GFAT1-linked TAB1 glutamylation sustains p38 MAPK activation and promotes lung cancer cell survival under glucose starvation.

Reprogrammed cell metabolism is deemed as one of the hallmarks of cancer. Hexosamine biosynthesis pathway (HBP) acts as an "energy sensor" in cells to regulate metabolic fluxes. Glutamine-fructose-6-phosphate amidotransferase 1 (GFAT1), the rate-limiting enzyme of HBP, is broadly found with elevated expression in human cancers though its exact and concrete role in tumorigenesis still remains unknown and needs further investigation. P38 mitogen-activated protein kinase (MAPK) is an important component of stress-signaling pathway and plays a critical role in cell fate decision, whereas the underlying mechanism of its activation under nutrient stress also remains elusive. In this study, we show that glucose deprivation induces the interaction of GFAT1 with transforming growth factor ß-activated kinase 1 binding protein 1 (TAB1) in a TAB1 S438 phosphorylation-dependent manner. Subsequently, the binding of GFAT1 to TAB1 facilitates TTLL5-GFAT1-TAB1 complex formation, and the metabolic activity of GFAT1 for glutamate production further contributes to TTLL5-mediated TAB1 glutamylation. In consequence, TAB1 glutamylation promotes the recruitment of p38α MAPK and thus drives p38 MAPK activation. Physiologically, GFAT1-TAB1-p38 signaling promotes autophagy occurrence and thus protects tumor cell survival under glucose deficiency. Clinical analysis indicates that both GFAT1 and TAB1 S438 phosphorylation levels correlate with the poor prognosis of lung adenocarcinoma patients. These findings altogether uncover an unidentified mechanism underlying p38 MAPK signaling regulation by metabolic enzyme upon nutrient stress and provide theoretical rationality of targeting GFAT1 for cancer treatment.

PTPS Facilitates Compartmentalized LTBP1 S-Nitrosylation and Promotes Tumor Growth under Hypoxia.

GTP cyclohydrolase I (GTPCH), 6-pyruvoyltetrahydropterin synthase (PTPS), and sepiapterin reductase (SR) are sequentially responsible for de novo synthesis of tetrahydrobiopterin (BH4), a known co-factor for nitric oxide synthase (NOS). The implication of BH4-biosynthesis process in tumorigenesis remains to be investigated. Here, we show that PTPS, which is highly expressed in early-stage colorectal cancer, is phosphorylated at Thr 58 by AMPK under hypoxia; this phosphorylation promotes PTPS binding to LTBP1 and subsequently drives iNOS-mediated LTBP1 S-nitrosylation through proximal-coupling BH4 production within the PTPS/iNOS/LTBP1 complex. In turn, LTBP1 S-nitrosylation results in proteasome-dependent LTBP1 protein degradation, revealing an inverse relationship between PTPS pT58 and LTBP1 stability. Physiologically, the repressive effect of PTPS on LTBP1 leads to impaired transforming growth factor ß (TGF-ß) secretion and thereby maintains tumor cell growth under hypoxia. Our findings illustrate a molecular mechanism underlying the regulation of LTBP1-TGF-ß signaling by the BH4-biosynthesis pathway and highlight the specific requirement of PTPS for tumor growth.

Correction to: c-Src confers resistance to mitotic stress through inhibition of DMAP1/Bub3 complex formation in pancreatic cancer.

Following publication of the work [1], authors reported the "flow cytometery plots" panel in Fig. 4e contained an inter-duplication in error.

Epithelial Wntless is dispensable for intestinal tumorigenesis in mouse models.

Wnt signaling is essential for the maintenance of adult stem cells and its aberrant activation is a stimulator of carcinogenesis. The transmembrane protein, Wntless, is an essential Wnt signaling component through regulating the secretion of Wnt ligands. Here, we generated a mouse model with specific Wntless knockout in intestinal epithelium to study its function in the intestinal epithelium. Wntless knockout exhibits no obvious defects in mice but significantly disrupted proliferation and differentiation of small intestinal organoids. We also discovered that these deficiencies could be partially rescued by Wnt3a supplement but not Wnt9b. To further investigate the role of Wntless in tumorigenesis, APC-deficient spontaneous intestinal tumors and chemical induced colorectal cancer mouse models were employed. To our surprise, intestinal epithelium-specific knockout of Wntless did not cause significant differences in tumor number and size. In summary, our data demonstrated that epithelial Wntless was required for the growth and differentiation of small intestinal organoids but not in live animals, suggesting the other tissues, such as mesenchymal tissue, play critical role for Wnt secretion in both intestinal homeostasis as well as tumorigenesis.

