Functional Study Of The Paraspeckle Protein1in DNA Damage Response

Paraspeckle protein1(PSPC1) was the first identified structural protein of the subnuclear structure paraspeckle. However, the exact physiological functions of PSPC1are still largely unknown. Previously, using a proteomic approach, we have shown that exposure to the DNA-damaging agent cisplatin can induce PSPC1expression in HeLa cells, indicating the possible involvement for PSPC1in DNA damage response (DDR). In the current study, the function of PSPC1in DDR was investigated. First it was found that besides cisplatin, another DNA-damaging agent Methyl methanesulfonate (MMS), could also induce the expression of PSPC1protein in HeLa cells. Abolishing PSPC1expression by siRNA significantly inhibited cell growth, caused spontaneous apoptosis, increased the level of ROS, as well as increased DNA damage, suggesting that PSPC1may be involved in DDR. However, PSPC1did not colocalize with yH2AX, a key player in DDR. In addition, PSPC1did not colocalize with53BP1nor RAD51, members of the homologous recombination repair pathway, indicating that PSPC1may not have direct involvement in these molecules-mediated DNA repair pathways. Interestingly, knock-down of PSPC1disrupted normal cell cycle distribution, with more cells entering the G2/M phase. Furthermore, while cisplatin induced G1/S arrest in HeLa cells, knock-down of PSPC1 caused cells to escape the G1/S checkpoint and enter mitosis, followed by more cells dying. Similarly, in G2/M arrest cells induced by MMS, knock-down of PSPC1increased the number of cells entering G2/M, and resulted in more cell death. In contrast, overexpression of PSPC1caused S phase arrest and less cells entering mitosis. Furthermore, co-immunoprecipitation result showed that PSPCl could interact with the ATR-interaction protein (ATRIP), implying that PSPC1might be involved in cell cycle checkpoint regulation through the interaction with ATRIP. Taken together, these results indicated a new role for PSPC1in maintaining genome integrity during DDR, particularly in the G1/S checkpoint. Specifically, PSPC1could be induced by DNA damage, which can lead to cycle arrest at C1/S phase for the damage to be repaired. When PSPC1is absent, cells cannot stop at S phase and enter G2/M with increased DNA damage, which eventually can lead to cell death.