Role of SUSHI domain containing 3 (SUSD3) in breast cancer and aromatase inhibitor responsiveness

Abstract

OBJECTIVE: Aromatase has been the most commonly used target for the hormonal treatment of breast cancer. We previously used microarray gene expression profiling on primary breast cancer tissues with or without a favorable response to an aromatase inhibitor (AI) to determine molecular predictors of clinical benefit. Sushi domain containing 3 (SUSD3) was among the top 3 differentially expressed genes from responders vs. non-responders to an AI. Thus, we investigated the function of SUSD3 in breast cancer. DESIGN: Real-time PCR validation of microarray analysis was performed. Breast and endometrial cancer cell lines were used to explore the correlation between ERα, PR and SUSD3 messenger RNA (mRNA). The regulation of SUSD3 expression after anti-estrogen, anti-progestin, estradiol (E2) and progesterone (P4) treatments was explored. The roles of ERα and PR in SUSD3 regulation were determined by knockdown of these receptors. MATERIALS AND METHODS: mRNA levels were determined by real-time PCR. Knockdown experiments were performed using small-interfering RNA (siRNA). Breast cancer cell lines were treated with anti-estrogen ICI 182780, anti-progestin ZK 98299, E2 and P4. RESULTS: SUSD3 mRNA expression was higher in responders of AI treatment (fold change 3.508 vs. 1, p= 0.0002) and in ERα/PR-positive tumors (fold change: 5.734 vs. 1, p< 0.0001). Elevated SUSD3 mRNA expression was found in highly PR-positive cell lines whereas decreased expression was found in ERα/PR-negative cell lines. E2 induced SUSD3 expression while ICI, ZK, or P4 decreased expression. siRNA knockdown of ERα or PR decreased SUSD3 mRNA levels. siRNA knockdown of SUSD3 decreased ERα and PR mRNA and protein levels. CONCLUSION: We demonstrate that estrogen, ERα, progesterone, and PR regulate SUSD3 both in vivo and in vitro in breast cancer tissues and cells. We postulate a short feedback loop whereby SUSD3 regulates ERα and/or PR expression and transcriptional function, and in turn, ERα and/or PR regulate SUSD3 expression.