Gene Expression and Signal Transduction in Transformatio

我们研究的主要目的是了解负责分化，细胞生长和肿瘤转化的分子和遗传机制。我们研究了小鼠和人类实验肿瘤系统中的癌基因、肿瘤抑制基因和信号转导蛋白，包括BALB/c小鼠浆细胞瘤、B细胞淋巴瘤和NIH 3 T3细胞等。这些都是有价值的实验模型，因为它们可以用来设计更具体的治疗和预防措施，人类多发性骨髓瘤，非霍奇金淋巴瘤，和其他人类恶性肿瘤。BALB/c浆细胞瘤与人伯基特淋巴瘤一样，其特征在于原癌基因c-Myc的组成性表达。为了确定哪些额外的遗传改变是完全转化所必需的，我们正在使用全球基因表达的微阵列杂交研究，以跟踪从癌前病变到完全恶性浆细胞肿瘤进展过程中基因表达的变化。我们也使用微阵列杂交研究来探测在小鼠浆细胞肿瘤发展中起作用的分子机制，以及某些转基因和病毒致癌基因加速这种肿瘤过程的机制。全球基因表达研究也在进行中，以确定这些肿瘤适应组织培养生长所需的生理变化。我们假设，这种使肿瘤细胞在培养容器的外源环境中生长的基因表达的适应性变化可能类似于人类肿瘤在侵袭或转移后在外源环境中生长所需的基因表达。我们正在研究丝氨酸/苏氨酸激酶的蛋白激酶C（PKC）家族的亚型特异性特征。我们一直关注δ和ε同工酶，它们对细胞增殖具有相反的影响。我们已经证明，大多数同工酶特异性决定簇位于催化的一半（羧基末端结构域），这些蛋白激酶通过创建相互嵌合的cDNA编码的分子，是半PKC-δ和半PKC-β。我们正在进一步解剖催化结构域的结构，以确定哪些亚结构域决定PKC亚型的特异性功能，重点是羧基末端的50个氨基酸，即“V5结构域”。“我们还研究了PKC参与细胞凋亡的性质，细胞形态和运动性的细胞凋亡相关变化，以及与c-Myc原癌基因的合作。我们已经表明，佛波酯激活过表达的PKC-δ破坏了人类和小鼠淋巴细胞中的肌动蛋白细胞骨架，导致膜皱褶的丧失，细胞运动所需的表面改变，以及这些细胞典型的细长形状的丧失。我们已经证明，这种效果是由于PKC介导的变化，在适配器分子，桩蛋白的关键酪氨酸残基的磷酸化。虽然PKC介导的酪氨酸磷酸化的损失的影响是间接的，我们也已经了解到，PKC-δ可以直接结合桩蛋白和磷酸化一个特定的苏氨酸，导致homotypic aggregation.We还表明，Myc和PKC亚型之一，PKC-γ，可以合作转化NIH 3 T3细胞在体外和体内，显然不需要核内Myc。我们正试图了解实现这一点的机制。

The chief objective of our research is to understand the molecular and genetic mechanisms responsible for differentiation, cell growth, and neoplastic transformation. We study the oncogenes, tumor-suppressor genes and signal-transducing proteins in mouse and human experimental tumor systems, including BALB/c mouse plasmacytomas, B-cell lymphomas, and NIH 3T3 cells, among others. These are valuable experimental models, because they can be used to devise more specific therapy and preventive measures for human multiple myeloma, non-Hodgkin's lymphomas, and other human malignancies. BALB/c plasmacytomas, like human Burkitt lymphomas, are characterized by constitutive expression of the proto-oncogene, c-Myc. To determine which additional genetic alterations are required for complete transformation, we are using microarray hybridization studies of global gene expression to follow changes in gene expression during progression from pre-malignant to fully malignant plasma cell tumors. We are also using microarray hybridization studies to probe the molecular mechanisms at work in development of plasma cell tumors in mice and the mechanisms whereby certain transgenes and viral oncogenes accelerate this neoplastic process. Global gene expression studies are also underway to determine the physiological changes necessary for these tumors to adapt to growth in tissue culture. It is our hypothesis that such adaptive changes in gene expression that enable tumor cells to grow in the foreign environment of culture vessels might be analogous to those needed for human tumors to grow in alien environments following invasion or metastasis.In the study of signal transduction in differentiation and neoplastic transformation, we are investigating the isoform-specific features of the protein kinase C (PKC) family of serine/threonine kinases. We have been focusing on the delta and epsilon isoenzymes, which have opposing effects on cell proliferation. We have shown that most of the isoenzyme-specific determinants are located in the catalytic half (the carboxyl-terminal domain) of these PKCs by creating reciprocal chimeric cDNAs that encode molecules that are half PKC-delta and half PKC-epsilon. We are further dissecting the structure of the catalytic domain to determine which sub-domains determine PKC isoform- specific functions, focusing on the carboxy-terminal 50 amino acids, the "V5 domain." We are also studying the nature of PKC's involvement in apoptosis, in cytoskeleton-related changes in cell shape and motility, and in cooperation with the c-Myc proto-oncogene. We have shown that phorbol ester-activation of overexpressed PKC-delta disrupts the actin cytoskeleton in human and mouse lymphocytes, leading to the loss of membrane ruffling, a surface alteration needed for cell movement, and the loss of the typical elongated shape of these cells. We have demonstrated that this effect is due to PKC-mediated changes in phosphorylation of key tyrosine residues in the adaptor molecule, paxillin. Whereas the PKC-mediated effects on loss of tyrosine phosphorylation are indirect, we also have learned that PKC-delta can directly bind paxillin and phosphorylate a specific threonine, leading to homotypic aggregation.We have also shown that Myc and one of the PKC isoforms, PKC-gamma, can cooperate to transform NIH3T3 cells in vitro and in vivo, apparently not requiring intra-nuclear Myc. We are trying to understand the mechanism whereby this is accomplished.