Insulin-like growth factor I-stimulated melanoma cell migration requires phosphoinositide 3-kinase but not extracellular-regulated kinase activation

Mechanisms of Melanoma Progression and Treatment Resistance: Role of Cancer Stem-like Cells

Melanoma is the third most common type of skin cancer, characterized by its heterogeneity and propensity to metastasize to distant organs. Melanoma is a heterogeneous tumor, composed of genetically divergent subpopulations, including a small fraction of melanoma-initiating cancer stem-like cells (CSCs) and many non-cancer stem cells (non-CSCs). CSCs are characterized by their unique surface proteins associated with aberrant signaling pathways with a causal or consequential relationship with tumor progression, drug resistance, and recurrence. Melanomas also harbor significant alterations in functional genes (BRAF, CDKN2A, NRAS, TP53, and NF1). Of these, the most common are the BRAF and NRAS oncogenes, with 50% of melanomas demonstrating the BRAF mutation (BRAFV600E). While the successful targeting of BRAFV600E does improve overall survival, the long-term efficacy of available therapeutic options is limited due to adverse side effects and reduced clinical efficacy. Additionally, drug resistance develops rapidly via mechanisms involving fast feedback re-activation of MAPK signaling pathways. This article updates information relevant to the mechanisms of melanoma progression and resistance and particularly the mechanistic role of CSCs in melanoma progression, drug resistance, and recurrence.

The transcription factor RUNX2 regulates receptor tyrosine kinase expression in melanoma

Receptor tyrosine kinases-based autocrine loops largely contribute to activate the MAPK and PI3K/AKT pathways in melanoma. However, the molecular mechanisms involved in generating these autocrine loops are still largely unknown. In the present study, we examine the role of the transcription factor RUNX2 in the regulation of receptor tyrosine kinase (RTK) expression in melanoma. We have demonstrated that RUNX2-deficient melanoma cells display a significant decrease in three receptor tyrosine kinases, EGFR, IGF-1R and PDGFRβ. In addition, we found co-expression of RUNX2 and another RTK, AXL, in both melanoma cells and melanoma patient samples. We observed a decrease in phosphoAKT2 (S474) and phosphoAKT (T308) levels when RUNX2 knock down resulted in significant RTK down regulation. Finally, we showed a dramatic up regulation of RUNX2 expression with concomitant up-regulation of EGFR, IGF-1R and AXL in melanoma cells resistant to the BRAF V600E inhibitor PLX4720. Taken together, our results strongly suggest that RUNX2 might be a key player in RTK-based autocrine loops and a mediator of resistance to BRAF V600E inhibitors involving RTK up regulation in melanoma.

Insights into the Shc Family of Adaptor Proteins

The Shc family of adaptor proteins is a group of proteins that lacks intrinsic enzymatic activity. Instead, Shc proteins possess various domains that allow them to recruit different signalling molecules. Shc proteins help to transduce an extracellular signal into an intracellular signal, which is then translated into a biological response. The Shc family of adaptor proteins share the same structural topography, CH2-PTB-CH1-SH2, which is more than an isoform of Shc family proteins; this structure, which includes multiple domains, allows for the posttranslational modification of Shc proteins and increases the functional diversity of Shc proteins. The deregulation of Shc proteins has been linked to different disease conditions, including cancer and Alzheimer’s, which indicates their key roles in cellular functions. Accordingly, a question might arise as to whether Shc proteins could be targeted therapeutically to correct their disturbance. To answer this question, thorough knowledge must be acquired; herein, we aim to shed light on the Shc family of adaptor proteins to understand their intracellular role in normal and disease states, which later might be applied to connote mechanisms to reverse the disease state.

Unbalancing p53/Mdm2/IGF-1R axis by Mdm2 activation restrains the IGF-1-dependent invasive phenotype of skin melanoma

Melanoma tumors usually retain wild-type p53; however, its tumor-suppressor activity is functionally disabled, most commonly through an inactivating interaction with mouse double-minute 2 homolog (Mdm2), indicating p53 release from this complex as a potential therapeutic approach. P53 and the tumor-promoter insulin-like growth factor type 1 receptor (IGF-1R) compete as substrates for the E3 ubiquitin ligase Mdm2, making their relative abundance intricately linked. Hence we investigated the effects of pharmacological Mdm2 release from the Mdm2/p53 complex on the expression and function of the IGF-1R. Nutlin-3 treatment increased IGF-1R/Mdm2 association with enhanced IGF-1R ubiquitination and a dual functional outcome: receptor downregulation and selective downstream signaling activation confined to the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway. This Nutlin-3 functional selectivity translated into IGF-1-mediated bioactivities with biphasic effects on the proliferative and metastatic phenotype: an early increase and late decrease in the number of proliferative and migratory cells, while the invasiveness was completely inhibited following Nutlin-3 treatment through an impaired IGF-1-mediated matrix metalloproteinases type 2 activation mechanism. Taken together, these experiments reveal the biased agonistic properties of Nutlin-3 for the mitogen-activated protein kinase pathway, mediated by Mdm2 through IGF-1R ubiquitination and provide fundamental insights into destabilizing p53/Mdm2/IGF-1R circuitry that could be developed for therapeutic gain.

