Potassium Channels, Glucose Metabolism and Glycosylation in Cancer Cells

Potassium channels emerge as one of the crucial groups of proteins that shape the biology of cancer cells. Their involvement in processes like cell growth, migration, or electric signaling, seems obvious. However, the relationship between the function of K+ channels, glucose metabolism, and cancer glycome appears much more intriguing. Among the typical hallmarks of cancer, one can mention the switch to aerobic glycolysis as the most favorable mechanism for glucose metabolism and glycome alterations. This review outlines the interconnections between the expression and activity of potassium channels, carbohydrate metabolism, and altered glycosylation in cancer cells, which have not been broadly discussed in the literature hitherto. Moreover, we propose the potential mediators for the described relations (e.g., enzymes, microRNAs) and the novel promising directions (e.g., glycans-orinented drugs) for further research.

Effects of kinetin riboside on proliferation and proapoptotic activities in human normal and cancer cell lines

Kinetin riboside (KR) is a N6-substituted derivative of adenosine. It is a natural compound which occurs in the milk of coconuts on the nanomole level. KR was initially shown to selectively inhibit proliferation of cancer cells and induce their apoptosis. We observed that KR inhibited growth (20-80%) of not only human cancer, but also normal cells and that this effect strongly depended on the type of cells. The anti-apoptotic Bcl-2 protein was downregulated, while proapoptotic Bax was upregulated in normal as well as in cancer cell lines, upon exposure to KR. Cytochrome c level increased in the cytosol upon treatment of cells with KR. The activity of caspases (ApoFluor®Green Caspase Activity Assay), as well as caspase-3 (caspase-3 activation assay) were increased mainly in cancer cells. The expression of procaspase 9 and its active form in the nucleus as well as in cytosol of KR-treated cells was elevated. In contrast, no effect of KR on caspase 8 expression was noted. The results indicated that non-malignant cells were less sensitive to KR then their cancer analogs and that KR most likely stimulated apoptosis mechanism of cancer cells through the intrinsic pathway.

Prolactin involvement in the regulation of the hypothalamic-pituitary-ovarian axis during the early luteal phase of the porcine estrous cycle

Our previous in vivo and in vitro studies revealed that prolactin (PRL) affected luteal function during the first days of the porcine estrous cycle. Since the mechanism by which the luteotrophic action of PRL might be mediated was not elucidated, the goal of the present study is to investigate the effects of short term, in vivo administration of PRL on in vitro functions of hypothalamic explants, adenohypophyseal cells and luteal cells of sows. Injections of PRL or saline (performed every 2h) started shortly after the preovulatory LH surge and lasted for 2 or 3 days. Peripheral blood plasma for determination of LH, PRL and progesterone (P(4)) was sampled at 4h intervals. Ovaries, pituitaries and the stalk median eminence (SME) dissected after slaughter were used for in vitro studies. Luteal and adenohypophysial cells as well as hypothalamic tissue were incubated/cultured with different treatments. Medium and plasma levels of GnRH, LH and P(4) were quantified by radioimmunoassays (RIAs). Corpora lutea (CL) were used for LH/human chorionic gonadotrophin (hCG) receptor analysis. In vivo and in vitro treatment with PRL increased the in vitro GnRH release by hypothalamic explants (P<0.05). GnRH-stimulated LH production was enhanced in PRL-treated sows compared to that of control sows (P<0.05). PRL injections had no effect on plasma P(4) concentrations during the treatment period. However, luteal secretion of P(4) (P=0.06) and LH/hCG receptor concentration (P=0.079) tended to be higher in PRL-treated sows in comparison to those of controls. The results indicate that PRL may be involved in the regulation of the hypothalamic-pituitary-ovarian axis at the beginning of the luteal phase of the porcine estrous cycle.

The morphometric parameters of adrenal cortex in sows: in normal condition and after prolactin infusion

The aim of this study was to examine the effect of experimental hyperprolactinemia on the stereological parameters of porcine adrenal cortex. In cyclic sows, after preovulatory luteinizing hormone (LH) peak, porcine prolactin (PRL, 0.3 mg) or saline were administered i.v. for 48 h at 2 h intervals. Next sows were slaughtered and adrenal glands were dissected. Stereological analysis of the left adrenal gland did not reveal any significant differences between control and PRL-treated sows. Experimental hyperprolactinemia did not affect the volume of particular cortical zones, the number and the volume of adrenocortical cells or the average volume of their cell nuclei. Moreover, we present for the first time a detailed stereological description of adrenal cortex in sows.

Luteotrophic action of prolactin during the early luteal phase in pigs: the involvement of protein kinases and phosphatases

Prolactin (PRL) involvement in the regulation of luteal steroidogenesis in pigs during the early luteal phase and pregnancy is well documented. The intracellular mechanism of PRL action in steroidogenic cells, however, is not fully recognized yet. In the current study, we have tested the hypothesis that protein kinase C (PKC) and tyrosine kinases (PTK) as well as serine-threonine (PP) and tyrosine phosphatases (PTP) are involved in PRL signaling in luteal cells originated from the early corpora lutea (CL) of cyclic sows. Luteal cells (50 000 cells/ml M199) were incubated for 8 h (37 degrees C) with PRL (200 ng) and low density lipoproteins (LDL) to stimulate P(4) production. In addition, treatments included: PKC inhibitors--staurosporine and chelerythrine chloride; tyrosine kinase inhibitors--genistein and tyrphostin; serine-threonine phosphatase inhibitors--okadaic acid, cantharidin (inhibitors of PP1/2A) and cypermethrin (inhibitor of PP2B); and tyrosine phosphatase inhibitor--sodium orthovanadate. Moreover, after incubation (37 degrees C) with PRL (200 ng) for 2, 5, 10 or 20 min, luteal cells were homogenized and cytosolic as well as membrane fractions have been obtained. This was followed by partial purification of the subcellular fractions by DEAE-cellulose chromatography and determination of PKC activity by measuring the transfer of (32)P from [gamma-(32)P]ATP to histone III-S. In unstimulated porcine luteal cells the major proportion of PKC activity was present in the cytosol. Incubation of luteal cells with PRL resulted in a rapid, time dependent increase in the amount of PKC activity in the membrane fraction and a decrease in the amount of PKC activity in the cytosol fraction. PKC activity in the membrane fraction was maximal after 5 min of exposure the cells to PRL. Inhibitors of PKC and PTK suppressed PRL and LDL-induced P(4) production by porcine luteal cells. It is of interest that stimulated P(4) production was also reduced by inhibitors of PTP and PP1/2A (okadaic acid, cantharidin). In contrast, cypermethrin did not affect P(4) production stimulated by PRL and LDL. The results of the current study support the hypothesis that PKC and tyrosine kinases are intracellular mediators of PRL action in porcine luteal cells during the first days of the estrous cycle. The involvement of protein phosphatases in transmission of the PRL signal in early luteal cells in pigs is also suggested.