Identification of a noncanonical function for ribose-5-phosphate isomerase A promotes colorectal cancer formation by stabilizing and activating β-catenin via a novel C-terminal domain

Abstract

Altered metabolism is one of the hallmarks of cancers. Deregulation of ribose-5-phosphate isomerase A (RPIA) in the pentose phosphate pathway (PPP) is known to promote tumorigenesis in liver, lung, and breast tissues. Yet, the molecular mechanism of RPIA-mediated colorectal cancer (CRC) is unknown. Our study demonstrates a noncanonical function of RPIA in CRC. Data from the mRNAs of 80 patients' CRC tissues and paired nontumor tissues and protein levels, as well as a CRC tissue array, indicate RPIA is significantly elevated in CRC. RPIA modulates cell proliferation and oncogenicity via activation of β-catenin in colon cancer cell lines. Unlike its role in PPP in which RPIA functions within the cytosol, RPIA enters the nucleus to form a complex with the adenomatous polyposis coli (APC) and β-catenin. This association protects β-catenin by preventing its phosphorylation, ubiquitination, and subsequent degradation. The C-terminus of RPIA (amino acids 290 to 311), a region distinct from its enzymatic domain, is necessary for RPIA-mediated tumorigenesis. Consistent with results in vitro, RPIA increases the expression of β-catenin and its target genes, and induces tumorigenesis in gut-specific promotor-carrying RPIA transgenic zebrafish. Together, we demonstrate a novel function of RPIA in CRC formation in which RPIA enters the nucleus and stabilizes β-catenin activity and suggests that RPIA might be a biomarker for targeted therapy and prognosis. Author summaryThe pentose phosphate pathway generates NADPH, pentose, and ribose-5-phosphate by RPIA for nucleotide synthesis. Deregulation of RPIA is known to promote tumorigenesis in liver, lung, and breast tissues; however, the molecular mechanism of RPIA-mediated CRC is unknown. Here, we demonstrate a role of RPIA in CRC formation distinct from its role in these other tissues. We showed that RPIA is significantly elevated in CRC. RPIA increased cell proliferation and oncogenicity via activation of β-catenin, with RPIA entering the nucleus to form a complex with APC and β-catenin. Further investigation suggested that RPIA protects β-catenin by preventing its phosphorylation, ubiquitination, and subsequent degradation. In addition, the C-terminus of RPIA (amino acids 290 to 311), a portion of the protein not previously characterized, is necessary for RPIA-mediated tumorigenesis. Finally, we observed that transgenic expression of RPIA increases the expression of β-catenin and its target genes and induces tumorigenesis. Our findings suggest that RPIA can enter the nucleus and associate with APC/β-catenin, and suggest precise treatment of human CRC by targeting its nonenzymatic domain.

Transcriptomically Revealed Oligo-Fucoidan Enhances the Immune System and Protects Hepatocytes via the ASGPR/STAT3/HNF4A Axis

“…Total RNA isolation and complementary DNA (cDNA) synthesis was conducted as described previously [ 25 ]. The RNA was isolated using a NucleoSpin ® RNA kit (Macherey-Nagel, Duren, Germany).…”

Crucial role of the pentose phosphate pathway in malignant tumors (Review)

“…It has been demonstrated that ribose-5-phosphate isomerase A (RPIA) regulates cancer growth and tumorigenesis (28). In addition, RPIA is significantly overexpressed in colorectal cancer and hepatocellular carcinoma (HCC) (29,30). RPIA also activates β-catenin by entering the nucleus to form a complex with adenomatous polyposis coli and β-catenin, thus modulating cell proliferation and oncogenicity (29).…”

WNK1 Kinase Stimulates Angiogenesis to Promote Tumor Growth and Metastasis

“…Therefore, WNK1 may affect tumor cell proliferation and angiogenesis by activating Wnt/β-catenin signaling. Our recent report on embryonic angiogenesis in zebrafish reveals an additional mechanism for VEGF to promote angiogenesis by PI3K-AKT-mediated phosphorylation of wnk1 at an amino-terminal threonine [25]. WNK1-SPAK/OSR1 regulates proliferation, invasion and gene expression in endothelial cells [30].…”

“…Transgenic fish that overexpresses ribose-5-phosphate isomerase A (RPIA) under the control of an intestinal fatty acid-binding protein (ifabp) promoter (Tg(ifabp:RPIA; myl7:EGFP) developed cancer in the gut at~3 months of age [25]. RPIA converts ribulose-5-phosphate to ribose-5-phosphate, a substrate for nucleotide biosynthesis.…”

“…Ribose-5-phosphate is used for nucleotide biosynthesis. Tg (ifabp:RPIA; myl7: EGFP) transgenic fish develop tumorigenesis in the gut of adult fish [25]. Tg (fabp10a: HBx-mCherry, src; myl7: EGFP) contains a fatty acid-binding protein-10a (fabp10a) promoter to drive the expression of Hepatitis B virus x protein (HBx) and src oncogene.…”