[Ca2+]i as a potential downregulator of alpha2beta1-integrin-mediated A2058 tumor cell migration to type IV collagen

The Role of Calcium Signaling in Melanoma

Calcium signaling plays important roles in physiological and pathological conditions, including cutaneous melanoma, the most lethal type of skin cancer. Intracellular calcium concentration ([Ca²⁺]i), cell membrane calcium channels, calcium related proteins (S100 family, E-cadherin, and calpain), and Wnt/Ca²⁺ pathways are related to melanogenesis and melanoma tumorigenesis and progression. Calcium signaling influences the melanoma microenvironment, including immune cells, extracellular matrix (ECM), the vascular network, and chemical and physical surroundings. Other ionic channels, such as sodium and potassium channels, are engaged in calcium-mediated pathways in melanoma. Calcium signaling serves as a promising pharmacological target in melanoma treatment, and its dysregulation might serve as a marker for melanoma prediction. We documented calcium-dependent endoplasmic reticulum (ER) stress and mitochondria dysfunction, by targeting calcium channels and influencing [Ca²⁺]i and calcium homeostasis, and attenuated drug resistance in melanoma management.

The Role of Calmodulin in Tumor Cell Migration, Invasiveness, and Metastasis

Calmodulin (CaM) is the principal Ca²⁺ sensor protein in all eukaryotic cells, that upon binding to target proteins transduces signals encoded by global or subcellular-specific changes of Ca²⁺ concentration within the cell. The Ca²⁺/CaM complex as well as Ca²⁺-free CaM modulate the activity of a vast number of enzymes, channels, signaling, adaptor and structural proteins, and hence the functionality of implicated signaling pathways, which control multiple cellular functions. A basic and important cellular function controlled by CaM in various ways is cell motility. Here we discuss the role of CaM-dependent systems involved in cell migration, tumor cell invasiveness, and metastasis development. Emphasis is given to phosphorylation/dephosphorylation events catalyzed by myosin light-chain kinase, CaM-dependent kinase-II, as well as other CaM-dependent kinases, and the CaM-dependent phosphatase calcineurin. In addition, the role of the CaM-regulated small GTPases Rac1 and Cdc42 (cell division cycle protein 42) as well as CaM-binding adaptor/scaffold proteins such as Grb7 (growth factor receptor bound protein 7), IQGAP (IQ motif containing GTPase activating protein) and AKAP12 (A kinase anchoring protein 12) will be reviewed. CaM-regulated mechanisms in cancer cells responsible for their greater migratory capacity compared to non-malignant cells, invasion of adjacent normal tissues and their systemic dissemination will be discussed, including closely linked processes such as the epithelial–mesenchymal transition and the activation of metalloproteases. This review covers as well the role of CaM in establishing metastatic foci in distant organs. Finally, the use of CaM antagonists and other blocking techniques to downregulate CaM-dependent systems aimed at preventing cancer cell invasiveness and metastasis development will be outlined.

Immunohistochemical Analysis of Collagen IV and Laminin Expression in Spontaneous Melanoma Regression in the Melanoma-Bearing Libechov Minipig

Spontaneous regression (SR) of human melanoma is a rare, well-documented phenomenon that is not still fully understood. Its detailed study cannot be performed in patients due to ethical reasons. Using the Melanoma-bearing Libechov Minipig (MeLiM) animals of various ages (from 3 weeks to 8 months) we implemented a long-term monitoring of melanoma growth and SR. We focused on immunohistochemical detection of two important extracellular matrix proteins, collagen IV and laminin, which are associated with cancer. We showed that SR of melanoma is a highly dynamic process. The expression of collagen IV and laminin correlated with changes in population of melanoma cells. Tumours of 3-week-old animals consisted primarily of melanoma cells with a granular expression of collagen IV and laminin around them. Thereafter, melanoma cells were gradually destroyed and tumour tissue was rebuilt into the connective tissue. Collagen IV expression slightly increased in tumours of 10-week-old pigs showing extracellular fibrous appearance. In tumours of older animals, areas lacking melanoma cells demonstrated a low expression and areas still containing melanoma cells a high expression of both proteins. We considered the age of 10 weeks as a turning point in the transition between tumour growth and SR of the MeLiM melanoma.

