Alternative splicing of human NT5E in cirrhosis and hepatocellular carcinoma produces a negative regulator of ecto-5'-nucleotidase (CD73).
Bottom Line: The two human isoforms exhibited functional differences, such that ectopic expression of canonical CD73 (CD73L) in human HepG2 cells was associated with decreased expression of the proliferation marker Ki67, whereas CD73S expression did not have an effect on Ki67 expression.Furthermore, CD73S complexed with CD73L and promoted proteasome-dependent CD73L degradation.The findings reveal species-specific CD73 regulation, with potential significance to cancer, fibrosis, and other diseases characterized by changes in CD73 expression and function.
Affiliation: Departments of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109.Show MeSH
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Mentions: We found that the two transcripts had comparable relative distribution profiles across 14 normal human tissues (Figure 2A), but NT5E-2 was expressed at significantly lower levels than NT5E-1 (Figure 2B). We also evaluated the relative expression of these two isoforms in nine human cancer cell lines (Figure 2C) and found that the two hepatocellular carcinoma (HCC) cell lines Huh7 and HepG2 expressed among the highest levels of the two transcripts relative to the other tested cell lines (AsPC-1, MCF7, NCI-H118, HT-29, K-562, CCRF-CEM, and MOLT-4).Therefore we focused our subsequent analysis on NT5E expression in normal and diseased livers. Because alternative splicing of genes is known to be altered in disease states (David and Manley, 2010; Singh and Cooper, 2012), we evaluated the expression of NT5E-2 in chronic human liver diseases, including HCV, NAFLD, and HCC. Whereas expression of NT5E-2 did not differ significantly in HCV and NAFLD compared with normal livers, it was dramatically increased in HCC surgical specimens (Figure 2D), pointing to a disease-specific regulation. Furthermore, relative to normal human liver, the expression levels of the NT5E-2 transcript were increased by one to two orders of magnitude in the HCC cell lines (Figure 3A), whereas NT5E-1 expression was either unchanged (Huh7) or decreased (HepG2).
Affiliation: Departments of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109.