The Role Of Ifitm3 In The Immune Response Of Brca-Deficient High Grade Serous Ovarian Carcinoma

Author

Han Cun, The University of Texas MD Anderson Cancer Center UTHealth Graduate School of Biomedical SciencesFollow

Author ORCID Identifier

0000-0002-1465-2267

Date of Graduation

8-2021

Document Type

Thesis (MS)

Program Affiliation

Biomedical Sciences

Degree Name

Masters of Science (MS)

Advisor/Committee Chair

Samuel C. Mok, PhD

Committee Member

Karen H. Lu, MD

Committee Member

Kwong K. Wong, PhD

Committee Member

Melinda S. Yates, PhD

Committee Member

Yuexin Liu, PhD

Committee Member

Barrett Lawson, MD

Abstract

Background: Prior studies showed that BRCA-deficient high grade serous ovarian carcinoma (HGSOC) had increased tumor infiltrating lymphocytes (TILs) compared to BRCA-wildtype (WT). To better understand the underlying immune mechanism in these tumors, a preliminary transcriptome analysis was performed on a set of microdissected HGSOC tumor specimens with BRCA1-mutation, BRCA2-mutation, or WT. This demonstrated an upregulation of IFITM3, an essential gene in modulating immune function. Based on these findings, we hypothesized that BRCA-deficient HGSOC have increased DNA damage leading to upregulation of IFITM3 and subsequent increase in antigen presentation and T-cell activation.

Methods: Following IRB approval, preliminary transcriptome analysis was performed followed by validation using immunohistochemistry (IHC) for IFITM3 expression in a larger cohort of patients with HGSOC. Various HGSOC cell lines, including BRCA1-null lines, were used to validate mRNA expression. Immune biomarkers were investigated using multiplex immunofluorescence (IF) and imaging mass cytometry (IMC) on our cohort, and HLA mRNA expression was evaluated in HGSOC cell lines. IFITM3 expression was manipulated in HGSOC cells using siRNAs to determine the effect of IFITM3 on the expression of immune-related genes and survival in HGSOC cell lines.

Results:A total of 57 samples were used including 12 with BRCA1-mutation, 9 BRCA2-mutation, and 36 WT. Tumors with BRCA mutations had a significantly higher IFITM3 protein expression compared to WT (p=0.0001). IFITM3 mRNA expression was also significantly higher in UWB1.289, a BRCA1-null cell line, than UWB1.289+BRCA1, the same cell line with BRCA1 gene function restored (p=0.0001). CD8+GranzymeB+ cell density was significantly higher in BRCA-deficient tumors compared to the WT (p=0.0004). HLA-F mRNA expression in UWB1.289 was significantly higher than in UWB1.289+BRCA1 (p=0.0001), and this correlated with IFITM3 mRNA expression (r=0.617, p=0.014). IFITM3 silencing leads to an increase in survival of BRCA1-null HGSOC cell lines (p

Conclusion: This study suggests that IFITM3 stimulates the immune response and decreases cancer cell growth in BRCA-deficient HGSOC. This novel relationship provides insight into the association of IFITM3 with DNA damage, which may be valid in other malignancies. Further examination of IFITM3 in HGSOC provides many opportunities to better understand the pathogenesis of ovarian carcinoma, potential screening methods, and therapeutic options.

Keywords

BRCA, ovary, cancer, immunology, IFITM3, tumor immune microenvironment