CYLD inhibits melanoma growth and progression through suppression of the JNK/AP-1 and β1-integrin signaling pathways

The molecular mechanisms mediating CYLD tumor suppressor function appear to be manifold. Here, we demonstrated that, in contrast to the increased levels of pJNK, CYLD was decreased in a majority of melanoma cell lines and tissues examined. Exogenous expression of CYLD but not its catalytically deficient mutant markedly inhibited melanoma cell proliferation and migration in vitro and subcutaneous tumor growth in vivo. In addition, the melanoma cells expressing exogenous CYLD were unable to form pulmonary tumor nodules following tail-vein injection. At the molecular level, CYLD decreased β1-integrin and inhibited pJNK induction by TNFα or cell-attachment to collagen IV. Moreover, CYLD induced an array of other molecular changes associated with modulation of the ‘malignant’ phenotype, including a decreased expression of cyclin D1, N-cadherin and nuclear Bcl3, and an increased expression of p53 and E-cadherin. Most interestingly, co-expression of the constitutively active MKK7 or c-Jun mutants with CYLD prevented the above molecular changes, and fully restored melanoma growth and metastatic potential in vivo. Our findings demonstrate that JNK/AP-1 signaling pathway underlies the melanoma growth and metastasis that is associated with CYLD loss-of-function. Thus, restoration of CYLD and inhibition of JNK and β1-integrin function represent potential therapeutic strategies for treatment of malignant melanoma.

Transiently entrapped circulating tumor cells interact with neutrophils to facilitate lung metastasis development

It is unknown why only a minority of circulating tumor cells trapped in lung capillaries form metastases and involvement of immune cells remains uncertain. A novel model has been developed in this study showing that neutrophils regulate lung metastasis development through physical interaction and anchoring of circulating tumor cells to endothelium. Human melanoma cells were i.v. injected into nude mice leading to the entrapment of many cancer cells; however, 24 hours later, very few remained in the lungs. In contrast, injection of human neutrophils an hour after tumor cell injection increased cancer cell retention by approximately 3-fold. Entrapped melanoma cells produced and secreted high levels of a cytokine called interleukin-8 (IL-8), attracting neutrophils and increasing tethering beta(2) integrin expression by 75% to 100%. Intercellular adhesion molecule-1 on melanoma cells and beta(2) integrin on neutrophils interacted, promoting anchoring to vascular endothelium. Decreasing IL-8 secretion from melanoma cells lowered extracellular levels by 20% to 50%, decreased beta(2) integrin on neutrophils by approximately 50%, and reduced neutrophil-mediated extravasation by 25% to 60%, resulting in approximately 50% fewer melanoma cells being tethered to endothelium and retained in lungs. Thus, transendothelial migration and lung metastasis development decreased by approximately 50%, showing that targeting IL-8 in melanoma cells has the potential to decrease metastasis development by disrupting interaction with neutrophils.

Immunoediting of leukocyte functions within the tumor microenvironment promotes cancer metastasis development

Attachment of tumor cells to the endothelium (EC) under flow conditions is critical for migration of tumor cells out of the vascular system to establish metastases. We found that neutrophils (PMN) increased melanoma cell extravasation. Endogenous IL-8 liberated from melanoma cells or from PMN induced by melanoma cells contributed to PMN-facilitated melanoma cell arrest on the EC in the microcirculation. Functional blocking of IL-8 receptors on PMN or neutralizing soluble IL-8 in the tumor circulation decreased the level of CD11b/CD18 up-regulation on PMN and subsequently reduced melanoma cell extravasation. We also found that targeting mutant V600EB-Raf interrupted melanoma cell extravasation in vitro and subsequent lung metastasis development in vivo. B-Raf encodes a RAS-regulated kinase that mediates cell growth and malignant transformation kinase pathway activation. Results showed that inhibition of V600EB-Raf reduced IL-8 secretion from melanoma cells and reduced the capacity of IL-8 production from the tumor microenvironment involving PMN. Furthermore, reduction in intercellular adhesion molecule-1 (ICAM-1) expression on melanoma cells was found after V600EB-Raf knockdown. These results provide new evidence for the complex role of secreted chemokine and PMN-melanoma adhesion in the recruitment of metastatic cancer cells to the EC, which are significant in fostering new approaches to cancer treatment through anti-inflammatory therapeutics.

