicable for clinical use for HBV suppression and hepatoma treatment. Together, one clue to the development of hepatome diagnosis and therapies directed against FIR/FIRΔexon2/PUF60 with small molecular weight chemicals that inhibit HBV cccDNA replication.

Post-transcriptional regulation of BRG1 by FIRΔexon2 in gastric cancer

“…1a, arrow) that potentially interacts with WD-like motifs, such as the UHM-ligand motif, in the degron pocket of FBW7 (Fig. 5a), and thus might interfere with ubiquitination of its substrate proteins 22,23,37,38 . To research this possibility, the interaction between UHM of FIR or PUF60 and the WDlike motif (W425 and D399) of FBW7 was examined by three-dimensional crystal structure analysis 22 .…”

“…5a), and thus might interfere with ubiquitination of its substrate proteins 22,23,37,38 . To research this possibility, the interaction between UHM of FIR or PUF60 and the WDlike motif (W425 and D399) of FBW7 was examined by three-dimensional crystal structure analysis 22 . The binding structure between SF3B1 and one of the splicing factors containing UHM and SPF45 (human splicing factor 45) has previously been clarified by X-ray crystal analysis (PDB code: #2PEH) 13 (Fig.…”

“…The regulation of BRG1 by FBW7 has been studied that BRG1 is a substrate of FBW7 and was found to suppress E-cadherin through the FBW7/BRG1/Snai1 axis in gastric cancer 4 . Since FIRΔexon2 was co-immunoprecipitated with WDrepeat proteins 9 , a potential interaction was assessed between FIRΔexon2 and the WD-like motif in the degron pocket of FBW7 by three-dimension crystal analysis 22,23 . Finally, low molecular weight chemicals that bind to FIRΔexon2 were identified from natural chemical libraries (RIKEN, Wako, Saitama, Japan) and we investigated their effect on BRG1/Snai1 pathway for clinical applications.…”

Anti‐FIRΔexon2, a splicing variant form of PUF60, autoantibody is detected in the sera of esophageal squamous cell carcinoma

“…Anti‐PUF60 autoantibodies are reportedly detected in the sera of patients with autoimmune diseases such as dermatomyositis, Sjögren's syndrome, and idiopathic inflammatory myopathy . This suggests that the combination of anti‐FIR Abs with other clinically available tumor markers, such as anti‐p53 Abs, CEA, and CA19‐9, could increase the specificity and accuracy of diagnosis . The present study aimed to explore the presence and significance of anti‐FIRΔexon2 Abs in the sera of patients with ESCC and to determine its use as a potential candidate marker.…”

“…26,27 This suggests that the combination of anti-FIR Abs with other clinically available tumor markers, such as anti-p53 Abs, CEA, and CA19-9, could increase the specificity and accuracy of diagnosis. [28][29][30][31][32] The present study aimed to explore the presence and significance of anti-FIRΔexon2 Abs in the sera of patients with ESCC and to determine its use as a potential candidate marker.…”