The mechanisms of preneoplastic nodule formation in the liver by loss of LKB1

我们以前报道过Lkb1+/-小鼠自发地发展为多发性肝结节病灶(NdFc)，随后是肝细胞癌。LKB1是Peutz-Jeghers综合征中突变的肿瘤抑制基因，编码丝氨酸/苏氨酸蛋白激酶。为了探讨NdFc与Lkb1+/-小鼠肝细胞癌形成的机制，我们比较了Lkb1+/-小鼠正常肝脏和肝细胞癌病变组织中的基因表达水平。我们确定了50个在肝细胞癌中表达上调的基因和50个表达下调的基因(比野生型基因高2倍以上)。这些列表包括炎症反应基因、细胞周期调控基因、转录因子和脂类代谢调控基因。我们进一步表明，-catenin的条件激活加速了Catnb+/lox(EX3)Lkb1+/-复合突变小鼠的肝细胞癌的发展，影响了NdFc中遭受Lkb1基因杂合性丢失(LOH)的发育不良的肝细胞。这些结果表明，Lkb1的丢失是导致肌萎缩症形成的原因，而W…更多的NT信号激活参与了随后的肝细胞癌的进展。这些顺序变化的组合应该是人类HC子集的实用模型。最近的生化研究表明，LKB1激活了14个AMPK相关的激酶，包括AMPK和MARKS(微管相关蛋白/微管亲和力调节激酶)。为了确定LKB1是否调节细胞中这些激酶的激活，我们建立了LKB1-/-小鼠胚胎成纤维细胞(MEF)和LKB1-基因敲除细胞系。在能量应激条件下，这些细胞内AMPK仍处于激活状态。在体外，LKB1磷酸化并激活Mark2，进而磷酸化KXGS基序上的微管相关蛋白Tau，并抑制微管蛋白聚合。在细胞中，强制表达LKB1抑制了微管的再生，而敲除LKB1则促进了微管的再生。这些结果表明，LKB1通过激活MARTS参与微管动力学的调节。较少

We previously reported that Lkb1+/-mice spontaneously developed multiple hepatic nodular foci (NdFc) followed by HCCs. LKB1, a tumor suppressor gene mutated in the Peutz-Jeghers syndrome, encodes a serine/threonine protein kinase. To investigate the mechanisms of NdFc and HCC formation in Lkb1+/-mice, we compared the gene expression levels between the normal liver and HCC lesions of Lkb1+/- mice. We identified 50 up-regulated and 50 down-regulated genes in HCC (more than 2-fold versus wild type). These lists included inflammatory response genes, cell cycle regulatory genes, transcriptional factors, and lipid metabolism regulatory genes. We further showed that the conditional activation of -catenin accelerated HCC development in the Catnb+/lox(ex3)Lkb1+/-compound mutant mice, affecting displastic hepatocytes in NdFc that suffered loss of heterozygosity (LOH) at the Lkb1 locus. These results indicate that the loss of Lkb1 is responsible for the formation of dyspastic NdFc, and that the W … More nt signaling activation is involved in the following progression toward HCC. A combination of these sequential changes should be a practical model for a subset of human HCCs. Recent biochemical studies have shown that LKB1 activates 14 AMP-activated protein kinase (AMPK)-related kinases including AMPK and MARKs (microtubule-associated protein/microtubule affinity-regulating kinases). To determine whether LKB1 regulated the activation of these kinases in cells, we established Lkb1-/-mouse embryonic fibroblasts (MEFs) and LKB1-knockdown cell lines. AMPK was still activated in these cells under the energy stress. LKB1 phosphorylated and activated MARK2, which in turn phosphorylated microtubule-associated protein Tau at the KXGS motif and suppressed tubulin polymerization in vitro. In cells, forced expression of LKB1 suppressed microtubule regrowth, whereas LKB1 knockdown accelerated it. These results indicate that LKB1 is involved in the regulation of microtubule dynamics through the activation of MARKS. Less