Jpk, a novel cell death inducer, regulates the expression of Hoxa7 in F9 teratocarcinoma cells, but not during apoptosis.

Hox proteins play critical role in animal pattern formation during embryogenesis. During the study on the regulation of Hox gene expression, a novel gene, Jpk, has been isolated as a putative regulatory factor associating with the upstream regulatory sequence of murine Hoxa7. Since overexpression of Jpk caused cell death in bacteria as well as in eukaryotic cells and Hox has been reported to participate in apoptosis, we tried to analyze the relationship between Jpk and Hoxa7 during apoptosis after confirming the regulatory effect of Jpk on the expression of Hoxa7 in F9 teratocarcinoma cells. For that purpose, an effector (pEGFP-Jpk) and reporter (pGL2-NM307) plasmid containing a luciferase gene under the 307 bp (NM307) of Hoxa7 upstream regulatory sequence was constructed. In the presence of Jpk (effector), luciferase activity was increased and this enhancement was decreased by siRNA against Jpk, suggesting that Jpk is a regulatory factor of Hoxa7. In order to see whether Jpk still regulates the expression of Hoxa7 during apoptosis, F9 cells were transiently transfected with pcDNA-Jpk, and the expression of Jpk, Hoxa7, and CHOP-10 was analyzed using RT-PCR. Hoxa7 and CHOP-10 were not upregulated in the presence of Jpk although Jpk seemed to cause apoptosis, indicating that the regulatory mechanism of Jpk on the expression of Hoxa7 might be different depending on the cell status, that is, an apoptotic or proliferative condition.