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Author(s): Jianyuan Luo [1]; Fei Su [1]; Delin Chen; Ariel Shiloh; Wei Gu (corresponding author) The p53 tumour suppressor is a transcriptional factor whose activity is modulated by protein stability [...]

Protein lysine acetylation affects colorectal cancer (CRC) distant metastasis through multiple pathways. In a previous proteomics screen, we found that isocitrate dehydrogenase 1 (IDH1) is hyperacetylated in CRC primary tumors and liver metastases. Here, we further investigate the function of IDH1 hyperacetylation at lysine 224 in CRC progression. We find that IDH1 K224 deacetylation promotes its enzymatic activity and the production of α‐KG, and we identify sirtuin‐2 (SIRT2) as a major deacetylase for IDH1. SIRT2 overexpression significantly inhibits CRC cell proliferation, migration, and invasion. IDH1 acetylation is modulated in response to intracellular metabolite concentration and regulates cellular redox hemostasis. Moreover, IDH1 acetylation reversely regulates HIF1α‐dependent SRC transcription which in turn controls CRC progression. Physiologically, our data indicate that IDH1 deacetylation represses CRC cell invasion and migration in vitro and in vivo, while the hyperacetylation of IDH1 on K224 is significantly correlated to distant metastasis and poor survival of colorectal cancer patients. In summary, our study uncovers a novel mechanism through which SIRT2‐dependent IDH1 deacetylation regulates cellular metabolism and inhibits liver metastasis of colorectal cancer. Synopsis: SIRT2 inhibits colorectal cancer cell invasion and metastasis by regulating IDH1 acetylation on K224. SIRT2 deacetylates IDH1 on Lys224 in colorectal cancer.IDH1 K224 acetylation activates HIF1α/SRC axis to promote colorectal cancer metastasis.IDH1 acetylation predicts poor prognosis in colorectal cancer. [ABSTRACT FROM AUTHOR]

As a genome guardian, p53 maintains genome stability by arresting cells for damage repair or inducing cell apoptosis to eliminate the damaged cells in stress response. Several nucleolar proteins stabilize p53 by interfering Mdm2-p53 interaction upon cellular stress, while other mechanisms by which nucleolar proteins activate p53 remain to be determined. Here, we identify NAT10 as a novel regulator for p53 activation. NAT10 acetylates p53 at K120 and stabilizes p53 by counteracting Mdm2 action. In addition, NAT10 promotes Mdm2 degradation with its intrinsic E3 ligase activity. After DNA damage, NAT10 translocates to nucleoplasm and activates p53-mediated cell cycle control and apoptosis. Finally, NAT10 inhibits cell proliferation and expression of NAT10 decreases in human colorectal carcinomas. Thus, our data demonstrate that NAT10 plays a critical role in p53 activation via acetylating p53 and counteracting Mdm2 action, providing a novel pathway by which nucleolar protein activates p53 as a cellular stress sensor. [ABSTRACT FROM AUTHOR]

Background: Hematopoietic stem cell (HSC) regulation is highly dependent on interactions with the marrow microenvironment, of which osteogenic cells play a crucial role. While evidence is accumulating for an important role of intrinsic miR-17 in regulating HSCs and HPCs, whether miR-17 signaling pathways are also necessary in the cell-extrinsic control of hematopoiesis hereto remains poorly understood. Methodology/Principal Findings: Using the immortalized clone with the characteristics of osteoblasts, FBMOB-hTERT, in vitro expansion, long-term culture initiating cell (LTC-IC) and non-obese diabetic/severe combined immunodeficient disease (NOD/SCID) mice repopulating cell (SRC) assay revealed that the ectopic expression of miR-17 partly promoted the ability of FBMOB-hTERT to support human cord blood (CB) CD34+ cell expansion and maintain their multipotency. It also seemed that osteoblastic miR-17 was prone to cause a specific expansion of the erythroid lineage. Conversely, deficient expression of miR-17 partly inhibited the hematopoietic supporting ability of FBMOB-hTERT. We further identified that HIF-1α is responsible for, at least in part, the promoted hematopoietic supporting ability of FBMOB-hTERT caused by miR-17. HIF-1α expression is markedly enhanced in miR-17 overexpressed FBMOB-hTERT upon interaction with CB CD34+ cells compared to other niche associated factors. More interestingly, the specific erythroid lineage expansion of CB CD34+ cells caused by osteoblastic miR-17 was abrogated by HIF-1α knock down. Conclusion/Significance: Our data demonstrated that CB CD34+ cell expansion can be partly promoted by osteoblastic miR-17, and in particular, ectopic miR-17 can cause a specific expansion of the erythroid lineage through augmenting HIF-1α in osteoblasts. [ABSTRACT FROM AUTHOR]

