Splicing regulator SLU7 is essential for maintaining liver homeostasis
María Elizalde, Raquel Urtasun, María Azkona, María U. Latasa, Saioa Goñi, Oihane García-Irigoyen, Iker Uriarte, Victor Segura, María Collantes, Mariana Di Scala, Amaia Lujambio, Jesús Prieto, Matías A. Ávila, Carmen Berasain
María Elizalde, Raquel Urtasun, María Azkona, María U. Latasa, Saioa Goñi, Oihane García-Irigoyen, Iker Uriarte, Victor Segura, María Collantes, Mariana Di Scala, Amaia Lujambio, Jesús Prieto, Matías A. Ávila, Carmen Berasain
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Research Article Hepatology

Splicing regulator SLU7 is essential for maintaining liver homeostasis

Abstract

A precise equilibrium between cellular differentiation and proliferation is fundamental for tissue homeostasis. Maintaining this balance is particularly important for the liver, a highly differentiated organ with systemic metabolic functions that is endowed with unparalleled regenerative potential. Carcinogenesis in the liver develops as the result of hepatocellular de-differentiation and uncontrolled proliferation. Here, we identified SLU7, which encodes a pre-mRNA splicing regulator that is inhibited in hepatocarcinoma, as a pivotal gene for hepatocellular homeostasis. SLU7 knockdown in human liver cells and mouse liver resulted in profound changes in pre-mRNA splicing and gene expression, leading to impaired glucose and lipid metabolism, refractoriness to key metabolic hormones, and reversion to a fetal-like gene expression pattern. Additionally, loss of SLU7 also increased hepatocellular proliferation and induced a switch to a tumor-like glycolytic phenotype. Slu7 governed the splicing and/or expression of multiple genes essential for hepatocellular differentiation, including serine/arginine-rich splicing factor 3 (Srsf3) and hepatocyte nuclear factor 4α (Hnf4α), and was critical for cAMP-regulated gene transcription. Together, out data indicate that SLU7 is central regulator of hepatocyte identity and quiescence.

Authors

María Elizalde, Raquel Urtasun, María Azkona, María U. Latasa, Saioa Goñi, Oihane García-Irigoyen, Iker Uriarte, Victor Segura, María Collantes, Mariana Di Scala, Amaia Lujambio, Jesús Prieto, Matías A. Ávila, Carmen Berasain

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Figure 4

Metabolic effects of Slu7 depletion in mouse liver: SLU7 plays a central role in glucose production and is essential for cAMP-mediated gene expression.

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Metabolic effects of Slu7 depletion in mouse liver: SLU7 plays a central...
(A) qPCR analysis of Pepck, G6pc, and G6pt expression in fed and fasted AAV-Ren– and AAV-shSLU7–infected mice. *P < 0.05 vs. AAV-Ren. (B and C) Hepatic glucose production after (B) pyruvate challenge and (C) glucagon challenge in AAV-Ren– and AAV-shSLU7–infected mice. *P < 0.05 vs. AAV-shSLU7. (D and E) PLC/PRF/5 and HepG2 cells were transfected with siGL or siSLU7. 48 hours later, cells were treated with 10 μM forskolin (FK) for 4 hours, prior to analysis of PEPCK and/or NR4A2 expression. (D) Representative Western blots of PEPCK, SLU7, and ACTIN control. (E) qPCR analysis of PEPCK, NR4A2, and ACTIN control. (F) ChIP assays using control (IgG) or anti-SLU7 antibodies in siGL- or siSLU7-transfected PLC/PRF/5 cells analyzing PEPCK and NR4A2 proximal promoters. (G) ChIP assays of PEPCK and NR4A2 promoters in siGL- and siSLU7-transfected PLC/PRF/5 cells. 48 hours after transfection, cells were treated with 10 μM forskolin for 30 minutes, then subjected to ChIP with anti-CBP and anti–RNA-Pol II antibodies. (H) SLU7 coimmunoprecipitated with P-CREB (arrow), CBP, and RNA-Pol II in PLC/PRF/5 cells. Lysates were immunoprecipitated with anti SLU7 antibodies or preimmune IgG. Representative Western blots of 3 experiments are shown.