Signal Transduction Unit, Section of Human Anatomy, Department of Morphology and Embryology, University of Ferrara, 44100 Ferrara, Italy.
J Proteome Res. 2010 Feb 5;9(2):752-60. doi: 10.1021/pr900581y.
Vav1, whose physiological expression is restricted to hematopoietic system, is one of the signaling proteins up-regulated by all-trans retinoic acid (ATRA) in acute promyelocytic leukemia (APL)-derived precursors, in which it promotes the overcoming of the differentiation blockade. High levels of tyrosine phosphorylated Vav1 accumulate in differentiating APL-derived cells, suggesting that one or more Vav1 tyrosine residues are involved in neutrophil differentiation of tumoral promyelocytes. Here, we have found that phosphorylation of Vav1 Y174, that is known to regulate Vav1 activity in mature neutrophils, is up-regulated by ATRA in NB4 cells. Nevertheless, this tyrosine residue does not seem crucial for the agonist-induced phenotypical differentiation of APL-derived cells. Mass spectrometry analysis performed on Vav1 from differentiating NB4 cells allowed to identify the highly conserved Y745 residue as a phosphorylated tyrosine that plays crucial roles in the completion of the maturation program of this cell line. In fact, the overexpression of a mutated form of Vav1, in which Y745 was replaced with a phenylalanine, significantly reduced the ATRA-induced CD11b expression and essentially abrogated the differentiation-related acquisition of the migratory capability. Even though the intracellular signaling involving Vav1 phosphorylated in Y745 is unknown, the identification of a tyrosine residue essential for differentiation of tumoral precursors may constitute the basis to identify new specific targets for differentiation therapy of APL.
Vav1 的生理表达仅限于造血系统，是全反式维甲酸（ATRA）在急性早幼粒细胞白血病（APL）衍生前体中上调的信号蛋白之一，它促进了分化阻滞的克服。在分化的 APL 衍生细胞中积累了高水平的酪氨酸磷酸化 Vav1，表明一个或多个 Vav1 酪氨酸残基参与肿瘤早幼粒细胞的中性粒细胞分化。在这里，我们发现 Vav1 的 Y174 磷酸化，已知其在成熟中性粒细胞中调节 Vav1 活性，在 NB4 细胞中被 ATRA 上调。然而，这个酪氨酸残基似乎对 APL 衍生细胞的激动剂诱导的表型分化不是至关重要的。对分化的 NB4 细胞中的 Vav1 进行质谱分析，鉴定出高度保守的 Y745 残基为磷酸化的酪氨酸，在该细胞系的成熟程序的完成中起着至关重要的作用。事实上，过表达一种突变形式的 Vav1，其中 Y745 被苯丙氨酸取代，显著降低了 ATRA 诱导的 CD11b 表达，并基本上消除了与分化相关的获得迁移能力。尽管涉及 Y745 磷酸化的 Vav1 的细胞内信号尚不清楚，但确定肿瘤前体分化所必需的酪氨酸残基可能构成鉴定 APL 分化治疗新的特异性靶标的基础。
