| Summary: | TBP1 expression increased around day 10 gestation in the mammary gland. Analysis of protein levels confirmed that the increase in TBP1 expression observed was due to an overall increase in 26S proteasome. The increase in TBP1 expression observed by differential display was at the stage when the mammary gland begins to respond to lactogenic hormone by differentiating and expressing the milk protein β casein. Studies in mammary epithelial cells (MEC) revealed the increase in the proteasome level was not lactogenic hormone dependent as the expression profile from the display results implied. We further cloned murine homologues of two other ATPases, TBP7 and Sug2 and performed a yeast two hybrid assay to determine if these ATPases interacted with one another. In order to address the role of TBP1 and the 26S proteasome in the mammary gland, a series of studies using a peptide inhibitor of the proteasome were performed on MECs. These results suggested that proteasome function was essential for MECs, and inhibition of the proteasome leads to the induction of apoptosis. This study showed that death was occurring from a specific stage in the cell cycle and that this was a p53 dependent response. To address the question of TBP1 function more specifically, a dominant negative TBP1 construct was generated. Constitutive expression studies suggested that TBP1 function was indeed essential for cell survival. A greater understanding of the function of the 26S proteasome in the processes of proliferation, differentiation and apoptosis should lead to an enhanced perception of the role proteolysis plays in normal mammary gland development.
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