NOVEL PROTEIN REGULATOR OF TUMOR SUPPRESSOR ARF & NF-kB

描述（由申请人提供）：利用替代阅读框架，哺乳动物ARF-INK 4 a基因座编码两种不相关的蛋白质，这两种蛋白质都在肿瘤抑制中起作用，ARF和细胞周期抑制剂p16。ARF与MDM2结合并阻断MDM2介导的p53泛素化和p53核输出，从而防止p53的胞质降解。 以前，我们和其他人发现，人类ARF结合MDM2癌蛋白，导致p53的稳定和转录激活，从而导致增殖停滞。 ARF水平通过暴露于致癌刺激物后的转录而增加，但ARF的翻译后调节在很大程度上未被探索。 最近，我们发现了一种新的蛋白质，LZAP，（亮氨酸拉链含有ARF结合蛋白），结合ARF在细胞核和调节ARF对MDM 2的生化活性。 除了调节MDM2活性外，最近发现ARF具有p53非依赖性效应，包括S期生长延迟、调节rRNA加工和抑制核因子κ B（NF-kB），这可能有助于在肿瘤发生中观察到的ARF的p53非依赖性效应。 除了对ARF的调节外，我们初步探索了LZAP在调节NF-κ B活性中的作用，发现LZAP的表达降低了基础和细胞因子刺激的NF-κ B活性，而内源性LZAP表达的抑制导致基础NF-κ B活性增加。 值得注意的是，发现LZAP直接结合细胞内的NFkB。 我们已经确定了一种新的蛋白质，调节ARF对MDM 2的活性，并降低NF-κ B的活性。 鉴于ARF和NF-kB在肿瘤发生中的重要性，LZAP的生物化学活性表明其可作为肿瘤抑制剂。 我们将进一步评估LZAP在调节ARF和NF-kB活性中的作用，并确定LZAP是否具有肿瘤抑制活性。

DESCRIPTION (provided by applicant): Utilizing alternative reading frames, the mammalian ARF-INK4a locus encodes two unrelated proteins that both function in tumor suppression, ARF and the cell cycle inhibitor, p16. ARF binds with MDM2 and blocks MDM2-directed ubiquitination of p53 and p53 nuclear export, thus preventing cytoplasmic degradation of p53. Previously, we, and others, found that human ARF binds the MDM2 oncoprotein leading to stabilization and transcriptional activation of p53 with a resultant proliferative arrest. ARF levels are increased through transcription following exposure to oncogenic stimuli, but post-translational regulation of ARF is largely unexplored. Recently, we have found a novel protein, LZAP, (leucine zipper containing ARF-binding protein) that binds ARF in the nucleus and regulates ARF biochemical activity toward MDM2. In addition to its regulation of MDM2 activity, ARF has recently been found to have p53-independent effects including S-phase growth delay, regulation of rRNA processing and inhibition of the nuclear factor kappa B (NF-kB), that may contribute to p53-independent effects of ARF observed in tumorigenesis. In addition to its regulation of ARF, we initially explored the role of LZAP in regulation of NF-kB activity and found that expression of LZAP decreased both basal and cytokine stimulated NF-kB activity, while inhibition of endogenous LZAP expression resulted in increased basal NF-kB activity. Remarkably, LZAP was found to bind directly to NFkB within cells. We have identified a novel protein that regulates ARF activity toward MDM2 and decreases NF-kB activity. Given the importance of ARF and NF-kB in tumorigenesis, the biochemical activities of LZAP suggest that it may serve as a tumor suppressor. We will further evaluate the role of LZAP in regulation of ARF and NF-kB activity and determine if LZAP has tumor suppressor activity.