LKB1 Drives Stasis and C/EBP-Mediated Reprogramming…

LKB1 is among the most frequently altered tumor suppressors in lung adenocarcinoma. Inactivation of Lkb1 accelerates the growth and progression of oncogenic KRAS-driven lung tumors in mouse models. However, the molecular mechanisms by which LKB1 constrains lung tumorigenesis and whether the cancer state that stems from Lkb1 deficiency can be reverted remains unknown. To identify the processes governed by LKB1 in vivo, we generated an allele which enables Lkb1 inactivation at tumor initiation and subsequent Lkb1 restoration in established tumors. Restoration of Lkb1 in oncogenic KRAS-driven lung tumors suppressed proliferation and led to tumor stasis. Lkb1 restoration activated targets of C/EBP transcription factors and drove neoplastic cells from a progenitor-like state to a less proliferative alveolar type II cell-like state. We show that C/EBP transcription factors govern a subset of genes that are induced by LKB1 and depend upon NKX2-1. We also demonstrate that a defining factor of the alveolar type II lineage, C/EBPα, constrains oncogenic KRAS-driven lung tumor growth in vivo. Thus, this key tumor suppressor regulates lineage-specific transcription factors, thereby constraining lung tumor development through enforced differentiation

Mouse cell lines. Cell lines were generated from primary tumors and mice previously transduced with lentiviral Cre. To establish cell lines, individual tumors were micro-dissected from tumor-bearing lungs, minced, and directly cultured in DMEM supplemented with 10% FBS (Phoenix Scientific), 1% penicillin-streptomycin-glutamate, and 0.1% amphotericin at 37 °C and 5% CO2 until cell lines were established. Cells were authenticated for genotype. To induce Lkb1 restoration, cells were treated with either 1 μM 4-hydroxytamoxifen dissolved in 100% ethanol or vehicle (1:2000 100% ethanol).

Results Generation of a conditionally inactivatable and restorable Lkb1XTR allele. To investigate the cellular and molecular pro[1]cesses governed by LKB1 in vivo, ….

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Stromal Cells Regulate Sialylations…

The goal of this study was to determine the role of sialylated N-glycans in MSCs. We show that IFN-gamma or exposure to culture media low in fetal bovine serum (FBS) increases sialylated N-glycans, while PDGF-BB reduces them. These stimuli alter mRNA levels of sialyltransferases such as ST3Gal1, ST6Gal1, or ST3Gal4, suggesting that sialylation of N-glycans is regulated by transcriptional control of sialyltransferases. We next show that 2,4,7,8,9-pentaacetyl-3Fax-Neu5Ac-CO2Me (3F-Neu5Ac) effectively inhibits sialylations in MSCs. Supplementation with 3F-Neu5Ac increases adhesion and migration of MSCs, as assessed by both videomicroscopy and wound/scratch assays. Interestingly, pre-treatment with 3F-Neu5Ac also increases the survival of MSCs in an in vitro ischemia model.

Materials and Methods – MSC Isolation and Expansion MSCs were isolated from commercially available human bone marrow. Bone marrow aspirates were passed through 90 µm pore strainer for isolation of bone spicules. Then, bone marrow aspirates were diluted with an equal volume of phosphate-buffered saline (PBS) and centrifuged over Ficoll at 700 g for 30 min. Mononuclear cells from the Buffy Coat and bone spicules (if any) were plated in plastic culture flasks, using Minimum Essential Medium α plus 10% Fetal Bovine Serum (FBS-Phoenix Scientific, San Marcos, CA, USA) (standard culture media). After two days, non-adherent cells were removed by washing 2–3 times with PBS. MSCs between passage 3–6 were used for experimentation to ensure pure MSC cultures. Additionally, higher passage cells may become senescent, which lead to alteration of gene expression, arrest in cell proliferation, and resistance to apoptosis.

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