Background: Enhancing white adipose tissue (WAT) browning combats obesity. The RIIβ subunit of cAMP-dependent protein kinase (PKA) is primarily expressed in the brain and adipose tissue. Deletion of the hypothalamic RIIβ gene centrally induces WAT browning, yet the peripheral mechanisms mediating this process remain unexplored. Methods: This study investigates the mechanisms underlying WAT browning in RIIβ-KO mice. Genetic approaches such as β3-adrenergic receptors (β3ARs) deletion and sympathetic denervation of WAT were utilized. Genome-wide transcriptomic sequencing and bioinformatic analysis were employed to identify potential mediators of WAT browning. siRNA assays were employed to knock down mTOR and lipin1 in vitro , while AAV-shRNAs were used for the same purpose in vivo . Results: We found that WAT browning substantially contributes to the lean and obesity-resistant phenotypes of RIIβ-KO mice. The WAT browning can be dampened by β 3 ARs deletion or WAT sympathetic denervation. We identified that adipocytic mTOR and lipin1 may act as mediators of the WAT browning. Inhibition of mTOR or lipin1 abrogates WAT browning and hinders the lean phenotype of RIIβ-KO mice. In human subcutaneous white adipocytes and mouse white adipocytes, β 3 AR stimulation can activate mTOR and causes lipin1 nuclear translocation; knockdown of mTOR and Lipin1 mitigates WAT browning-associated gene expression, impedes mitochondrial activity. Moreover, mTOR knockdown reduces lipin1 level and nuclear translocation, indicating that lipin1 may act downstream of mTOR. Additionally, in vivo knockdown of mTOR and Lipin1 diminished WAT browning and increased adiposity. Conclusions: The β 3 AR-activated mTOR-lipin1 axis mediates WAT browning, offering new insights into the molecular basis of PKA-regulated WAT browning. These findings provide potential adipose target candidates for the development of drugs to treat obesity., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

Hepatocellular carcinoma (HCC) is one of the most prevalent and lethal cancers. It has been demonstrated that aberrant expression of miRNAs plays an important role in HCC development. Here, we observed decreased miR-125b expression status in tumor samples from HCC patients, and the five years survival rate of HCC patients with low miR-125b expression is poor. By using bioinformatics prediction tools combining with luciferase reporter assay, we identified that miR-125b can suppress the expression of SIRT6 by directly targeting the seed-matching region of its 3'UTR. Based on the analysis via TCGA and clinical samples data, the expression of SIRT6 showed negatively correlated with the expression of mir-125b. After knocking-out the expression of SIRT6 through CRISPR/Cas9, HCC cells showed the decreased cell viability and invasiveness, which had the similar function upon the overexpression of the miR-125b. The function induced by overexpression of miR-125b can be rescued by the restoration of SIRT6. Further experiments demonstrated that the HCC cells showed the significant cellular senescence and apoptosis upon overexpression of miR-125b or knockout SIRT6, which is in accordance with the compromised cell malignancy. Thus, we conclude that, by targeting SIRT6, miR-125b can function as a tumor suppressor to induce the cellular senescence and apoptosis in hepatocellular carcinogenesis and could provide a novel insight for HCC treatment., Competing Interests: None.

The mitochondrial serine hydroxymethyltransferase SHMT2, which catalyzes the rate-limiting step in serine catabolism, drives cancer cell proliferation, but how this role is regulated is undefined. Here, we report that the sirtuin SIRT5 desuccinylates SHMT2 to increase its activity and drive serine catabolism in tumor cells. SIRT5 interaction directly mediated desuccinylation of lysine 280 on SHMT2, which was crucial for activating its enzymatic activity. Conversely, hypersuccinylation of SHMT2 at lysine 280 was sufficient to inhibit its enzymatic activity and downregulate tumor cell growth in vitro and in vivo Notably, SIRT5 inactivation led to SHMT2 enzymatic downregulation and to abrogated cell growth under metabolic stress. Our results reveal that SHMT2 desuccinylation is a pivotal signal in cancer cells to adapt serine metabolic processes for rapid growth, and they highlight SIRT5 as a candidate target for suppressing serine catabolism as a strategy to block tumor growth. Significance: These findings reveal a novel mechanism for controlling cancer cell proliferation by blocking serine catabolism, as a general strategy to impede tumor growth. Cancer Res; 78(2); 372-86. ©2017 AACR ., (©2017 American Association for Cancer Research.)

The bone marrow (BM) microenvironment, heavily composed of osteoblasts, plays a key role during the normal development of hematopoiesis. Endogenous miR-22 has an important function in the hematopoietic development and osteoblastic differentiation. It is unclear whether miR-22 in osteoblasts from the BM microenvironment also has an important function in the development of hematopoiesis. This study found that the capacity of hTERT-transduced fetal bone marrow osteoblasts (FBMOB-hTERT) cells to expand human cord blood (CB) CD34 + cells and maintain the multipotency of CB CD34 + cells is decreased upon ectopic expression of miR-22. Further experiments revealed that with the existence of CB CD34 + cells, the expression of β-catenin in FBMOB-hTERT cells is decreased upon ectopic expression of miR-22. The reduced ability of FBMOB-hTERT cells to expand human CB CD34 + cells and maintain the multipotency of CB CD34 + cells upon ectopic miR-22 was partly rescued by overexpression of β-catenin. The study indicated that the ability of osteoblasts to expand human CB CD34 + cells and maintain the multipotency of CB CD34 + cells is decreased upon ectopic expression of miR-22. The decreased expression of β-catenin is, at least partly, responsible for the reduced ability of osteoblasts for expanding and supporting CB CD34 + cells upon ectopic expression of miR-22.