BRAIN CAPILLARY ENDOTHELIAL-CELLS EXPRESS 2 FORMS OF ERYTHROPOIETIN RECEPTOR MESSENGER-RNA

To study the existence of the erythropoietin receptor (Epo-R) mRNA in brain capillary endothelial cells, the reverse transcription (RT) PCR was performed using total RNAs from rat brain capillary endothelial ce lls (RBECs) and MBEC4, which is one of the established mouse brain cap illary endothelial cell lines. Southern analysis of the RT-PCR product s indicated that both RBECs and MBEC4 expressed an authentic form of E po-R mRNA as a minor form and an intron-5-inserted form of Epo-R mRNA, thus a soluble form of Epo-R mRNA, as a major form. Furthermore, the effect of recombinant human erythropoietin (rHuEpo) on the DNA synthes is in RBECs was analyzed. rHuEpo showed a dose-dependent mitogenic act ion on RBECs as a competence factor. Radioiodinated rHuEpo was bound s pecifically to RBECs with time, cell number and dose dependencies. Bin ding studies with I-125-rHuEpo showed that RBECs had a single class of receptors with low-affinity (K-d = 860 pM) and that the number of sit es/cell (10 300) was abundant. These results suggest that blain capill ary endothelial cells express not only an authentic form of Epo-R but also a soluble form of Epo-R and that erythropoietin acts directly on brain capillary endothelial cells as a competence factor.