HeLa S‐3 cells were treated with 195mPt‐radiolabeled cis‐diamminedichloroplatinum(II) (CDDP) under various conditions, and the relationship between lethal effect and the number of Pt atoms binding to DNA, RNA and proteins was examined. The mean lethal concentrations for the cells treated with CDDP at 37°C for 1, 2 and 3 h were 2.8, 2.0 and 1.1 μg/ml, respectively. By using identically treated cells, the number of Pt atoms combined with DNA, RNA and protein molecules were determined after fractionation of the cells using the method of Schneider. In this way, the Do values given as the drug concentration were substituted for the number of Pt atoms combined with each fraction, then the target volumes expressed as the reciprocals of Do values were calculated for each fraction. The results provide strong support for the idea that DNA is the primary target for cell killing by CDDP, and the target volumes were 5.17 × 104, 5.71 × 104 and 1.03 × 104 nucleotides for 1, 2 and 3 h treated cells, respectively.

The effects on the cellular viability and induction and repair kinetics of DNA strand breaks in HeLa cells were examined after exposure to a thermal neutron beam and compared with those after gamma-irradiation. The thermal neutron survival curve had no initial shoulder. The relative biological effectiveness (r.b.e.) value of the neutron beam was determined to be 2.2 for cell killing (ratio of D0 values), 1.8 and 0.89 for single strand breakage (ssb) by alkaline sedimentation and alkaline elution respectively, and for double strand breakage (dsb) 2.6 by neutral elution. No difference was observed between thermal neutrons and gamma-rays in the repair kinetics of ssb and dsb. It is suggested that the effect induced by the intracellular nuclear reaction, 14N(n,p)14C is mainly responsible for the high r.b.e. values observed.

No abstract

Tuberous sclerosis complex (TSC) is an autosomal dominant inherited disorder characterized by benign tumors (hamartomas) in various organs. The brain is one of the most severely affected organs with neuropsychiatric disorders including epilepsy, mental retardation and autism. The identification of TSC genes (TSC1 and TSC2) and their gene products (hamartin and tuberin, respectively), revealed that they function together as a complex. However, mutations in TSC2 are often accompanied by more severe neurologic deficits. Here, we show that hamartin and tuberin play different roles in NGF-treated cultured neuronal cells PC12h. The level of hamartin in PC12h cells was slightly and gradually increased, while those of tuberin rapidly increased upon NGF-induced neuronal differentiation in PC12h cells. Antisense for TSC1 (TSC1-AS) or TSC2-AS reduced expression of hamartin or tuberin, respectively, and enhanced S-phase of cell cycle in PC12h cells. Suppression of hamartin significantly enhanced neurite outgrowth after NGF-treatment in PC12h cells, while suppression of tuberin inhibited neurite outgrowth. Expression of activated V14RhoA reverted TSC1-AS induced abnormal neurite development. These results suggest that loss of hamartin results in abnormal neurite elongation through Rho inactivation in NGF-treated PC12h cells, which may be associated with the neurological manifestations of TSC.

ABSTRACT. Whenrat 3Y1 fibroblastic cells are cultured toward con fluency, the cells go through maximum cell density (overshoot) before reaching post-confluence stationary cell density. After overshooting, a number of floating cells are found in the medium. In a long-term culture, a cyclic change in cell number, an increase after each mediumrefreshment and subsequent cell loss within a few days has been observed so that the cell populations in the monolayer maintain post-confluence stationary cell density at a constant level. The floating cells excluded trypan blue, but they had no ability to attach to the substrate and to form colonies after being reseeded in fresh medium. They had condensed and uniformly electron-dense chromatin with sharply circumscribed edges. Their DNAcontained a laddering pattern in harmony with internucleosomal cleavage. The features were those of apoptosis. Whenfloating cells appeared, apoptotic bodies were also observed in the monolayer. Most of them were found within the cytoplasm of intact cells, suggesting that apoptotic bodies were also faded away from the culture by being rapidly engulfed by neighboring intact cells. These suggest that apoptosis and subsequent detachment from the monolayer or engulfment by neighboring intact cells, in addition to inhibition of cell division, are basic mechanisms on the process of density-dependent regulation in monolayer culture of rat 3Y1 cells.