Reduction of intracellular pH inhibits constitutive expression of Cyclooxygenase-2 in human colon cancer cells

Lactate maintainsBCR/Abl expression and signalinginChronic Myeloid Leukemia cells under nutrient restriction

This study was directed to deepen the effects of nutrient shortage on BCR/Abl_protein expression and signaling in chronic myeloid leukemia (CML) cells. The backbone of the study was cell culture in medium lacking glucose, the consumption of which we had previously shown to drive BCR/Abl_protein suppression, and glutamine, the other main nutrient besides glucose. In this context, we focused on the role of lactate, the main by-product of glucose metabolism under conditions of rapid cell growth, in particular as a modulator of the maintenance of CML stem/progenitor cell potential, a crucial determinant of disease course and relapse of disease. The results obtained indicated that lactate is a powerful surrogate of glucose to prevent the suppression of BCR/Abl signaling and is therefore capable to maintain BCR/Abl-dependent CML stem/progenitor cell potential. A number of metabolism-related functional and phenotypical features of CML cells were also determined. Among these, we focused on the effect of lactate on oxygen consumption rate, the dependence of this effect on the cell surface lactate carrier MCT-1, and the relationship of the lactate effect to pyruvate and to the activity of mitochondrial pyruvate carrier.

Intracellular and Extracellular Tumor pH Measurement in a Series of Patients With Oral Cancer

Reversed pH gradient is an intrinsic feature of tumor phenotype resulting from an upregulation of glycolysis. This is crucial for tumor cell proliferation, invasion, metastasis, drug resistance, and apoptosis. Comprehension of mechanisms of pH regulation in tumors is of paramount importance for therapeutic implications. This is a preliminary report of a larger prospective study dedicated to the measurements of neutral or slightly alkaline pH/extracellular pH (pHi/pHe) in human patients affected by tumors of the head and neck. During surgery, four specimens were obtained from six patients with cancer: two from the tumor site and two from contralateral areas or sane areas near the tumor. pHe and pHi were measured and compared within normal and neoplastic tissues. Our data indicate that human spontaneous tumors show similar reversed gradients as observed in previous analysis on animal tumor models and cell lines.

HIF-1: hypoxia-inducible factor or dysoxia-inducible factor?

Hypoxia-inducible factor 1 (HIF-1) activates the transcription of genes involved in diverse aspects of cellular and integrative physiology, including energy metabolism, cell growth, survival, invasion, migration or angiogenesis. The activity of this transcription factor is known to be increased by hypoxia, but also by a growing number of apparently unrelated factors that can activate it even in nonhypoxic conditions. Here I propose a model in which an alteration in oxygen metabolism is the key cellular event involved in HIF-1 activation under hypoxic and nonhypoxic conditions. This new perspective unifies previously unrelated observations and predicts cellular processes and therapeutic strategies that may modify HIF-1 activity. This may have relevance, for instance, to cancer, as HIF-1 overexpression is observed in many human cancers and has been associated with increased patient mortality.

14-3-3sigma expression is an independent prognostic parameter for poor survival in colorectal carcinoma patients

PURPOSE

14-3-3sigma is an intracellular, dimeric, phosphoserine binding protein that is expressed in epithelial cells and involved in cancer development. In this study, we examined the expression of 14-3-3sigma and evaluated its clinical significance in colorectal carcinoma.

EXPERIMENTAL DESIGN

Expression of 14-3-3sigma was analyzed by Western blot in nine colorectal carcinoma cell lines, eight paired colorectal carcinoma tissues, and normal mucosas. Immunohistochemistry was used to evaluate expression of 14-3-3sigma in tissues of 121 colorectal carcinoma patients and to correlate it with clinical parameters.

RESULTS

Western blot analysis of colorectal carcinoma cell lines and tissues revealed strong 14-3-3sigma expression in four of eight cell lines and 14-3-3sigma overexpression in carcinomas compared with normal mucosa in six of eight colorectal carcinoma tissue pairs. Immunohistochemical analysis revealed 14-3-3sigma overexpression in 38.8% of colorectal carcinoma samples. Furthermore, highly positive immunoreactivity was significantly correlated with tumor differentiation (P < 0.001) and pT stage (P < 0.003). In Kaplan-Meier analysis, 14-3-3sigma overexpression was associated with a significantly decreased survival time compared with negatively stained or low stained cases (P < 0.0096). In multivariate regression analysis, 14-3-3sigma expression emerged as a significant independent parameter (P < 0.037).