PDGF receptor-{beta} modulates metanephric mesenchyme chemotaxis induced by PDGF AA

PDGF B chain or PDGF receptor (PDGFR)-beta-deficient (-/-) mice lack mesangial cells. To study responses of alpha- and beta-receptor activation to PDGF ligands, metanephric mesenchymal cells (MMCs) were established from embryonic day E11.5 wild-type (+/+) and -/- mouse embryos. PDGF BB stimulated cell migration in +/+ cells, whereas PDGF AA did not. Conversely, PDGF AA was chemotactic for -/- MMCs. The mechanism by which PDGFR-beta inhibited AA-induced migration was investigated. PDGF BB, but not PDGF AA, increased intracellular Ca(2+) and the production of reactive oxygen species (ROS) in +/+ cells. Transfection of -/- MMCs with the wild-type beta-receptor restored cell migration and ROS generation in response to PDGF BB and inhibited AA-induced migration. Inhibition of Ca(2+) signaling facilitated PDGF AA-induced chemotaxis in the wild-type cells. The antioxidant N-acetyl-l-cysteine (NAC) or the NADPH oxidase inhibitor diphenyleneiodonium (DPI) abolished the BB-induced increase in intracellular Ca(2+) concentration, suggesting that ROS act as upstream mediators of Ca(2+) in suppressing PDGF AA-induced migration. These data indicate that ROS and Ca(2+) generated by active PDGFR-beta play an essential role in suppressing PDGF AA-induced migration in +/+ MMCs. During kidney development, PDGFR beta-mediated ROS generation and Ca(2+) influx suppress PDGF AA-induced chemotaxis in metanephric mesenchyme.

Melanoma cell extravasation under flow conditions is modulated by leukocytes and endogenously produced interleukin 8

Attachment of tumor cells to the endothelium (EC) under flow conditions is critical for the migration of tumor cells out of the vascular system to establish metastases. Innate immune system processes can potentially promote tumor progression through inflammation dependant mechanisms. White blood cells, neutrophils (PMN) in particular, are being studied to better understand how the host immune system affects cancer cell adhesion and subsequent migration and metastasis. Melanoma cell interaction with the EC is distinct from PMN-EC adhesion in the circulation. We found PMN increased melanoma cell extravasation, which involved initial PMN tethering on the EC, subsequent PMN capture of melanoma cells and maintaining close proximity to the EC. LFA-1 (CD11a/CD18 integrin) influenced the capture phase of PMN binding to both melanoma cells and the endothelium, while Mac-1 (CD11b/CD18 integrin) affected prolonged PMN-melanoma aggregation. Blocking E-selectin or ICAM-1 (intercellular adhesion molecule) on the endothelium or ICAM-1 on the melanoma surface reduced PMN-facilitated melanoma extravasation. Results indicated a novel finding that PMN-facilitated melanoma cell arrest on the EC could be modulated by endogenously produced interleukin-8 (IL-8). Functional blocking of the IL-8 receptors (CXCR1 and CXCR2) on PMN, or neutralizing soluble IL-8 in cell suspensions, significantly decreased the level of Mac-1 up-regulation on PMN while communicating with melanoma cells and reduced melanoma extravasation. These results provide new evidence for the complex role of hemodynamic forces, secreted chemokines, and PMN-melanoma adhesion in the recruitment of metastatic cancer cells to the endothelium in the microcirculation, which are significant in fostering new approaches to cancer treatment through anti-inflammatory therapeutics.

Distinct role of hydrodynamic shear in leukocyte-facilitated tumor cell extravasation

Previously, we found polymorphonuclear neutrophils (PMNs) increased melanoma cell extravasation under flow conditions (Intl J Cancer 106: 713-722, 2003). In this study, we characterized the effect of hydrodynamic shear on PMN-facilitated melanoma extravasation using a novel flow-migration assay. The effect of shear stress and shear rate on PMN-facilitated melanoma extravasation was studied by increasing the medium viscosity with dextran to increase shear stress independently of shear rate. Under fixed shear rate conditions, melanoma cell extravasation did not change significantly. In contrast, the extravasation level increased at a fixed shear stress but with a decreasing shear rate. PMN-melanoma aggregation and adhesion to the endothelium via beta(2)-integrin/intracellular adhesion molecule-1 (ICAM-1) interactions were also studied. Lymphocyte function-associated molecule-1 (LFA-1; CD11a/CD18) influenced the capture phase of PMN binding to both melanoma cells and the endothelium, whereas Mac-1 (CD11b/CD18) affected prolonged PMN-melanoma aggregation. Blockage of E-selectin or ICAM-1 on the endothelium or ICAM-1 on the melanoma surface reduced PMN-facilitated melanoma extravasation. We have found PMN-melanoma adhesion is correlated with the inverse of shear rate, whereas the PMN-endothelial adhesion correlated with shear stress. Interleukin-8 (IL-8) also influenced PMN-melanoma cell adhesion. Functional blocking of the PMN IL-8 receptors, CXCR1 and CXCR2, decreased the level of Mac-1 upregulation on PMNs while in contact with melanoma cells and reduced melanoma extravasation. We have found PMN-facilitated melanoma adhesion to be a complex multistep process that is regulated by both microfluid mechanics and biology.

