Paoletti F, Vannucchi A M, Mocali A, Caporale R, Burstein S A
Istituto di Patologia Generale, Universita' di Firenze, Italy.
Blood. 1995 Oct 1;86(7):2624-31.
Friend murine erythroleukemia cells (MELCs) have been reevaluated in terms of their nature and potential pathways of differentiation. MELC induced with 5 mmol/L hexamethylene bisacetamide (HMBA), in addition to expression of known markers of the erythroid phenotype, were also found to exhibit traits of the megakaryocytic lineage. Erythroid differentiation was shown by the typical synthesis and accumulation of hemoglobin (Hb); megakaryoblastoid differentiation of MELCs upon induction was shown by increased specific activity of acetylcholinesterase (AChE). Incubation of MELCs with 5 mmol/L HMBA in RPMI supplemented with 1% fetal calf serum (FCS) (instead of the usual 5%), induced cells to selectively express high levels of AChE (up to approximately 170 mU/mg protein) with little activation of Hb synthesis (less than 5% B+ cells). The increase in AChE levels was a general phenomenon affecting the whole cell population and approached its maximum within 3 days of incubation with the inducer. Subsequently, MELCs become committed to terminal division, undergoing growth arrest and expression of the megakaryocytic phenotype even after the removal of HMBA. There were no appreciable changes of basal AChE levels in MELCs that were either made resistant to HMBA or treated with 0.1 mmol/L hemin that activated differentiated erythroid function without commitment. Phorbol 12-myristate 13-acetate (PMA), known to repress induced Hb synthesis in these cells, did not prevent the full increase in AChE when incubated with MELCs 2 days before HMBA addition. HMBA-induced MELCs always underwent AChE increase that was more or less pronounced depending on the low or high serum content in culture, respectively. Conversely, Hb expression was permitted only when MELCs were transferred in the late phase or at the end of commitment from low to high serum media. Variations of FCS content in culture media proved to be a simple and reliable approach to change the MELC response to inducers and to modulate expression of either megakaryocytic or mixed erythromegakaryocytic phenotype. These findings suggested that MELC might be considered, at least, as a bipotential model of differentiation to be used for studies on regulation of either megakaryocytic or erythroid markers and on competition between the two hematopoietic lineages. In this regard, it was intriguing that AChE levels attained under selective induction (low serum) were always higher than under conditions allowing coexpression of both AChE and Hb (high serum). Moreover, MELCs were also found to bind the specific rat-antimouse platelet monoclonal antibody 4A5.(ABSTRACT TRUNCATED AT 400 WORDS)
已对友系小鼠红白血病细胞（MELCs）的性质和潜在分化途径进行了重新评估。用5 mmol/L己二甲基双乙酰胺（HMBA）诱导的MELCs，除了表达红系表型的已知标志物外，还表现出巨核细胞系的特征。红系分化通过血红蛋白（Hb）的典型合成和积累得以体现；诱导后MELCs的巨核母细胞样分化通过乙酰胆碱酯酶（AChE）比活性的增加得以显示。在补充有1%胎牛血清（FCS）（而非通常的5%）的RPMI中，将MELCs与5 mmol/L HMBA孵育，可诱导细胞选择性地高水平表达AChE（高达约170 mU/mg蛋白），而Hb合成的激活很少（B+细胞少于5%）。AChE水平的升高是一种影响整个细胞群体的普遍现象，在与诱导剂孵育3天内达到最大值。随后，MELCs进入终末分裂，即使在去除HMBA后仍经历生长停滞并表达巨核细胞表型。对HMBA耐药或用0.1 mmol/L血红素处理的MELCs，其基础AChE水平没有明显变化，血红素可激活分化的红系功能而不导致细胞定向分化。已知能抑制这些细胞中诱导的Hb合成的佛波醇12 -肉豆蔻酸酯13 -乙酸酯（PMA），在添加HMBA前2天与MELCs孵育时，并不阻止AChE的充分升高。HMBA诱导的MELCs总是会出现AChE升高，其程度或多或少取决于培养物中血清含量的低或高。相反，只有当MELCs在定向分化后期或结束时从低血清培养基转移至高血清培养基时，才会允许Hb表达。培养基中FCS含量的变化被证明是一种简单可靠的方法，可改变MELCs对诱导剂的反应，并调节巨核细胞或混合红巨核细胞表型的表达。这些发现表明，MELCs至少可被视为一种双潜能分化模型，用于研究巨核细胞或红系标志物的调控以及两种造血谱系之间的竞争。在这方面，有趣的是，在选择性诱导（低血清）条件下达到的AChE水平总是高于允许AChE和Hb共表达的条件（高血清）下的水平。此外，还发现MELCs能结合特异性大鼠抗小鼠血小板单克隆抗体4A5。（摘要截断于400字）
