Cellular changes in HeLa cells and cervix cells after treatment with cyclic nucleotides

A lipidomics investigation of the induced hypoxia stress on HeLa cells by using MS and NMR techniques

Induced hypoxia stress on cervical cancer derived cells (HeLa cells) leads to significant changes in their membrane lipid profiles. The lipidome of HeLa cells was characterized by a joint approach wherein liquid chromatography-mass spectrometry (LC-MS) analysis was followed by high resolution NMR measurements. Multivariate data analysis showed apparent separation between control and hypoxia-treated HeLa cells and thus demonstrated hypoxia effects on lipid metabolism. The most striking finding was that hypoxia stimulation significantly reduced the total amount of cellular phosphoinositols (PI) but caused a prominent increase in the amount of lyso phosphocholines (lyso-PC) and lyso phosphoethanolamines (lyso-PE). The observed decrease of PI amount under hypoxic conditions is probably due to the accumulation of cellular myo-inositol, which is known to play a critical role in de novo synthesis of PI. Moreover, our study suggests that polyunsaturated phospholipid species are stronger biomarkers for discriminating the effect of hypoxia treatment. The evaluation of changes in the average unsaturation index (UI) of the membrane lipids acyl chains reveals that UI slightly increases in several lipid classes, thus affecting membrane fluidity and further membrane-dependent functions. The plausible mechanisms by which HeLa cells adapt to hypoxia conditions are also briefly reported.

Cell membrane changes of structure and function in protein kinase inhibitor-induced polyploid cells

Exogenous cyclic AMP has been thought to be a chemical without marked pharmacological effect until now, as it is not capable of penetrating the cell membrane in most eucaryotic cells. The present study obtained results consistent with those of most previous studies, showing that exogenous cyclic AMP itself did not interfere with the cell cycle even at the high dose of 100 microM. However, it was found that K252a, a potent inhibitor of protein kinases including protein kinase C, induced DNA re-replication, i.e. DNA synthesis at a elevated DNA ploidy in cells that had not undergone cytokinesis (leading to polyploidization), and that exogenous cyclic AMP markedly potentiated the K252a-induced polyploidization at a very low dose similar to the effective dose of membrane-permeable cyclic AMP analogue dibutyryl cyclic AMP. These findings suggested that the cell membrane changed during the formation of polyploid cells. This supposition was confirmed by scanning electron microscopy to observe structural changes and by determination of cellular attachment to investigate functional changes.

Alterations in membrane lipid dynamics of leukemic cells undergoing growth arrest and differentiation: dependency on the inducing agent

The effect of various differentiation inducers on membrane cell dynamics was studied using HL-60 and K562 leukemic cell lines. Membrane lipid dynamics was measured by the steady-state fluorescence polarization (P) method utilizing either 1,6-diphenyl-1,3,5-hexatriene (DPH) or the trimethyl ammonium derivative of DPH (TMA-DPH), which ascertains anchorage of the label to the membrane-water-lipid interface. Decrease in membrane microfluidity was observed in HL-60 cells undergoing differentiation into macrophages by 1,25-dihydroxyvitamin D3 and by K562 cells induced to differentiate by DMSO. Sodium butyrate caused an increase in membrane fluidity in K562 cells undergoing differentiation into erythroid-like cells while in HL-60 cells a dual effect was observed. At 0.4 mM concentration, in which the cells were induced to differentiate along the monocyte pathway, a decrease in membrane fluidity was observed, while at 1 mM concentration an increase in membrane fluidity occurred. Interferon-gamma (IFN-gamma) induced an increase in membrane fluidity in both cell lines. Using HL-60 cells fluorescently labeled by TMA-DPH, similar results indicating fluidization of the membrane following IFN-gamma treatment were obtained. Advanced fluorescence lifetime measurements, evaluated either by phase modulation spectrofluorometry or by single photon correlation fluorometry confirmed that the decrease in fluorescence polarization by IFN-gamma resulted from membrane fluidization and not from elongation of the probe's excited state lifetime. It is suggested that the inducer mode of action, and not the differentiation route, determine the outcome of changes in membrane microviscosity.