Bergamottin isolated from Citrus bergamia exerts in vitro and in vivo antitumor activity in lung adenocarcinoma through the induction of apoptosis, cell cycle arrest, mitochondrial membrane potential loss and inhibition of cell migration and invasion

The objective of the present study was to investigate the in vitro and in vivo anticancer properties of bergamottin, a natural furanocoumarin, against human non-small cell lung carcinoma (NSCLC) A549 cells. We also studied its effect on cell proliferation, cell cycle arrest, cell invasion, cell migration as well as cell apoptosis. Antiproliferative activity of bergamottin was estimated by the MTT assay. Phase contrast and fluorescence microscopy as well as flow cytometry using Annexin V-FITC assay were used to study induction of apoptosis by bergamottin in these cells. The effects of bergamottin on cell cycle phase distribution as well as on mitochondrial membrane potential were also demonstrated using flow cytometry. In vitro wound healing assay was used to study the effect of bergamottin on cell migration. The effects of bergamottin on tumor progression were also observed using a nude mouse model. The mice were divided into 4 groups and treated with bergamottin injected intraperitoneally. Bergamottin induced dose-dependent as well as time-dependent cytotoxic effects as well as inhibition of colony formation in the A549 cancer cells. Bergamottin also suppressed cancer cell invasion as well as cancer cell migration. Phase contrast microscopy and fluorescence microscopy revealed that bergamottin induced cell shrinkage, chromatin condensation and the cells became rounded and detached from each other. Bergamottin also induced a potent cell cycle arrest at the G2/M phase of the cell cycle. Experiments in mice showed that 25, 50 and 100 mg/kg bergamottin injection reduced the tumor weight from 1.61 g in the phosphate-buffered saline (PBS)-treated group (control) to 1.21, 0.42 and 0.15 g in the bergamottin-treated groups, respectively. The results of the present study revealed that bergamottin was able to inhibit lung cancer cell growth both in a cell model and a xenograft mouse model by inducing apoptosis, mitochondrial membrane potential loss, G2/M cell cycle arrest as well as inhibiting cell migration and invasion.

Effect of Adipocyte Secretome in Melanoma Progression and Vasculogenic Mimicry

Obesity, favored by the modern lifestyle, acquired epidemic proportions nowadays. Obesity has been associated with various major causes of death and morbidity including malignant neoplasms. This increased prevalence has been accompanied by a worldwide increase in cutaneous melanoma incidence rates during the last decades. Obesity involvement in melanoma aetiology has been recognized, but the implicated mechanisms remain unclear. In the present study, we address this relationship and investigate the influence of adipocytes secretome on B16-F10 and MeWo melanoma cell lines. Using the 3T3-L1 adipocyte cell line, as well as ex vivo subcutaneous (SAT) and visceral (VAT) adipose tissue conditioned medium, we were able to show that adipocyte-released factors play a dual role in increasing melanoma cell overall survival, both by enhancing proliferation and decreasing apoptosis. B16-F10 cell migration and cell-cell and cell-matrix adhesion capacity were predominantly enhanced in the presence of SAT and VAT released factors. Melanocytes morphology and melanin content were also altered by exposure to adipocyte conditioned medium disclosing a more dedifferentiated phenotype of melanocytes. In addition, exposure to adipocyte-secreted molecules induced melanocytes to rearrange, on 3D cultures, into vessel-like structures, and generate characteristic vasculogenic mimicry patterns. These findings are corroborated by the released factors profile of 3T3-L1, SAT, and VAT assessed by microarrays, and led us to highlight the mechanisms by which adipose secretome from sub-cutaneous or visceral depots promote melanoma progression. J. Cell. Biochem. 117: 1697-1706, 2016. © 2015 Wiley Periodicals, Inc.

Druggable targets in pediatric neurocutaneous melanocytosis: Molecular and drug sensitivity studies in xenograft and ex vivo tumor cell culture to identify agents for therapy

BACKGROUND

Neurocutaneous melanocytosis (NCM) is a rare congenital disorder that presents with pigmented cell lesions of the brain or leptomeninges in children with large or multiple congenital melanocytic nevi. Although the exact pathological processes involved are currently unclear, NCM appears to arise from an abnormal development of melanoblasts or melanocyte precursors. Currently, it has an extremely poor prognosis due to rapid disease progression and lack of effective treatment modalities.

METHODS

In this study, we report on an experimental approach to examining NCM cells by establishing subcutaneous tumors in nude mice, which can be further expanded for conducting molecular and drug sensitivity experiments.

RESULTS

Analysis of the NRAS gene-coding sequences of an established NCM cell line (YP-MEL) and NCM patient cells revealed heterogeneity in NRAS Q61K that activated mutation and possibly consequential differential sensitivity to MEK inhibition. Gene expression studies were performed to compare the molecular profiles of NCM cells with normal skin fibroblasts. In vitro cytotoxicity screens of libraries of targeted small-molecule inhibitors revealed prospective agents for further evaluation.

