The extracellular matrix (ECM) is a complex network of extracellular-secreted macromolecules, such as collagen, enzymes and glycoproteins, whose main functions deal with structural scaffolding and biochemical support of cells and tissues. ECM homeostasis is essential for organ development and functioning under physiological conditions, while its sustained modification or dysregulation can result in pathological conditions. During cancer progression, epithelial tumor cells may undergo epithelial-to-mesenchymal transition (EMT), a morphological and functional remodeling, that deeply alters tumor cell features, leading to loss of epithelial markers (i.e., E-cadherin), changes in cell polarity and intercellular junctions and increase of mesenchymal markers (i.e., N-cadherin, fibronectin and vimentin). This process enhances cancer cell detachment from the original tumor mass and invasiveness, which are necessary for metastasis onset, thus allowing cancer cells to enter the bloodstream or lymphatic flow and colonize distant sites. The mechanisms that lead to development of metastases in specific sites are still largely obscure but modifications occurring in target tissue ECM are being intensively studied. Matrix metalloproteases and several adhesion receptors, among which integrins play a key role, are involved in metastasis-linked ECM modifications. In addition, cells involved in the metastatic niche formation, like cancer associated fibroblasts (CAF) and tumor associated macrophages (TAM), have been found to play crucial roles in ECM alterations aimed at promoting cancer cells adhesion and growth. In this review we focus on molecular mechanisms of ECM modifications occurring during cancer progression and metastatic dissemination to distant sites, with special attention to lung, liver and bone. Moreover, the functional role of cells forming the tumor niche will also be reviewed in light of the most recent findings.

Activation of the cAMP-dependent protein kinase A (PKA) pathway may induce cAMP-response elementbinding protein (CREB) phosphorylation either directly or via cross-talk mechanisms with other signal transduction pathways. In this study, we have investigated in striatal primary cultures the mechanism by which activation of the cAMP/PKA-dependent pathway leads to CREB phosphorylation via the extracellular signal-regulated kinase (ERK)-dependent pathway. We have found that PKA-induced CREB phosphorylation and CREB-dependent transcription are mediated by calcium (Ca 2؉ ) release from intracellular stores and are blocked by inhibitors of the protein kinase C and ERK pathways. This mechanism appears to be mediated by the small G-protein Rap1, whose activation appears to be primed by PKA-induced Ca 2؉ release but not further induced by direct or indirect PKA-or protein kinase C-dependent phosphorylation. These results suggest that, in striatal neurons, intracellular Ca 2؉ release, Rap1, and ERK pathway play a crucial role in the PKA-induced CREB phosphorylation and CREB-dependent transcription.The dopaminergic striatal system is the main target of the antipsychotic agents used in the treatment of schizophrenia (1) and of the psychostimulant drugs cocaine and amphetamines (2). The prolonged administration of these drugs increases the synaptic availability of dopamine and induces many dopaminedependent adaptive responses culminating in the transcription of striatal cAMP-response element (CRE) 1 -dependent genes, such as the immediate early gene c-fos and the neuropeptides dynorphin, substance P, and enkephalins. CREB phosphorylation, initially thought to be mediated exclusively by the cAMP/protein kinase A (PKA) pathway (3), is also induced by Ca 2ϩ -dependent signal transduction pathways. Two members of the Ca 2ϩ /calmodulin-dependent kinase family (CaMK), CaMKII (4) and CaMKIV (5, 6), are activated by Ca 2ϩ entry through an L-type voltage-sensitive Ca 2ϩ channel or glutamate N-methyl-D-aspartic acid (NMDA) receptors (7) and induce CREB phosphorylation. Moreover, Ca 2ϩ influx via Ltype voltage-sensitive Ca 2ϩ channel or ␣-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors and the release of Ca 2ϩ from intracellular stores, elicited by the stimulation of growth factors receptors, activate the extracellular signal-related protein kinase (ERK)/mitogen-activated protein kinase pathway and induce CREB phosphorylation via the ribosomal S6 kinase 2 in PC12 cells (8,9), in primary neuronal cultures (10, 11), and in brain slices (12).The ERK pathway plays a pivotal role in stimulus-dependent gene regulation in the central nervous system, because pharmacological manipulations of the ERK pathway functionality affect the synaptic plasticity mechanisms supposed to underlie learning and memory (13). The cascade responsible of the ERK pathway activation requires the stimulus-dependent recruitment of the small G protein Ras, which in turn activates the Raf and MEK kinases. Although Ca 2ϩ -dependent activation of Ras has be...

