Gold M R, Sanghera J S, Stewart J, Pelech S L
Biomedical Research Centre, University of British Columbia, Vancouver, Canada.
Biochem J. 1992 Oct 1;287 ( Pt 1)(Pt 1):269-76. doi: 10.1042/bj2870269.
Cross-linking of membrane immunoglobulin (mIg), the B lymphocyte antigen receptor, with anti-receptor antibodies stimulates tyrosine phosphorylation of a number of proteins, including one of 42 kDa. Proteins with a similar molecular mass are tyrosine-phosphorylated in response to receptor stimulation in other cell types and have been identified as serine/threonine kinases, termed mitogen-activated protein (MAP) kinases or extracellular signal-regulated kinases (ERKs). The MAP kinases constitute a family of related kinases, at least three of which have molecular masses of 40-45 kDa. In this paper we show that mIg cross-linking stimulated the myelin basic protein phosphotransferase activity characteristic of MAP kinase in both mature and immature murine B cell lines. This enzyme activity co-purified on three different columns with a 42 kDa protein that was tyrosine-phosphorylated (pp42) in response to mIg cross-linking and which reacted with a panel of anti-(MAP kinase) antibodies. Although immunoblotting with the anti-(MAP kinase) antibodies showed that these B cell lines expressed both 42 kDa and 44 kDa forms of MAP kinase, only the 42 kDa form was activated and tyrosine-phosphorylated to a significant extent. Activation of protein kinase C (PKC) with phorbol esters also resulted in selective tyrosine phosphorylation and activation of the 42 kDa MAP kinase. This suggested that mIg-induced MAP kinase activation could be due to stimulation of PKC by mIg. However, mIg-stimulated MAP kinase activation and pp42 tyrosine phosphorylation was only partially blocked by a PKC inhibitor, the staurosporine analogue Compound 3. In contrast, Compound 3 completely blocked the ability of phorbol esters to stimulate MAP kinase activity and induce tyrosine phosphorylation of pp42. Thus mIg may activate MAP kinase by both PKC-dependent and -independent mechanisms.
膜免疫球蛋白（mIg）即B淋巴细胞抗原受体，与抗受体抗体交联可刺激多种蛋白质的酪氨酸磷酸化，包括一种42kDa的蛋白质。在其他细胞类型中，类似分子量的蛋白质会因受体刺激而发生酪氨酸磷酸化，并已被鉴定为丝氨酸/苏氨酸激酶，称为丝裂原活化蛋白（MAP）激酶或细胞外信号调节激酶（ERK）。MAP激酶构成一个相关激酶家族，其中至少三种激酶的分子量为40 - 45kDa。在本文中，我们表明mIg交联在成熟和未成熟的鼠B细胞系中均刺激了MAP激酶特有的髓鞘碱性蛋白磷酸转移酶活性。这种酶活性在三种不同的柱子上与一种42kDa的蛋白质共纯化，该蛋白质在mIg交联后发生酪氨酸磷酸化（pp42），并与一组抗（MAP激酶）抗体发生反应。尽管用抗（MAP激酶）抗体进行免疫印迹显示这些B细胞系同时表达42kDa和44kDa形式的MAP激酶，但只有42kDa形式被显著激活并发生酪氨酸磷酸化。用佛波酯激活蛋白激酶C（PKC）也导致42kDa MAP激酶的选择性酪氨酸磷酸化和激活。这表明mIg诱导的MAP激酶激活可能是由于mIg对PKC的刺激。然而，mIg刺激的MAP激酶激活和pp42酪氨酸磷酸化仅被PKC抑制剂星形孢菌素类似物化合物３部分阻断。相比之下，化合物３完全阻断了佛波酯刺激MAP激酶活性和诱导pp42酪氨酸磷酸化的能力。因此，mIg可能通过PKC依赖和非依赖机制激活MAP激酶。
