A novel peroxisome proliferator-activated receptor γ isoform with dominant negative activity generated by alternative splicing
A novel peroxisome proliferator-activated receptor γ isoform with dominant negative activity generated by alternative splicing
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DOI：
10.1074/jbc.m502716200
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发表时间：
2005-07-15
影响因子：
4.8
通讯作者：
Colantuoni, V
中科院分区：
文献类型：
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作者：
Sabatino, L;Casamassimi, A;Colantuoni, V
我们研究了过氧化物酶体增殖物激活受体γ（PPARG）基因座，试图确定表达的序列标签和/或保守的非编码序列的内含子序列含有开放阅读框架，并可能能够编码新的蛋白质。我们确定了一个新的PPARG转录本，定义γ ORF 4，它在内含子4中含有通读。预期的翻译蛋白缺乏由外显子5和6编码的配体结合结构域。我们鉴定了人肿瘤细胞系和组织中的转录本，合成了cDNA，并将其克隆到表达载体中。使用瞬时转染，我们发现γ ORF 4 cDNA被翻译成一个主要的核蛋白，不反式激活报告基因。此外，亚型相对于PPAR γ是显性负性的。有趣的是，γ ORF 4在一系列散发性结直肠癌中体内表达。在某些情况下，它也在肿瘤附近的粘膜中表达，尽管水平较低，这表明它可能与肿瘤发生有关。γ ORF 4的致瘤作用与我们的发现一致，即γ ORF 4不仅失去了抑制细胞生长的能力，而且还获得了刺激细胞生长的潜力。总之，这项研究表明，γ ORF 4在体内表达，它失去了一些PPAR γ的特性，并且它影响了PPAR γ的功能。对抗PPAR γ的能力表明γ ORF 4在结直肠癌的发病机制中起作用。
We examined the peroxisome proliferator-activated receptor gamma ( PPARG) locus in an attempt to identify expressed sequence tags and/or conserved non-coding sequences in the intron sequences containing open reading frames and potentially able to encode new proteins. We identified a new PPARG transcript, defined gamma ORF4, which harbors a readthrough in intron 4. The expected translated protein lacks the ligand-binding domain encoded by exons 5 and 6. We identified the transcript in human tumor cell lines and tissues, synthesized the cDNA, and cloned it in expression vectors. Using transient transfections, we found that gamma ORF4 cDNA is translated into a predominantly nuclear protein that does not transactivate a reporter gene. Moreover, the isoform is dominant negative versus PPAR gamma. Interestingly, gamma ORF4 was expressed in vivo in a series of sporadic colorectal cancers. In some cases, it was expressed, albeit at lower levels, also in the mucosa adjacent to the tumors, suggesting that it may be related to tumorigenesis. A tumorigenic effect of gamma ORF4 is in line with our finding that gamma ORF4 has not only lost the capacity to restrain cell growth but has acquired the potential to stimulate it. In conclusion, this study demonstrates that gamma ORF4 is expressed in vivo, that it has lost some PPAR gamma properties, and that it affects PPAR gamma functioning. The ability to counteract PPAR gamma suggests that gamma ORF4 plays a role in the pathogenesis of colorectal cancers.