CONCLUSIONS

Our studies provide an experimental platform for the generation of NCM cells for preclinical studies and the production of molecular and in vitro data with which to identify druggable targets for the treatment.

A majority of human melanoma cell lines exhibits an S phase-specific defect in excision of UV-induced DNA photoproducts

It is well established that efficient removal of highly-promutagenic UV-induced dipyrimidine photoproducts via nucleotide excision repair (NER) is required for protection against sunlight-associated malignant melanoma. Nonetheless, the extent to which reduced NER capacity might contribute to individual melanoma susceptibility in the general population remains unclear. Here we show that among a panel of 14 human melanoma strains, 11 exhibit significant inhibition of DNA photoproduct removal during S phase relative to G0/G1 or G2/M. Evidence is presented that this cell cycle-specific NER defect correlates with enhanced apoptosis and reduced clonogenic survival following UV irradiation. In addition, melanoma strains deficient in S phase-specific DNA photoproduct removal manifest significantly lower levels of phosphorylated histone H2AX at 1 h post-UV, suggesting diminished activation of ataxia telangiectasia and Rad 3-related (ATR) kinase, i.e., a primary orchestrator of the cellular response to UV-induced DNA replication stress. Consistently, in the case of DNA photoproduct excision-proficient melanoma cells, siRNA-mediated depletion of ATR (but not of its immediate downstream effector kinase Chk1) engenders deficient NER specifically during S. On the other hand simultaneous siRNA-mediated depletion of ataxia telangiectasia mutated kinase (ATM) and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) exerts no significant effect on either phosphorylation of H2AX at 1 h post-UV or the efficiency of DNA photoproduct removal. Our data suggest that defective NER exclusively during S phase, possibly associated with decreased ATR signaling, may constitute an heretofore unrecognized determinant in melanoma pathogenesis.

Interleukin-24 inhibits cell migration and invasion in the neuroblastoma cell line SH-SY5Y

Neuroblastomas are common pediatric solid tumors with a variable clinical course; approximately 50% of patients present with metastatic disease at diagnosis. The development of metastatic lesions often causes a fatal outcome. Therefore, the prevention of metastases during the early stage of tumor development is critical for the improvement of the prognosis of neuroblastoma patients. We previously observed the suppression of neuroblastoma growth in response to overexpression of interleukin-24 (IL-24) in vitro and in vivo. IL-24 exerts its tumor-suppressive effects by multiple mechanisms, including the balance of Bcl-2 family proteins toward the pro-apoptotic pathway and the activation of the caspase cascade. In this study, we used adenovirus-mediated IL-24 (Ad-IL24) to examine the effect of the ectopic production of IL-24 on cell migration and invasion in human neuroblastoma cells. We found that IL-24 effectively inhibits SH-SY5Y neuroblastoma cell migration and invasion by changing subcellular localization and cellular levels of β-catenin and regulating the levels of proteins associated with cell migration and invasion. Thus, IL-24 should be considered a therapeutic agent that can inhibit primary neuroblastoma growth and that may prevent metastasis.

Diallyl sulfide, diallyl disulfide, and diallyl trisulfide inhibit migration and invasion in human colon cancer colo 205 cells through the inhibition of matrix metalloproteinase-2, -7, and -9 expressions

Diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS) are major organosulfur compounds exiting in garlic (Allium sativum). These compounds are reported to exhibit various pharmacological properties such as antibacteria, antiangiogenesis, anticancer, and anticoagulation, and they also induce cytotoxicity and induction of apoptosis in human cancer cells. Although these compounds show wide spectrum of biological activities, there are no reports to show that DAS, DADS, and DATS affected migration and invasion of human colon cancer cells, and their exact molecular mechanisms are not well investigated. Therefore, the purpose of this study was to determine whether DAS, DADS, and DATS affected the invasion and migration abilities of colo 205 human colon cancer cells. The results indicate that DAS, DADS, and DATS at 10 and 25 μM inhibited the migration and invasion of colo 205 cells in the order of DATS < DADS < DAS. DATS is the highest for inhibition of migration and invasion of colo 205 cells. DAS, DADS, and DATS induce downregulation expression of PI3K, Ras, MEKK3, MKK7, ERK1/2, JNK1/2, and p38 and then lead to the inhibition of MMP-2, -7, and -9. DAS, DADS, and DATS inhibited NF-κB and COX-2 for leading to the inhibition of cell proliferation. Taken together, these results demonstrated that application of DAS, DADS, and DATS might serve as potential antimetastatic drugs.

Silencing of a large microRNA cluster on human chromosome 14q32 in melanoma: biological effects of mir-376a and mir-376c on insulin growth factor 1 receptor

Background

Metastatic melanoma is a devastating disease with limited therapeutic options. MicroRNAs (miRNAs) are small non coding RNA molecules with important roles in post-transcriptional gene expression regulation, whose aberrant expression has been implicated in cancer.