PAK4 Phosphorylates Fumarase and Blocks TGFß-Induced Cell Growth Arrest in Lung Cancer Cells.

The metabolic activity of fumarase (FH) participates in gene transcription linking to tumor cell growth. However, whether this effect is implicated in lung cancer remains unclear. Here, we show TGFß induces p38-mediated FH phosphorylation at Thr 90, which leads to a FH/CSL (also known as RBP-Jκ)/p53 complex formation and FH accumulation at p21 promoter under concomitant activation of Notch signaling; in turn, FH inhibits histone H3 Lys 36 demethylation and thereby promotes p21 transcription and cell growth arrest. In addition, FH is massively phosphorylated at the Ser 46 by PAK4 in non-small cell lung cancer (NSCLC) cells, and PAK4-phosphorylated FH binds to 14-3-3, resulting in cytosolic detention of FH and prohibition of FH/CSL/p53 complex formation. Physiologically, FH Ser 46 phosphorylation promotes tumorigenesis through its suppressive effect on FH Thr 90 phosphorylation-mediated cell growth arrest in NSCLC cells and correlates with poor prognosis in patients with lung cancer. Our findings uncover an uncharacterized mechanism underlying the local effect of FH on TGFß-induced gene transcription, on which the inhibitory effect from PAK4 promotes tumorigenesis in lung cancer. SIGNIFICANCE: Fumarase counteracts CSL via its metabolic activity to facilitate TGFß-induced cell growth arrest, an effect largely blocked by PAK4-mediated phosphorylation of fumarase.

C-Src confers resistance to mitotic stress through inhibition DMAP1/Bub3 complex formation in pancreatic cancer.

BACKGROUND: Chromatin modification at mitosis is closely related to transcriptional reactivation in the subsequent cell cycle. We reasoned this process is deregulated by oncogenic signals, which would contribute to mitotic stress resistance in pancreatic cancer. Here, we show DMAP1/Bub3 complex mediates mitotic stress-induced cellular apoptosis, while this effect is counteracted by c-Src in pancreatic cancer cells. Our study aims to uncover an unidentified mechanism underlying the distinct response to mitotic stress between normal cells and pancreatic cancer cells. METHODS: The interaction between Bub3 and DMAP1 upon mitotic stress signaling was determined through molecular and cell biological methods. The inhibitory effect of c-Src on DMAP1/Bub3-mediated DNA methylation and gene transcription profile was investigated. The association between c-Src-mediated DMAP1 phosphorylation and paclitaxel activity in vivo and clinicopathologic characteristics were analyzed. RESULTS: Mitotic arrest induced p38-dependent phosphorylation of Bub3 at Ser211, which promotes DMAP1/Bub3 interaction. DMAP1/Bub3 complex is recruited by TAp73 to the promoter of anti-apoptotic gene BCL2L1, thus mediates the DNA methylation and represses gene transcription linked to cell apoptosis. Meanwhile, DMAP1 was highly phosphorylated at Tyr 246 by c-Src in pancreatic cancer cells, which impedes DMAP1/Bub3 interaction and the relevant cellular activites. Blocking DMAP1 pTyr-246 potentiates paclitaxel-inhibited tumor growth. Clinically, DMAP1 Tyr 246 phosphorylation correlates with c-Src activity in human pancreatic cancer specimens and poor prognosis in pancreatic cancer patients. CONCLUSIONS: Our findings reveal a regulatory role of Bub3 in DMAP1-mediated DNA methylation upon mitotic stress and provide the relevance of DMAP1 pTyr-246 to mitotic stress resistance during pancreatic cancer treatment.

O-GlcNAcylation of fumarase maintains tumour growth under glucose deficiency.

Chromatin-associated fumarase (FH) affects histone methylation via its metabolic activity. However, whether this effect is involved in gene transcription remains to be clarified. In this study, we show that under glucose deprivation conditions, AMPK phosphorylates FH at Ser75, which in turn forms a complex with ATF2 and participates in promoter activation. FH-catalysed fumarate in promoter regions inhibits KDM2A demethylase activity, and thus maintains the H3K36me2 profile and facilitates gene expression for cell growth arrest. On the other hand, FH is found to be O-GlcNAcylated at the AMPK phosphorylation site; FH-ATF2-mediated downstream events are impeded by FH O-GlcNAcylation, especially in cancer cells that display robust O-GlcNAc transferase (OGT) activity. Consistently, the FH-Ser75 phosphorylation level inversely correlates with the OGT level and poor prognosis in pancreatic cancer patients. These findings uncover a previously uncharacterized mechanism underlying transcription regulation by FH and the linkage between dysregulated OGT activity and growth advantage of cancer cells under glucose deficiency.