ABSTRACT
Eicosapentaenoic acid (EPA), an n-3 polyunsaturated fatty acid that is abundant in the fish-based diets of populations that exhibit a remarkably low incidence of cancer, exerts anticancer activity in vitro and in animal models of experimental cancer. Here we define the molecular basis for the anticancer effects of EPA. EPA inhibits cell division by inhibiting translation initiation. This is a consequence of the ability of EPA to release Ca2+ from intracellular stores while inhibiting their refilling via capacitative Ca2+ influx that results in partial emptying of intracellular Ca2+ stores and thereby activation of protein kinase R. Protein kinase R phosphorylates and inhibits eukaryotic initiation factor 2alpha, resulting in inhibition of protein synthesis at the level of translation initiation, preferentially reducing the synthesis and expression of growth-regulatory proteins, including G1 cyclins, and causes cell cycle arrest in G1. In a KLN-205 squamous cell carcinoma mouse model, daily oral administration of EPA resulted in a significant reduction of tumor size and expression of cyclin D1 in the tumor tissues. Furthermore, EPA-treated tumors showed a significant increase in the proportion of diploid cells, indicative of cell cycle arrest in G0-G1, and a significant reduction of malignant hypertetraploid cells. These results characterize EPA as a member of an emerging new class of anticancer compounds that inhibit translation initiaton.
Subject(s)
Antineoplastic Agents/pharmacology , Eicosapentaenoic Acid/pharmacology , Protein Biosynthesis/drug effects , 3T3 Cells , Administration, Oral , Animals , Calcium/metabolism , Carcinoma, Squamous Cell/drug therapy , Cell Cycle/drug effects , Cyclin D1/metabolism , Cyclin E/metabolism , Dose-Response Relationship, Drug , Eicosapentaenoic Acid/genetics , Female , G1 Phase/drug effects , Mice , Mice, Inbred DBA , Neoplasms, Experimental , Phosphorylation , Ploidies , Resting Phase, Cell Cycle/drug effects , Time Factors , Transfection , Ubiquitins/metabolism , ras Proteins/metabolismABSTRACT
Human testicular capillaries interconnect Leydig cells and seminiferous tubules. Microcirculation and blood flow are therefore essential for the maintenance of spermatogenesis. The expression and the localisation of ET (endothelin) and its receptors in testicular tissue, in seminiferous tubules and in human testicular capillaries were studied. ET-1 mRNA was detected in whole testicular tissue and in seminiferous tubules whereas isolated testicular capillaries were negative. Big ET-1 (Big endothelin 1) and ET peptides were localised in Leydig and Sertoli cells whereas interstitial and intramural capillaries (within the lamina propria) remained unstained. ET was also found in mature spermatids. ET-A (endothelin receptor A) mRNA was detected in seminiferous tubules and whole testicular tissue whereas testicular blood vessels were negative. ET-A immunostaining was displayed in Leydig and Sertoli cells and in spermatids. ET-B (endothelin receptor B) mRNA was detected in whole testicular tissue, seminiferous tubules and in testicular capillaries. ET-B peptide was prominent in Leydig cells, peritubular cells, endothelial cells and pericytes of interstitial and intramural capillaries as well as in vascular endothelial and smooth muscle cells. From these results we conclude that ET produced in Leydig and Sertoli cells can act in a paracrine manner via ET-B on the human testicular microvasculature and the peritubular cells. The presence of both ET-A and ET-B in Leydig cells and of ET-A in Sertoli cells leads to the assumption that ET could influence these cells as an autocrine factor.
Subject(s)
Endothelin-1/analysis , Endothelin-2/analysis , Receptors, Endothelin/analysis , Testis/chemistry , Blotting, Southern , DNA Primers/chemistry , Endothelin-1/genetics , Endothelin-2/genetics , Humans , Immunoenzyme Techniques , Leydig Cells/chemistry , Leydig Cells/cytology , Male , Microcirculation/chemistry , Microcirculation/cytology , RNA, Messenger/biosynthesis , Receptor, Endothelin A , Receptor, Endothelin B , Receptors, Endothelin/genetics , Reverse Transcriptase Polymerase Chain Reaction , Seminiferous Tubules/chemistry , Seminiferous Tubules/cytology , Sertoli Cells/chemistry , Sertoli Cells/cytology , Testis/blood supply , Testis/cytologyABSTRACT
Expression of mRNA of endothelin-1 (ET-1) and its receptors, endothelin receptor A (ET-A) and endothelin receptor B (ET-B), in human epididymis was assessed by reverse transcription-polymerase chain reaction (RT-PCR). Immunohistochemistry was performed on longitudinal sections through whole normal human epididymides. ET-1 mRNA was detected in caput, corpus and cauda epididymidis. Immunohistochemically, ET-1 was localized mainly in ciliated cells of efferent ducts and in some principal cells of epididymal duct. Larger arteries, but not epididymal microvasculature, contained ET-1 immunoreactivity. ET-A and ET-B mRNAs were detected in caput, corpus and cauda epididymidis. In efferent ducts, ET-A immunoreactivity was localized in ciliated cells. In the proximal region of the epididymal duct, ET-A immunostaining was localized mainly in basal cells whereas the distal region was devoid of ET-A immunoreactivity. Throughout the epididymis, blood vessels stained positive for ET-B. Furthermore, ET-B immunoreactivity was found in ciliated cells of efferent ducts and in basal cells of the distal epididymal duct. The fact that ciliated cells of efferent ducts contain ET-1 and both types of receptors indicates that ET-1 acts as an autocrine factor in these cells. ET-1 produced by efferent ducts and epididymal duct may control epididymal blood flow in a paracrine manner via ET-B receptors in epididymal blood vessels.
