Department of Hematology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Bunkyoku, Tokyo 113-8519, Japan.
Int J Oncol. 2013 Feb;42(2):419-28. doi: 10.3892/ijo.2012.1729. Epub 2012 Dec 6.
PECAM-1 (CD31) is an immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing surface glycoprotein expressed on various hematopoietic cells as well as on endothelial cells. PECAM-1 has been shown to play roles in regulation of adhesion, migration and apoptosis. The BCR/ABL fusion tyrosine kinase is expressed in chronic myeloid leukemia and Philadelphia-positive (Ph+) acute lymphoblastic leukemia cells, and its inhibition by the clinically used tyrosine kinase inhibitors imatinib or dasatinib induces apoptosis of these cells. In the present study, we demonstrate that PECAM-1 is tyrosine phospho-rylated in its ITIM motifs in various BCR/ABL-expressing cells including primary leukemia cells. Studies using imatinib and dasatinib as well as transient expression experiments in 293T cells revealed that PECAM-1 was phosphorylated directly by BCR/ABL, which was enhanced by the imatinib-resistant E255K and T315I mutations, or partly by the Src family tyrosine kinases, including Lyn, which were activated dependently or independently on BCR/ABL. We also demonstrate by using a substrate trapping mutant of SHP2 that tyrosine phosphorylated PECAM-1 binds SHP2 and is a major substrate for this tyrosine phosphatase in BCR/ABL-expressing cells. Overexpression of PECAM-1 in BCR/ABL-expressing cells, including K562 human leukemia cells, enhanced cell adhesion and partially inhibited imatinib-induced apoptosis involving mitochondria depolarization and caspase-3 cleavage, at least partly, in an ITIM-independent manner. These data suggest that PECAM-1 may play a role in regulation of apoptosis as well as adhesion of BCR/ABL-expressing cells to modulate their imatinib sensitivity and would be a possible candidate for therapeutic target in Ph+ leukemias.
PECAM-1（CD31）是一种免疫受体酪氨酸基抑制基序（ITIM）包含的表面糖蛋白，表达于各种造血细胞以及内皮细胞。PECAM-1 已被证明在调节黏附、迁移和凋亡中发挥作用。BCR/ABL 融合酪氨酸激酶在慢性髓性白血病和费城阳性（Ph+）急性淋巴细胞白血病细胞中表达，其被临床使用的酪氨酸激酶抑制剂伊马替尼或达沙替尼抑制可诱导这些细胞凋亡。在本研究中，我们证明了 PECAM-1 在包括原代白血病细胞在内的各种 BCR/ABL 表达细胞中其 ITIM 基序中的酪氨酸发生磷酸化。使用伊马替尼和达沙替尼以及在 293T 细胞中转瞬表达实验的研究表明，PECAM-1 被 BCR/ABL 直接磷酸化，该磷酸化被伊马替尼耐药的 E255K 和 T315I 突变或部分 Src 家族酪氨酸激酶增强，包括 Lyn，其被 BCR/ABL 依赖性或独立性激活。我们还通过使用 SHP2 的底物捕获突变体证明，酪氨酸磷酸化的 PECAM-1 与 SHP2 结合，并成为 BCR/ABL 表达细胞中这种酪氨酸磷酸酶的主要底物。在包括 K562 人白血病细胞在内的 BCR/ABL 表达细胞中过表达 PECAM-1，增强细胞黏附，并部分抑制伊马替尼诱导的凋亡，涉及线粒体去极化和 caspase-3 裂解，至少部分以 ITIM 非依赖性方式。这些数据表明 PECAM-1 可能在调节 BCR/ABL 表达细胞的凋亡以及黏附中发挥作用，以调节其对伊马替尼的敏感性，并可能成为 Ph+白血病的治疗靶点。
