Serum regulation of the estrogen responsiveness of the human breast cancer cell line MCF-7.

Initially after receiving MCF-7 cells, we were able to confirm their estrogen responsiveness. We observed significant increases in thymidine incorporation, in thymidine kinase activity, and in cell numbers in response to 10(-8) M estradiol. Subsequently, however, the cells failed to show a response to estradiol. A growth response to estradiol could be restored by increasing the serum concentration in the medium. Cells grown in 15% serum (calf or human) responded to estradiol with increased rates of growth and thymidine incorporation and increased activities of thymidine kinase and DNA polymerase. We suggest that there is present in serum a "factor" which can influence the expression of a growth response to estradiol.

Enhanced disease resistance conferred by expression of an antimicrobial magainin analog in transgenic tobacco.

Magainins are a group of short peptides originally isolated from frog skin and thought to function as a natural defense mechanism against infection due to their antimicrobial properties. The engineered magainin analog peptide Myp30 was found to inhibit spore germination of the oomycete, Peronospora tabacina (Adam) in vitro, and the growth of a bacterial pathogen Erwinia carotovora subsp. carotovora (Jones). Transgenic tobacco (Nicotiana tabacum L.) plants expressing Myp30 were evaluated for resistance to these pathogens. The expression of the peptide only to an extracellular location resulted in significant reduction in sporulation and lesion size due to P. tabacina infection. A significant increase in resistance to the bacterial pathogen was also observed regardless of the targeting location of the peptide.