RESUMO
Sphingolipids are involved in the regulation of cell proliferation. It has been reported that diacylglycerol and sphingosine-1-phosphate generation, during the synthesis of phospho-sphingolipids, is necessary for both, G1-S transition of cell cycle during the sustained activation of protein kinase C in various cell models (MDCK, Saccharomyces and Entamoeba) and AKT pathway activation. During the estrous cycle of the rat, AKT signaling is the main pathway involved in the regulation of uterine cell proliferation. The aim of the present study was to investigate the role of sphingolipid synthesis during proliferation of uterine cells in the estrous cycle of the rat. On metestrus day, when both luminal and glandular uterine epithelia present the maximal BrdU-labeled cells (S phase cells), there was an increase in the relative abundance of total sphingomyelins, as compared to estrus day. Myriocin, a sphingolipid synthesis inhibitor administered on estrus day, before the new cell cycle of epithelial cells is initiated, decreased the abundance of sphingomyelin, accompanied by proliferation arrest in uterine epithelial cells on metestrus day. In order to study the sphingolipid signaling pathway affected by myriocin, we evaluated the activation of the PKC-AKT-GSK3b-Cyclin D3 pathway. We observed that total and phosphorylated protein kinase C diminished in uterine epithelial cells of myriocin treated animals. Interestingly, cyclin D3 nuclear localization was blocked by myriocin, concomitantly with a decrease in nuclear pRb expression. In conclusion, we demonstrate that sphingolipid synthesis and signaling are involved in uterine epithelial cell proliferation during the estrous cycle of the rat.
Assuntos
Endométrio/fisiologia , Células Epiteliais/fisiologia , Metestro/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Esfingolipídeos/biossíntese , Animais , Ciclina D3/metabolismo , Ácidos Graxos Monoinsaturados , Feminino , Quinase 3 da Glicogênio Sintase/metabolismo , Fosforilação , Proteína Quinase C/metabolismo , Ratos Wistar , Proteína do Retinoblastoma/metabolismoRESUMO
3H-dihydroalprenolol (DHA) -- receptor binding was studied in membrane preparations from metestrous uterine tissue, both in presence and absence of exogenous prostaglandin (PG) F2 alpha at 10(-9) M. In addition, the uptake of 3H-noradrenaline (NA) by uterine segments from estrous and metestrous rats and the influences of PGF2 alpha (10(-9) M), cocaine (10(-5) M) corticosterone (5.10(-5) M), normetanephrine (10(-6) M) or acetylsalicylic acid (ASA: 10(-4) M), were explored. The Scatchard analysis of experimental data with 3H-DHA with or without added PGF2 alpha indicates the existence of a single class of high affinity receptors and no differences were found, in presence of PGF2 alpha, regarding the control dissociation constant or the control maximal sites of specific binding. On the other hand, the uptake of 3H-NA by uterine segments at metestrus was significantly greater than at estrus. In metestrous uteri PGF2 alpha (10(-9) M) reduced significantly NA uptake. ASA enhanced NA uptake by uteri from estrous rats, an influence prevented by PGF2 mu. In uterine segments isolated at estrus, cocaine, corticosterone and normetanephrine failed to alter 3H-NA uptake, whereas in preparations isolated at metestrus, corticosterone and normetanephrine reduced the uptake, but cocaine did not evoke any influence. Results are discussed in terms of previous findings documenting an amplification of the negative inotropic influence of NA mediated by the activation of beta-adrenoceptors, both in estrous or in metestrous preparations incubated with PGF2 alpha. Such previous findings cannot be explained by changes in the number of NA receptors or by a greater affinity of tissue receptors for the agonist, but rather by differences in NA uptake controlling its effective concentration at the biophase, near receptor sites. Interrelationships along sex hormones (estradiol), prostaglandins (PGF2 alpha) and catecholamines (NA) in uteri, are also discussed.