Control of melanoma cell invasion by type IV collagen

Malignant melanoma is the leading cause of death from diseases of the skin. This review summarizes the data from the literature and our laboratory addressing the effects of type IV collagen on melanoma progression. Many different sequences from type IV collagen promote melanoma cell adhesion, migration and invasion. The triple helical conformation of the collagenous domain plays a critical role in some of these interactions. However, recent studies from our group demonstrated that a sequence from the alpha3(IV) NC1 domain inhibits melanoma cell proliferation, migration and invasion by decreasing MMP production and activation. Peptide sequences from the alpha1(IV), alpha2(IV) and alpha3(IV) chains named arresten, canstatin and tumstatin, respectively were shown to inhibit angiogenesis. Further investigations regarding the inhibitory effects of the alpha(IV) NC1 domains will have a paramount relevance for the design of efficient strategies to limit melanoma development.

Induction of a metastatogenic tumor cell type by neurotransmitters and its pharmacological inhibition by established drugs

The active migration of tumor cells, a crucial requirement for metastasis development and cancer progression, is regulated by signal substances including neurotransmitters. We investigated the migration of tumor cells within a three-dimensional collagen matrix using time-lapse videomicroscopy and computer-assisted analysis of the migration path. Tumor cell migration is induced by norepinephrine, dopamine and substance P. We show that this induced migration, using MDA-MB-468 breast and PC-3 prostate carcinoma cells, can be inhibited by using specific, clinically established receptor antagonists to the beta2-adrenoceptor, the D2 receptor, or the neurokinin-1 receptor, respectively. All of the investigated neurotransmitters significantly activated the cyclic adenosine-monophosphate response element binding protein (CREB). Furthermore, microarray analysis revealed changes of gene expression toward a highly motile tumor cell type, including an upregulation of the alpha2 integrin, which is an essential adhesion receptor for collagen in migration. The gene for the tumor suppressor gelsolin was downregulated. These 2 critical alterations were confirmed on the protein level by flow-cytometry and immunoblotting, respectively. Neurotransmitters thus induce a metastatogenic tumor cell type by directly regulating gene expression and increased migratory activity, which can be prevented by established neurotransmitter antagonists.

Intracellular calcium transients are necessary for platelet-derived growth factor but not extracellular matrix protein–induced vascular smooth muscle cell migration

PURPOSE

Vascular smooth muscle cell (SMC) migration is a critical component of the hyperplastic response that leads to recurrent stenosis after interventions to treat arterial occlusive disease. We investigated the relationship between intracellular calcium ([Ca(2+)](i)) and migration of vascular SMCs in response to platelet-derived growth factor (PDGF) and extracellular matrix (ECM) proteins.

METHODS

Human saphenous vein SMCs were used for all experiments. SMC migration in response to agonists was measured with a microchemotaxis assay. A standard fluorimetric assay was used to assess changes in [Ca(2+)](i) in response to the various combinations of growth factors and ECM proteins.

RESULTS

The calcium ionophore A23187 produced a rapid rise in [Ca(2+)](i) and a corresponding 60% increase in SMC migration, whereas chelation of [Ca(2+)](i) with BAPTA (1,2-bis [aminophenoxy] ethane-N,N,N',N'-tetraacetic acid) produced a fivefold decrease in PDGF-induced chemotaxis, suggesting that [Ca(2+)](i) is both sufficient and necessary for SMC migration. Stimulation of SMCs with PDGF produced an early peak followed by a late plateau in [Ca(2+)](i). To establish a relationship between temporal fluctuations in [Ca(2+)](i) and SMC migration, SMCs were pretreated with caffeine and ryanadine, which eliminated the initial peak but not the late plateau in [Ca(2+)](i), and had no effect on chemotaxis in response to PDGF. Incubation of SMCs with nickel chloride eliminated the late plateau, but had no effect on the initial peak in [Ca(2+)](i), and reduced PDGF-stimulated migration by fivefold. We then evaluated the role of calcium in SMC migration induced by ECM proteins such as laminin, fibronectin, and collagen types I and IV. All four matrix proteins stimulated SMC migration, but none produced an elevation in [Ca(2+)](i). Moreover, preincubation of SMCs with caffeine and ryanadine or nickel chloride had no effect on ECM protein-induced chemotaxis.

CONCLUSION

[Ca(2+)](i) transients are necessary for PDGF but not ECM protein-induced SMC chemotaxis. Moreover, the ability of PDGF to stimulate vascular SMC migration appears dependent on influx of extracellular calcium through membrane channels.

