Magnesium accumulation upon cyclin M4 silencing activates microsomal triglyceride transfer protein improving NASH

Background & Aims: Perturbations of intracellular magnesium (Mg) homeostasis have implications for cell physiology. The cyclin M family, CNNM, perform key functions in the transport of Mg across cell membranes. Herein, we aimed to elucidate the role of CNNM4 in the development of non-alcoholic steatohepatitis (NASH). Methods: Serum Mg levels and hepatic CNNM4 expression were characterised in clinical samples. Primary hepatocytes were cultured under methionine and choline deprivation. A 0.1% methionine and choline-deficient diet, or a choline-deficient high-fat diet were used to induce NASH in our in vivo rodent models. Cnnm4 was silenced using siRNA, in vitro with DharmaFECT and in vivo with Invivofectamine® or conjugated to N-acetylgalactosamine. Results: Patients with NASH showed hepatic CNNM4 overexpression and dysregulated Mg levels in the serum. Cnnm4 silencing ameliorated hepatic lipid accumulation, inflammation and fibrosis in the rodent NASH models. Mechanistically, CNNM4 knockdown in hepatocytes induced cellular Mg accumulation, reduced endoplasmic reticulum stress, and increased microsomal triglyceride transfer activity, which promoted hepatic lipid clearance by increasing the secretion of VLDLs. Conclusions: CNNM4 is overexpressed in patients with NASH and is responsible for dysregulated Mg transport. Hepatic CNNM4 is a promising therapeutic target for the treatment of NASH. Lay summary: Cyclin M4 (CNNM4) is overexpressed in non-alcoholic steatohepatitis (NASH) and promotes the export of magnesium from the liver. The liver-specific silencing of Cnnm4 ameliorates NASH by reducing endoplasmic reticulum stress and promoting the activity of microsomal triglyceride transfer protein.Ministerio de Ciencia e Innovación, Programa Retos-Colaboración RTC2019-007125-1 (for JS and MLM-C); Instituto de Salud Carlos III, Proyectos de Investigación en Salud DTS20/00138 (for JS and MLM-C); Departamento de Industria del Gobierno Vasco (for MLM-C); Ministerio de Ciencia, Innovación y Universidades MICINN: SAF2017-87301-R and RTI2018-096759-A-100 integrado en el Plan Estatal de Investigación Cientifica y Técnica y Innovación, cofinanciado con Fondos FEDER (for MLM-C and TCD, respectively); BIOEF (Basque Foundation for Innovation and Health Research); EITB Maratoia BIO15/CA/014; Asociación Española contra el Cáncer (MLM-C, TCD); Fundación Científica de la Asociación Española Contra el Cancer (AECC Scientific Foundation) Rare Tumor Calls 2017 (for MLM); La Caixa Foundation Program (for MLM); Fundacion BBVA UMBRELLA project (for MLM); BFU2015-70067-REDC, BFU2016-77408-R, and BES-2017- 080435 (MINECO / FEDER, UE) and the FIGHT-CNNM2 project from the EJP RD Joint Transnational Call (JTC2019) (Ref. AC19/ 00073) (for LAM-C); RTI2018-095134-B-100 and Grupos de Investigación del Sistema Universitario Vasco (IT971-16) (for PA); National Institutes of Health under grant CA217817 (for DB); AGL2014-54585-R, AGL-2017-86927-R and EQC2018-004897-P from MINECO; PC0148-2016-0149 and PAI-BIO311 from Junta de Andalucía (for FM). Ciberehd_ISCIII_MINECO is funded by the Instituto de Salud Carlos III. We thank Silence Therapeutics plc. for the financial support provided. We thank MINECO for the Severo Ochoa Excellence Accreditation to CIC bioGUNE (SEV- 2016-0644)

PKN3 is required for malignant prostate cell growth downstream of activated PI 3-kinase

Chronic activation of the phosphoinositide 3-kinase (PI3K)/PTEN signal transduction pathway contributes to metastatic cell growth, but up to now effectors mediating this response are poorly defined. By simulating chronic activation of PI3K signaling experimentally, combined with three-dimensional (3D) culture conditions and gene expression profiling, we aimed to identify novel effectors that contribute to malignant cell growth. Using this approach we identified and validated PKN3, a barely characterized protein kinase C-related molecule, as a novel effector mediating malignant cell growth downstream of activated PI3K. PKN3 is required for invasive prostate cell growth as assessed by 3D cell culture assays and in an orthotopic mouse tumor model by inducible expression of short hairpin RNA (shRNA). We demonstrate that PKN3 is regulated by PI3K at both the expression level and the catalytic activity level. Therefore, PKN3 might represent a preferred target for therapeutic intervention in cancers that lack tumor suppressor PTEN function or depend on chronic activation of PI3K