Stathmin expression in immortalized and oncogene transformed cells

Stathmin is a major cytosolic phosphoprotein that is highly expressed in le ukemic cells and many other malignant cell types. The high level of stathmi n expression in a wide variety of cancer cells suggested that this phosphop rotein may play a role in the process of malignant tr transformation. We co mpared the levels of stathmin expression in low passage primary embryonic f ibroblasts and in their immortalized counterparts. The immortalized cells h ad a markedly higher rate of proliferation that was associated with a four fold increase in the level of stathmin expression. In contrast, transformat ion of the immortalized fibroblasts with seven different activated oncogene s did not result in significant changes in the level of stathmin expression nor in a consistent increase in their rate of proliferation. These observa tions do not support a direct role for the activation of stathmin gene expr ession in the transformed phenotype. We suggest that the increased levels o f stathmin in transformed cells compared to non-transformed cells may be a reflection of differences in their rate of proliferation and state of diffe rentiation.