Results

We show that the expression of miRNAs from a large cluster on human chromosome 14q32 is significantly down-regulated in melanoma cell lines, benign nevi and melanoma samples relative to normal melanocytes. This miRNA cluster resides within a parentally imprinted chromosomal region known to be important in development and differentiation. In some melanoma cell lines, a chromosomal deletion or loss-of-heterozygosity was observed in the cis-acting regulatory region of this cluster. In several cell lines we were able to re-express two maternally-induced genes and several miRNAs from the cluster with a combination of de-methylating agents and histone de-acetylase inhibitors, suggesting that epigenetic modifications take part in their silencing. Stable over-expression of mir-376a and mir-376c, two miRNAs from this cluster that could be re-expressed following epigenetic manipulation, led to modest growth retardation and to a significant decrease in migration in-vitro. Bioinformatic analysis predicted that both miRNAs could potentially target the 3'UTR of IGF1R. Indeed, stable expression of mir-376a and mir-376c in melanoma cells led to a decrease in IGF1R mRNA and protein, and a luciferase reporter assay indicated that the 3'UTR of IGF1R is a target of both mir-376a and mir-376c.

Conclusions

Our work is the first to show that the large miRNA cluster on chromosome 14q32 is silenced in melanoma. Our results suggest that down-regulation of mir-376a and mir-376c may contribute to IGF1R over-expression and to aberrant negative regulation of this signaling pathway in melanoma, thus promoting tumorigenesis and metastasis.

An insulin-like growth factor 1 receptor inhibitor induces CYP3A4 expression through a pregnane X receptor-independent, noncanonical constitutive androstane receptor-related mechanism

Inhibition of insulin-like growth factor-1 receptor (IGF-1R) signaling represents an attractive therapeutic strategy for cancer treatment. A first-generation IGF-1R inhibitor (R)-4-(3-(3-chlorophenyl)-3-hydroxypropyl)-3-(4-methyl-6-morpholino-1H-benzo[d]imidazol-2-yl)pyridin-2(1H)-one (BMS-536924), however, was associated with potent CYP3A4 induction mediated by pregnane X receptor (PXR; NR1I2) transactivation. Structural activity-based modification led to the synthesis of 4-(1-(2-(4-((2-(4-chloro-1H-pyrazol-1-yl)ethyl)amino)-2-oxo-1,2-dihydropyridin-3-yl)-4-methyl-1H-benzo[d]imidazol-6-yl)piperidin-4-yl) piperazine-1-carboxylate (BMS-665351) with no PXR activity while maintaining its ability to inhibit IGF-1R. However, BMS-665351 significantly induces CYP3A4 expression in human primary hepatocytes (HPHs). Here, we report a novel nonclassical constitutive androstane receptor (CAR; NR1I3)-related pathway of BMS-665351-mediated CYP3A4 induction. BMS-665351 treatment resulted in the significant induction of CYP3A4 in HPHs and HepG2 cells, but failed to activate either PXR or CAR in cell-based reporter assays. Moreover, BMS-665351 at concentrations that induce CYP3A4 expression was unable to translocate human CAR from the cytoplasm to the nucleus of HPHs, which represents the initial step of CAR activation. Nevertheless, quantitative polymerase chain reaction analysis demonstrated that BMS-665351 significantly enhanced the expression of CYP3A4 in CAR- but not PXR-transfected HepG2 and Huh7 cells. It is noteworthy that BMS-665351 selectively induced the expression of CAR but not PXR in all tested hepatic cell systems. Synergistic induction of CYP3A4 was observed in HPHs cotreated with BMS-665351 and prototypical activators of CAR but not PXR. In summary, our results indicate that BMS-665351-mediated induction of CYP3A4 is CAR-dependent, but BMS-665351 itself is not a typical activator of either CAR or PXR, rather it functions as a selective inducer of CAR expression and increases CYP3A4 through a noncanonical CAR-related mechanism.

Survivin enhances motility of melanoma cells by supporting Akt activation and {alpha}5 integrin upregulation

Survivin expression in melanoma is inversely correlated with patient survival. Transgenic mice harboring melanocyte-specific overexpression of survivin exhibit increased susceptibility to UV-induced melanoma and metastatic progression. To understand the mechanistic basis for metastatic progression, we investigated the effects of survivin on the motility of human melanocytes and melanoma cells. We found that survivin overexpression enhanced migration on fibronectin and invasion through Matrigel, whereas survivin knockdown under subapoptotic conditions blocked migration and invasion. In melanocytes, survivin overexpression activated the Akt and mitogen-activated protein kinase pathways. Akt phosphorylation was required for survivin-enhanced migration and invasion, whereas Erk phosphorylation was required only for enhanced invasion. In both melanocytes and melanoma cells, survivin overexpression was associated with upregulation of α5 integrin (fibronectin receptor component), the antibody-mediated blockade or RNA interference-mediated knockdown of which blocked survivin-enhanced migration. Knockdown of α5 integrin did not affect Akt activation, but inhibition of Akt phosphorylation prevented α5 integrin upregulation elicited by survivin overexpression. Together, our results showed that survivin enhanced the migration and invasion of melanocytic cells and suggested that survivin may promote melanoma metastasis by supporting Akt-dependent upregulation of α5 integrin.

