Caterina A. M. La Porta

CXCR6, a Newly Defined Biomarker of Tissue-Specific Stem Cell Asymmetric Self-Renewal, Identifies More Aggressive Human Melanoma Cancer Stem Cells

Background A fundamental problem in cancer research is identifying the cell type that is capable of sustaining neoplastic growth and its origin from normal tissue cells. Recent investigations of a variety of tumor types have shown that phenotypically identifiable and isolable subfractions of cells possess the tumor-forming ability. In the present paper, using two lineage-related human melanoma cell lines, primary melanoma line IGR39 and its metastatic derivative line IGR37, two main observations are reported. The first one is the first phenotypic evidence to support the origin of melanoma cancer stem cells (CSCs) from mutated tissue-specific stem cells; and the second one is the identification of a more aggressive subpopulation of CSCs in melanoma that are CXCR6+. Methods/Findings We defined CXCR6 as a new biomarker for tissue-specific stem cell asymmetric self-renewal. Thus, the relationship between melanoma formation and ABCG2 and CXCR6 expression was investigated. Consistent with their non-metastatic character, unsorted IGR39 cells formed significantly smaller tumors than unsorted IGR37 cells. In addition, ABCG2+ cells produced tumors that had a 2-fold greater mass than tumors produced by unsorted cells or ABCG2- cells. CXCR6+ cells produced more aggressive tumors. CXCR6 identifies a more discrete subpopulation of cultured human melanoma cells with a more aggressive MCSC phenotype than cells selected on the basis of the ABCG2+ phenotype alone. Conclusions/Significance The association of a more aggressive tumor phenotype with asymmetric self-renewal phenotype reveals a previously unrecognized aspect of tumor cell physiology. Namely, the retention of some tissue-specific stem cell attributes, like the ability to asymmetrically self-renew, impacts the natural history of human tumor development. Knowledge of this new aspect of tumor development and progression may provide new targets for cancer prevention and treatment.

AQP1 is not only a water channel: it contributes to cell migration through Lin7/beta-catenin.

Background AQP1 belongs to aquaporins family, water-specific, membrane-channel proteins expressed in diverse tissues. Recent papers showed that during angiogenesis, AQP1 is expressed preferentially by microvessels, favoring angiogenesis via the increase of permeability In particular, in AQP1 null mice, endothelial cell migration is impaired without altering their proliferation or adhesion. Therefore, AQP1 has been proposed as a novel promoter of tumor angiogenesis. Methods/Findings Using targeted silencing of AQP1 gene expression, an impairment in the organization of F-actin and a reduced migration capacity was demonstrated in human endothelial and melanoma cell lines. Interestingly, we showed, for the first time, that AQP1 co-immunoprecipitated with Lin-7. Lin7-GFP experiments confirmed co-immunoprecipitation. In addition, the knock down of AQP1 decreased the level of expression of Lin-7 and β-catenin and the inhibition of proteasome contrasted partially such a decrease. Conclusions/Significance All together, our findings show that AQP1 plays a role inside the cells through Lin-7/β-catenin interaction. Such a role of AQP1 is the same in human melanoma and endothelial cells, suggesting that AQP1 plays a global physiological role. A model is presented.

Drug resistance in melanoma : new perspectives

Melanoma is the most aggressive form of skin cancer and advantages stages are inevitably resistant to conventional therapeutic agents. In particular, the inability of undergo apoptosis in response to chemotherapy and other external stimuli poses a selective advantage for tumor progression, metastasis formation as well as resistance to therapy in melanoma. Herein, we will review the discovery of MDR transporters and the apoptotic mechanisms used by melanoma cells. Furthermore, the novel strategies to overcome tumor chemoresistance will also discuss. In particular, we will review the cancer stem cell hypothesis and how the failure of MDR reversal agents might increase the therapeutic index of substrate antineoplastic agents.

Unique Expression and Localization of Aquaporin- 4 and Aquaporin-9 in Murine and Human Neural Stem Cells and in Their Glial Progeny

Aquaporins (AQP) are water channel proteins that play important roles in the regulation of water homeostasis in physiological and pathological conditions. AQP4 and AQP9, the main aquaporin subtypes in the brain, are expressed in the adult forebrain subventricular zone (SVZ), where neural stem cells (NSCs) reside, but little is known about their expression and role in the NSC population, either in vivo or in vitro. Also, no reports are available on the presence of these proteins in human NSCs. We performed a detailed molecular and phenotypical characterization of different AQPs, and particularly AQP4 and AQP9, in murine and human NSC cultures at predetermined stages of differentiation. We demonstrated that AQP4 and AQP9 are expressed in adult murine SVZ‐derived NSCs (ANSCs) and that their levels of expression and cellular localization are differentially regulated upon ANSC differentiation into neurons and glia. AQP4 (but not AQP9) is expressed in human NSCs and their progeny. The presence of AQP4 and AQP9 in different subsets of ANSC‐derived glial cells and in different cellular compartments suggests different roles of the two proteins in these cells, indicating that ANSC‐derived astrocytes might maintain in vitro the heterogeneity that characterize the astrocyte‐like cell populations in the SVZ in vivo. The development of therapeutic strategies based on modulation of AQP function relies on a better knowledge of the functional role of these channels in brain cells. We provide a reliable and standardized in vitro experimental model to perform functional studies as well as toxicological and pharmacological screenings.

Mechanism of drug sensitivity and resistance in melanoma.

