Coordinate Regulation of p53 and c-MYC in an HTLV-1 Model of Carcinogenesis

描述（由申请人提供）：人类t细胞白血病病毒1型（HTLV-1）感染并转化CD4+ th淋巴细胞，是成人t细胞白血病/淋巴瘤（ATL）的病因，ATL是一种侵袭性血液恶性肿瘤，对大多数抗癌方式具有抗性。重要的是，促进致癌细胞转化和t细胞白血病发生的分子事件仍有待完全确定。HTLV-1基因组中被称为pX的保守3'核苷酸序列编码的几种非结构性和调节性蛋白（Tax, Rex, p30II, p13II, p12I, p8I, Hbz）解除了细胞信号通路的调节，促进了肿瘤t细胞的转化。虽然逆转录病毒反激活子Tax被认为是HTLV-1的主要癌蛋白，但其他pX因子在肿瘤发生和恶性疾病进展中的作用尚未得到广泛研究。我们在这一领域取得了重大进展，并提供了HTLV-1 p30II蛋白与c-MYC癌蛋白相互作用的第一个证据，并增加了c-MYC依赖性的转激活和致癌潜力，这依赖于TIP60乙酰转移酶对p30II/c-MYC转录复合物的募集。在体外，显性阴性的TIP60Q377E/G380E突变体抑制p30II和c-MYC之间的合作，并消除致癌灶的形成。在生化蛋白相互作用研究中，p30II的tip60相互作用域已被定位到位于p30II蛋白暴露表面的aa残基99-154。TIP60乙酰转移酶是c-MYC和p53肿瘤抑制因子的转录辅助因子。我们的初步数据进一步证明p30II诱导p53并与p53相互作用，并激活G2/M抗凋亡基因14-3-3s。令人惊讶的是，野生型p53增强了p30II/c-MYC诱导的癌性转化。p53 dna结合突变体p53- r175h抑制p30II/c-MYC的致癌活性。TIP60使p53的赖氨酸残基K120乙酰化，并差异调节细胞生长停止/生存和促凋亡信号的表达。由于c-myc癌基因激活诱导p53依赖的细胞凋亡，我们假设p30II协同调节p53存活基因（如14-3- 3s、p21Waf1/Cip1、p53R2、gadd45、tigar）和c-myc，以防止c-myc诱导的细胞死亡，促进htlv -1感染细胞的异常淋巴细胞增殖。该研究将建立在我们的初步研究基础上，解决以下具体目标：(1)确定HTLV-1 p30II-TIP60和p30II-p53生化相互作用如何调节c-MYC和p53功能。(2)确定p53如何增强p30II与c-MYC之间的合作促进癌性转化。我们的研究结果暗示了一种新的范式，即通过与常见转录辅助因子TIP60的相互作用来转化病毒，从而解除c-MYC和p53的调控。提出的研究将促进我们对癌蛋白和肿瘤抑制因子在病毒癌变中的作用的基本理解。

DESCRIPTION (provided by applicant): The human T-cell leukemia virus type-1 (HTLV-1) infects and transforms CD4+ Th-lymphocytes and is the etiological agent of adult T-cell leukemia/lymphoma (ATL), an aggressive hematological malignancy that is resistant to most anticancer modalities. Importantly, the molecular events that contribute to oncogenic cellular transformation and T-cell leukemogenesis remain to be completely defined. Several nonstructural and regulatory proteins (Tax, Rex, p30II, p13II, p12I, p8I, Hbz) encoded by a conserved 3' nucleotide sequence, known as pX, in the HTLV-1 genome deregulate cellular signaling pathways and promote neoplastic T-cell transformation. While the retroviral transactivator, Tax, is considered to be the major oncoprotein of HTLV-1, the roles of the other pX factors in tumorigenesis and the progression of malignant disease have not been extensively studied. We have made significant progress in this area and provided the first evidence that the HTLV-1 p30II protein interacts with the c-MYC oncoprotein and augments c-MYC-dependent transactivation and oncogenic potential, dependent upon recruitment of the TIP60 acetyltransferase to p30II/c-MYC transcription complexes. A dominant-negative TIP60Q377E/G380E mutant inhibits cooperation between p30II and c-MYC and abrogates oncogenic foci- formation in vitro. The TIP60-interacting domain of p30II has been mapped in biochemical protein- interaction studies to aa residues 99-154, which reside on an exposed surface of the p30II protein. The TIP60 acetyltransferase is a transcriptional cofactor for both c-MYC and the p53 tumor suppressor. Our preliminary data further demonstrate that p30II induces and interacts with p53 and transactivates the G2/M anti-apoptotic gene, 14-3-3s. Surprisingly, wildtype p53 enhances oncogenic transformation induced by p30II/c-MYC. A p53 DNA-binding mutant, p53-R175H, inhibited p30II/c-MYC oncogenic activity. TIP60 acetylates lysine residue K120 of p53 and differentially regulates the expression of cellular growth-arrest/survival and pro-apoptotic signals. As c-myc oncogene activation induces p53- dependent apoptosis, we hypothesize that p30II coordinately regulates p53 survival genes (e.g., 14-3- 3s, p21Waf1/Cip1, p53R2, gadd45, tigar) and c-MYC to prevent c-MYC-induced cell-death and promote aberrant lymphoproliferation in HTLV-1-infected cells. The proposed research will build upon our preliminary studies by addressing the following Specific Aims: (1) to determine how HTLV-1 p30II-TIP60 and p30II-p53 biochemical interactions modulate c-MYC and p53 functions. (2) To determine how p53 enhances the cooperation between p30II and c-MYC to promote oncogenic transformation. Our findings allude to a novel paradigm for the deregulation of c-MYC and p53 by transforming viruses through interactions with the common transcriptional cofactor, TIP60. The proposed studies will advance our fundamental understanding of the roles of oncoproteins and tumor suppressors in viral carcinogenesis. PUBLIC HEALTH RELEVANCE: Many cancer-inducing viruses promote aberrant cellular growth and proliferation through interactions with oncoproteins and tumor suppressors. We have demonstrated that the HTLV-1 p30II protein interacts with a common transcriptional cofactor of c-MYC and p53 and coordinately regulates c-MYC oncogenic activity and p53 anti-apoptotic functions. The proposed research will advance our understanding of the molecular events involved in retroviral carcinogenesis and may elucidate new targets for anticancer therapy. This R15 AREA project will provide excellent cancer research training opportunities for undergraduates and graduate students to better prepare them for future careers in the basic or clinical oncological sciences.