Transcriptional activation of prion protein gene in growth-arrested and differentiated mouse erythroleukemia and human neoplastic cells

The prion protein (PrPC) is a GPI-anchored sialoglycoprotein that has attracted worldwide attention over the years due to its involvement in the pathogenesis of transmissible spongiform encephalopathies in sheep (scrapie), cattle (BSE), and humans (CJD). To understand the precise role of the Prn-p gene in cell growth and differentiation we investigated the expression pattern of the Prn-p gene in proliferating cells and in cells arrested in growth either by confluency or by induction of terminal differentiation. Viral-transformed mouse spleen hematopoietic cells named murine erythroleukemia (MEL) and other types of inducible cells (human neuroectodermal RD/TE-671, myoid RD cells) were employed. Cells grown exponentially, at confluency, or irreversibly arrested in growth at terminal differentiation state were analyzed by fluorescence cell sorting and Northern blot hybridization to estimate the steady-state level of PrP mRNA at different phases of the cell cycle. MEL cells that failed to differentiate from treatment with N-6-methyladenosine (N(6)mAdo), an inhibitor of differentiation, were also analyzed for PrP mRNA level. Our results indicate the following: (a) growth arrest of cells at G, phase by confluency or by induction of terminal differentiation led to increased accumulation of PrP mRNA transcripts, an event observed also in differentiated MEL, RD/TE-671, and RD cells independent of the inducer used; (b) treatment of MEL cells with N(6)mAdo prevented early activation of the Pm-p gene in cells treated with the inducer; and (9) cell-free nuclear runoff studies showed enhanced expression of the Prn-p gene due to transcriptional activation. These findings indicate, for the first time, that the Prn-p gene, which is thought to be a housekeeping gene, is transcriptionally activated in G, phase in confluent and terminally differentiated cells. This information may be valuable in understanding the overaccumulation of PrP in some differentiated tissues and may let us repress Prn-p gene activation by novel agents. (C) 2001 Academic Frees.