A Role for Human DNA Polymerase λ in Alternative Lengthening of Telomeres

Telomerase negative cancer cell types use the Alternative Lengthening of Telomeres (ALT) pathway to elongate telomeres ends. Here, we show that silencing human DNA polymerase (Pol λ) in ALT cells represses ALT activity and induces telomeric stress. In addition, replication stress in the absence of Pol λ, strongly affects the survival of ALT cells. In vitro, Pol λ can promote annealing of even a single G-rich telomeric repeat to its complementary strand and use it to prime DNA synthesis. The noncoding telomeric repeat containing RNA TERRA and replication protein A negatively regulate this activity, while the Protection of Telomeres protein 1 (POT1)/TPP1 heterodimer stimulates Pol λ. Pol λ associates with telomeres and colocalizes with TPP1 in cells. In summary, our data suggest a role of Pol λ in the maintenance of telomeres by the ALT mechanism.     

The Role of Non-Specific Interactions in Canonical and ALT-Associated PML-Bodies Formation and Dynamics

In this work, we put forward a hypothesis about the decisive role of multivalent nonspecific interactions in the early stages of PML body formation. Our analysis of the PML isoform sequences showed that some of the PML isoforms, primarily PML-II, are prone to phase separation due to their polyampholytic properties and the disordered structure of their C-terminal domains. The similarity of the charge properties of the C-terminal domains of PML-II and PML-VI isoforms made it possible for the first time to detect migration of PML-VI from PML bodies to the periphery of the cell nucleus, similar to the migration of PML-II isoforms. We found a population of “small” (area less than 1 µm²) spherical PML bodies with high dynamics of PML isoforms exchange with nucleoplasm and a low fraction of immobilized proteins, which indicates their liquid state properties. Such structures can act as “seeds” of functionally active PML bodies, providing the necessary concentration of PML isoforms for the formation of intermolecular disulfide bonds between PML monomers. FRAP analysis of larger bodies of toroidal topology showed the existence of an insoluble scaffold in their structure. The hypothesis about the role of nonspecific multiple weak interactions in the formation of PML bodies is further supported by the change in the composition of the scaffold proteins of PML bodies, but not their solidification, under conditions of induction of dimerization of PML isoforms under oxidative stress. Using the colocalization of ALT-associated PML bodies (APBs) with TRF1, we identified APBs and showed the difference in the dynamic properties of APBs and canonical PML bodies.     

小剂量高三尖杉酯碱联合全反式维甲酸及三氧化二砷治疗急性早幼粒细胞白血病的临床研究

目的:观察在初发急性早幼粒细胞白血病（APL）中应用小剂量高三尖杉醋碱(HHT)联合全反式维甲酸(ATRA)以及三氧化二砷（ATO）作为诱导治疗方案的疗效及诱导治疗期间的不良事件发生情况,并与去甲氧柔红霉素（IDA）联合ATRA及ATO的治疗方案进行对比分析。方法:选取了2004年1月至2013年12月期间收治的的145例APL患者的资料进行回顾性分析,其中HHT治疗组74例,IDA治疗组71例,对比分析两组的完全缓解率（CR）,总生存率（OS）以及无事件生存率（EFS）及不良反应发生情况。结果:145例患者的CR率为97.2%（141/145）,HHT组与IDA组两组的CR率相似（98.6% vs. 95.7%,P=0.36）,到达CR时间分别为32.9 d和33.3 d（P=0.645）,获得分子生物学缓解时间分别为1.9月和2.2月（P=0.091）,无显著统计学差异。有4例患者早期死亡（2.8%）,其中3例死于颅内出血,1例死于呼吸窘迫（ARDS）。平均随访45.6月（0.17～131.5月）,两组间的OS和EFS均无统计学差异（P=0.9 ,P=0.093）。一共13例患者复发,其中分子生物学复发5例,中枢神经系统复发2例,两组的复发率差异无统计学意义（6.7% vs. 11.2%,P=0.342）。在亚组分析中,无论是中低危还是高危患者中,两组的OS和EFS也没有显示出统计学差异（均P＞0.05）。在不良反应方面,HHT组的血液学毒性显著低于IDA组（P=0.003）,合并1级发热的患者比例低于IDA组（28.3% vs. 45.1%, P=0.037）。其他肝肾及心脏等重要脏器损害,重要脏器出血等发生率在两组间无统计学差异。结论:ATRA及ATO分别联合小剂量HHT和IDA的方案在初治APL患者中的疗效近似,但联合小剂量HHT组的血液学毒性更小,相应的感染发生率更低。