Figure 8
Sp1 expression regulates lung tumor progression. (a) Sp1 expression is maintained at the lowest level in normal cells. Until cell transformation or tumor formation, Sp1 expression is highly upregulated. When tumor cells became more invasive or malignant, Sp1 expression is obviously decreased. (b) The lowest Sp1 level for basal gene transcription is maintained by protein instability triggered by sumoylation and ubiquitination. In lung tumor cells, the Sp1 level is upregulated for proliferation accompanied by the increased level of E-cadherin for adhesion. In highly invasive lung tumor cells, E-cadherin, which anchors β-catenin near the plasma membrane, is lost because of the downregulation of Sp1 level triggered by protein instability. Consequently, downregulation of Sp1 level increases the amount of nuclear β-catenin for gene transcription related to metastasis.
