Barr L F, Campbell S E, Baylin S B
Department of Medicine, Johns Hopkins Hospital, Baltimore, Maryland 21205, USA.
Cell Growth Differ. 1997 Apr;8(4):381-92.
The overexpression of c-myc frequently accompanies the relapse of small cell lung cancer (SCLC) cells and contributes to the poor prognosis of this tumor. In this study, we confirm that transfected c-myc results in decreased homotypic cell aggregation and increased proliferative capacity of SCLC cells when nutrient conditions are adequate. We also find that c-myc contributes to apoptosis when cells are nutrient depleted, and flow cytometry suggests that this enhanced apoptosis is associated with a failure to halt cell cycling, consistent with the experience in other cell types. We previously found that protein kinase C-beta (PKC-beta) expression in NCI H209 (209) SCLC cells increases markedly with c-myc transfection (L. F. Barr et al., Cancer Res., 51: 5514-5519, 1991), and we hypothesized that PKC-beta may mediate some of the effects of c-myc in these cells. We test this hypothesis by transfection of rat PKC-beta 1 and bovine PKC-beta 2 isoforms into 209 cells before and after transfection with c-myc. PKC-beta 1 transfection has no effect on these cells. However, PKC-beta 2 expression has distinct phenotypic consequences. In the parental cells, PKC-beta 2 expression results in increased homotypic cell aggregation and a prolonged doubling time. Furthermore, PKC-beta 2 expression increases the fraction of these cells in G0-G1. In the cells which express a transfected c-myc gene, PKC-beta 2 expression improves the survival of cells in low serum by decreasing myc-induced apoptosis. This effect was associated with, and may be mediated by, a selection for cells in the G0-G1 fraction. We postulate that transfection of c-myc into SCLC cells may select for those expressing the PKC-beta 2 gene because this signal transduction event protects against myc-induced apoptosis.
c-myc的过表达常伴随小细胞肺癌（SCLC）细胞复发，并导致该肿瘤预后不良。在本研究中，我们证实，当营养条件充足时，转染c-myc会导致SCLC细胞同型细胞聚集减少、增殖能力增强。我们还发现，当细胞营养耗尽时，c-myc会促进细胞凋亡，流式细胞术表明这种增强的细胞凋亡与细胞周期停滞失败有关，这与其他细胞类型的情况一致。我们之前发现，NCI H209（209）SCLC细胞中蛋白激酶C-β（PKC-β）的表达随c-myc转染而显著增加（L.F. Barr等人，《癌症研究》，51: 5514 - 5519，1991），我们推测PKC-β可能介导c-myc在这些细胞中的某些作用。我们通过在转染c-myc之前和之后将大鼠PKC-β1和牛PKC-β2亚型转染到209细胞中来验证这一假设。PKC-β1转染对这些细胞没有影响。然而，PKC-β2的表达具有明显的表型后果。在亲本细胞中，PKC-β2的表达导致同型细胞聚集增加和倍增时间延长。此外，PKC-β2的表达增加了这些细胞在G0 - G1期的比例。在表达转染c-myc基因的细胞中，PKC-β2的表达通过减少myc诱导的细胞凋亡提高了低血清条件下细胞的存活率。这种作用与G0 - G1期细胞的选择有关，并且可能由其介导。我们推测，将c-myc转染到SCLC细胞中可能会选择那些表达PKC-β2基因的细胞，因为这种信号转导事件可防止myc诱导的细胞凋亡。
