Campbell K S, Bedzyk W D, Cambier J C
E.I. Dupont, Newark, DE 19714, USA.
Mol Immunol. 1995 Nov;32(16):1283-94. doi: 10.1016/0161-5890(95)00088-7.
The B cell antigen receptor complex (BCR) is composed of a membrane-spanning immunoglobulin molecule (mIg) non-covalently associated with heterodimers of the transmembrane proteins Ig-alpha and Ig-beta. The cytoplasmic domains of Ig-alpha and Ig-beta do not contain kinase domains but are phosphorylated on tyrosine residues immediately upon receptor ligation. The mechanism and kinase responsible for initial Ig-alpha and Ig-beta phosphorylation following receptor ligation is unknown, In an attempt to better understand this process, Ig-alpha and Ig-beta phosphorylation was examined in response to treatment of permeabilized B cells with the pharmacologic agents, aluminum fluoride (AlFx) and sodium orthovanadate (Na3VO4). AlFx is known to stimulate GTP-binding proteins while Na3VO4 inhibits protein tyrosine phosphatases (PTPs), both of which are involved in the BCR signalling cascade. In these studies, AlFx and Na3VO4 stimulated rapid tyrosine phosphorylation of Ig-alpha, Ig-beta, and additional cellular proteins, including the protein tyrosine kinase (PTK) Lyn. The tyrosine phosphorylation does not appear to be mediated through GTP-binding proteins, since GTP gamma S did not stimulate tyrosine phosphorylation. As expected, however, PTPs modulate the phosphorylation state of these proteins since another PTP inhibitor, phenylarsine oxide (PAO), increased phosphorylation of Ig-alpha, Ig-beta and other proteins in this system. Interestingly, the extent and kinetics of the mIg-associated Lyn and Ig-alpha/Ig-beta phosphorylation was correlated, suggesting that Lyn may mediate receptor phosphorylation. Alternatively, Lyn, may be a downstream effector of phosphorylated Ig-alpha and Ig-beta as suggested by the reported ability of biphosphorylated Ig-alpha to activate Fyn PTK in vitro. Finally, all components necessary for Na3VO4, but not AlFx, stimulation of phosphorylation are membrane associated. The data are consistent with modulation of phosphorylation of Ig-alpha and Ig-beta through both PTP inhibition and AlFx treatment, and a common intermediary in or effector of these phosphorylation pathways appears to be the Lyn kinase.
B细胞抗原受体复合物（BCR）由一个跨膜免疫球蛋白分子（mIg）组成，该分子与跨膜蛋白Ig-α和Ig-β的异二聚体非共价结合。Ig-α和Ig-β的胞质结构域不包含激酶结构域，但在受体连接后立即在酪氨酸残基上发生磷酸化。受体连接后负责初始Ig-α和Ig-β磷酸化的机制和激酶尚不清楚。为了更好地理解这一过程，研究人员用药物氟化铝（AlFx）和原钒酸钠（Na3VO4）处理通透的B细胞，检测Ig-α和Ig-β的磷酸化情况。已知AlFx能刺激GTP结合蛋白，而Na3VO4能抑制蛋白酪氨酸磷酸酶（PTP），二者均参与BCR信号级联反应。在这些研究中，AlFx和Na3VO4刺激了Ig-α、Ig-β以及其他细胞蛋白（包括蛋白酪氨酸激酶（PTK）Lyn）的快速酪氨酸磷酸化。酪氨酸磷酸化似乎不是通过GTP结合蛋白介导的，因为GTPγS并未刺激酪氨酸磷酸化。然而，正如预期的那样，PTP调节这些蛋白的磷酸化状态，因为另一种PTP抑制剂苯砷氧化物（PAO）增加了该系统中Ig-α、Ig-β和其他蛋白的磷酸化。有趣的是，与mIg相关的Lyn以及Ig-α/Ig-β磷酸化的程度和动力学是相关的，这表明Lyn可能介导受体磷酸化。或者，如双磷酸化Ig-α在体外激活Fyn PTK的报道能力所表明的，Lyn可能是磷酸化Ig-α和Ig-β的下游效应器。最后，Na3VO4而非AlFx刺激磷酸化所需的所有成分都与膜相关。这些数据与通过PTP抑制和AlFx处理对Ig-α和Ig-β磷酸化的调节一致，并且这些磷酸化途径的共同中间体或效应器似乎是Lyn激酶。
