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American Journal of Pathology, Vol 141, 1125-1137, Copyright © 1992 by American Society for Investigative Pathology

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Expression of a chimeric helix-loop-helix gene, Id-SCL, in K562 human leukemic cells is associated with nuclear segmentation

AN Goldfarb, ML Wolf and JM Greenberg
Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, Minneapolis.

We have designed a chimeric gene, Id-SCL, in which the 3' helix-loop- helix encoding portion of the presumptive oncogene SCL/tal is joined to the 5' coding portion of Id, an inhibitory helix-loop-helix gene. The predicted protein product of this chimeric gene contains the helix-loop- helix dimerization domain of SCL/tal, but, lacking a basic DNA binding domain, is predicted to have the inhibitory function of the Id product. Expression of the Id-SCL fusion gene in stably transfected K562 cells reproducibly resulted in nuclear segmentation and depressed growth rates; both of these phenotypic effects demonstrated a dosage dependence on the levels of Id-SCL mRNA and protein expressed in the various clones. Electron microscopy of cells expressing high levels of Id-SCL mRNA showed a significant increase in cytoplasmic perinuclear thin filaments and diminution of marginal heterochromatin in the nuclei. No other changes in hematopoietic differentiation status were observed in association with Id-SCL expression. Expression of intact Id and SCL/tal genes, as well as deletion mutants of Id and SCL/tal, independently transfected into K562 cells, indicated that the nuclear segmentation effect is dependent on the presence of a protein possessing a helix-loop-helix domain but lacking a basic domain. Our studies suggest that the balance of transcriptional inhibitory and stimulatory helix-loop-helix proteins in cells may be important determinants of proliferation and of structural organization within cells.




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Copyright © 1992 by the American Society for Investigative Pathology.