Leibowitz Brian J, Cohick Wendie S
Department of Animal Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey, USA.
J Cell Physiol. 2009 Jul;220(1):182-8. doi: 10.1002/jcp.21748.
TNF-alpha and IGF-I exert opposing effects on mammary epithelial cell (MEC) growth and survival. However, both increase IGF binding protein-3 (IGFBP-3) expression, a multifunctional protein that plays both IGF-dependent as well as independent roles in these processes. We have reported that IGF-I utilizes the PI3-K and MAPK pathways to induce IGFBP-3 expression in bovine MEC. Here we show that TNF-alpha requires the SAPK pathway p38, but not JNK, to induce IGFBP-3 expression. Contrary to reports in cancer cell lines, TNF-alpha retained its ability to decrease DNA synthesis in cells transfected with IGFBP-3 siRNA. It also retained its ability to inhibit IGF-I-stimulated DNA synthesis in these cells. In contrast, the ability of IGF-I to increase DNA synthesis was attenuated with IGFBP-3 knockdown. IGFBP-3 knockdown also decreased basal DNA synthesis, indicating that a certain level of IGFBP-3 may be required for cell proliferation. While TNF-alpha alone failed to induce apoptosis, it increased cell death when added with the JNK agonist anisomycin (ANS). TNF-alpha and ANS were unable to induce apoptosis when either IGFBP-3 or JNK-2 was knocked-down, suggesting that both JNK and IGFBP-3 may interact with a downstream molecule central to apoptosis. There are reports that IGFBP-3 promotes either cell proliferation or apoptosis in different cell systems. However, this is the first report that endogenous IGFBP-3 is required for the action of both stimulatory and inhibitory factors within the same cell line. Therefore, the actions of IGFBP-3 are not pre-determined, but instead governed by cellular context such as JNK activation.
肿瘤坏死因子-α（TNF-α）和胰岛素样生长因子-I（IGF-I）对乳腺上皮细胞（MEC）的生长和存活具有相反的作用。然而，二者均能增加胰岛素样生长因子结合蛋白-3（IGFBP-3）的表达，IGFBP-3是一种多功能蛋白，在这些过程中发挥着依赖IGF以及不依赖IGF的作用。我们曾报道，IGF-I利用磷脂酰肌醇-3激酶（PI3-K）和丝裂原活化蛋白激酶（MAPK）途径诱导牛乳腺上皮细胞中IGFBP-3的表达。在此我们表明，TNF-α诱导IGFBP-3表达需要应激活化蛋白激酶（SAPK）途径中的p38，而非应激活化蛋白激酶（JNK）。与癌细胞系中的报道相反，TNF-α在用IGFBP-3小干扰RNA（siRNA）转染的细胞中仍保持其降低DNA合成的能力。它在这些细胞中也保留了抑制IGF-I刺激的DNA合成的能力。相比之下，IGF-I增加DNA合成的能力在IGFBP-3基因敲低时减弱。IGFBP-3基因敲低也降低了基础DNA合成，表明细胞增殖可能需要一定水平的IGFBP-3。虽然单独的TNF-α未能诱导细胞凋亡，但当与JNK激动剂茴香霉素（ANS）一起添加时，它会增加细胞死亡。当IGFBP-3或JNK-2被敲低时，TNF-α和ANS无法诱导细胞凋亡，这表明JNK和IGFBP-3可能都与细胞凋亡的一个下游核心分子相互作用。有报道称，IGFBP-3在不同细胞系统中促进细胞增殖或凋亡。然而，这是第一份关于内源性IGFBP-3是同一细胞系中刺激和抑制因子作用所必需的报道。因此，IGFBP-3的作用并非预先确定，而是由细胞环境（如JNK激活）决定。
