Stathmin expression in immortalized and oncogene transformed cells.

Stathmin is a major cytosolic phosphoprotein that is highly expressed in leukemic cells and many other malignant cell types. The level of stathmin expression in a wide variety of cancer cells suggested that this phosphoprotein may play a role in the process of malignant transformation. We compared the levels of stathmin expression in low passage primary embryonic fibroblasts and in their immortalized counterparts. The immortalized cells had a markedly higher rate of proliferation that was associated with a four fold increase in the level of stathmin expression. In contrast, transformation of the immortalized fibroblasts with seven different activated oncogenes did not result in significant changes in the level of stathmin expression nor in a consistent increase in their rate of proliferation. These observations do not support a direct role for the activation of stathmin gene expression in the transformed phenotype. We suggest that the increased levels of stathmin in transformed cells compared to non-transformed cells may be a reflection of differences in their rate of proliferation and state of differentiation.