Date of Award

2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular Biology

Abstract

Breast cancer is the second leading cause of cancer-related deaths among women in the US. Histone modifications are common epigenetic changes that have been implicated in several breast cancers, including HER2+ breast cancers. Current therapies, such as trastuzumab, block the HER2 receptor to reduce tumor growth. Unfortunately, HER2+ breast cancers have found ways to overcome these therapies, leading to tumor resistance, metastases, and poor survival outcomes. A better understanding of the underlying mechanisms contributing to HER2+ breast cancer resistance may lead to the discovery of novel therapeutic strategies to improve patient outcomes.One prognostic marker for poor survival in women with HER2+ breast cancer is high RNA expression of the critical epigenetic regulator, KMT2D. Our preliminary data showed that BT474 HER2+ cells that had acquired resistance to trastuzumab expressed higher levels of KMT2D than those of the isogenic, parental trastuzumab-sensitive cells. KMT2D was also shown to be necessary for maintaining resistance in BT474 trastuzumab-resistant cells. However, the effects of KMT2D on HER2+ breast cancers and the mechanism by which KMT2D confers resistance to BT474 cells was not well understood. We identified that KMT2D is necessary for in vivo cell growth, cell migration, and cell-cell adhesion in BT474 sensitive and resistant cells. Trastuzumab sensitivity assays determined that KMT2D is necessary for resistance in BT474 cells. Using unbiased sequencing and siRNA knockdown approaches, we identified several direct gene targets of KMT2D and KMT2D-regulated cellular pathways which may contribute to BT474 drug resistance. One gene, ITGB6, encodes for integrin subunit beta 6 and was found to be decreased upon KMT2D depletion. ITGB6 regulates processes which contribute to cancer progression and metastases, including cellular proliferation and cell-adhesion. Interestingly, when we depleted KMT2D or ITGB6 in our HER2+ cells, we saw a decrease in cell-cell adhesion. Notably, when we overexpressed ITGB6 under conditions of KMT2D knockdown in our BT474 sensitive and resistant cells, we saw a partial rescue in cell-cell adhesion. Migration studies have also identified a potential role for KMT2D in promoting cell migration. Overall, KMT2D appears to directly regulate ITGB6 expression, which may be responsible for BT474 cell-cell adhesion, and other aggressive phenotypes.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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