The vasoconstrictor peptide endothelin (ET-1) exerts its physiological and pathological effects via activation of ET(A) and ET(B) receptor (ET-R) subtypes. In this study, we demonstrate that both ET-R subtypes are highly expressed in rat astrocytes in vivo, indicating that these cells are potential targets of the biological effects of ET-1 in the brain. In cultured cortical astrocytes, both ET-R subtypes are expressed, and selective stimulation of ET(B)-R with ET-1 induces phosphorylation of cAMP response element-binding protein (CREB). The signal transduction pathway activated by ET-1 includes the Rap1/B-Raf and the Ras/Raf-1 complexes, protein kinase C (PKC) together with extracellular signal-regulated kinases (ERK), and the ribosomal S6 kinase (RSK) isoforms RSK2 and RSK3, two kinases that lie immediately downstream of ERK and are able to phosphorylate CREB. Moreover, ET-1 activates the p38 mitogen-activated protein kinase (MAPK)-dependent, but not the c-jun N-terminal kinase (JNK)-dependent pathway. By using selective protein kinase inhibitors and expression of dominant-negative Rap1 protein, we also found that the Rap1/PKC/ERK-dependent pathway induces the phosphorylation of activating transcription factor-1, CREB, and Elk-1, whereas the p38MAPK-dependent pathway only causes CREB phosphorylation. ET-1-induced transcription of the immediate early gene c-fos requires the concomitant activation of both the PKC/ERK- and p38MAPK-dependent pathways, because inhibitors of either pathway block the ET-1-induced increase of c-fos mRNA. Our findings indicate that changes in the expression of cAMP response element-dependent immediate and delayed response genes could play a pivotal role in the physiological effects elicited by ET-1 in astrocytes.

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Glioblastoma is known to be one of the most lethal and untreatable human tumors. Surgery and radiotherapy in combination with classical alkylating agents such as temozolomide offer little hope to escape a poor prognosis. For these reasons, enormous efforts are currently devoted to refine in vivo and in vitro models with the specific goal of finding new molecular aberrant pathways, suitable to be targeted by a variety of therapeutic approaches, including novel pharmaceutical formulations and immunotherapy strategies. In this review, we will first discuss current molecular classification based on genomic and transcriptomic criteria. Also, the state of the art in current clinical practice for glioblastoma therapy in the light of the recent molecular classification, together with ongoing phases II and III clinical trials, will be described. Finally, new pharmaceutical formulations such as nanoparticles and viral vectors, together with new strategies entailing the use of monoclonal antibodies, vaccines and immunotherapy agents, such as checkpoint inhibitors, will also be discussed.

In cancer cells integrins modulate important cellular events that regulate the metastasic cascade which involves detachment from the tumor mass, dissemination and attachment to the oncogenic niche. The α5β1, αvβ3 and αvβ5 integrins are widely expressed in different cancer types and recognize the tripeptide Arg-Gly-Asp (RGD) motif present in several extracellular matrix proteins. In human glioblastoma, αvβ3 integrin expression correlates with tumor grade, suggesting that this integrin may play a crucial role in the highly infiltrative behavior of high grade gliomas. However, few selective RGD-like antagonists have been developed and few studies have investigated their effects in in vitro models of human glioblastoma. In this study, we investigated several cellular effects and the underlying molecular mechanisms exerted by a new small-molecule RGD antagonist, 1a-RGD, in the U251 and U373 human glioblastoma cell lines. Treatment with 1a-RGD (20 μM) demonstrated a weak effect on cell viability and cell proliferation but strongly inhibited cell attachment and cell migration together with actin cytoskeleton disassembly. Prolonged 1a-RGD treatment (72 h) induced anoikis, assessed by Annexin staining and nucleosome assay, particularly in the detached cells. When integrin-linked transduction pathways were investigated, 1aRGD was found to exert a marked reduction in focal adhesion kinase (FAK) phosphorylation without affecting the AKT- and ERK-dependent pathways. Our data indicate that 1a-RGD, probably via modulation of the FAK-dependent pathway, inhibits cell migration and attachment and induces anoikis in glioblastoma cells. This novel finding suggests that the development of an RGD-like molecule may represent a promising tool for the pharmacological approach aimed at reducing the malignancy of glioblastoma cells.

Despite the interest aroused by sigma receptors (SRs) in the area of oncology, their role in tumor biology remains enigmatic. The predominant subcellular localization and main site of activity of SRs are the endoplasmic reticulum (ER). Current literature data, including recent findings on the sigma 2 receptor subtype (S2R) identity, suggest that SRs may play a role as ER stress gatekeepers. Although SR endogenous ligands are still unknown, a wide series of structurally unrelated compounds able to bind SRs have been identified. Currently, the identification of novel antiproliferative molecules acting via SR interaction is a challenging task for both academia and industry, as shown by the fact that novel anticancer drugs targeting SRs are in the preclinical-stage pipeline of pharmaceutical companies (i.e., Anavex Corp. and Accuronix). So far, no clinically available anticancer drugs targeting SRs are still available. The present review focuses literature advancements and provides a state-of-the-art overview of SRs, with emphasis on their involvement in cancer biology and on the role of SR modulators as anticancer agents. Findings from preclinical studies on novel anticancer drugs targeting SRs are presented in brief.

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