The effect of mercury on trees and their mycorrhizal fungi.

The Oak Ridge Reservation, established in 1942, was the designated site for the construction of the atomic bomb. During a 20-year period from 1944 to 1963 radioactive and toxic chemical pollutants, especially mercury compounds were released into the surrounding waterways. Tree diversity and mycorrhizal presence and abundance were analyzed in the mercury-contaminated floodplains of East Fork Poplar Creek Oak Ridge (EFPC) (Tennessee). A subsequent greenhouse study was conducted to assess the phytotoxic effects of different mercuric solutions on Platanus occidentalis (American Sycamore), inoculated with soils from EFPC. Total soil mercury in the field had no effect on tree diversity. Organic species of mercury proved to be more toxic than inorganic species of mercury and soil inoculants from EFPC had no protective effects against Hg toxicity in our greenhouse study. Comparison of the effects of mercury contamination in our field and greenhouse studies was difficult due to uncontrolled factors.

Effect of ablation or inhibition of stromal matrix metalloproteinase-9 on lung metastasis in a breast cancer model is dependent on genetic background.

Matrix metalloproteinases (MMP) are a family of enzymes with a myriad of functions. Lately, we have come to realize that broad-spectrum inhibition of these enzymes, as was tried unsuccessfully in multiple phase III trials in cancer patients, is likely unwise given the protumorigenic and antitumorigenic functions of various family members. Here, we used the multistage mammary tumor model MMTV-PyVT to investigate roles for either MMP7 or MMP9 in tumor progression. We found no effect of genetic ablation of MMP7 or MMP9 on the multifocal tumors that developed in the mammary glands. Lack of MMP7 also had no effect on the development of lung metastases, suggesting that MMP7 is irrelevant in this model. In contrast, MMP9 deficiency was associated with an 80% decrease in lung tumor burden. The predominant cellular source of MMP9 was myeloid cells, with neutrophils being the largest contributor in tumor-bearing lungs. Experimental metastasis assays corroborated the role of host-derived MMP9 in lung metastasis and also facilitated determination of a time frame most relevant for the MMP9-mediated effect. The lung tumors from MMP9-deficient mice showed decreased angiogenesis. Surprisingly, the antimetastatic outcome of MMP9 ablation seemed to be dependent on strain. Only mice that had genetic background derived from C57BL/6 showed reduced metastasis, whereas mice fully of the FVB/N background showed no significant effect. These strain-specific responses were also observed in a study using a highly selective pharmacologic inhibitor of MMP9 and thus suggest that responses to MMP inhibition are controlled by genetic differences.