Possible involvement of a lanthanide-sensitive protein kinase C substrate in lanthanide promotion of neoplastic transformation.
Possible involvement of a lanthanide-sensitive protein kinase C substrate in lanthanide promotion of neoplastic transformation.
复制标题
镧系元素敏感蛋白激酶 C 底物可能参与镧系元素促进肿瘤转化。
作者：
B. Smith;T. Gindhart;N. Colburn
稀土元素镧和铽（0.1-1.0 mM），钙的药理学类似物，诱导肿瘤转化的12-O-十四酰基佛波醇-13-乙酸酯（TPA）敏感（P+），并在较小程度上TPA耐药（P-）前肿瘤小鼠JB 6表皮细胞。在P+细胞系中诱导了每10（4）个细胞最多2500个锚定非依赖性集落，该反应与佛波醇酯（1.6-16 nM）诱导的反应相当。P-系中镧系元素诱导的最大集落产量是P+系中的20%（约550个集落），并且在TPA诱导小于30个集落/10（4）个细胞的条件下观察到。镧系元素和TPA对P+细胞的集落大小产生协同效应。镧系元素不是仅仅通过模拟高钙来促进转化：添加外源性细胞外钙（高达50.0 mM）或使用钙离子载体（高达毒性浓度）来增加细胞内钙不会促进转化。镧将取代钙激活部分纯化的蛋白激酶C（PKC），钙依赖性佛波酯受体。然而，镧系元素必须通过PKC激活以外的机制来促进转化，因为镧系元素未能激活完整JB 6细胞中的PKC。三个独立的实验表明，镧对完整细胞中的PKC依赖性事件缺乏影响。首先，与TPA相反，镧预处理的JB 6细胞没有产生升高的磷酸化的80 kd底物。第二，镧预处理并不引起长时间暴露后PKC活性的降低。第三，镧和TPA影响表皮生长因子结合的不同幅度，时间过程和钙依赖性。然而，我们发现，在P+，P-和致瘤细胞系，是敏感的镧和增加其迁移在十二烷基硫酸钠-聚丙烯酰胺凝胶从23至21 kD的PKC底物。上述数据表明：（i）阳离子结合的改变可能足以诱导转化的表型;和（ii）镧系元素促进肿瘤转化可能与镧系元素敏感的PKC底物有关，但不是由于直接的PKC激活。
The rare earth elements lanthanum and terbium (0.1-1.0 mM), pharmacological analogs of calcium, induced neoplastic transformation of 12-O-tetradecanoylphorbol-13-acetate (TPA)-sensitive (P+) and to a lesser extent TPA-resistant (P-) preneoplastic mouse JB6 epidermal cells. A maximum of 2500 anchorage-independent colonies per 10(4) cells were induced in P+ lines, a response comparable to that induced by phorbol esters (1.6-16 nM). The maximum lanthanide-induced colony yield in P- lines was 20% of that in P+ lines (approximately 550 colonies), and was observed under conditions where TPA induced less than 30 colonies per 10(4) cells. Lanthanides and TPA produced a synergistic effect on colony size in P+ cells. Lanthanides are not promoting transformation merely by mimicking high calcium: adding exogenous extracellular calcium (up to 50.0 mM) or using calcium ionophore (up to toxic concentrations) to increase intracellular calcium does not promote transformation. Lanthanum will substitute for calcium in activating partially purified protein kinase C (PKC), the calcium-dependent phorbol ester receptor. However, lanthanides must be promoting transformation by a mechanism other than PKC activation because lanthanides failed to activate PKC in intact JB6 cells. Three independent experiments showed a lack of lanthanum effect on PKC-dependent events in intact cells. First, in contrast to TPA, lanthanum pretreatment of JB6 cells did not produce elevated phosphorylation of an 80-kd substrate. Second lanthanum pretreatment did not cause decreased PKC activity after prolonged exposure. Third, lanthanum and TPA affected epidermal growth factor binding with a different magnitude, time course and calcium dependency. We found, however, a PKC substrate in P+, P- and tumorigenic cell lines that is sensitive to lanthanum and increases its migration in sodium dodecylsulfate-polyacrylamide gels from 23 to 21 kd. The above data suggest that: (i) alterations in cation binding may be sufficient for inducing the transformed phenotype; and (ii) lanthanide promotion of neoplastic transformation may be linked to a lanthanide-sensitive PKC substrate, but is not due to a direct PKC activation.