Melanoma is the most aggressive form of skin cancer and advanced stages are inevitably resistant to conventional therapeutic agents. In particular, the inability of undergo apoptosis in response to chemotherapy and other external stimuli poses a selective advantage for tumor progression, metastasis formation as well as resistance to therapy in melanoma. Herein, we will review the molecular mechanisms of sensitivity and/or resistance of the most important drugs used in the treatment of melanoma. Furthermore, the novel strategies to overcome tumor chemoresistance will also be discussed. In particular, we will review the cancer stem cell hypothesis and how the failure of MDR reversal agents might increase the therapeutic index of substrate antineoplastic agents.

Role of the Number of Microtubules in Chromosome Segregation during Cell Division

Faithful segregation of genetic material during cell division requires alignment of chromosomes between two spindle poles and attachment of their kinetochores to each of the poles. Failure of these complex dynamical processes leads to chromosomal instability (CIN), a characteristic feature of several diseases including cancer. While a multitude of biological factors regulating chromosome congression and bi-orientation have been identified, it is still unclear how they are integrated so that coherent chromosome motion emerges from a large collection of random and deterministic processes. Here we address this issue by a three dimensional computational model of motor-driven chromosome congression and bi-orientation during mitosis. Our model reveals that successful cell division requires control of the total number of microtubules: if this number is too small bi-orientation fails, while if it is too large not all the chromosomes are able to congress. The optimal number of microtubules predicted by our model compares well with early observations in mammalian cell spindles. Our results shed new light on the origin of several pathological conditions related to chromosomal instability.

Cancer Stem Cells: Lessons From Melanoma

The model of cancer stem cells in tumor development states that tumors contain a subset of cells that both self renew and give rise to differentiated progeny. Like normal adult tissue stem cells, cancer stem cells are a minority of the whole tumor and are the only cells that are able to maintain tumor growth indefinitely. In the present review is critically discussed the actually existence of a cancer stem cell subpopulation in melanoma. The self-renewal signaling pathways as well as specific markers like as CD133, ABCB5 and ABCG2 recently identified in putative melanoma cancer stem cells are also discussed.The model of cancer stem cells in tumor development states that tumors contain a subset of cells that both self renew and give rise to differentiated progeny. Like normal adult tissue stem cells, cancer stem cells are a minority of the whole tumor and are the only cells that are able to maintain tumor growth indefinitely. In the present review is critically discussed the actually existence of a cancer stem cell subpopulation in melanoma. The self-renewal signaling pathways as well as specific markers like as CD133, ABCB5 and ABCG2 recently identified in putative melanoma cancer stem cells are also discussed.

Pertussis toxin-sensitive G-protein mediates galanin's inhibition of scopolamine-evoked acetylcholine release in vivo and carbachol-stimulated phosphoinositide turnover in rat ventral hippocampus

The effects of intracerebroventricular (i.c.v.) injections of pertussis toxin were investigated on the inhibitory action of galanin on acetylcholine release and phosphoinositide breakdown stimulated by muscarinic agents in rat ventral hippocampus. Pertussis toxin (0.6 micrograms, i.c.v., 96 h) counteracted the in vitro inhibitory effect of galanin (3.1 nmol) on phosphoinositide breakdown stimulated by carbachol without altering the stimulatory action of the cholinergic agonist on signal transduction, in miniprisms from rat ventral hippocampus. Pertussis toxin also abolished the in vivo effect of galanin on scopolamine-stimulated acetylcholine release in vivo but did not affect basal acetylcholine release. The results indicate that pertussis toxin-sensitive G-protein(s) mediates the galanin receptor regulation of pre- and postsynaptic cholinergic functions in the ventral hippocampus.

The Water Channels, New Druggable Targets to Combat Cancer Cell Survival,Invasiveness and Metastasis

Cell viability and motility are critical for cancer progression. Among a plethora of mechanisms that regulate these phenotypes, the balance of water and monovalent metal cations plays a pivotal role in the dynamics of focal contacts and cytoskeletal rearrangements at the cells leading edge. Furthermore, cell survival requires the optimal concentration of water and solutes. This balance is largely maintained by aquaporins (AQPs), a family of 13 small integral plasma membrane proteins whose major function is the transport of water and small solutes across the plasma membrane. We review the recent knowledge about the role of AQPs in cell migration, survival, tumor angiogenesis and metastasis with the focus on therapeutic possibilities to prevent these clinically unfavourable events. The review discusses the inhibition of AQP expression and/or AQP-mediated water influx by acetazolamide, cyclophosphamide, topiramate, thiopental, phenobarbital and propofol. Down-regulation of water transport by these drugs affects cancer cell migration and metastasis. We conclude that AQPs can be considered a point where the mechanisms of survival and motility converge. Therapeutic targeting of AQPs may thus be advantageous for blocking the mechanism common for a number of key cancer phenotypes.

Do cancer cells undergo phenotypic switching? The case for imperfect cancer stem cell markers

The identification of cancer stem cells in vivo and in vitro relies on specific surface markers that should allow to sort cancer cells in phenotypically distinct subpopulations. Experiments report that sorted cancer cell populations after some time tend to express again all the original markers, leading to the hypothesis of phenotypic switching, according to which cancer cells can transform stochastically into cancer stem cells. Here we explore an alternative explanation based on the hypothesis that markers are not perfect and are thus unable to identify all cancer stem cells. Our analysis is based on a mathematical model for cancer cell proliferation that takes into account phenotypic switching, imperfect markers and error in the sorting process. Our conclusion is that the observation of reversible expression of surface markers after sorting does not provide sufficient evidence in support of phenotypic switching.