Maitra Urmila, Seo Jin, Lozano Mary M, Dudley Jaquelin P
Section of Molecular Genetics and Microbiology, The University of Texas at Austin, 24th and Speedway, ESB 226, Austin, TX 78712-0162, USA.
Mol Cell Biol. 2006 Oct;26(20):7466-78. doi: 10.1128/MCB.01083-06. Epub 2006 Aug 5.
Cutl1/CCAAT displacement protein (CDP) is a transcriptional repressor of mouse mammary tumor virus (MMTV), a betaretrovirus that is a paradigm for mammary-specific gene regulation. Virgin mammary glands have high levels of full-length CDP (200 kDa) that binds to negative regulatory elements (NREs) to repress MMTV transcription. During late pregnancy, full-length CDP levels decline, and a 150-kDa form of CDP (CDP150) appears concomitantly with a decline in DNA-binding activity for the MMTV NREs and an increase in viral transcripts. Developmental regulation of CDP was recapitulated in the normal mammary epithelial line, SCp2. Western blotting of tissue and SCp2 nuclear extracts confirmed that CDP150 lacks the C terminus. Transfection of tagged full-length and mutant cDNAs into SCp2 cells and use of a cysteine protease inhibitor demonstrated that CDP is proteolytically processed within the homeodomain to remove the C terminus during differentiation. Mixing of virgin and lactating mammary extracts or transfection of mutant CDP cDNAs missing the homeodomain into cells containing full-length CDP also abrogated NRE binding. Loss of DNA binding correlated with increased expression of MMTV and other mammary-specific genes, indicating that CDP150 is a developmentally induced dominant-negative protein. Thus, a novel posttranslational process controls Cutl1/CDP activity and gene expression in the mammary gland.
Cutl1/CCAAT 位移蛋白（CDP）是小鼠乳腺肿瘤病毒（MMTV）的转录抑制因子，MMTV 是一种β逆转录病毒，是乳腺特异性基因调控的范例。未孕乳腺中全长 CDP（200 kDa）水平较高，它与负调控元件（NREs）结合以抑制 MMTV 转录。在妊娠后期，全长 CDP 水平下降，同时出现 150 kDa 形式的 CDP（CDP150），伴随 MMTV NREs 的 DNA 结合活性下降以及病毒转录本增加。正常乳腺上皮细胞系 SCp2 重现了 CDP 的发育调控。组织和 SCp2 核提取物的蛋白质免疫印迹证实 CDP150 缺乏 C 末端。将标记的全长和突变 cDNA 转染到 SCp2 细胞中，并使用半胱氨酸蛋白酶抑制剂表明，CDP 在同源结构域内被蛋白水解加工，在分化过程中去除 C 末端。将未孕和泌乳乳腺提取物混合或把缺失同源结构域的突变 CDP cDNA 转染到含有全长 CDP 的细胞中也消除了 NRE 结合。DNA 结合的丧失与 MMTV 和其他乳腺特异性基因表达增加相关，表明 CDP150 是一种发育诱导的显性负性蛋白。因此，一种新的翻译后过程控制乳腺中 Cutl1/CDP 的活性和基因表达。
