Unexpected and coordinated expression of Spi-1. Fli-1, and megakaryocytic genes in four Epo-dependent cell lines established from transgenic mice displaying erythroid-specific expression of a thermosensitive SV40 T antigen

Most erythroleukemic cell lines established in vitro coexpress erythrocytic and megakaryocytic markers that often are associated with expression of Sp i-1 and or Fli-1 transcription factors known as transactivators of megakary ocyte-specific promoters, In the present study, He examined the possibility of establishing new cell lines keeping strictly erythroid-specific, proper ties in vitro through the targeted and conditional immortalization of eryth rocytic progenitors. For that purpose, we established several lines of tran sgenic mice displaying erythroid-specific expression of a thermosensitive S V40 T antigen. As expected, these transgenic mice developed splenomegaly du e to the massive amplification of Tcr 119 positive erythroid nucleated cell s expressing T antigen. Despite this drastic effect in vivo, the in vitro i mmortalization of erythropoietin-dependent erythroid progenitors unexpected ly occurred at low frequency, and all Pour cell lines established expressed both erthrocytic (globins) and megakaryocytic markers (glycoprotein IIb, p latelet factor 4) as well as Spi-1 and Fli-1 transcripts at permissive temp erature. Snitching the cells to the nonpermissive temperature led to a mark ed increase in globin gene expression and concomitant decrease in expressio n of Spi-1, Fli-1. and megakaryocytic genes in an erythropoietin-dependent manner, Interestingly, enhanced expression of Spi-1 and FU-I genes already was detected in the Tcr 119 positive cell population of transgenic mice spl een in vivo. However, like normal Ter 119 erythroid cells, these Ter 119 po sitive cells from transgenic mice still expressed high levels of beta-globi n and,very low or undetectable glycoprotein IIb and platelet factor I megak aryocytic transcripts, Taken together, these data indicate that the unexpec ted expression of megakaryocytic genes is a specific properly of immortaliz ed cells that cannot be explained only bg enhanced expression of Spi-1 and or Fli-1 genes, (C) 1999 International Society for Experimental Hematology. Published by Elsevier Science Inc.