Daniel M T, Koken M, Romagné O, Barbey S, Bazarbachi A, Stadler M, Guillemin M C, Degos L, Chomienne C, de Thé H
Laboratoire d'Hématologie, CNRS 43, Centre Hayem, Paris, France.
Blood. 1993 Sep 15;82(6):1858-67.
Acute promyelocytic leukemia (APL) is thought to be caused by the t(15,17) translocation that fuses the PML gene to that of the retinoic acid receptor alpha (RAR alpha) and generates a PML/RAR alpha fusion protein. Yet, paradoxically, APL cells are exquisitely sensitive to retinoic acid (RA), as they terminally differentiate upon RA exposure. In this report, we have examined the expression of PML and PML/RAR alpha in normal and APL cells. By immunofluorescence or immunocytochemistry, we show that PML has a speckled nuclear pattern of expression that contrasts with that of PML/RAR alpha (mostly a micropunctuated nuclear pattern or a cytoplasmic localization). The APL-derived cell line NB4 that expresses both the PML and PML/RAR alpha genes also shows the fine micropunctuated nuclear pattern, suggesting a dominant effect of the fusion protein over the localization of wild-type PML. RA treatment of NB4 cells or clones expressing PML/RAR alpha gradually leads to a PML pattern before apparent morphologic maturation. In 14 untreated APL patients, the PML-reactive proteins were cytoplasmic (by immunocytochemistry) or both cytoplasmic and nuclear with a micropunctuated pattern (by immunofluorescence). Strikingly, in 4 patients, after 1 to 2 weeks of RA therapy, the speckled nuclear PML pattern reappeared concomitant with the onset of differentiation. These results establish that fusion of PML to RAR alpha results in an altered localization of PML that is reverted upon RA treatment. This observation, which highlights the importance of PML, is likely to be a key to unravelling the molecular mechanism of both leukemogenesis and RA-induced differentiation of APL.
急性早幼粒细胞白血病（APL）被认为是由t(15;17)易位所致，该易位使早幼粒细胞白血病（PML）基因与维甲酸受体α（RARα）基因融合，产生PML/RARα融合蛋白。然而，矛盾的是，APL细胞对维甲酸（RA）极为敏感，因为它们在接触RA后会终末分化。在本报告中，我们检测了正常细胞和APL细胞中PML及PML/RARα的表达。通过免疫荧光或免疫细胞化学方法，我们发现PML呈现斑点状核表达模式，这与PML/RARα的表达模式（大多为微点状核模式或胞质定位）形成对比。同时表达PML和PML/RARα基因的APL来源细胞系NB4也呈现精细的微点状核模式，提示融合蛋白对野生型PML的定位具有显性作用。用RA处理NB4细胞或表达PML/RARα的克隆，在明显的形态成熟之前，会逐渐导致PML模式的出现。在14例未经治疗的APL患者中，PML反应性蛋白呈胞质表达（通过免疫细胞化学检测），或呈胞质和核内微点状模式表达（通过免疫荧光检测）。引人注目的是，在4例患者中，经过1至2周的RA治疗后，斑点状核PML模式重新出现，同时伴有分化的开始。这些结果表明，PML与RARα的融合导致PML定位改变，而这种改变在RA治疗后得以恢复。这一观察结果突出了PML的重要性，可能是揭示APL白血病发生机制及RA诱导分化分子机制的关键。
