Focal adhesion kinase-dependent apoptosis of melanoma induced by tyrosine and phenylalanine deficiency

We found previously that restriction of tyrosine (Tyr) and phenylalanine (Phe) inhibited growth and metastasis of B16BL6 murine melanoma and arrested these cells in the G0-G1 phase of the cell cycle. Here, we report that deprivation of these two amino acids in vitro induces apoptosis in B16BL6 and in human A375 melanoma cells but not in nontransformed, neonatal murine epidermal cells or human infant foreskin fibroblasts. Four days after deprivation of Tyr and Phe in vitro, 37% of B16BL6 and 51% of A375 melanoma cells were undergoing apoptosis. Apoptosis was not associated with elevation in intracellular calcium or alteration in p53 or c-myc protein expression. Expression and Tyr phosphorylation of focal adhesion kinase (FAK) were inhibited in both melanoma cell lines by deprivation of Tyr and Phe but not by deprivation of glutamine or serum. Tyr phosphorylation of FAK in Tyr- and Phe-deprived melanoma cells was enhanced within 30 min of refeeding with complete DMEM. FAK protein expression recovered within 60 min, and cell viability recovered within 24 h. Genistein, a tyrosine kinase inhibitor that specifically inhibits Tyr phosphorylation of FAK, did not induce apoptosis in A375 melanoma cells at a concentration of 50 microM. Genistein prevented the recovery of cell viability upon refeeding with Tyr and Phe to previously deprived A375 melanoma cells. These data collectively indicate that apoptosis induced by Tyr and Phe deprivation is FAK-dependent.     

Polarization dependences of electroluminescence and absorption of vertically correlated InAs/GaAs QDs

The results of experimental studies concerning the optical polarization anisotropy of electroluminescence and absorption spectra of systems with a varied number of tunnel-coupled vertically correlated In(Ga)As/GaAs quantum dots (QDs), built into a double-section laser with equal-length sections, are presented. One such system is a QD superlattice exhibiting the Wannier-Stark effect. The involvement of heavyhole ground states in optical transitions for light polarized both in the plane perpendicular to the growth axis (X-Y) and along the growth direction Z of the structure was observed. The degree of polarization anisotropy depends on the height of vertically correlated QDs and the QD superlattice: the total thickness of all In(Ga)As QD layers and GaAs spacers between the QDs, which is related to the Z component of the wave function of heavy-hole ground states for vertically correlated QDs and for the QD superlattice.     

Passive mode-locked laser based on quantum dot superlattice

Passive mode-locking is achieved in two sectional lasers with an active layer based on superlattice formed by ten layers of quantum dots. Tunnel coupling of ten layers changes the structural polarization properties: the ratio between the TE and TM polarization absorption coefficients is less by a factor of 1.8 in the entire electroluminescence spectrum range for the superlattice.     

Positive chronotropic actions of parathyroid hormone and parathyroid hormone-related peptide are associated with increases in the current, I(f), and the slope of the pacemaker potential

BACKGROUND: The classic calciotropic hormone parathyroid hormone (PTH) and its paracrine factor parathyroid hormone-related protein (PTHrP) both increase heart rate. METHODS AND RESULTS: We used standard electrophysiological techniques to study the effects of PTH and PTHrP on isolated rabbit sinus node, isolated canine Purkinje fibers, and disaggregated rabbit sinus node myocytes. Sinus node maximum diastolic potential, activation voltage, and amplitude were unchanged by PTH or PTHrP (P>.05). However, the slope of phase 4 and the automatic rate were increased at PTH and PTHrP > or = 10 nmol/L (P<.05). Comparable results were seen in canine Purkinje fibers. We then used the perforated-patch technique to study the I(f) pacemaker current in sinus node. PTH 12.5 nmol/L and PTHrP 12.5 to 18 nmol/L increased I(f) at -65 mV by 68+/-41% (n=5) and 69+/-50% (n=5), respectively. Actions of both agents were reversible. The increase in I(f) appeared to result from a change in maximal conductance and not a shift in the voltage dependence of activation. CONCLUSIONS: These observations provide, for the first time, direct electrophysiological support for the chronotropic actions of PTH and PTHrP. They suggest that classic hormones and paracrine factors can have multiple functions and that in the case of PTH and PTHrP, a newly recognized action is to alter automaticity directly.     

