Regulation of proteasome expression in developing and transformed cells.

The proteasome is a unique protease complex found in all eukaryotic cells and has multiple functions for essential activities. In this work we showed that it is expressed at high level in immature, rapidly growing cells, such as those in early embryonic tissues and cancer cells (Fig. 7). The increase of its expression is down-regulated on differentiation of the cells. However, lymphatic blastocytes grow rapidly and express high levels of proteasomes, but are differentiated. Therefore, the proteasome is not expressed at high levels only in immature cells, but is also involved specifically in nuclear activities of cells during rapid growth, possibly regulating proteinous factors in the cell cycle.