Activation of Prn-p gene and stable transfection of Prn-p cDNA in leukemia MEL and neuroblastorna N2a cells increased production of PrPC but not prevented DNA fragmentation initiated by serum deprivation

Prion protein (PrPC) via its isoform PrPSC is involved in the pathogenesis of transmissible spongiform encephalopathies (TSEs). We observed that murine erythroleukemia (MEL) cells arrested in phase G(I) undergo transcriptional activation of Prn-p gene. Here, we explored the potential role of activation of Prn-p gene and cytosolic accumulation of PrPc in growth arrest, differentiation, and apoptotic DNA fragmentation by stably transfecting MEL and N2a cells with Prn-p cDNA. Stably transfected MEL cells (clones# 6, 12,20,38,and42) were assessed for growth and differentiation, while clones N2a13 and N2a8 of N2a cells for growth and apoptosis by flow cytometry using Annexin V and propidium iodide (PI). Our results indicate that (a) Induction of terminal differentiation of stably transfected MEL cells led to growth arrest, activation of Prn-p gene, concomitant expression of transfected Prn-p cDNA, suppression of box gene, cytosolic accumulation of PrPC, and DNA fragmentation. The latter was also induced in non-differentiated MEL cells growing under serum-free conditions; (b) similarly, serum deprivation promoted growth arrest, apoptosis/necrosis associated with DNA fragmentation in parental N2a and N2a13 cells that produced relative high level of PrPc and not PrPsc. These data indicate that activation of Prn-p gene and expression of transfected Prn-p cDNA in cells of both hematopoietic and neuronal origin occurred concomitantly, and led to cytosolic accumulation of PrPc and DNA damage induced by serum deprivation. PrPc production failed to protect DNA fragmentation induced by serum deprivation. The question how does PrPc contribute to growth arrest and DNA fragmentation is discussed.