CST与Primpol相互作用在调控端粒损伤诱导的DNA复制和诱导ALT发生的作用及机制研究

端粒损伤可以激活损伤诱导的非S期端粒合成BITS，继而引发端粒的ALT表型产生。前期研究证实CST既可以参与端粒的损伤应答又能在ALT细胞的端粒维持过程中发挥重要作用，然而其在BITS诱导ALT发生中的机制尚不清晰。本研究中，我们发现其相互作用蛋白PrimPol可能参与调控了BITS诱导的ALT产生。我们认为CST识别损伤端粒并招募PrimPol，利用其引发酶活性在损伤位点下游重启并合成单链DNA，进而产生ssDNA gap。ssDNA gap被SLX4等酶识别并切割后，形成双链DNA损伤，进而引发依赖于Rad52的端粒重组延伸，暨ALT。PrimPol是迄今发现的首个具有引发酶活性并参与BITS的DNA聚合酶，其通过引发单链合成、诱导双链损伤并激活重组延伸，将是一种全新的ALT形成机制。本研究将为全面理解ALT阳性肿瘤细胞中端粒DNA维持机制奠定基础，也为ALT肿瘤的治疗提供了新的靶标。

Telomeric DNA Break could Induce non-S-phase Telomere Synthesis (BITS), which promotes alternative telomere lengthening (ALT) through crosslink repair. We have previously reported that the telomere binding complex CST could take part in telomere damage response and be involved in ALT formation. However, the detailed mechanism for its function in BITS-induced ALT hasn’t been clearly resolved. Here, we proved that CST interacting protein PrimPol may play an essential role in this process. We proposed that CST could recruit PrimPol to the telomeric damage sites, which initiates the synthesis of the downstream ssDNA and forms ssDNA gaps via its primase activity. Subsequently, the ssDNA gap could be recognized and resolved by the nuclease SLX4, which generates double-strand breaks (DSB) at telomeres. Finally, the spontaneous telomeric DSB could be repaired by strand crosslink and Rad52 dependent homologous recombination. In summary, PrimPol is the first identified DNA polymerase function in BITS-induced ALT, through the primase activity. This study will not only broaden our knowledge of the mechanism of telomeric DNA replication in ALT tumor cells but also guide our current cancer therapy which is based on regulating telomere replication.