👤 Takafumi Taguchi

Dual specific phosphatases (DUSPs) are a family of phosphatases, including DUSP4, DUSP5, and DUSP6, that function as negative regulators of the RAF/MEK/ERK pathway. These DUSPs have been extensively studied in various human cancers, particularly those with KRAS mutations. Our previous research indicated that these DUSPs are downregulated by KRAS knockdown in KRAS mutant lung cancer cell lines and upregulated in an hTERT/Cdk4-immortalized normal human bronchial cell line HBEC3-KT expressing mutant KRAS Show less

Dietary protein deficiency and amino acid imbalance cause hepatic fat accumulation. We previously demonstrated that only arginine deficiency or total amino acid deficiency in a diet caused significant hepatic triglyceride (TG) accumulation in young Wistar rats. In this study, we explored the mechanisms of fatty liver formation in these models. We fed 6-week-old male Wistar rats a control diet (containing an amino acid mixture equivalent to 15% protein), a low-total-amino acid diet (equivalent to 5% protein; 5PAA), and a low-arginine diet (only the arginine content is as low as that of the 5PAA diet) for 2 weeks. Much greater hepatic TG accumulation was observed in the low-arginine group than in the low-total-amino acid group. The lipid consumption rate and fatty acid uptake in the liver did not significantly differ between the groups. In contrast, the low-total-amino acid diet potentiated insulin sensitivity and related signaling in the liver and enhanced de novo lipogenesis. The low-arginine diet also inhibited hepatic very-low-density lipoprotein secretion without affecting hepatic insulin signaling and lipogenesis. Although the arginine content of the low-arginine diet was as low as that of the low-total-amino acid diet, the two diets caused fatty liver via completely different mechanisms. Enhanced lipogenesis was the primary cause of a low-protein diet-induced fatty liver, whereas lower very-low-density lipoprotein secretion caused low-arginine diet-induced fatty liver. Show less

Carbamoyl phosphate synthetase 1 (CPS1) drives ammonia conversion to carbamoyl phosphate, and its overexpression supports pyrimidine synthesis and tumor growth, highlighting the potential of CPS1 inhibition as a therapeutic target. In this issue of Cell Chemical Biology, Yao et al. (2020) introduce H3B-120 as a promising novel inhibitor of CPS1. Show less

Differential diagnosis among basal cell adenoma (BCA), basal cell adenocarcinoma (BCAC), adenoid cystic carcinoma (ACC) and pleomorphic adenoma (PA) of the salivary gland can be challenging due to their similar histological appearance. Although frequent nuclear β-catenin expression and CTNNB1 mutations have been reported in BCA, further details of the Wnt/β-catenin signal alterations are unclear. The aim of this study was to assess the diagnostic utility of Wnt/β-catenin signal alteration in BCA and morphological mimics. We performed immunohistochemical staining for β-catenin and mutation analysis for Wnt/β-catenin-related genes (CTNNB1, APC, AXIN1 and AXIN2) in BCA (n = 34), BCAC (n = 3), ACC (n = 67) and PA (n = 31). We also analyzed ACC-specific MYB and MYBL1 gene rearrangements by fluorescence in situ hybridization (FISH). Nuclear β-catenin expression (≥3%) was present in 32/34 cases (94.1%) of BCA, and the nuclear β-catenin labeling index was significantly higher than in other tumor types (p = < 0.0001). In BCA, we found mutations in CTNNB1, APC and AXIN1 genes (41.1%, 2.9% and 8.8%, respectively). In BCAC, nuclear β-catenin expression with CTNNB1 mutation was present in 1/3 cases (33.3%). As for ACC, nuclear β-catenin expression was observed in 3/67 cases (4.4%), but all 3 cases harbored either MYB or MYBL1 gene rearrangement. The results suggest that nuclear β-catenin immunoreactivity with appropriate criteria may be helpful to distinguish BCA from histologically similar tumors. However, a minor subset of ACCs with nuclear β-catenin expression require careful diagnosis. In addition, Wnt/β-catenin signal alteration may play a role in the pathogenesis of BCA and BCAC. Show less

