C-MYC EXPRESSION DURING ALV LYMPHOMAGENESIS

禽白血病病毒(ALV)诱导鸡B细胞淋巴瘤 整合前病毒长末端重复序列(LTR) C-myc原癌基因。出现不稳定或短暂的转录因子 调节c-myc的高表达，如LTR增强的c-myc和病毒基因 蛋白质被抑制后，转录被特异性降低 综合。这种不稳定性只在淋巴瘤的未成熟B细胞中观察到。 敏感株，而抗淋巴瘤的鸡株表现稳定 Ltr增强转录(不受蛋白质合成抑制的影响)， 提示LTR增强的c-myc转录的不稳定调节是 对肿瘤易感性很重要。提出了一个模型，在该模型中， 不稳定的LTR结合蛋白瞬时下调c-myc 淋巴瘤易感性靶向幼稚B细胞的高表达 鸟，以促进靶细胞存活和肿瘤进展。在抵抗中 鸟类，稳定高水平的c-myc表达将阻止肿瘤的诱导。 这一假设将通过基因组DNA聚合酶链来检验。 用聚合酶链式反应(PCR)扩增技术监测肿瘤的出现和存活 法氏囊卵泡在不同阶段与前病毒c-myc整合 ALV感染对淋巴瘤敏感和抵抗的鸡胚。这个 克隆前C-myc转化法氏囊卵泡的阶段 出现的整合将通过原位聚合酶链式反应分析进行检查。比较 O敏感和抵抗的鸟类将提供对发育的洞察力 抗药性禽类肿瘤诱导受阻的年龄。的表达方式 这些卵泡中的c-myc将通过免疫组织化学直接检测。 染色，以确定c-myc程序的差异 高表达可调节靶细胞存活或肿瘤进展。 一组克隆抗体将被用来识别这些关键的 B细胞正常发育受阻的阶段。 用一种检测染色体断裂的方法来分析细胞凋亡 确定c-myc高表达诱导的细胞死亡是否与肿瘤有关 抵抗。C-myc高表达对潜在下游基因的影响 还将对基因进行检查。将比较细胞周期蛋白D1基因的表达 通过对转化和正常法氏囊的免疫组织化学分析 以确定这个重要的细胞周期调控基因是否可以 C-myc在B细胞肿瘤诱导过程中的促增殖作用 在活体内。C-myc对翻译机制的影响也将是 核糖体RNA表达的原位杂交分析 转化的和正常的法氏囊毛囊。这些研究将提供 C-myc原癌基因诱导B细胞肿瘤的调控 癌基因，以及控制淋巴肿大易感性的机制。 对ALV淋巴肿大发生机制的了解可用于 C-myc癌基因在多种类型人类癌症中的激活研究 包括B淋巴瘤、肺癌和乳腺癌。

Avian leukosis virus (ALV) induces B cell lymphoma in chickens, after integration of proviral long terminal repeat (LTR) sequences next to the c-myc proto-oncogene. Labile or short-lived transcription factors appear to regulate c-myc hyperexpression, as LTR-enhanced c-myc and viral gene transcription is specifically decreased after inhibition of protein synthesis. This lability is observed only in immature B cells of lymphoma- susceptible strains, while lymphoma-resistant chicken strains show stable LTR-enhanced transcription (unaffected by inhibition o protein synthesis), suggesting that labile regulation of LTR-enhanced c-myc transcription is important for tumor susceptibility. A model has been proposed in which the labile LTR binding proteins transiently down-regulate c-myc hyperexpression in the target immature B cells of lymphoma-susceptible birds, to promote target cell survival and tumor progression. In resistant birds, stable high level c-myc expression would prevent tumor induction. This hypothesis will be examined using genomic DNA polymerase chain reaction (PCR) amplification to monitor the appearance and survival of bursal follicles with proviral c-myc integrations at various stages after ALV infection of lymphoma-susceptible and -resistant chicken embryos. The stage when transformed bursal follicles with clonal proviral c-myc integrations appear will be examined by in situ PCR analysis. Comparison o susceptible and resistant birds will give insight to the developmental age when tumor induction is blocked in resistant birds. The expression of c-myc in these follicles will be directly examined by immunohistochemical staining, to determine if differences in the program of c-myc hyperexpression could regulate target cell survival or tumor progression. A panel of monoclonal antibodies will be used to identify these critical stages when the normal program of B cell development is blocked. Analysis of apoptosis using an assay to detect chromosome breakdown will determine if c-myc hyperexpression-induced cell death is involved in tumor resistance. The effects of c-myc hyperexpression on potential downstream genes will also be examined. Cyclin D1 gene expression will be compared by immunohistochemical analysis of transformed and normal bursal follicles, to determine if this important cell cycle regulatory gene could mediate the proliferative effects of c-myc during B cell tumor induction in vivo. The effects of c-myc on the translational machinery will also be examined by in situ hybridization analysis of ribosomal RNA expression in transformed and normal bursal follicles. These studies will provide insight to the regulation of B cell tumor induction by the c-myc proto- oncogene, and the mechanism controlling susceptibility to lymphomagenesis. An understanding of the mechanism of ALV lymphomagenesis can be applied to studies of c-myc oncogene activation in many types of human cancers including B lymphoma, lung cancer, and breast cancer.