Role of phosphodiesterase 1 in the pathophysiology of diseases and potential therapeutic opportunities.

Cyclic nucleotide phosphodiesterases (PDEs) are superfamily of enzymes that regulate the spatial and temporal relationship of second messenger signaling in the cellular system. Among the 11 different families of PDEs, phosphodiesterase 1 (PDE1) sub-family of enzymes hydrolyze both 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) in a mutually competitive manner. The catalytic activity of PDE1 is stimulated by their binding to Ca2+/calmodulin (CaM), resulting in the integration of Ca2+ and cyclic nucleotide-mediated signaling in various diseases. The PDE1 family includes three subtypes, PDE1A, PDE1B and PDE1C, which differ for their relative affinities for cAMP and cGMP. These isoforms are differentially expressed throughout the body, including the cardiovascular, central nervous system and other organs. Thus, PDE1 enzymes play a critical role in the pathophysiology of diseases through the fundamental regulation of cAMP and cGMP signaling. This comprehensive review provides the current research on PDE1 and its potential utility as a therapeutic target in diseases including the cardiovascular, pulmonary, metabolic, neurocognitive, renal, cancers and possibly others.

Autotaxin signaling via lysophosphatidic acid receptors contributes to vascular endothelial growth factor-induced endothelial cell migration.

Important roles for vascular endothelial growth factor (VEGF) and autotaxin (ATX) have been established for embryonic vasculogenesis and cancer progression. We examined whether these two angiogenic factors cooperate in regulation of endothelial cell migratory responses. VEGF stimulated expression of ATX and LPA1, a receptor for the ATX enzymatic product lysophosphatidic acid (LPA), in human umbilical vein endothelial cells. Knockdown of ATX expression significantly decreased mRNA levels for the receptors LPA1, LPA2, S1P1, S1P2, S1P3, and VEGFR2 and abolished cell migration to lysophosphatidylcholine, LPA, recombinant ATX, and VEGF. Migration to sphingosylphosphorylcholine and sphinogosine-1-phosphate was also reduced in ATX knockdown cells, whereas migration to serum remained unchanged. Furthermore, ATX knockdown decreased Akt2 mRNA levels, whereas LPA treatment strongly stimulated Akt2 expression. We propose that VEGF stimulates LPA production by inducing ATX expression. VEGF also increases LPA1 signaling, which in turn increases Akt2 expression. Akt2 is strongly associated with cancer progression, cellular migration, and promotion of epithelial-mesenchymal transition. These data show a role for ATX in maintaining expression of receptors required for VEGF and lysophospholipids to accelerate angiogenesis. Because VEGF and ATX are upregulated in many cancers, the regulatory mechanism proposed in these studies could apply to cancer-related angiogenesis and cancer progression. These data further suggest that ATX could be a prognostic factor or a target for therapeutic intervention in several cancers.

Autotaxin.

Autotaxin is a protein of approximately 900 amino acids discovered in the early 1990s. Over the past 15 years, a strong association between cancer cells and autotaxin production has been observed. Recent publications indicate that autotaxin and the capacity of cancer to metastasise are intimately linked. The discovery of new molecular targets in pharmacology is a mixture of pure luck, hard work and industrial strategy. Despite a crucial and desperate need for new therapeutic tools, many targets are approached in oncology, but only a few are validated and end up at the patient bed. Outside the busy domain of kinases, few targets have been discovered that can be useful in treating cancer, particularly metastatic processes. The fortuitous relationship between autotaxin and lysophosphatidic acid renders the results of observations made in the diabetes/obesity context considerably important. The literature provides observations that may aid in redesigning experiments to validate autotaxin as a potential oncology target.

TCDD induces cell migration via NFATc1/ATX-signaling in MCF-7 cells.

Breast cancer is characterized, among others, by the concurrence of lipophilic xenobiotica such as 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) with hypoxic tissue conditions. This condition activates the transcription factors hypoxia inducible factor-1alpha (HIF-1alpha) and aryl hydrocarbon receptor (AhR) that are known to promote tumor progression. An interrelation between these transcription factors and nuclear factor of activated T-cells (NFAT) was implied by gene array analysis. In the present study, the interplay of the three transcription factors was studied and correlated with the migration of MCF-7 cells in response to TCDD and/or hypoxia. An AhR-activation by 10nM TCDD and HIF-1alpha activation by 5% oxygen induced activation of NFATc1. The effects were inhibited by cyclosporine A (CsA), suggesting that the activation of NFAT by AhR or HIF-1alpha signaling is calcineurin-dependent. The expression/activity of the NFAT target gene autotaxin (ATX) was increased. ATX is known to stimulate migration of tumor cells. The hydrolysis product of ATX, lysophosphatidic acid (LPA), increased the migration of MCF-7 cells under normoxia but not under hypoxia. This effect correlated with increased migration observed after TCDD treatment. Hypoxia did not promote migration of MCF-7 cells, suggesting that ATX down-stream signaling was inhibited by hypoxia. In conclusion, the TCDD-mediated activation of NFATc1 is suggested to promote cell migration via ATX/LPA-signaling.