Hochberg M, Gabay C, Laskov R
The Hubert H. Humphrey Center for Experimental Medicine and Cancer Research, The Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Leuk Lymphoma. 1998 Aug;30(5-6):637-49. doi: 10.3109/10428199809057576.
Non-Hodgkin's B-lymphomas (B-NHL) are a very heterogeneous group of B-cell neoplasias originating from the germinal centers of lymphatic follicles. Thus, they represent a suitable experimental model to study the molecular basis of certain key events which take place in the lymphatic follicles, including somatic hypermutation and heavy chain isotypic switch. An unusual B-NHL cell line ("Farage") not producing Ig polypeptide chains was previously shown to rearrange its IgH and Igkappa genes and transcribe seemingly normal size mu and kappa mRNAs. In an attempt to characterize the phenotype of Farage cells better and to elucidate the molecular basis of the failure of Farage cells to synthesize Ig chains, we sequenced its VH and Vkappa rearranged gene segments by PCR and RT-PCR. It was found that both V genes are somatically, heavily mutated compared to their germline counterparts. In addition, this rearranged VDJ gene of the heavy chain is not transcribed. Instead, the Farage cells express a low level of a new family of germline transcripts starting with a VH like sequence, continuing with a small segment of the 3'VH germline flanking region, and ending within the Cmu region. These transcripts lack D and J segments and do not contain the open reading frame of the full-length Cmu protein. Thus, Farage cells fail to produce mu heavy chains due to silencing of the expression of the conventional VDJCmu transcript and expression of unusual Cmu-germline transcripts. In contrast to the IgH genes, the rearranged VJ gene of Farage is transcribed and gives rise to a full-size kappa-mRNA. This transcript, however, is not translated to a full-length kappa-chain, as it contains a stop codon in its coding region. All the above show that Farage cells are unable to produce Ig polypeptide chains, due to somatic mutations altering the kappa-chain gene, and mutations and/or regulatory events that shutoff the transcription of the IgH gene. The heavily mutated Vkappa and Vkappa genes found, support the conclusion that the Farage cell line originated either from germinal center cells or from the mantle zone of the lymphoid follicle.
非霍奇金B淋巴细胞瘤（B-NHL）是一组起源于淋巴滤泡生发中心的非常异质性的B细胞肿瘤。因此，它们是研究淋巴滤泡中发生的某些关键事件分子基础的合适实验模型，这些事件包括体细胞超突变和重链同种型转换。先前已证明一种不产生Ig多肽链的异常B-NHL细胞系（“Farage”）可重排其IgH和Igκ基因，并转录出看似正常大小的μ和κ mRNA。为了更好地表征Farage细胞的表型，并阐明Farage细胞无法合成Ig链的分子基础，我们通过PCR和RT-PCR对其VH和Vκ重排基因片段进行了测序。结果发现，与它们的种系对应物相比，这两个V基因都发生了大量体细胞突变。此外，重链的这种重排VDJ基因未被转录。相反，Farage细胞表达低水平的一类新的种系转录本，其起始于类似VH的序列，接着是3'VH种系侧翼区域的一小段，然后在Cμ区域内结束。这些转录本缺乏D和J片段，并且不包含全长Cμ蛋白的开放阅读框。因此，Farage细胞由于常规VDJCμ转录本表达的沉默和异常Cμ种系转录本的表达而无法产生μ重链。与IgH基因相反，Farage的重排VJ基因被转录并产生全长κ mRNA。然而，该转录本未被翻译成全长κ链，因为它在其编码区域中包含一个终止密码子。以上所有表明，由于体细胞突变改变了κ链基因，以及导致IgH基因转录关闭的突变和/或调控事件，Farage细胞无法产生Ig多肽链。所发现的大量突变的Vκ和Vκ基因支持了Farage细胞系起源于生发中心细胞或淋巴滤泡套区细胞的结论。
