Role Of The Nuclear Envelope In Intracellular Protein So

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。我们发现Ca+2/钙调蛋白是核输入的激活剂，并提出Ca+2在细胞激活过程中对核输入的调节作用。我们还证明了多功能凝集素钙网蛋白在核输出中的作用。我们认为GTP和Ca+2控制着核孔的双向转运，从而协调调节核转运和其他信号转导途径。核孔复合体包含许多蛋白质，这些蛋白质含有磷酸和O-GlcNAc，它们附着在丝氨酸和苏氨酸残基上。我们对核孔蛋白的糖基化和磷酸化进行了广泛的研究。这种翻译后修饰也存在于RNA聚合酶II和许多聚合酶II转录因子上。O-GlcNAc的加入和去除是发生在细胞质和核质中的动态过程。O-GlcNAc从UDP-GlcNAc转移到蛋白质，UDP-GlcNAc是一种糖核苷酸，其水平由己糖胺生物合成途径调节。己糖胺生物合成途径是一种能量可用性的细胞传感器，已被认为参与了包括瘦素在内的许多基因产物的调节，瘦素是ob基因的产物。O-linked GlcNAc转移酶可能介导一种新的聚糖依赖性信号转导途径。我们分子克隆并鉴定了负责核孔蛋白和转录因子糖基化的人O-linked GlcNAc转移酶。当在大肠杆菌中表达时，人O-linked GlcNAc转移酶具有催化活性。尽管该酶存在于许多靶组织中，但它在人类胰腺β细胞中表达最高，与葡萄糖感应的作用一致。基于其底物特异性和分子特征，我们提出O-linked GlcNAc转移酶是糖尿病（NIDDM）中葡萄糖反应通路失调的最终步骤。参与GlcNAc去除的细胞质O-GlcNAcase也被克隆并以重组形式表达。利用反向遗传学、基因敲除和其他转基因模型，我们目前正在探索这些必需蛋白在信号转导和糖尿病发病机制中的作用。

Nuclear transport is critical for 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. We also demonstrated a role for the multifunctional lectin calreticulin in nuclear export. We suggest that bi-directional transport across the nuclear pore is controlled by GTP and Ca+2, thus providing coordinate regulation of nuclear transport and other signal transduction pathways. The Nuclear pore complex contains numerous proteins bearing both phosphate and O-GlcNAc attached to Ser and Thr residues. We have studied the glycosylation and phosphorylation of nuclear pore proteins extensively. This post-translational modification is also present on RNA polymerase II, and numerous polymerase II transcription factors. Addition and removal of O-GlcNAc are dynamic processes occurring in the cytoplasm and nucleoplasm. O-GlcNAc is transferred to proteins from UDP-GlcNAc, a sugar nucleotide whose levels are regulated by the hexosamine biosynthetic pathway. The hexosamine biosynthetic pathway is a cellular sensor of energy availability and has been suggested to be involved in the regulation of a number of gene products including leptin, the product of the ob gene. O-linked GlcNAc transferase may mediate a novel glycan-dependent signal transduction pathway. We have molecularly cloned and characterized the human O-linked GlcNAc transferase responsible for glycosylating nuclear pore proteins and transcription factors. When expressed in E. coli, the human O-linked GlcNAc transferase is catalytically active. Although the enzyme is found in a number of target tissues, it is most highly expressed in human pancreatic beta cells, consistent with a role in glucose-sensing. Based on its substrate specificity and molecular features, we have proposed that O-linked GlcNAc transferase is the terminal step in a glucose-responsive pathway that becomes disregulated in diabetes mellitus (NIDDM). The cytoplasmic O-GlcNAcase involved in GlcNAc removal has also been cloned and expressed in recombinant form. Using reverse genetics, knockout, and other transgenic models we are currently exploring the role of these essential proteins in signal transduction and the pathogenesis of diabetes mellitus.