Cancer is characterized by the aberrant utilization of normal cellular signal transduction pathways. Hemopoietic cells require growth factors for their self-renewal and differentiation. Interleukin-3 (IL-3) is a cytokine secreted by activated T cells which supports the growth of hemopoietic precursor cells. Using non-transformed IL3-dependent murine cell lines, which represent early hemopoietic cells, we have isolated factor-independent transformants which are tumorigenic. Unlike the parental cells, the factor-independent cells secreted IL-3, were rearranged at the IL-3 locus, and overexpressed the IL-3 receptor. Therefore, we proposed they were transformed by an autocrine mechanism. The goal of this proposal is to delineate the mechanisms by which these and similar hemopoietic cells are rendered malignant. To accomplish this objective, the following specific aims are proposed:
Aim 1. To determine the mechanism of activation of IL-3 expression, Aim 2. To determine whether IL-3 gene rearrangement is sufficient to transform cells to factor-independence, Aim 3. To determine whether increased expression of the IL-3 receptor is associated with transformation, and Aim 4. To determine the mechanisms by which spontaneous, chemical and chronic retroviral infection can activate IL-3 gene expression.
Aim l. will test the hypothesis that transposition of an intracisternal type A particle to the 3' side of the IL-3 locus acts either as an enhancer or displaces DNA sequences implicated in mRNA stability, thereby prolonging IL-3 expression.
Aim 2. will test the hypothesis that rearrangement of the IL-3 gene enables factor-dependent cells to grow in the absence of exogenous IL-3 and also results in malignant transformation.
Aim 3. will test the hypothesis, that in concert with the increased expression of the IL-3 gene, upregulation of the cognate receptor is often necessary for autocrine transformation, Aim 4. will test the hypothesis that abrogation of factor-dependency often occurs as the result of insertional mutagenesis. An understanding of the mechanisms of IL-3 gene activation and rearrangement, which occurs in some murine factor-dependent cells and human acute lymphocytic leukemias, may aid in the pathogenesis, prevention and treatment of hemopoietic malignancies and will provide insights into the mechanisms of regulation of normal and abnormal cellular growth.
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