Regulation of the Transcription Factor UBF by CHP

钙调神经磷酸酶同源蛋白（calcalineurin homologous protein， CHP）是一种Ca2+结合蛋白，具有多种功能，包括调节离子交换剂和钙调神经磷酸酶活性以及组成性囊泡运输。我们最近发现CHP定位于核膜，并且CHP的过表达抑制细胞增殖。上游结合因子UBF是RNA聚合酶I （P01 I）转录起始复合物的必需组分，具有转录核rDNA基因的功能。因此，UBF在核糖体生物合成和细胞增殖中起着关键作用。我们有证据表明CHP和UBF之间的一种新的体内相互作用是Ca2+敏感的。本研究将探讨CHP与UBF相互作用调节UBF功能的假设，主要有两个目的：1)研究CHP与UBF的调节关联，2)确定CHP与UBF相互作用的功能意义。目的1确定UBF是否直接与CHP结合，如果是，是否依赖于Ca2+，并研究CHP和UBF在体内的调节分布。目的2研究CHP的丰度、Ca2+结合和膜关联是否调节UBF修饰和/或UBF介导的rDNA转录。这些实验的结果将促进我们对CHP和UBF如何独立调节以及它们如何相互作用调节UBF功能的认识。

DESCRIPTION (provided by applicant) Calcineurin homologous protein, CHP, is a Ca2+-binding protein with diverse functions, including regulation of ion exchanger and calcineurin activities and constitutive vesicular transport. We have recently found that CHP is localized to the nuclear envelope and that overexpression of CHP inhibits cell proliferation. Upstream binding factor, UBF, is a necessary component of the transcription initiation complex of RNA polymerase I (P01 I) that functions to transcribe nuclear rDNA genes. Thus UBF is a key player in ribosome biosynthesis and cell proliferation. We have evidence demonstrating a novel in vivo interaction between CHP and UBF that is Ca2+-sensitive. This proposal will investigate the hypothesis that the interaction between CHP and UBF regulates UBF function, and is comprised of two primary Aims: 1) Investigate the regulated association of CHP with UBF, and 2) Determine the functional significance of the interaction of CHP with UBF. Aim 1 determines whether UBF binds directly to CHP and, if so, whether it is Ca2+-dependent, and investigates the regulated distribution of CHP and UBF in vivo. Aim 2 investigates whether the abundance, Ca2+ binding, and membrane association of CHP regulate UBF modifications and/or UBF-mediated rDNA transcription. Results of these experiments will advance our knowledge of how CHP and UBF are independently regulated as well as how their interaction regulates UBF function.