CONCLUSIONS

These results provide evidence that 14-3-3sigma expression increases during carcinoma progression in a subset of colorectal carcinoma. The overexpression of this antigen identifies patients at high risk. It is tempting to suggest that 14-3-3sigma overexpression either promotes tumor proliferation and/or prevents apoptotic signal transduction in colorectal carcinoma. Thus, targeting 14-3-3sigma might be a new therapeutic strategy in colorectal carcinoma.

Troglitazone's rapid and sustained activation of ERK1/2 induces cellular acidosis in LLC-PK1-F+cells: physiological responses

We studied the signal pathway through which troglitazone (TRO) acts in inducing cellular acidosis in LLC-PK1-F+cells in relation to ammoniagenesis and DNA synthesis. Cells were grown to confluent monolayers in 30-mm chambers and monitored for intracellular pH (pHi) by the BCECF assay and activated ERK by phospo-ERK1/2 antibodies. TRO induces a severe cellular acidosis (pHi6.68 ± 0.10 vs. 7.28 ± 0.07 time control at 4 min, P < 0.01), whereas phospho-ERK1/2 to total ERK1/2 ratio increases 3.4-fold ( P < 0.01). To determine whether ERK1/2 was activated by cellular acidosis or TRO was acting via MEK1/2 to activate ERK1/2, cells were pretreated with specific inhibitors of MEK1/2 activity, PD-098059 and U-0126, followed by the addition of TRO or vehicle. With MEK1/2 activity inhibited, TRO treatment failed to activate ERK1/2. Preventing ERK1/2 activation abrogated the TRO-induced cellular acidosis and maintained the pHiwithin the low normal range (7.06 ± 0.11). To determine whether blocking ERK activation prevents TRO's inhibitory effect on NHE activity, cells were acid-loaded and the recovery response was monitored as ΔpHi/ t over a 4-min recovery period. TRO inhibited NHE activity by 85% ( P < 0.01), whereas blocking ERK activation restored the response. We measured activated ERK levels and pHiafter 3- and 18-h exposure to TRO or extracellular acidosis (pHe = 6.95) to determine whether ERK activation was sustained. Whereas both TRO and extracellular acidosis increased activated ERK and decreased pHiafter 3 h, only TRO sustained this response at 18 h. Furthermore, both enhanced ammoniagenesis and decreased DNA synthesis reflected the effect of TRO to induce and sustain a cellular acidosis.

Direct interaction and cooperative role of tumor suppressor p16 with band 3 (AE1)

By using the C-terminal 112-residue of band 3 to screen the K562 cDNA library, we find that the p16 interacts with band 3, which was confirmed both in yeast and in mammalian cells. Functional experiments show that p16 facilitates the movement of band 3 to plasma membrane with increased anion transport activity in 293t cells. Moreover, expression of endogenous p16 in 293t cells was increased at 24 and 36 h after transfection with band 3. Our findings provide a novel regulation pathway for both band 3 and p16.

Inhibition by cytoplasmic nucleotides of a new cation channel in freshly isolated human and rat type II pneumocytes

Here we report a 26- to 29-pS cation channel abundantly expressed in freshly isolated and primary cultured type II cells from rat or healthy human lungs. The channel was never spontaneously active in cell-attached patches but could be activated by cell permeabilization with beta-escin. Excised patch-clamp experiments revealed activation by Ca(2+) concentrations at the cytoplasmic side in the micromolar range. High concentrations of amiloride (>10 microM) at the extracellular side did not inhibit. The channel was equally permeable for K(+) and Na(+) but was essentially impermeable for Cl(-), Ca(2+), and Mg(2+). It was blocked by adenosine nucleotides (cytoplasmic side) with the following order of potency: AMP approximately ADP (EC(50) </= 10 microM) > ATP >> adenosine >> cyclic AMP. The blocking effect of ATP was reproduced by its nonhydrolyzable analogs AMPPNP or ATP-gamma-S. GTP did not inhibit. Cd(2+) blocked the channel with an EC(50) approximately 55.5 nM. We conclude that type II cells express a Ca(2+)-dependent, nucleotide-inhibited, nonselective, and Ca(2+)-impermeable cation channel (NSC(Ca/AMP)) with tonically suppressed activity. RT-PCR confirmed expression of TRPM4b, a channel with functional characteristics almost identical with NSC(Ca/AMP). Potential physiological roles are discussed.