Extracellular nucleotides as novel, underappreciated pro-metastatic factors that stimulate purinergic signaling in human lung cancer cells

Abstract

BackgroundOne of the challenging problems of current radio-chemotherapy is recurrence and metastasis of cancer cells that survive initial treatment. We propose that one of the unwanted effects of radiochemotherapy is the release from damaged (“leaky”) cells of nucleotides such as ATP and UTP that exert pro-metastatic functions and can directly stimulate chemotaxis of cancer cells.MethodsTo address this problem in a model of human lung cancer (LC), we employed several complementary in vitro and in vivo approaches to demonstrate the role of extracellular nucleotides (EXNs) in LC cell line metastasis and tumor progression. We measured concentrations of EXNs in several organs before and after radiochemotherapy. The purinergic receptor agonists and antagonists, inhibiting all or selected subtypes of receptors, were employed in in vitro and in vivo pro-metastatic assays.ResultsWe found that EXNs accumulate in several organs in response to radiochemotherapy, and RT-PCR analysis revealed that most of the P1 and P2 receptor subtypes are expressed in human LC cells. EXNs were found to induce chemotaxis and adhesion of LC cells, and an autocrine loop was identified that promotes the proliferation of LC cells. Most importantly, metastasis of these cells could be inhibited in immunodeficient mice in the presence of specific small molecule inhibitors of purinergic receptors.ConclusionsBased on this result, EXNs are novel pro-metastatic factors released particularly during radiochemotherapy, and inhibition of their pro-metastatic effects via purinergic signaling could become an important part of anti-metastatic treatment.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-015-0469-z) contains supplementary material, which is available to authorized users.

Sheath Cell Invasion and Trans-differentiation Repair Mechanical Damage Caused by Loss of Caveolae in the Zebrafish Notochord

“…We then performed a quantitative LC-MS [23] for UTP and ATP and found that both were significantly enriched in NP compared to AF (Fig.3E). Interestingly, nucleotide release has been shown to promote cell migration in zebrafish [24], and mammals [25, 26]. Moreover, UTP has been found accumulating within lysosomes [27, 28], and we showed previously that notochord vacuoles are lysosome related organelles [2].…”

Nucleotides and nucleoside signaling in the regulation of the epithelium to mesenchymal transition (EMT)

“…Importantly, it was shown that UDP is released in response to chemotherapy, highlighting a putative mechanism for drug resistance [101]. This observation is relevant from a translational perspective and it suggests that the P2Y6 receptor is a potential pharmacological target in breast cancer; moreover, it emphasizes the role played by released nucleotides (ATP and UTP) during radiochemotherapy as strong pro-metastatic factors [102].…”

Does it make sense to target one tumor cell chemotactic factor or its receptor when several chemotactic axes are involved in metastasis of the same cancer?

“…Human cells in murine tissues can be detected directly by FACS if the injected cells carry fluorescent markers (e.g., transduced with the gene encoding GFP protein or labeled ex vivo with PKH26) or indirectly by detecting human DNA in murine tissues using RQ-PCR (e.g., to detect human DNA specific for α satellite sequences) and comparing the amplification result to a standard curve established by mixing human and murine cells in different ratios [8,20]. From the percentage of human DNA present in DNA extracts, we can estimate how many human cells were present in a given organ using this standard curve [8,24]. Before injection into experimental animals, the cancer cells may be stimulated with pro-metastatic factors or exposed to the inhibitor of their corresponding receptors.…”

“…Finally, metastasis and migration of RMS cells are also affected by several other factors, such as extracellular microvesicles (ExMVs) [59,60], thrombin [12], and even extracellular nucleotides (e.g., ATP, UTP) [24]. The list of these factors is still open, and new candidates are being identified.…”

“…In this review we will summarize several years of experience in identifying and blocking crucial pro-metastatic axes involved in the metastasis of human rhabdomyosarcoma (RMS) cells [6,12,[20][21][22][23][24][25]. Our observations, obtained with an RMS cell metastasis model, are also relevant to other types of malignancies, as significant redundancy in pro-metastatic ligand-receptor axes exists for almost all tumor types studied so far.…”