Defective nucleolar localization and dominant interfering properties of a parafibromin L95P missense mutant causing the hyperparathyroidism-jaw tumor syndrome
Defective nucleolar localization and dominant interfering properties of a parafibromin L95P missense mutant causing the hyperparathyroidism-jaw tumor syndrome
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DOI：
10.1677/erc-09-0272
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发表时间：
2010-06-01
影响因子：
3.9
通讯作者：
Simonds, William F.
中科院分区：
文献类型：
--
作者：
Panicker, Leelamma M.;Zhang, Jian-Hua;Simonds, William F.
甲状旁腺功能亢进-下颌肿瘤综合征（HPT-JT）是一种家族性癌症综合征，可由HRPT2/CDC73的种系失活引起，HRPT2/CDC73是一种推定的肿瘤抑制基因，编码副纤维蛋白，副纤维蛋白是转录调节蛋白PAF1复合物的一个组成部分，与酵母蛋白Cdc73p同源。绝大多数已发现的HRPT2/CDC73种系突变是截断或移码突变，由于错义突变而导致功能丧失的情况很少见。我们在这里报告了一个因种系L95P错义突变而导致HPT-JT的亲缘关系。我们在体外研究了突变的parafibromin，以了解其假定的功能丧失的基础。当在培养细胞中转染时，L95P突变体的表达水平低于野生型（wt）的parafibromin，这种差异不能通过抑制蛋白酶体降解途径来克服。L95P突变体parafibromin保留了与内源性PAF1复合物组分组装的能力，共免疫沉淀证明了这一点。亚细胞定位分析显示，与wt相比，L95P突变体的核仁定位明显不足，这种缺陷可能是由于L95P突变体上游假定的核仁定位信号被破坏所致。在NIH-3T3和HEK 293细胞中，转染L95P突变体（而不是wt），细胞周期进展加快，细胞存活率提高，这显然是由于内源性的parafibromin作用受到显性干扰。随着L95P突变，核仁定位的丧失和生长刺激表型的获得同时提高了副纤白蛋白必须与核仁中的靶标相互作用才能充分发挥其肿瘤抑制功能的可能性。内分泌相关的癌症（2010）17 513-524
The hyperparathyroidism-jaw tumor syndrome (HPT-JT) is a familial cancer syndrome that can result from germline inactivation of HRPT2/CDC73, a putative tumor suppressor gene that encodes parafibromin, a component of the transcriptional regulatory PAF1 complex with homology to the yeast protein Cdc73p. The vast majority of HRPT2/CDC73 germline mutations identified have been truncation or frameshift mutations, and loss of function due to missense mutation is rare. We report here a kindred with HPT-JT due to a germline L95P missense mutation in parafibromin. The mutant parafibromin was studied in vitro to understand the basis of its presumed loss-of-function. When transfected in cultured cells, the L95P mutant was expressed to a lower level than wild-type (wt) parafibromin, a difference that was not overcome by inhibition of the proteasomal degradation pathway. The L95P mutant parafibromin retained the ability to assemble with endogenous PAF1 complex components as evidenced by co-immunoprecipitation. Analysis of subcellular localization showed that the L95P mutant was markedly deficient in nucleolar localization compared to the wt, an impairment likely resulting from disruption of a putative nucleolar localization signal immediately upstream of the L95P mutation. Transfection of the L95P parafibromin mutant, but not the wt, enhanced cell cycle progression and increased cell survival in NIH-3T3 and HEK 293 cells, resulting apparently from dominant interference with endogenous parafibromin action. The simultaneous loss of nucleolar localization and acquisition of a growth stimulatory phenotype with the L95P mutation raise the possibility that parafibromin must interact with targets in the nucleolus to fully execute its tumor suppressor functions. Endocrine-Related Cancer (2010) 17 513-524