The H55N polymorphism in the Cs gene of A/J mice has been linked to low activity of the enzyme in skeletal muscles. The aim of the study was to test this hypothesis and examine effects of low citrate synthase (CS) activity on palmitate metabolism in muscle cells. Results of the study showed that carriers of the wild type (WT) Cs (C57BL/6J and Balb/cByJ mouse strains) had higher CS activity (p < 0.01) than carriers of the A/J variant (B6.A-(rs3676616-D10Utsw1)/KjnB6 and A/J mouse strains) in the heart, liver and gastrocnemius muscle. Furthermore, the recombinant CS protein of WT showed higher CS activity than the A/J variant. In C2C12 muscle cells the shRNA mediated 47% knockdown of CS activity reduced the rate of fatty acid oxidation compared to the control cells. In summary, our results are consistent with the hypothesis that H55N substitution causes a reduction in CS activity. Furthermore, low CS activity interferes with metabolic flexibility of muscle cells.

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The imipramine ONC201 exerts a novel anti-proliferative activity over a wide spectrum of cancer cell types. ONC201 activates integrated stress response pathway that is associated with induction of Damage Inducible Transcript 3 (DDIT3, also known as C/EBP homologous protein or CHOP). We questioned whether the ONC201/CHOP crosstalk is regulated by diverse signaling pathways in non-metastatic versus metastatic cancer cell lines. Therefore, the Dukes' type B colorectal adenocarcinoma non-metastatic (SW480) and metastatic (LS-174T) cell lines were treated with ONC201. Cell proliferation and apoptosis were evaluated by MTT assay, flow cytometry analysis, gene expression was assessed by Affymetrix microarray, and key regulatory proteins were validated by Western blot assays. Unlike LS-174T cells, SW480 cells were resistant to ONC201 treatment. Gene ontology pathway enrichment analysis of differentially expressed genes revealed substantial differences between LS-174T and SW480 responsiveness to ONC201 treatment. In both cell lines, CHOP expression was upregulated in response to ONC201 treatment, however, its upstream regulatory mechanisms were not identical. Although, PERK, ATF6 and IRE1 ER-stress pathways were found to upregulated CHOP in both cell types, the BAK/BAX pathway was a notable regulator of CHOP in the metastatic LS-174T cells alone. In addition, CHOP RNA splicing profiles were varied between the two cell lines, which was further modified in response to ONC201 treatments. In conclusion, we delineated the signaling mechanisms regulating the expression of CHOP in non-metastatic versus metastatic colorectal cells in response to ONC201 treatment. The observed differences were related to cellular plasticity and metabolic reprogramming.