While the cell wall strictly controls cell size and morphology in bacteria, spheroplasts lack cell walls and can become enlarged in growth medium under optimal conditions. Optimal conditions depend on the bacterial species. We frequently observed extreme enlargement of spheroplasts of the radiation-resistant bacterium Deinococcus grandis in Difco Marine Broth 2216, but not in TGY broth (a commonly used growth medium for Deinococcus). Thorough investigation of media components showed that the presence of Mg or Ca promoted extreme spheroplast enlargement, synthesizing the outer membrane. Our findings strongly suggest that Mg or Ca enlarges spheroplasts, which could change the lipid composition of the spheroplast membrane.
Lysophosphatidic acid (LPA), which interacts with G protein-coupled transmembrane LPA receptors exhibits several biological effects, such as cell proliferation, migration, and differentiation. Recently, it has been reported that alteration of LPA receptor genes occurs in several cancer cells. In this study, to assess the biological role of LPA receptor-3 (LPA3 ) in the pathogenesis of tumor cells, we generated the Lpar3-expressing cells (RHa3B12 and RHa3G8) from rat hepatoma RH7777 cells, and examined their abilities of cell migration and tumorigenicity, compared with the Lpar3-unexpressing cells. In cell motility and invasion assays, RHa3B12 and RHa3G8 cells showed significantly higher intrinsic activity without LPA treatment than control RH7777AB cells. LPA treatment further increased cell motility and invasion of these cells. The cell motility of RHa3B12 and RHa3G8 cells stimulated by LPA treatment was significantly suppressed by pretreatment with inhibitors of Gi or Gq proteins. In a soft agar assay, the large sized colonies were formed in RHa3B12 and RHa3G8 cells, but not in RH7777AB cells. The cell survival of RHa3G8 cells treated with cisplatin (CDDP) or doxorubicin (DOX) was higher than that of RH7777AB cells, correlating with the elevated expression levels of multidrug-resistance related genes, Mdr1a, Mdr1b, and Gstp1. These results suggest that LPA3 may be involved in progression and aggressiveness of rat hepatoma RH7777 cells.
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