RT-PCR-based tyrosine kinase display profiling of canine melanoma: IGF-1 receptor as a potential therapeutic target

Canine malignant melanoma (CMM) resembles human malignant melanoma in terms of metastatic behavior, refractoriness to standard therapy, and tumor antigen expression but it is largely unknown how CMM resembles human melanoma with regard to molecular pathogenesis and cellular signaling. No attempt has been made to systematically define the repertoire of tyrosine kinases (TKs) expressed in CMM. This study used a reverse transcription-PCR display technique to evaluate the expression of multiple TKs in the 17CM98 CMM cell line. RT-PCR was performed using degenerate primers coding for highly conserved regions flanking the kinase domains of many TKs and the repertoire of TKs expressed was determined using standard molecular cloning techniques. Sequencing 46 clones yielded canine homologs of insulin-like growth factor-1 receptor (IGF-1R) (50%), JAK1 (17%), PDGFR-a (11%), FGFR1 (9%), Axl (7%), Abl (4%), and PTK2 (2%). Interestingly, IGF-1R, JAK1, and Axl were detected in human melanoma using similar techniques, supporting the cross-species validity of this assay. Given the abundance of IGF-1R clones, we determined the biological effect of rhIGF-1 in 17CM98 cells. IGF-1 stimulated cell proliferation and vascular endothelial growth factor production in 17CM98, and addition of the IGF-1R inhibitor ADW742 abrogated IGF-1-induced phenotypic changes. Expression of IGF-1R mRNA was detected in five of five additional CMM cell cultures, and IGF-1R protein was detected in five of six primary tumors evaluated, suggesting that IGF-1R expression may be common in CMM and may provide a novel target for future therapy. In conclusion, this study suggests that similar TKs are expressed in human and canine melanoma, and shows potential antitumor effects of IGF-1R inhibition in CMM.

Phosphoglucose isomerase/autocrine motility factor promotes melanoma cell migration through ERK activation dependent on autocrine production of interleukin-8

It is well known that phosphoglucose isomerase/autocrine motility factor (AMF) promotes cell migration in an autocrine manner in various tumor cells. However, it remains unclear whether certain cytokines modulate the effects of AMF on tumor cell migration. Because interleukin (IL)-8, a proinflammatory cytokine, is produced by melanoma cells and has been correlated with melanoma migration, the migratory ability of melanoma cells induced by AMF may also involve induction of IL-8 expression. In the present study, we assessed whether AMF promotes melanoma cell migration through autocrine production of IL-8. We found that AMF stimulation increased IL-8 production through up-regulation of IL-8 mRNA transcription, especially in biologically early stage melanoma cells. AMF-induced migration of these cells was inhibited by a specific neutralizing antibody against IL-8. The IL-8 production induced by AMF was mediated by the ERK1/2 pathways. These findings suggest that melanoma migration induced by AMF is mediated by autocrine production of IL-8 as a novel downstream modulator of the AMF signaling pathway.

Rac activation and inactivation control plasticity of tumor cell movement

Tumor cells exhibit two different modes of individual cell movement. Mesenchymal-type movement is characterized by an elongated cellular morphology and requires extracellular proteolysis. In amoeboid movement, cells have a rounded morphology, are less dependent on proteases, and require high Rho-kinase signaling to drive elevated levels of actomyosin contractility. These two modes of cell movement are interconvertible. We show that mesenchymal-type movement in melanoma cells is driven by activation of the GTPase Rac through a complex containing NEDD9, a recently identified melanoma metastasis gene, and DOCK3, a Rac guanine nucleotide exchange factor. Rac signals through WAVE2 to direct mesenchymal movement and suppress amoeboid movement through decreasing actomyosin contractility. Conversely, in amoeboid movement, Rho-kinase signaling activates a Rac GAP, ARHGAP22, that suppresses mesenchymal movement by inactivating Rac. We demonstrate tight interplay between Rho and Rac in determining different modes of tumor cell movement, revealing how tumor cells switch between different modes of movement.

