Mutant p53-R273H mediates cancer cell survival and anoikis resistance through AKT-dependent suppression of BCL2-modifying factor (BMF)

p53 is the most frequently mutated tumor-suppressor gene in human cancers. Unlike other tumor-suppressor genes, p53 mutations mainly occur as missense mutations within the DNA-binding domain, leading to the expression of full-length mutant p53 protein. Mutant p53 proteins not only lose their tumor-suppressor function, but may also gain new oncogenic functions and promote tumorigenesis. Here, we showed that silencing of endogenous p53-R273H contact mutant, but not p53-R175H conformational mutant, reduced AKT phosphorylation, induced BCL2-modifying factor (BMF) expression, sensitized BIM dissociation from BCL-X_L and induced mitochondria-dependent apoptosis in cancer cells. Importantly, cancer cells harboring endogenous p53-R273H mutant were also found to be inherently resistant to anoikis and lack BMF induction following culture in suspension. Underlying these activities is the ability of p53-R273H mutant to suppress BMF expression that is dependent on constitutively active PI3K/AKT signaling. Collectively, these findings suggest that p53-R273H can specifically drive AKT signaling and suppress BMF expression, resulting in enhanced cell survivability and anoikis resistance. These findings open the possibility that blocking of PI3K/AKT will have therapeutic benefit in mutant p53-R273H expressing cancers.

Smoking among Chinese patients with schizophrenia

OBJECTIVES

This study aimed to determine the prevalence of smoking among Chinese with schizophrenia, and to determine if smokers and nonsmokers differ in their age of onset of illness and neuroleptic requirement.

METHOD

One hundred and ninety-five patients were assessed by a single rater using the Brief Psychiatric Rating Scale (BPRS) and the Simpson-Angus Scale. Other historical, demographic and treatment variables were recorded from case records and interviews with patients and family members.

RESULTS

A higher rate of smoking was found in patients with schizophrenia than in the general population. There was no significant difference between the smokers and non-smokers in their respective neuroleptic dosages and extrapyramidal side-effects but the smokers had a significantly higher BPRS score.

CONCLUSIONS

Racial difference is proposed to account for this discrepancy from other Western studies. The contribution of nicotine towards aggravating schizophrenic symptoms is also considered.

Inorganic phosphate is the major component of the thermostable cytoplasmic fraction which stimulates mitochondrial anion uniport

A low molecular weight thermostable cytoplasmic fraction isolated from rat liver homogenate when pre-incubated with mitochondria increases the rate at which anions enter mitochondria via the pH-dependent anion-conducting channel in the inner membrane. The crude fraction obtained by centrifuging and heating the liver homogenate was purified by gel filtration and chromatography on DEAE-cellulose. The resulting factor is stable to heating at 100 degrees C, freeze-drying and extremes of pH. Inorganic phosphate co-purified with activity and activity was lost when the phosphate was removed by barium salt precipitation. A pure sample of KH2PO4 produced stimulation of anion conductivity. These results show that the major portion of the activity which stimulates anion uniport can be accounted for by the presence of phosphate in the crude and purified fractions. Mersalyl blocks stimulation when added before, but not when added after, incubation with phosphate which shows that the stimulation is produced by phosphate in the mitochondrial matrix. The proposed role of this factor in thyroid hormone action is discussed in the light of its identification as inorganic phosphate.

The pH-dependent anion-conducting channel of the mitochondrial inner membrane is potently inhibited by zinc ions

Zinc is a potent reversible inhibitor of the pH-dependent anion-conducting channel in the mitochondrial inner membrane, 50% inhibition was produced by 1.5 microM added Zn2+ at which point free Zn2+ was < or = 10(-8) M. Inhibition by Zn2+ is rapid but can be prevented or rapidly reversed by excess EDTA. Concentrations of Zn2+ higher than 4 microM caused reversal of inhibition to a variable extent depending on the anion. Under these conditions Zn2+ did not inhibit ribose entry, the phosphate transporter, or the pH-insensitive component of the NO3- uniport.

Effect of buffers and osmolality on anion uniport across the mitochondrial inner membrane

The effects of buffers and osmolality of the suspending medium on the pH-dependent anion uniport across the inner membrane of isolated rat liver mitochondria have been studied using the light scattering technique to measure passive osmotic swelling. In contrast to some other transport processes the rates of entry of chloride and other anions via the anion-conducting channel decreased steeply with increasing solute concentration. This effect appears to be a result of increased osmolality or decreased matrix volume rather than inhibition by the anion since it was also produced by increasing the osmolality by addition of non-penetrant solutes. The effects of some pH buffers on the mitochondrial anion-conducting channel were also investigated. Some zwitterionic buffers had little effect other than that produced by increasing osmolality but Tricine, Popso and Caps produced marked additional inhibition of anion uniport and several other zwitterionic buffers were also inhibitory. The correlation between increased anion conductivity and increased matrix volume supports the proposal that this channel functions in regulation of the volume of the mitochondrial matrix.

Calcium ion activation of the anion-conducting channel in the rat liver mitochondrial inner membrane

Stimulation of the rat liver mitochondrial inner-membrane anion-conducting channel by aeration is dependent on the concentration of Ca2+ ions in the assay medium. Ca2+ activates anion conduction in both aerated and non-energised mitochondria but acts over a wider concentration range and produces a greater increase in anion-conductivity in aerated mitochondria. EGTA reverses Ca2+ stimulation but takes several seconds to act, indicating slow release of Ca2+ from the activation site possibly on the matrix side of the inner mitochondrial membrane. It is suggested that this channel may respond to hormone-induced changes in cytosolic Ca2+ concentration.