Units of DNA replication in S-phase human cells

Current methods of physical mapping allow the estimation of genomic distances (i.e. DNA contents) from linear distances between DNA markers in interphase nuclei, and in this study we estimated the size of focal centers of DNA replication in cultured S-phase human cells. Our results indicate that the conformation of S-phase chromosome fibres in the range of contour lengths 0.1-3.0 microns fits the random walk model and, therefore, the quantitative methods of interphase mapping can be applied to the estimation of sizes of replication units. The obtained data show the existence of multiple non-clustered small units less than 150 kb in size, equivalent to small replicons detected by fiber DNA radioautography, and also a significant fraction of big units more than 500 kb in size, representing groups of small replicons and/or big replicons. These big units are detected as chains of small replication foci, probably reflecting the structural chromatin organization in well-known loop domains, since the experimentally induced decrease of replicons to the average size 12 kb does not lead to any change in the pattern of indicated chains.     

Alpha-fetoprotein-mediated targeting--a new strategy to overcome multidrug resistance of tumour cells in vitro

The possibility of overcoming the multidrug resistance of human malignant cells by using doxorubicin conjugated to alpha-fetoprotein (AFP) was studied. It was shown that this type of antitumour drugs, penetrating the cell by receptor-mediated endocytosis with AFP as a vehicle, raises the sensitivity of the tumour cells that are resistant due to the expression of the multidrug resistance gene mdr1. The sensitivity of antibiotic-resistant cell lines SKVLB (a human ovarian carcinoma) and MCF-7 AdrR (a human breast carcinoma) increased by 10- and 4-fold, respectively, when AFP-conjugated doxorubicin was used. The rationale of using human AFP-antitumour drug conjugates for the development of new chemotherapeutic approaches to cancer treatment is discussed.     

Influence of ionizing radiation on proliferation, c-myc expression and the induction of apoptotic cell death in two breast tumour cell lines differing in p53 status

PURPOSE: To determine the capacity of ionizing radiation to inhibit proliferation, to suppress c-myc expression and to induce apoptotic cell death in the p53 wild-type MCF-7 cell line and the p53 mutated MDA-MB231 cell line. MATERIALS AND METHODS: Growth inhibition and cell killing were determined by cell number and trypan blue exclusion. Apoptosis was assessed through cell morphology and fluorescent end-labelling. c-myc expression was monitored by Northern blotting. RESULTS: Inhibition of cell proliferation by ionizing radiation was similar in both cell lines. MDA-MB231 cells accumulated in G2 while MCF-7 cells accumulated in both the G1 and G2 phases of the cell cycle after irradiation. There was no evidence of apoptosis in either cell line. In MCF-7 cells, growth inhibition correlated closely with an early dose-dependent suppression of c-myc expression; in MDA-MB231 cells, there was no correspondence between growth inhibition and a transient, dose-independent reduction in c-myc message. CONCLUSIONS: These findings suggest that in the absence of classical apoptotic cell death, radiosensitivity is not predictably related to the p53 status of the cell. While both p53 and c-myc may be linked to the DNA damage response pathway, neither p53 nor c-myc are essential for growth arrest in response to ionizing radiation.     

Sequestration of the lung arising from the circumflex coronary artery

The patterns of macroscopic growth of 20 first generation human tumor xenografts (16 renal cell carcinomas and 4 squamous cell carcinomas of the head and neck region) were studied with the recursion formula of the Gompertz function. This method enables the characterization of each tumor growth pattern by two parameters: (i) parameter a, which correlates with the starting growth rate of the tumor and (ii) parameter b, which is a measure of the intensity of growth deceleration as a function of tumor growth. A statistically significant prediction of the establishment of a xeno-transplantation line after serial subpassaging (in 9/20 tumors) according to the characteristics of first passage growth curves (p<0. 01) is reported. Especially parameter b, the value of the growth deceleration, highly correlates with serial growth: tumors showing less growth deceleration (higher b-values) during first passage more frequently develop into transplantation lines. On the contrary line development could not be predicted on the basis of the a-values of the first passage growth curves alone (p=0.137). This observation adds to the accumulating evidence, that the process of tumor growth deceleration is a pivotal parameter of tumor biology. Moreover, the present evaluation substantially reduces the time needed to assay serial growth of tumor xenografts for prognostic purposes making this assay potentially more attractive for clinical use.