Calmodulin-driven Nuclear Trafficking linked to diabetes and insulin signaling

调节核转运对于维持转录因子、核激酶和复制因子的水平和活性至关重要。我们确定了Ca+2/钙调素作为核输入的激活剂，并建议在细胞活化过程中的调节核输入的Ca+2的作用。这种进化上古老的钙依赖性输入途径被提出来促进细胞活化期间核蛋白的不同子集的摄取。随着钙调素依赖性核输入缺陷导致某些形式的人类性别逆转的发现，Ca+2-钙调素调节的转运途径的生理意义变得清晰。HMG盒结构转录因子SRY和SOX 9必须进入支持细胞的细胞核，并与靶DNA紧密结合，才能正常发育。因此，SRY作为雄性的主要触发器;需要SRY的核转运来释放该触发器。在患有常染色体性逆转（Swyers综合征，Campomelic发育不良）的人类患者的子集中，SRY和SOX 9的核转运被阻断。与这些缺陷相关的突变位于SRY和SOX 9氨基末端附近的保守钙调素结合基序中。因此，SOX家族的转录因子似乎使用Ca+2/钙调蛋白作为输入受体和允许核输入和DNA结合的分子开关。当三种胰岛素相关受体在小鼠中被消融时，发生类似的常染色体性逆转表型，这表明细胞内信号级联可能影响SRY和SOX 9的正常功能。最近，编码TCF 7 L2的基因被证明是冰岛人群中的糖尿病易感基因。该转录因子是含有钙调素结合基序的HMG盒家族的成员。钙调素的核蛋白的进口，而功能冗余的经典RAN依赖性途径，受到细胞内Ca+2动员的独立调节。钙调素依赖性输入异常是常染色体性反转患者的主要缺陷。这些性逆转综合征代表了导致人类疾病的核输入途径缺陷的第一个直接例子。涉及SOX家族转录因子的其他人类疾病可能在钙调蛋白依赖性核输入中具有类似的缺陷。除了在哺乳动物中的HMG盒转录因子的进口的分析，我们最近表明，钙调蛋白依赖性的核输入途径在酵母中的功能。我们目前正在采取遗传方法来定义这种新的输入途径的其他成分，并寻求确定该过程的小分子抑制剂。由于SOX 2蛋白对干细胞多能性特别重要，我们目前的重点是了解核输入在其调控中的作用。在线虫中，pop-1是与bar-1相关的关键结构转录因子，bar-1是β-连环蛋白的蠕虫同源物。这些研究是在酵母和C. elegans系统。 与已知的核运输途径的关系正在进行遗传和生物化学研究。 这些新方法正在临床和基础科学研究中转化为潜在的成像策略。

Regulated nuclear transport is critical for the maintenance of the levels and activities of transcription factors, nuclear kinases, and replication factors. We identified Ca+2/calmodulin as an activator of nuclear import and suggested a role for Ca+2 in the regulation of nuclear import during cell activation. This evolutionarily ancient, calcium-dependent import pathway was proposed to facilitate uptake of a distinct subset of nuclear proteins during cell activation. The physiological significance of the Ca+2-calmodulin-regulated transport pathway became clear with the finding that defects in calmodulin-dependent nuclear import underlie certain forms of human sex reversal. The HMG-box architectural transcription factors SRY and SOX9 must enter the nucleus of Sertoli cells and bind tightly to target DNA for proper male gonad development. Thus, SRY acts as the primary trigger for maleness; nuclear transport of SRY is required to release this trigger. In a subset of human patients with autosomal sex reversal (Swyers syndrome, Campomelic dysplasia) nuclear transport of SRY and SOX9 is blocked. The mutations associated with these defects reside in a conserved calmodulin-binding motif near the amino terminus of SRY and SOX9. Thus, the SOX family of transcription factors appears to use Ca+2/calmodulin both as import receptor and molecular switch allowing for nuclear import and DNA binding. A similar autosomal sex reversal phenotype occurs when three insulin-related receptors are ablated in mice suggesting that intracellular signaling cascades may impact the normal functions of SRY and SOX9. More recently, the gene encoding TCF7L2 was shown to be a diabetes susceptibility locus in the Icelandic population. This transcription factor is a member of the HMG-box family containing a calmodulin-binding motif. The import of nuclear proteins by calmodulin, while functionally redundant with the canonic Ran-dependent pathway, is subject to independent regulation by intracellular Ca+2 mobilization. Abnormalities in calmodulin-dependent import emerge as the primary defect in patients with autosomal sex-reversal. These sex-reversal syndromes represent the first direct examples of a defect in a nuclear import pathway leading to human disease. Other human disorders involving SOX-family transcription factors may have similar defects in calmodulin dependent nuclear import. In addition to analysis of the import of the HMG-box transcription factors in mammals, we have recently shown that the calmodulin-dependent nuclear import pathway functions in yeast. We are currently taking genetic approaches to define additional components of this novel import pathway and seek to identify small molecule inhibitors of the process. Because the SOX2 protein is particularly important for Stem Cell pluripotency, our focus is currently on understanding the role of nuclear import in its regulation. In the nematode, pop-1 is a key architectural transcription factor associated with bar-1, the worm homolog of Beta-catenin. These studies are being carried out in the yeast and C. elegans systems. The relationship with known nuclear transport pathways is being investigated genetically and biochemically. These novel approaches are being translated into potential imaging strategies in both clinical and basic science studies.