The PML gene encodes a phosphoprotein associated with the nuclear matrix (original) (raw)

The t(15;17)(q22;q12) translocation is the cytogenetic hallmark of acute promyelocytic leukemia (APL). The PML and retinoic acid receptor-& (RA&) transcription factor genes are involved at the translocation breakpoint. To elucidate the biologic function of PML, antipeptide antibody against PML protein was raised in rabbits. This antibody was able to detect a 90-kD PML protein and a 110-kD PML-RARa fusion protein by Western blotting and a nuclear speckled pattern in all cell lines by immunofluorescent staining. In K562 and NIH/3T3 cells transfected with a PML expression plasmid, we found PML to be associated with the nuclear matrix. Our results also showed that PML is a phosphoprotein. A weak signal was detected in a Western blot containing the immunoprecipitated PML protein using the phosphotyrosine-specific monoclonal antibody. Therefore, at least one of the sites B ECAUSE THE NONRANDOM chromosome translocation t(15; 17)(q22;q12) can be found in over 95% of patients with acute promyelocytic leukemia (APL),'.' one can infer that genes involved in this unique translocation event play a role in its pathogenesis. Studies from several laboratories have confirmed that the t(15; 17) translocation occurs within the zinc finger transcription factor gene, PML, and the retinoic acid receptor-a (RARa) gene."' Because an extremely high number of APL patients can be induced to complete clinical remission by all-trans retinoic acid (ATRA),'"' it is believed that disruption of the RARa gene by the translocation plays a role in the leukemogenesis. However, evidence indicates that, when the myeloid leukemia cell line HL-60 loses its RA inducibility, this inducibility can be completely restored by other forms of RAR or retinoic X receptor (RXR)," suggesting that the loss of RARa function by APL cells may not be a critical event in leukemogenesis. Recent reports showed that the fusion protein PML-RARa encoded from the t(15; 17) breakpoint is responsible for RA inducibility in APL, because transfection of the PML-RARa cDNA into the human myeloid leukemia cell line U937 conferred RA inducibility." Furthermore, APL-derived NB4 cells that lose their RA inducibility also lose expression of the PML-RARa protein."