Protein kinase C-betaII represses hepatocyte growth factor-induced invasion by preventing the association of adapter protein Gab1 and phosphatidylinositol 3-kinase in melanoma cells

The hepatocyte growth factor (HGF) signaling pathway was examined in human normal melanocytes and three malignant melanoma cell lines. HGF-induced activation of c-Met, its receptor-tyrosine kinase, was observed in both melanocytes and melanoma cells, whereas phosphatidylinositol 3-kinase (PI3K), a downstream target of c-Met, was not activated in the melanocytes but enhanced in the melanoma cell lines. The electrophoretic mobility of Gab1, the scaffolding adapter protein that couples activated c-Met and PI3K, was slower in the melanocytes than that in the melanoma cells, and the mobility shifted to that of the melanoma cells after treatment with alkaline phosphatase, indicating that Gab1 is highly phosphorylated on serine and threonine in the melanocytes. Introduction of protein kinase C (PKC)-betaII into the melanoma cells, which is expressed in melanocytes but absent in melanoma cells, resulted in serine and threonine phosphorylation of Gab1 and also prevented tyrosine phosphorylation of Gab1 and its association with PI3K. Furthermore, the introduction of PKC-betaII suppressed HGF-induced activation of PI3K, and attenuated the in vitro invasion activity of the melanoma cells. These results indicate that the HGF signaling process from Gab1 to PI3K is negatively regulated by PKC-betaII, and its loss is critical for melanoma cells to gain invasive potential.

RaLP, a New Member of the Src Homology and Collagen Family, Regulates Cell Migration and Tumor Growth of Metastatic Melanomas

The Src homology and collagen (Src) family of adaptor proteins comprises six Shc-like proteins encoded by three loci in mammals (Shc, Rai, and Sli). Shc-like proteins are tyrosine kinase substrates, which regulate diverse signaling pathways and cellular functions, including Ras and proliferation (p52/p46Shc), phosphatidylinositol 3-kinase and survival (p54Rai), and mitochondrial permeability transition and apoptosis (p66Shc). Here, we report the identification, cloning, and sequence characterization of a new member of the Shc family that we termed RaLP. RaLP encodes a 69-kDa protein characterized by the CH2-PTB-CH1-SH2 modularity, typical of the Shc protein family, and expressed, among adult tissues, only in melanomas. Analysis of RaLP expression during the melanoma progression revealed low expression in normal melanocytes and benign nevi, whereas high levels of RaLP protein were found at the transition from radial growth phase to vertical growth phase and metastatic melanomas, when tumor cells acquire migratory competence and invasive potential. Notably, silencing of RaLP expression in metastatic melanomas by RNA interference reduced tumorigenesis in vivo. Analysis of RaLP in melanoma signal transduction pathways revealed that (a) when ectopically expressed in RaLP-negative melanocytes and nonmetastatic melanoma cells, it functions as a substrate of activated insulin-like growth factor-1 and epidermal growth factor receptors and increases Ras/mitogen-activated protein kinase (MAPK) signaling and cell migration, whereas (b) its silencing in RaLP-positive melanoma cells abrogates cell migration in vitro, without affecting MAPK signaling, suggesting that RaLP activates both Ras-dependent and Ras-independent migratory pathways in melanomas. These findings indicate that RaLP is a specific marker of metastatic melanomas, a critical determinant in the acquisition of the migratory phenotype by melanoma cells, and a potential target for novel anti-melanoma therapeutic strategies.

Insulin-like growth factors control cell migration in health and disease

Insulin-like growth factors I and II (IGF-I and IGF-II) have an ancient origin and play essential roles in fundamental biological processes. Although IGFs are principally known for their roles in regulating cell growth and survival, their ability to influence cell motility is just as significant. In the past 20 years, research has provided indisputable evidence for the regulatory role of IGFs in the migration of various cell types. Cell migration is crucial for reproduction, development, and tissue regeneration; IGFs play an important role in coordinating these processes. Moreover, studies continue to uncover the IGFs' role in stimulating cancer cell migration, invasion and metastasis. This review surveys current knowledge on the cell migration-modulating properties of IGFs and the biochemical pathways by which these peptides regulate cell movement in both physiological and pathological conditions.

Regulatory role of c-Met in insulin-like growth factor-I receptor-mediated migration and invasion of human pancreatic carcinoma cells

Pancreatic carcinoma cells overexpress the insulin-like growth factor-I (IGF-I) receptor (IGF-IR) and the hepatocyte growth factor (HGF) receptor, c-Met, which are both known to mediate tumor cell migration and invasion. We hypothesized that IGF-IR and c-Met cooperate to induce migration and invasion of human pancreatic carcinoma cells and that IGF-I-mediated migration and invasion depend on c-Met. Migration and invasion assays were done with the human pancreatic cancer cell line L3.6pl treated with PBS, IGF-I, HGF, or IGF-I plus HGF. To determine if c-Met is necessary for IGF-IR-mediated migration and invasion, c-Met was down-regulated in L3.6pl cells via adenoviral infection with a c-Met ribozyme before IGF-I treatment. IGF-I and HGF increased cell migration and invasion. Furthermore, IGF-I plus HGF had a greater than additive effect on cell migration and invasion compared with either growth factor alone. Down-regulation of c-Met nearly completely inhibited IGF-I-mediated migration and invasion. Our findings suggest that IGF-IR and c-Met cooperate to induce migration and invasion of human pancreatic carcinoma cells. Furthermore, c-Met is required for both HGF- and IGF-I-mediated migration and invasion. Elucidation of the signaling pathways that contribute to tumor progression and metastasis should provide a foundation for the development of targeted therapies for pancreatic carcinoma.

