Low Molecular Weight Cyclin E Deregulates Dna Replication and Damage Repair to Promote Genomic Instability In Breast Cancer

<p>Low molecular weight cyclin E (LMW-E) are oncogenic forms of cyclin E that are post translationally generated by neutrophil elastase (NE) mediated cleavage of the 50 KDa full-length cyclin E1 (FL-cycE, encoded by <em>CCNE1</em>gene). The resultant N-terminus deleted (40 amino acids) form of LMW-E is detected in breast cancer cells and tumor tissues, but not in normal mammary epithelial cells or adjacent normal tissues. Unlike FL-cycE, LMW-E drives mammary epithelial cell transformation in human cells and spontaneous mammary tumor formation in transgenic mouse models, but the oncogenic mechanisms of LMW-E and its unique function(s) independent of FL-cycE are not fully understood. It is currently assumed that LMW-E drives the tumorigenic process by promoting G1/S cell cycle transition and accelerating mitotic exit. Biochemical features such as longer protein half-life, higher affinity to its kinase partner CDK2, and resistance to endogenous CDK inhibitors such as p21 and p27 all promote the tumorigenic ability of LMW-E. Clinical studies in breast cancer reveal that overexpression of LMW-E predicts recurrence and poor survival in breast cancer patients independent of molecular subtype, Ki67 status, nodal status, or tumor grade, suggesting LMW-E may be driving breast cancer development independent of its role in cell proliferation.</p> <p>In the current study, we tested the hypothesis that LMW-E promotes genomic instability by deregulating DNA replication and damage repair. We generated immortalized pre-cancerous human mammary epithelial cells (hMECs) engineered to express doxycycline inducible LMW-E or FL-cycE in <em>CCNE1</em> knock-out background. We found that, unlike LMW-E, FL-cycE overexpression led to DNA replication stress and DNA damage accumulation, resulting in reduced cell viability. LMW-E overexpression, on the other hand, promoted cell survival under replication stress, resulting in persistent genomic instability. RNA-sequencing results showed LMW-E but not FL-cycE overexpression enhanced DNA replication and damage repair pathways. Molecularly, LMW-E but not FL-cycE strongly interacted with CDC6, bound to chromatin, and facilitated replication stress tolerance by upregulating pre-replication complex assembly. LMW-E also mediated DNA repair by upregulating the levels of RAD51 and C17orf53, showing a dominant repairing effect over DNA damage induced by FL-cycE. Moreover, targeting the replication stress response pathway ATR-CHK1-RAD51 with small molecule inhibitors significantly decreased viability of LMW-E overexpressing hMECs and breast cancer cells. Lastly, we showed that positive LMW-E status was associated with genomic instability in tumors from a cohort of 725 patients diagnosed with early-stage breast cancer, further supporting our hypothesis that LMW-E promotes genomic instability to fuel breast cancer development.</p> <p>Collectively, our findings delineated a novel role for LMW-E in breast tumorigenesis mediated by replication stress tolerance and genomic instability, providing novel therapeutic strategies for LMW-E overexpressing breast cancers.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation (PhD)

Year dc:date.available

2023

Authors dc:creator

• Li, Mi
• <p>https://orcid.org/0000-0002-6038-4144</p>

Contributors dc:contributor

• Khandan Keyomarsi, Ph.D.
• Junjie Chen, Ph.D.
• Sendurai Mani, Ph.D.

• Low molecular weight cyclin E
• cell cycle
• DNA replication
• DNA damage repair
• genomic instability
• copy number variation
• CCNE1
• CDC6
• ATR-CHK1-RAD51
• breast cancer
• Cancer Biology

Repository record dc:identifier

https://digitalcommons.library.tmc.edu/utgsbs_dissertations/1237

OAI identifier oai:identifier

oai:digitalcommons.library.tmc.edu:utgsbs_dissertations-2294