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Access Type

WSU Access

Date of Award

January 2022

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Pharmaceutical Sciences

First Advisor

Wanqing Liu

Abstract

Fatty Acid Desaturase-1 (FADS1) is a key rate-limiting enzyme in polyunsaturated fatty acid (PUFA) metabolism responsible for the biosynthesis of eicosapentaenoic acid (EPA) and arachidonic acid (ARA) from essential fatty acids which both play an important role in cancer cell biology. Previous studies have shown that FADS1 has aberrant expression in several cancers including colon, pancreas, breast, and laryngeal cancers. However, the causal role of FADS1 in malignancies is not fully understood. The ultimate goal of this dissertation is to understand the role of FADS1 gene in the tumor biology and cancer therapy of renal cell carcinoma (RCC). RCC is the most common type of kidney cancer. Over 30% of patients with localized tumors eventually develop metastases. According to American Cancer Society (ACS), the five-year relative survival rate for distant stages of RCC is only 14%. Metastatic RCC (mRCC) is intrinsically refractory to conventional chemotherapy drugs. It remains an unmet medical need to further understand the mechanism underlying the poor survival related to metastatic RCCs and develop new strategies to improve it. We investigated the function of FADS1 across various cancer types utilizing The TCGA database using multiple bioinformatics and statistical tools. We identified that FADS1 is a cancer predictor for poor cancer survival, especially in RCC. Compared to normal tissue, the mRNA expression of FADS1 is significantly increased in primary tumors while even higher in metastatic and recurrent tumors. Mechanistically, pathway analysis demonstrated that FADS1 is associated with cell cycle control genes, DNA damage response and cholesterol biosynthesis. Interestingly, FADS1 expression is higher when TP53 is mutated. Tumors with increased FADS1 expression also demonstrated an increased fibroblasts, and macrophages infiltration among most cancer types. Single nucleotide polymorphisms (SNPs) which are well-known expression quantitative trait loci (eQTLs) for FADS1 in normal human tissues were also significantly correlated with FADS1 expression in tumors of various tissue types, suggesting that they could be used as a marker to stratify cancer patients according to the level of FADS1 expression in their tumor tissue. Following our bioinformatic finding, we inhibited the activity of FADS1 in RCC to examine its role in tumor cell growth and viability in vitro and in vivo. Using either chemical inhibitor or shRNA against FADS1 suppressed cell proliferation in 786-O and A498 cell lines. Moreover, FADS1 knockdown (KD) resulted in smaller tumor formation in vivo. Further mechanistic study revealed induction of endoplasmic reticulum stress response signaling in FADS1 KD cells. In fact, FADS1 KD cells were more sensitive to ER stress inducers. Inhibition of FADS1 resulted in higher expression of ATF4 and ATF3. We confirmed that ATF3 was the downstream mediator of FADS1 in RCC cells. In addition, we observed a lipid reprogramming regulation after FADS1 inhibition that showed increased fatty acid uptake and increased lipid droplet formation. The metabolomic analysis on FADS1 inhibition also revealed lower level of UDP-N-Acetyl-Glucosamine (UDP-NacGlc) that is used for protein folding in ER lumen. These data suggested that FADS1-mediated ER stress signaling regulates the expression of ATF3 and serves as a promising therapeutic target for the treatment of RCC.

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