The Molecular Mechanism Of CHD1L Degraded By CHFR In Breast Cancer

Breast cancer is the most common female cancer worldwide, which is a significanthealth issue for women. DNA damage and repair play a crucial role in breast cancer.CHD1L is a DNA damage response gene, which can quickly recruited to the sitesof DNA damage. Meanwhile CHD1L is overexpressed in many tumors as aproto-oncogene. But the relationship between CHD1L and breast cancer has not yetbeen reported. Therefore, our study focusing on the molecular mechanisms of CHD1Lhas important significance for prevention, diagnosis and treatment of breast cancer.The first part is about the protein expressions of CHD1L in breast cancer. Theresults show that there was a significant difference between cancer and adjacentnoncancerous tissues in the expression of different levels of CHD1L protein. But, wereported that the mRNA level of CHD1L was no significant difference between tumortissues and adjacent noncancerous tissues of breast cancer, suggesting that increasinglevel of CHD1L protein was not induced by high expression of mRNA. The survivalrate was significant different between positive expression group and negative group.To further explore the molecular mechanisms of CHD1L highly expressed inbreast cancer，we carried out the second phase of the study. We screened the interactedprotein of CHD1L by tandem affinity purification combined with mass spectrometry,and discovered that CHFR as a ubiquitin ligase, is a new CHD1L interacting protein.CHFR also involved in DNA damage repair. CHD1L is a tumor suppressor gene, whichis weakly expressed or can not detected in breast cancer. The results further verified theinteraction between CHFR and CHD1L through co-immunoprecipitation in vivo andvitro. And then we identified that the PBZ domain of CHFR binding to PARylationedCHD1L. PARP inhibitors affect the interaction of the two proteins, which indicates theinteraction depends on PAR. Ubiquitination assay showed that CHD1L could bestrongly ubiquitinated by CHFR, which acted as ubiquitin ligase E3. As a result, theactivated pathway of ubiquitin-proteasome degradation regulates the protein levelof CHD1L. In summary, our study found the interaction between CHFR and CHD1L, anddescribed the interaction mode of the two proteins and its biological significance inbreast cancer. In addition, a new optimal hypothesis for the failure of PARP inhibitorsin breast cancer was proposed.