Binding of the EcoRII DNA methyltransferase to azacytosine-containing DNA protects the enzyme from digestion by proteases. The limit digest yields a product having a Mr on SDS-PAGE 20% less than the intact protein. The N terminus of the tryptic digestion product was sequenced and found to be missing the N terminal 82 amino acids. Under the conditions used unbound enzyme was digested to small peptides. Protection of the enzyme from protease digestion implies that the enzyme undergoes major conformational changes when bound to DNA. The trypsin sensitive region of the EcoRII methyltransferase occurs prior to the first constant region shared with other procaryotic DNA(cytosine-5)methyltransferases. To determine if this region played a role in substrate binding or specificity, N-terminal deletion mutants were studied. Deletion of 97 amino acids resulted in a decrease of enzyme activity. Further deletions caused a complete loss of activity. Enzyme deleted through amino acid 85 was purified and found to have the same specificity as wild type however there was an increase in Km for both S-adenosylmethionine (AdoMet) and DNA of 27 and 18 fold respectively. The N-terminus of the EcoRII methylase, although a variable region present in many procaryotic DNA(cytosine-5)methylases, plays no role in determining enzyme specificity, although it does contribute to the interaction with both AdoMet and DNA.

Blinded reviewers and editors in this study, but not nonblinded reviewers, gave better scores to authors with more previous articles. These results suggest that blinded reviewers may provide more unbiased reviews and that nonblinded reviewers may be affected by various types of bias.

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BackgroundAnaplastic thyroid cancer (ATC) is one of the most lethal human malignancies. Its rapid onset and resistance to conventional therapeutics contribute to a mean survival of six months after diagnosis and make the identification of thyroid-cancer-initiating cells increasingly important.Methodology/Principal FindingsIn prior studies of ATC cell lines, CD133+ cells exhibited stem-cell-like features such as high proliferation, self-renewal and colony-forming ability in vitro. Here we show that transplantation of CD133+ cells, but not CD133− cells, into immunodeficient NOD/SCID mice is sufficient to induce growth of tumors in vivo. We also describe how the proportion of ATC cells that are CD133+ increases dramatically over three months of culture, from 7% to more than 80% of the total. This CD133+ cell pool can be further separated by flow cytometry into two distinct populations: CD133+/high and CD133+/low. Although both subsets are capable of long-term tumorigenesis, the rapidly proliferating CD133+/high cells are by far the most efficient. They also express high levels of the stem cell antigen Oct4 and the receptor for thyroid stimulating hormone, TSHR. Treating ATC cells with TSH causes a three-fold increase in the numbers of CD133+ cells and elicits a dose-dependent up-regulation of the expression of TSHR and Oct4 in these cells. More importantly, immunohistochemical analysis of tissue specimens from ATC patients indicates that CD133 is highly expressed on tumor cells but not on neighboring normal thyroid cells.Conclusions/SignificanceTo our knowledge, this is the first report indicating that CD133+ ATC cells are solely responsible for tumor growth in immunodeficient mice. Our data also give a unique insight into the regulation of CD133 by TSH. These highly tumorigenic CD133+ cells and the activated TSH signaling pathway may be useful targets for future ATC therapies.