RNA interference-induced reduction in CD98 expression suppresses cell fusion during syncytialization of human placental BeWo cells

AbstractThe physiological importance of CD98 surface antigen in regulating placental trophoblast cell fusion has been studied in a cell model of syncytialization (the cytotrophoblast cell line BeWo following increased intracellular cAMP by forskolin treatment) using RNA interference. CD98 protein abundance (determined by Western blot) was decreased by 40–50% following double-stranded small interfering RNA transfection. Cell fusion (determined by quantitative flow cytometry) was similarly inhibited and human chorionic gonadotropin secretion was suppressed. These findings show that CD98 is involved in the process of cell fusion necessary for syncytiotrophoblast formation

Functional and molecular characterization of a peptide transporter in the rat PC12 neuroendocrine cell line

AbstractWe have studied functional properties of peptide transport in the pheochromocytoma neuroendocrine cell line from rat. The neutral peptide D-Phe-L-Ala (resistant to hydrolysis) is a good substrate for uptake into these cells. Transport is substantially inhibited by diethylpyrocarbonate pretreatment and is stimulated by external acidification. It is sodium-independent and, unexpectedly, insensitive to membrane potential. Peptide uptake is inhibited by a wide variety of other di- and tripeptides but not by amino acids. The neuropeptide kyotorphin (opioid dipeptide (L-Tyr-L-Arg)) inhibits uptake of labelled peptide and trans-stimulates efflux showing that it is a transported substrate. These findings are discussed in relation to the molecular basis and physiological role of this transport system

Peptide aminonitrogen transport by the lactating rat mammary gland

AbstractRecent studies have shown that the lactating mammary gland is able to utilize plasma-derived dipeptides for milk protein synthesis. However, it was not clear whether the peptides were hydrolysed followed by uptake of the constituent amino acids or were taken up intact. In view of this, we have designed experiments to investigate (a) whether the lactating rat mammary gland is capable of transporting hydrolysis-resistant dipeptides and (b) whether or not mammary cells are able to hydrolyse peptides, including glutathione, extracellularly. The uptake of the hydrolysis-resistant dipeptides d-[3H]Phe-l-Gln and d-[3H]Phe-l-Glu by the perfused rat mammary gland was low. Concomitant addition of l-Leu-l-Ala (50 mM) had no effect on the clearance of either labelled dipeptide suggesting that the small, albeit significant, uptake of the dipeptides is not via a high affinity peptide transporter (PepT1/PepT2). All anionic dipeptides tested (l-Glu-l-Ala, l-Asp-l-Ala, l-Ala-l-Asp, l-Asp-Gly, Gly-l-Asp and Gly-l-Glu) with the exception of d-Phe-l-Glu were able to trans-accelerate the efflux of labelled d-aspartate from preloaded rat mammary tissue (explants and perfused mammary gland). It appears that these peptides were being hydrolysed extracellularly followed by the uptake of free anionic amino acids via the mammary tissue high affinity, Na+-dependent anionic amino acid carrier operating in the exchange mode. Glutathione was able to trans-accelerate d-aspartate efflux from lactating rat mammary tissue in a fashion which was sensitive to the peptidase inhibitor acivicin. This suggests that γ-glutamyltranspeptidase hydrolyses glutathione to produce l-glutamate which is subsequently transported via the high-affinity anionic amino acid carrier. Hydrolysis of peptides followed by uptake of the constituent amino acids may provide an important source of amino acids for milk protein synthesis