CLINICAL RELEVANCE

Recurrent stenosis after angioplasty or surgical bypass remains a significant challenge in treating vascular occlusive disease. In addition to growth factors, extracellular matrix (ECM) proteins may be potent agonists of this process. In this study we show that the influx of extracellular calcium is an important mechanism for platelet-derived growth factor-induced smooth muscle cell migration but not ECM-induced migration. Of note, in clinical trials calcium channel blockers failed to inhibit recurrent stenosis. Our data provide mechanistic insight to help explain this negative outcome in that therapies designed to inhibit restenosis depend on the effects of both growth factors and ECM proteins.

Neutrophils influence melanoma adhesion and migration under flow conditions

We have studied human melanoma cell (C8161) adhesion and migration in response to stimulation by soluble collagen IV (CIV) using a modified Boyden chamber. In this modified chamber, shear flow can be introduced over the cell-substrate interface, affecting tumor cell chemotactic migration through a microporous filter. A relatively high level of intercellular adhesion molecule-1 (ICAM-1) was found on C8161 cells. In contrast, levels of beta(2)-integrins (e.g., LFA-1 and Mac-1), the molecules that would be necessary for C8161 stable adhesion to the endothelium substrate, were found to be very low on these melanoma cells. As a result, C8161 transendothelial migration under a flow condition of 4 dyn/cm(2) decreased by 70% as compared to static migration. When human neutrophils (PMNs) were present in the tumor cell suspension, C8161 migration recovered by 85% over C8161 cells alone under the 4 dyn/cm(2) flow condition. Blocking ICAM-1 on C8161 cells or Mac-1 on PMNs significantly inhibited C8161-PMN adhesion and subsequent C8161 migration through the endothelium under flow conditions. In addition, increased interleukin-8 production and Mac-1 expression by PMNs were detected when they were co-cultured with C8161 melanoma cells. These results suggest that transmigration of C8161 cells under flow conditions can be influenced by PMNs, mediated by Mac-1/ICAM-1 adhesive interactions and enhanced by altered cytokine production.

Melanoma cell migration to type IV collagen requires activation of NF-kappaB

Chemotaxis is the consequence of environmental factors engaging their receptors to initiate signaling cascades. However, the biochemical mechanisms controlling this phenomenon are not clear. We employed an in vitro modified Boyden 48-well chemotaxis migration system to characterize the role of signal transducers in type IV collagen (CIV) induced A2058 human melanoma cell migration. Using specific pharmacological inhibitors and a series of dominant-negative and constitutively active signaling proteins, we show that Ras and Rac GTPases, PI-3K, and PKC participate in cell migration mediated by beta1 integrins. Collagen also induces a time- dependent degradation of IkappaB-alpha and an increase in nuclear translocation of NF-kappaB which is dependent on PKC pathway. More importantly, collagen-stimulated melanoma cell migration directly correlated with an increase in NF-kappaB transactivation. Furthermore, CIV induced an increase in beta1 integrin mRNA levels. Specific NF-kappaB inhibitors Helenalin and SN-50 inhibited melanoma cell migration to collagen, indicating a novel requirement for NF-kappaB transactivation in cell chemotaxis mediated by beta1 integrin signals. These results describe signal transduction events that are initiated by type IV collagen through beta1 integrins and demonstrate an important role for NF-kappaB in regulating melanoma chemotaxis.

In vitro characterization and micromechanics of tumor cell chemotactic protrusion, locomotion, and extravasation

The objective of this paper is to introduce some novel in vitro applications in characterizing human melanoma cell protrusion and migration in response to soluble extracellular matrix protein stimulation. Specifically, we describe two assay systems: (1) dual-micropipette manipulation and (2) flow-migration chamber. Applications of the dual-micropipet technique provided kinetic measure of cell movement, cyclic pseudopod protrusion, and subsequent cell locomotion governed by chemotactic molecular transport dynamics. Chemotactic concentration gradient was found to influence significantly pseudopod protrusion frequency and locomotion speed, but not the protrusion extension. To further characterize active tumor cell extravasation, a process that involves dynamic tumor cell adhesion to vascular endothelium under flow conditions and subsequent transendothelial migration in response to chemotactic signals from the interstitial space, we developed a flow-migration chemotaxis system. This assay enabled characterization of tumor cell transcellular migration in terms of chemotactic signal gradients, shear forces, and cell-substrate adhesion. Results suggest that shear flow plays significant roles in tumor cell extravasation that is regulated by both tumor cell motility and tumor cell adhesion to endothelial molecules in a cooperative process.