No abstract

A new transforming gene has been molecularly cloned from hamster SHOK cells transformed with DNA extracted from a human thyroid carcinoma cell line and named the cot (cancer Osaka thyroid) oncogene. cDNA sequencing disclosed that this oncogene codes for a protein with 415 amino acid residues, and computer matching showed 42 to 48% similarity matches with serine protein kinases. Its gene product was identified as a 52-kDa protein by transcription and translation in vitro. Expression of cot cDNA under transcriptional control by a retroviral long terminal repeat induced morphological transformation of NIH 3T3 cells as well as SHOK cells. Protein kinase activity associated with constructed p6(a-Cot was detected by immune complex kinase assay with anti-gag antiserum. The cot oncogene was overexpressed in transformed SHOK cells and found to have a rearranged 3' end in the last coding exon, which probably resulted in a deletion and an altered C' terminus in the transforming protein. This DNA rearrangement appeared to have occurred during transfection of the tumor DNA into hamster SHOK cells and not in the original thyroid tumor.

Rat liver contains a high concentration (7-8mM) of reduced glutathione and its level changes rapidly when starving or feeding rats. We concluded that one of the functions of liver glutathione was to act as a reservoir of cysteine. When starved rats were fed a protein-free diet, the increase in liver glutathione was dependent on the amount of cysteine added to the diet. A cysteine-dependent increase of glutathione was also observed in rats fed a diet containing gelatin with cysteine, but the increase was relatively lowered compared with rats fed a protein-free diet containing the same amount of cysteine. This suppression of the increase in glutathione was observed much more clearly when the gelatin diet was fortified with tryptophan in addition to cysteine. In the presence of tryptophan, L-[35S]-cysteine in the diet appeared to be incorporated primarily into liver and serum proteins, and degradation of liver glutathione must also have been enhanced. Addition of excess cysteine to the diet masked the effects of gelatin and tryptophan, stimulated glutathione synthesis in the liver as well as incorporation of dietary cysteine into protein fractions. Prolonged starvation of rats or injection of dibutyryl-3',5'-cyclic AMP lowered the glutathione level,but the level did not decrease below 2 to 3 mM. These findings suggest that there may be at least two pools of glutathione. A labile fraction, constituting one-third to one-half the total liver glutathione, probably serves as a reservoir of cysteine which can be released by gamma-glutamyl-transferase when necessary.

The frequency of exposure to strong magnetic fields has increased as the magnetic-resonance image-diagnostic technique (MRI) and passenger transport systems based on the principle of magnetic levitation have come into wider use. Accordingly, it has become necessary to more systematically assess their influence on the body and set strict guidelines on acceptable limits of magnetism exposure. Therefore, we have assessed the influence of an uniform static magnetic field (8 T in maximum) on normal erythrocytes. The erythrocytes were oriented with their disk plane parallel to the magnetic field direction. These erythrocytes were influenced even by 1 T and almost 100% of them were oriented when exposed to 4 T. Furthermore, the degree of orientation was not influenced by the state of hemoglobin (oxy: diamagnetic, deoxy and met: paramagnetic). The dependence of the measured degree of orientation on the intensity of the magnetic field was in good agreement with the theoretical equation for the magnetic orientation of diamagnetic substances. As a result of a numerical analysis based on the equation, the anisotropic diamagnetic susceptibility of erythrocytes was found to be delta chi = 8 x 10(-22) electromagnetic units/erythrocyte. It was almost in agreement with the calculated value delta chi = 6 x 10(-22) emu/erythrocyte estimated from the diamagnetism of the membrane constituents of erythrocyte.