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（LTR）序列， c-myc原癌基因不稳定或寿命短的转录因子出现 调节c-myc过表达，如LTR增强的c-myc和病毒基因 在抑制蛋白质表达后， 合成.这种不稳定性仅在淋巴瘤的未成熟B细胞中观察到- 敏感株，而淋巴瘤抗性鸡株显示稳定 LTR增强的转录（不受蛋白质合成抑制的影响）， 这表明LTR增强的c-myc转录的不稳定调节是 对肿瘤易感性很重要。已经提出了一个模型，其中 不稳定LTR结合蛋白瞬时下调c-myc 在淋巴瘤易感的靶未成熟B细胞中的高表达 鸟类，以促进靶细胞存活和肿瘤进展。抗病 在禽类中，稳定的高水平c-myc表达将防止肿瘤诱导。 这一假设将使用基因组DNA聚合酶链进行检验 PCR反应（PCR）扩增以监测 前病毒c-myc整合的囊卵泡在不同阶段， ALV感染淋巴瘤易感和抗性鸡胚的研究的 当用克隆前病毒c-myc转化囊滤泡时的阶段 将通过原位PCR分析检测出现整合。比较 o易感和抗性鸟类将使我们了解 在耐药鸟类中肿瘤诱导被阻断的年龄。的表达 免疫组化直接检测这些卵泡中的c-myc 染色，以确定是否存在c-myc程序的差异 过表达可调节靶细胞存活或肿瘤进展。 一组单克隆抗体将用于识别这些关键的 当B细胞发育的正常程序被阻断时的阶段。 使用检测染色体断裂的测定分析细胞凋亡将 确定c-myc过度表达诱导的细胞死亡是否参与肿瘤 阻力c-myc过表达对细胞下游电位的影响 基因也将被检查。 将比较细胞周期蛋白D1基因表达 通过对转化和正常法氏囊的免疫组织化学分析， 卵泡，以确定这一重要的细胞周期调控基因是否可以 介导c-myc在B细胞肿瘤诱导过程中的增殖作用 in vivo. c-myc对翻译机制的影响也将在 通过核糖体RNA表达的原位杂交分析， 转化的和正常的囊滤泡。这些研究将提供 对c-myc原核表达调控B细胞肿瘤诱导的研究进展 癌基因，以及控制淋巴瘤发生易感性的机制。 对ALV淋巴瘤发生机制的理解可以应用于 多种人类癌症中c-myc癌基因激活的研究 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.