Studies on Expression-Mechanism (s) of Malignant Phenotypes Using Growth-Factor Gene-Transfer Methods

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The growth and development of a murine myeloid leukemia cell line, NFS-60, is dependent upon several hemopoietic growth factors such as interleukin-3 (IL-3), GM-CSF, G-CIF, and erythropoietin. We established a subclone (1-7) which was exclusively responsive to IL-3 and introduced into it a murine IL-3 gene. Ten IL-3-independent cell lines with autonomous proliferation were established from the transfected parental 1-7 subclone. The IL-3 activity, secreted from the IL3-independent cell lines into conditioned media, varied from less than 10 to 280 U/mL. Two representative transfectants, clone 1-7/7 (#7) producing the highest IL-3 activity and clone I-7/5 (#5) producing the lowest activity, were mainly investigated. Only a single copy of the IL-3 gene was introduced into each cell line, but. the level of its transdescription was different, i. e. the #7 cells expressed the IL-3 gene approximately ten times more than the #5 cells. A remarkable difference in extracellular IL-3 activity was found between the two cell lines while the intracellular IL-3 activity was not so different. The growth curve of the #5 cells in the presence of exogenous IL-3 was similar to that seen in the absence of IL-3. Anti-IL-3 antiserum did not inhibit the proliferation of the transfected cells. These results suggested that IL-3 secreted outside the transfected cells might not be obligatory for autonomous growth and that intracellular IL-3 might play an important role in autocrine growth. Simultaneously, the IL-3 gene-transfected cells exhibited remarkable changes in membrane glycosphingolipids (GSLs), especially in acidic sialoGSLs (gangliosides). The IL-3 gene transfection characteristically induced a new appearance of ganglioside GD3, which is known to be intimately related to malignant transformation. In addition, considerable changes of neutral GSLs were observed in the transfectants, i. e. the total amount and some constituents significantly increased.