Liver kinase B1 ( LKB1 ) is a tumor suppressor in lung adenocarcinoma (LADC). We investigated the proteomic profiles of 45 LADC cell lines with and without LKB1 inactivation. Carbamoyl phosphate synthetase 1 (CPS1), the first rate-limiting mitochondrial enzyme in the urea cycle, was distinctively overexpressed in LKB1-inactivated LADC cell lines. We therefore assessed the role of CPS1 and its clinical relevance in LKB1-inactivated LADC. Mass spectrometric profiling of proteome and metabolome and function of CPS1 were analyzed in LADC cell lines. CPS1 and LKB1 expression in tumors from 305 LADC and 160 lung squamous cell carcinoma patients was evaluated by immunohistochemistry. Kaplan-Meier and Cox regression analyses were applied to assess the association between overall survival and CPS1 and LKB1 expression. All statistical tests were two-sided. CPS1 knockdown reduced cell growth, decreased metabolite levels associated with nucleic acid biosynthesis pathway, and contributed an additive effect when combined with gemcitabine, pemetrexed, or CHK1 inhibitor AZD7762. Tissue microarray analysis revealed that CPS1 was expressed in 65.7% of LKB1-negative LADC, and only 5.0% of LKB1-positive LADC. CPS1 expression showed statistically significant association with poor overall survival in LADC (hazard ratio = 3.03, 95% confidence interval = 1.74 to 5.25, P < .001). Our findings suggest functional relevance of CPS1 in LKB1-inactivated LADC and association with worse outcome of LADC. CPS1 is a promising therapeutic target in combination with other chemotherapy agents, as well as a prognostic biomarker, enabling a personalized approach to treatment of LADC. Show less

The activity of 6-phosphofructo-1-kinase is strictly controlled by fructose-2,6-bisphosphate, the level of which is regulated by another enzyme, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK2/FBP2). PFK2/FBP2 is a bifunctional enzyme, having kinase and phosphatase activities, and regulates both glycolysis and gluconeogenesis. Here, we examined the hormonal regulation of the PFK2/FBP2 gene in vitro using the reporter assay, the electromobility shift assay (EMSA), and the chromatin immunoprecipitation (ChIP) assay in HuH7 cells and also using the mouse liver in vivo. We found that the transcriptional activity of the PFK2/FBP2 gene was stimulated by insulin and inhibited by cAMP and glucocorticoid. Liver X receptor (LXR) α showed a potent and specific stimulatory effect on PFK2/FBP2 gene transcription. Deletion and mutagenesis analyses identified the LXR response element (LXRE) in the 5'-promoter region of the PFK2/FBP2 gene. Binding of LXRα was confirmed by the EMSA and ChIP assay. Endogenous PFK2/FBP2 mRNA in the mouse liver was increased in the fasting/refeeding state compared with the fasting state. Altogether, PFK2/FBP2 gene transcription is found to be regulated in a way that is more similar to other glycolytic enzyme genes than to gluconeogenic genes. Furthermore, our data strongly suggest that LXRα is one of the key regulators of PFK2/FBP2 gene transcription. Show less

Both glucocorticoid and insulin are known to have an anabolic effect on lipogenesis. Acetyl-CoA, an intermediate product of glycolysis, is supplied for fatty acid synthesis when carbohydrate intake is sufficient. Acetyl-CoA carboxylase (ACC), consisting of two isoenzymes ACC1 and ACC2, mediates the conversion from acetyl-CoA to malonyl-CoA, and thus plays a key role for the regulation of lipogenesis. In this study, we surveyed the effects of glucocorticoid and insulin on the transcriptional activity of the alternative promoters of ACCs (PI-PIII for ACC1, and PI and PII for ACC2) using the HepG2 human hepatocyte cell line in vitro. We also examined the roles of the insulin and/or glucose-regulated transcriptional factor(s) such as SREBP1c, LXRalpha/beta, and ChREBP on each promoter of the ACC genes. We found that both insulin and glucocorticoid had potent positive effects on all the promoters examined, and additive effects of both hormones were recognized in ACC1 PI and ACC2 PI. Furthermore, a representative insulin-responsive transcription factor SREBP1c showed significant stimulatory effects on all the promoters of ACC genes, among which those on ACC1 PIII and ACC2 PI were most prominent. On the other hand, the effect of LXRalpha was rather selective; it showed a marked stimulatory effect only on ACC1 PII. LXRbeta and ChREBP had minimal, if any, effects on some of the promoters. Altogether, our data suggest that insulin and glucocorticoid have positive effects on both ACC1 and ACC2 gene transcription. SREBP1c might be a master regulator of the expression of both genes regardless of the promoter utilized, whereas LXRalpha seems to play a promoter-specific role. Since ACC1 facilitates lipogenesis by stimulating fatty acid synthesis and ACC2 inhibits lipolysis, both insulin and glucocorticoid seem to play an important role in the pathogenesis of obesity and/or hepatic steatosis. Show less