The Role of Merlin Phosphorylation on its Tumor Suppressive Activity

NF 2肿瘤抑制基因编码一种细胞内膜相关蛋白，称为merlin或 神经鞘蛋白，属于细胞色素相关蛋白的带4.1家族（ERM蛋白）， 将细胞表面糖蛋白连接到肌动蛋白细胞骨架。梅林的生长抑制取决于它的能力 以形成有效的N项/C项关联。梅林存在于“开放”（非活动形式）和“封闭”（活动 生长抑制型）构象，其由分子间的分子内缔合调节， 蛋白质的N-和C-末端。许多研究表明，梅林磷酸化在细胞内起着重要的作用。 在决定其构象和结合活性中起重要作用。最近，我们发现野生型梅林， 而不是患者来源的突变体（L 64 P），选择性地结合PIKE-L并抑制磷酸肌醇3-激酶（PI 3-激酶）。 激酶）活性。PIKE（PI 3-激酶增强剂）是脑特异性GT3，其结合PI 3-激酶， 刺激其脂质激酶活性。这种PI 3-激酶活性的抑制是由于merlin破坏了PI 3-激酶的活性。 PIKE-L与PI 3-激酶的结合。merlin的诱导显著减少PI 3-激酶/Akt信号传导 神经鞘瘤细胞中的信号通路。磷酸化和磷酸肌醇脂质结合协调介导 ERM蛋白的激活。然而，Akt是否磷酸化merlin和磷酸肌醇脂质结合到 梅林还控制梅林的活动仍然难以捉摸。我们假设merlin在生理上受到 PI 3-激酶/Akt级联反应的负反馈机制。具体来说，我们将测试Akt是否 磷酸化merlin并调节其构象和亚细胞定位。此外，我们将 确定Akt磷酸化和PI（3，4，5）P3是否协同介导merlin与 关键的下游效应物，导致梅林的肿瘤抑制活性消失。鉴定 介导merlin磷酸化和结合活性的信号传导途径不仅对于 了解梅林的生理功能，也为今后开发新药 治疗这种疾病。

The NF2 tumor suppressor gene encodes an intracellular membrane-associated protein, called merlin or schwannomin, which belongs to the band 4.1 family (ERM proteins) of cytoskeleton-associated proteins that link cell surface glycoproteins to the actin cytoskeleton. Merlin growth suppression is dependent on its ability to form a productive N-term/C-term association. Merlin exists in "open" (inactive form) and "closed" (active growth suppressiveform) conformations, which are regulated by an intramolecular association between the N- and C-termini of the protein. Numerous studies demonstrate that merlin phosphorylation plays an essential role in dictating its conformation and binding activity. Recently, we showed that wild-type merlin, but not patient-derived mutant (L64P), selectively binds PIKE-L and inhibits Phosphoinositol 3-kinase (PI 3- kinase) activity. PIKE (PI 3-Kinase Enhancer) is a brain-specific GTPase that binds to PI 3-kinase and stimulates its lipid kinase activity. This suppression of PI 3-kinase activity results from merlin disrupting the binding of PIKE-L to PI 3-kinase. Induction of merlin substantially diminishes PI 3-kinase/Akt signaling pathway in Schwannoma cells. Phosphorylation and phosphoinositol lipids binding coordinately mediate the activation of ERM proteins. However, whether Akt phosphorylates merlin and phosphoinositol lipids bind to merlin also control merlin activity remains elusive. We hypothesize that merlin is physiologically regulated by a negative feed-back mechanism of PI 3-kinase/Akt cascade. Specifically, we will test whether Akt phosphorylates merlin and modulates its conformation and subcellular localization. In addition, we will determine whether Akt phosphorylation and PI (3,4,5)P3 synergistically mediate merlin's binding activity to the critical downstream effectors, resulting in abolishing merlin's tumor suppressive activity. Identification of signaling pathways mediating merlin phosphorylation and binding activity is essential not only for understanding the physiological functions of merlin, but also for the future development of novel drug treatments for this disease.