Peroxisome proliferator-activated receptor alpha activation decreases metastatic potential of melanoma cells in vitro via down-regulation of Akt

PURPOSE

Peroxisome proliferator-activated receptors (PPAR) regulate lipid and glucose metabolism but their anticancer properties have been recently studied as well. We previously reported the antimetastatic activity of the PPARalpha ligand, fenofibrate, against melanoma tumors in vivo. Here we investigated possible molecular mechanisms of fenofibrate anti metastatic action.

EXPERIMENTAL DESIGN

Monolayer cultures of mouse (B16F10) and human (SkMell88) melanoma cell lines, soft agar assay, and cell migration assay were used in this study. In addition, we analyzed PPARalpha expression and its transcriptional activity in response to fenotibrate by using Western blots and liciferase-based reporter system.

RESULTS

Fenofibrate inhibited migration of B16F10 and SkMel188 cells in Transwell chambers and colony formation in soft agar. These effects were reversed by PPAR inhibitor, GW9662. Western blot analysis revealed time-dependent down-regulation of Akt and extracellular signal-regulated kinase l/2 phosphorylation in fenofibrate-treated cells. A B16F10 cell line stably expressing constitutively active Akt mutant was resistant to fenofibrate. In contrast, Akt gene silencing with siRNA mimicked the fenofibrate action and reduced the migratory ability of B16F1O cells. In addition, fenofibrate strongly sensitized BI6FIO cells to the proapoptotic drug staurosporine, further supporting the possibility that fenofibrate-induced down-regulation of Akt function contributes to fenofibrate-mediated inhibition of metastatic potential in this experimental model.

CONCLUSIONS

Our results show that the PPAR-dependent antimetastatic activity of fenofibrate involves down-regulation of Akt phosphorylation and suggest that supplementation with this drug may improve the effectiveness of melanoma chemotherapy.

Chemistry and Biology of Moverastins, Inhibitors of Cancer Cell Migration, Produced by Aspergillus

Cancer cell migration is a required step in cancer metastasis. We screened for inhibitors of cancer cell migration of microbial origin, and obtained moverastin, a member of the cylindrol family, from Aspergillus sp. F7720. However, the results of an NMR spectroscopic analysis raised the possibility that moverastin is a mixture of two diastereomers. Separation of the C-10 epimers of synthetic moverastin and a bioassay revealed that both diastereomers (moverastins A and B) had inhibitory effects on cell migration. Furthermore, we demonstrated that moverastins A and B inhibited FTase in vitro, and they also inhibited both the membrane localization of H-Ras and the activation of the PI3K/Akt pathway in EC17 cells. Thus, moverastins inhibited the migration of tumor cells by inhibiting the farnesylation of H-Ras, and subsequent H-Ras-dependent activation of the PI3K/Akt pathway.

beta1A integrin expression is required for type 1 insulin-like growth factor receptor mitogenic and transforming activities and localization to focal contacts

The cells' ability to proliferate in response to growth factor stimulation is significantly altered during cancer progression. To investigate the mechanisms underlying these alterations in prostate cancer, the role and expression of beta1A integrin and type 1 insulin-like growth factor receptor (IGF-IR), known to contribute to cell proliferation and transformation, were analyzed. Using small interfering RNA oligonucleotides to down-regulate beta1A, we show that beta1A expression is required for IGF-IR-mediated prostate cancer cell proliferation and anchorage-independent growth. In vivo, using age-matched transgenic adenocarcinoma of mouse prostate (TRAMP) mice at different stages of prostate cancer [prostatic intraepithelial neoplasia, PIN; well-differentiated adenocarcinoma, WD; and poorly differentiated adenocarcinoma, PD], the expression of beta1A and of IGF-IR was studied. beta1A and IGF-IR expression levels were concurrently up-regulated in high PIN and WD, whereas their expression did not correlate in late-stage PD. In contrast to the up-regulated expression of beta1A, the levels of beta1C, a beta1 cytoplasmic variant that inhibits cell proliferation, were down-regulated in all stages of prostate cancer. A similar expression pattern was observed for a beta1C downstream effector, Grb2-associated binder-1 (Gab1) which is known to inhibit IGF-IR phosphorylation. To analyze in vitro the mechanistic implications of beta1A, beta1C, and Gab1 deregulation in prostate cancer, we investigated whether expression of either beta1 variant in beta1-null cells affected IGF-IR localization. We found that IGF-IR and beta1A were colocalized in highly specialized integrin signaling compartments, designated focal contacts. However, in the presence of beta1C, IGF-IR remained diffuse on the cell surface and did not localize to focal contacts. The findings that beta1 integrins and IGF-IR are concurrently deregulated and that expression of beta1 integrins is necessary to achieve appropriate IGF-IR intracellular distribution point to the important role that the cross-talk between these receptors may have during prostate cancer progression and will be helpful in formulating new therapeutic strategies.

