Cleavage of the HIV replication primer tRNALys,3 in human cells expressing bacterial anticodon nuclease.

Anticodon nuclease is a bacterial restriction enzyme directed against tRNA(Lys). We report that anticodon nuclease also cleaves mammalian tRNA(Lys) molecules, with preference and site specificity shown towards the natural substrate. Expression of the anticodon nuclease core polypeptide PrrC in HeLa cells from a recombinant vaccinia virus elicited cleavage of intracellular tRNA(Lys),3. The data justify an inquiry into the possible application of anticodon nuclease as an inhibitor of tRNA(Lys),3-primed HIV replication. They also indicate that the anticodon region of tRNA(Lys) is a substrate recognition site and suggest that PrrC harbors the enzymatic activity.

Comparison of transferrin receptors, iron content and isoferritin profile in normal and malignant human breast cell lines.

We studied the mode of iron transport and storage in a human breast cancer cell line (HT-24) in comparison with a breast epithelial cell line (HBL-100). It was found that HT-24 cells incorporated over 18 h more 59Fe as compared to HBL-100 (24 vs. 16%). Yet, the number of surface transferrin-binding sites was less in cancer cells (6.2 x 10(5)) than in epithelial cells (8 x 10(5)). Moreover, the transferrin receptors in cancer cells were less affected by iron overloading as compared with epithelial cells. Following immunoprecipitation of isoferritins with specific monoclonal antibodies (MoAbs), it was found that the quantity of de novo synthesized normal ferritin immunoprecipitated with CM-G-8 MoAb was similar in both cancer and epithelial cells. However, the amount of 59Fe incorporated into the protein was significantly higher in HBL-100 cells. In contrast, HT-24 cells synthesized a high amount of placental-like isoferritin (PLF) immunoprecipitated with CM-H-9 MoAb which was significantly higher (p less than 0.001) than in epithelial cells. This isoferritin was characterized by its low iron incorporation. It is noteworthy that the ratio of PLF to normal ferritin was 2:1 in cancer cells and 0.7:1 in epithelial cells, indicating that PLF is a major type of isoferritin synthesized by HT-24 breast cancer cells. Furthermore, a significant amount of PLF was expressed on the surface of cancer cells as compared to epithelial cells. The results of this study suggest that iron supply and distribution in breast neoplastic cells are not controlled similarly to normal cells.

Expression of messenger RNA species coding for a Mr 43,000 peptide associated with ferritin in human leukemia-K562 cells and its down regulation during differentiation.

In the current study it was found that K-562 erythroleukemia cells express the superheavy (S) mRNA and the 43 Kd S peptide which were recently discovered in activated T-lymphocytes. The S mRNA was identified by its cross-hybridization with ferritin H complementary DNA probe and the S peptide (Mr 43,000) was identified by its immunoprecipitation with CM-H-9 monoclonal antibody specific for placental isoferritin. During terminal differentiation by hemin the level of S mRNA decreased below detection, with a concomitant diminution in the biosynthesis of the S peptide. In contrast, a significant increase in the level of ferritin light (L) and heavy (H) mRNAs was observed, resulting in an increase in the rate of biosynthesis of the H and L ferritin subunits. Removal of iron by desferrioxamine reduced the biosynthesis of ferritin L and H chains without altering the level of the corresponding mRNAs. Treatment with desferrioxamine did not affect either the level of S mRNA or the biosynthesis of the S peptide. This is a demonstration of a new mRNA species which is expressed in leukemic cells and is down-regulated during cell differentiation.

T-cell mitogenesis stimulates the synthesis of a mRNA species coding for a 43-kDa peptide reactive with CM-H-9, a monoclonal antibody specific for placental isoferritin.

In studying the changes that occur in concanavalin A-activated T lymphocytes, an mRNA species was discovered by hybridization of poly(A)+ mRNA with a human ferritin heavy chain cDNA probe. This ferritin mRNA, termed superheavy chain mRNA, differed from the known human ferritin heavy chain mRNAs by its larger size and degree of homology. The superheavy chain mRNA was isolated by sucrose-gradient centrifugation and translated in vitro in a cell-free system. The products obtained included two peptides (superheavy) of 43kDa that reacted with CM-H-9, a monoclonal antibody specific for placental isoferritin. De novo synthesis in intact transformed T cells revealed the synthesis of the superheavy chain peptides that were immunoprecipitated by anti-ferritin monoclonal antibody CM-G-8 and by placental isoferritin specific monoclonal antibody CM-H-9. The above results indicated that blast transformation of human T cells stimulated the appearance of a unique mRNA species that coded for a superheavy chain peptide associated with placental isoferritin, which was not detected in resting T cells.