Gauthier E R, Piché L, Lemieux G, Lemieux R
Canadian Red Cross Blood Transfusion Service, Quebec, Canada.
Cancer Res. 1996 Mar 15;56(6):1451-6.
The development of an increasing number of tumors has been shown to involve the deregulation of not only cell proliferation but also normal cell death by apoptosis. Expression of the bcl-2 proto-oncogene has been shown to inhibit the apoptotic cell death of many types of cells. Recent work also has revealed the existence of several bcl-2-related genes that also can inhibit (e.g., bcl-X(L) and Mcl-1) or activate (e.g., bax, bcl-X(s), bag, and bad) apoptosis in several systems. Myelomas are antibody-secreting tumor cells derived from terminally differentiated B lymphocytes, and previous work from our laboratory showed that murine SP2/0 myeloma cells and derived B-cell hybridomas were highly sensitive to apoptosis induction by a block of gene expression (cycloheximide). Additional work revealed that a related murine myeloma cell line, P3X63Ag8.653, was resistant to apoptosis induction in similar conditions. To understand the genetic basis of this differential susceptibility, we examined the expression of apoptosis-related genes in these cell lines. Northern blot experiments showed no significant difference in the expression of myc and bax apoptosis-promoting genes in susceptible (SP2/0 and D5) and resistant (P3X63) cell lines. Also, no significant expression of the bcl-2 gene could be detected in these cell lines. However, a much higher expression level of bcl-X(L) mRNA was observed in apoptosis-resistant P3X63Ag8.653 cells. The role of bcl-X(L) was supported by the finding that expression of bcl-X(L) cDNA in transfected, apoptosis-sensitive D5 cells increased the viability of these cells greatly and reduced DNA fragmentation following apoptosis induction. Significant bcl-X(L) but not bcl-2 expression was also detected in three other murine myeloma cell lines (MOPC 315, RPC 5.4, and J558) derived from different plasmacytoma tumors. These results indicate a predominant role of bcl-X(L) in preventing apoptosis in myeloma cells and suggest that the expression of bcl-2 or bcl-X(L) genes in B-cell tumors depends on the differentiation stage of the precursor normal cell.
越来越多肿瘤的发生不仅涉及细胞增殖失调，还涉及正常细胞通过凋亡的死亡调控异常。bcl-2原癌基因的表达已被证明可抑制多种类型细胞的凋亡。最近的研究还揭示了几种与bcl-2相关的基因的存在，它们在多个系统中也能够抑制（如bcl-X(L)和Mcl-1）或激活（如bax、bcl-X(s)、bag和bad）凋亡。骨髓瘤是源自终末分化B淋巴细胞的抗体分泌肿瘤细胞，我们实验室之前的研究表明，小鼠SP2/0骨髓瘤细胞和衍生的B细胞杂交瘤对通过基因表达阻断（环己酰亚胺）诱导的凋亡高度敏感。进一步的研究发现，一种相关的小鼠骨髓瘤细胞系P3X63Ag8.653在类似条件下对凋亡诱导具有抗性。为了解这种差异敏感性的遗传基础，我们检测了这些细胞系中凋亡相关基因的表达。Northern印迹实验表明，在敏感（SP2/0和D5）和抗性（P3X63）细胞系中，myc和bax促凋亡基因的表达没有显著差异。此外，在这些细胞系中未检测到bcl-2基因的显著表达。然而，在抗凋亡的P3X63Ag8.653细胞中观察到bcl-X(L) mRNA的表达水平要高得多。转染的、对凋亡敏感的D5细胞中bcl-X(L) cDNA的表达大大提高了这些细胞的活力，并减少了凋亡诱导后的DNA片段化，这一发现支持了bcl-X(L)的作用。在源自不同浆细胞瘤肿瘤的其他三种小鼠骨髓瘤细胞系（MOPC 315、RPC 5.4和J558）中也检测到了显著的bcl-X(L)表达，但未检测到bcl-2表达。这些结果表明bcl-X(L)在预防骨髓瘤细胞凋亡中起主要作用，并表明B细胞肿瘤中bcl-2或bcl-X(L)基因的表达取决于前体正常细胞的分化阶段。