Insulinlike growth factor-I-mediated migration and invasion of human colon carcinoma cells requires activation of c-Met and urokinase plasminogen activator receptor

OBJECTIVE

To determine whether insulinlike growth factor-I (IGF-I) and hepatocyte growth factor (HGF) cooperate to induce migration and invasion of human colorectal carcinoma (CRC) cells and whether the effects of IGF-I and/or HGF are mediated through activation of the urokinase plasminogen activator (uPA)/uPA receptor (uPAR) system, a central mediator of tumor-cell migration and invasion.

SUMMARY BACKGROUND DATA

CRC cells must invade through the basement membrane of the colon and migrate to form metastases. CRC cells are known to overexpress IGF-I receptor (IGF-IR), c-Met, and uPAR, 3 cell-surface receptors known to mediate cell migration and invasion. We hypothesized that IGF-IR and c-Met cooperate to induce migration and invasion in CRC cells and that this signaling is dependent on uPAR.

METHODS

KM12L4 human CRC cells were treated with IGF-I, HGF, or IGF-I + HGF in transwell migration and invasion chambers; cells that had migrated or invaded were counted. To determine the role of c-Met in IGF-I-induced migration and invasion, c-Met was inhibited by infection of cells with an adenovirus containing a c-Met ribozyme; transwell assays were then repeated. To determine the role of the uPA/uPAR system in IGF-I-induced CRC cell migration and invasion, transwell assays were repeated after pretreating cells with the uPA inhibitor amiloride or with neutralizing antibodies to uPA and uPAR.

RESULTS

IGF-I and HGF, alone or in combination, increased cell migration and invasion. The c-Met ribozyme inhibited IGF-I- and HGF-mediated migration and invasion, indicating that c-Met is essential for these processes. uPA and uPAR inhibition blocked IGF-I- and HGF-mediated migration and invasion, suggesting that uPAR is downstream of IGF/IGF-IR and HGF/c-Met in the signaling pathways that mediate cell migration and invasion.

CONCLUSIONS

IGF-I and HGF cooperate to induce migration and invasion of CRC cells, and c-Met and uPA/uPAR are required for IGF-I-mediated migration and invasion. In our in vitro model of CRC migration and invasion, uPA and uPAR appear to be downstream of IGF-IR and c-Met and are required for migration and invasion. Elucidation of the pathways that contribute to tumor progression and metastasis should provide a foundation for the rational development and use of targeted therapies for CRC.

Ectopic production of MDA-7/IL-24 inhibits invasion and migration of human lung cancer cells

We have previously observed the suppression of lung tumor growth in response to overexpression of melanoma differentiation-associated gene-7 (MDA-7)/interleukin-24 (IL-24; approved gene symbol IL24) in vitro and in vivo. MDA-7/IL-24 exerts its tumor-suppressive effects by multiple mechanisms, including the activation of the caspase cascade and the inhibition of angiogenesis. In this study, we used an adenoviral vector (Ad-mda7) to examine the effect of the ectopic production of MDA-7/IL-24 on cell migration and invasion by human non-small-cell lung carcinoma cells. Lung tumor cells (H1299 and A549) treated in vitro with Ad-mda7 migrated and invaded less than cells treated with phosphate-buffered saline (PBS) or Ad-Luc (vector control). MDA-7/IL-24 inhibited migration and invasion by down-regulating the production of phosphatidylinositol 3-kinase/protein kinase B, focal adhesion kinase, and matrix metalloproteinase-2 and -9 relative to PBS and Ad-Luc. Furthermore, tumor cells treated with Ad-mda7 ex vivo or with DOTAP:Chol-mda7 complex in vivo formed significantly fewer tumors in an experimental lung metastasis model. These results show that MDA-7/IL-24 inhibits invasion and migration by lung cancer cells by down-regulating proteins associated with these processes, resulting in reduced metastasis. Thus, Ad-mda7 should be considered a therapeutic agent that can inhibit primary tumor growth and prevent metastasis.

Melanoma chondroitin sulfate proteoglycan enhances FAK and ERK activation by distinct mechanisms

Melanoma chondroitin sulfate proteoglycan (MCSP) is an early cell surface melanoma progression marker implicated in stimulating tumor cell proliferation, migration, and invasion. Focal adhesion kinase (FAK) plays a pivotal role in integrating growth factor and adhesion-related signaling pathways, facilitating cell spreading and migration. Extracellular signal–regulated kinase (ERK) 1 and 2, implicated in tumor growth and survival, has also been linked to clinical melanoma progression. We have cloned the MCSP core protein and expressed it in the MCSP-negative melanoma cell line WM1552C. Expression of MCSP enhances integrin-mediated cell spreading, FAK phosphorylation, and activation of ERK1/2. MCSP transfectants exhibit extensive MCSP-rich microspikes on adherent cells, where it also colocalizes with α4 integrin. Enhanced activation of FAK and ERK1/2 by MCSP appears to involve independent mechanisms because inhibition of FAK activation had no effect on ERK1/2 phosphorylation. These results indicate that MCSP may facilitate primary melanoma progression by enhancing the activation of key signaling pathways important for tumor invasion and growth.