Construction of intracellular asymmetry and asymmetric division in Escherichia coli

The design principle of establishing an intracellular protein gradient for asymmetric cell division is a long-standing fundamental question. While the major molecular players and their interactions have been elucidated via genetic approaches, the diversity and redundancy of natural systems complicate the extraction of critical underlying features. Here, we take a synthetic cell biology approach to construct intracellular asymmetry and asymmetric division in Escherichia coli, in which division is normally symmetric. We demonstrate that the oligomeric PopZ from Caulobacter crescentus can serve as a robust polarized scaffold to functionalize RNA polymerase. Furthermore, by using another oligomeric pole-targeting DivIVA from Bacillus subtilis, the newly synthesized protein can be constrained to further establish intracellular asymmetry, leading to asymmetric division and differentiation. Our findings suggest that the coupled oligomerization and restriction in diffusion may be a strategy for generating a spatial gradient for asymmetric cell division.

Human fibroblasts contain a proteolytic activity which is inhibited by the Bowman-Birk protease inhibitor

The Bowman Birk protease inhibitor (BBI) has been shown to be an effective suppressor of carcinogenesis in vivo and in vitro. In this report we demonstrate that normal human fibroblasts and Bloom cells contain a BBI-inhibitable proteolytic activity. The enzyme cleaves gelatin, has a molecular mass of 43 kDa, and is located in the cytosol. This activity has maximal activity at pH 8 and was inhibited by diisopropylfluorophosphate but was not affected by EDTA or 1,10-phenanthroline, indicating that this enzyme is a serine protease. We have reported previously that a similar BBI-inhibitable activity is present in C3H/10T1/2 mouse embryo fibroblast cells. Our results suggest that a common "target enzyme" of the BBI is present in mouse and human cells.

The interaction of the potato-derived chymotrypsin inhibitor with C3H/10T1/2 cells

Protease inhibitors have been shown to be effective suppressors of carcinogenesis in vitro and in vivo. For example, the potato-derived chymotrypsin inhibitor 1 (CI-1) suppresses radiation transformation of C3H/10T1/2 cells in vitro. In the current study, we have investigated the interaction of CI-1 with C3H/10T1/2 cells. At the concentrations examined, CI-1 was non-toxic and had no effect on the doubling time or saturation density of these cells. This compound was taken up by these cells in a time dependent manner. Analysis of CI-1 from treated cells on a chymotrypsin affinity column revealed that active inhibitor was present in the cells. Additionally, CI-1, as well as the soybean derived Bowman-Birk inhibitor and chymostatin, blocked the cleavage of the peptide substrate Suc-Ala-Ala-Pro-Phe-MCA by intact C3H/10T1/2 cells. We have previously demonstrated that this substrate will reduce the transformation yield following treatment of cells with ionizing radiation. Our results suggest that CI-1 may inhibit transformation of C3H/10T1/2 cells in vitro by inhibiting the activity of Suc-Ala-Ala-Pro-Phe-MCA hydrolyzing activity in these cells.