Vannucchi A M, Grossi A, Paoletti F, Rafanelli D, Bacci P, Ferrini P R
Division of Hematology, University of Florence, USL, Italy.
Exp Hematol. 1992 Dec;20(11):1296-301.
Murine Friend-derived erythroleukemia cells (MEL) are generally believed to be unipotential progenitors inducible to terminal erythroid differentiation. However, we found that MEL can constitutively incorporate significant amounts of radiolabeled serotonin ([3H]5-HT). Because this process is typical of cells belonging to the megakaryocytic lineage, we investigated the significance and mechanisms of 5-HT incorporation in the MEL system. We observed that: 1) normal murine erythroid cells and erythroid progenitors do not incorporate [3H]5-HT, as well as normal murine myeloid cells and the human myeloid cell line HL-60; on the other hand, the human erythroleukemia cell lines K562 and HEL, which have been shown to constitutively express megakaryocytic features, were able to incorporate [3H]5-HT; 2) MEL incorporated 5-HT by an active and saturable mechanism, dependent on temperature and sodium concentration in the medium; and 3) 5-HT uptake was very rapid. Moreover, because about 65% of cell-associated radioactivity was no longer displaced by the cold substrate, we assumed it to represent "true" cytoplasmic internalization. Finally, 5-HT incorporation by MEL was inhibited by clomipramine, ouabain, and reserpine, which are known inhibitors of 5-HT uptake in platelets. The commitment of MEL to terminal erythroid differentiation by hexamethylene bisacetamide or dimethyl sulfoxide greatly reduced the capacity to incorporate [3H]5-HT. These results seem to suggest that the MEL system, although mainly erythroid as regards its differentiation capability, constitutively expresses features of the megakaryocytic lineage, possibly disclosed by the ability to incorporate 5-HT. This hypothesis was further supported by the findings that 30%-40% of uninduced MEL were labeled by a polyclonal antibody raised against murine platelets that selectively recognized megakaryocytes in murine bone marrow smears.
鼠源Friend病毒诱导的红白血病细胞（MEL）通常被认为是可诱导终末红系分化的单能祖细胞。然而，我们发现MEL能够持续摄取大量放射性标记的血清素（[³H]5-羟色胺）。由于这一过程是巨核细胞系细胞的典型特征，我们研究了MEL系统中5-羟色胺摄取的意义及机制。我们观察到：1）正常鼠类红系细胞和红系祖细胞不摄取[³H]5-羟色胺，正常鼠类髓系细胞和人髓系细胞系HL-60也不摄取；另一方面，已被证明持续表达巨核细胞特征的人红白血病细胞系K562和HEL能够摄取[³H]5-羟色胺；2）MEL通过一种依赖于温度和培养基中钠浓度的主动且可饱和的机制摄取5-羟色胺；3）5-羟色胺摄取非常迅速。此外，由于约65%与细胞相关的放射性不再被冷底物置换，我们认为其代表“真正的”细胞质内化。最后，氯米帕明、哇巴因和利血平可抑制MEL摄取5-羟色胺，已知它们是血小板中5-羟色胺摄取的抑制剂。六亚甲基双乙酰胺或二甲基亚砜使MEL向终末红系分化，这大大降低了其摄取[³H]5-羟色胺的能力。这些结果似乎表明，MEL系统尽管在分化能力方面主要为红系，但持续表达巨核细胞系的特征，这可能通过摄取5-羟色胺的能力得以揭示。针对鼠血小板产生的多克隆抗体可选择性识别鼠骨髓涂片中的巨核细胞，该抗体标记了30%-40%未诱导的MEL，这一发现进一步支持了这一假说。
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