Investigating Singleminded 2s in Regulation of Breast Cancer Progression and Therapeutic Resistance

Abstract

Breast cancer is a leading cause of cancer-related death for women in the USA. Estrogen receptor positive breast cancers (ER+BC) comprise over 70% of BC cases and are targeted via ER modulation therapies. Despite this, ER+BC patients can experience recurrence within 20 years and the majority of BC related can be attributed to metastatic ER+BC. Thus, there is an increased need to investigate novel biomarkers and therapeutic targets for treatment of ER+ patients with recurrence and metastasis. Here, we identify loss of the bHLH/PAS transcription, singleminded 2s (SIM2s) as a novel marker for progression and recurrence of ER+BC. In this study, we demonstrate a relationship between SIM2s, the NFkB signaling pathway, PI3K/AKT signaling, cyclooxygenase-2 (COX-2/PTGS2), and Semaphorin7a (SEMA7A) in ER+BC which may serve as a therapeutic target to reduce breast cancer progression. Inflammation raises challenges in treating and preventing the spread of breast cancer. Specifically, the NFkB pathway contributes to cancer progression by stimulating proliferation and preventing apoptosis. PTGS2 is a target gene of NFkB and is upregulated in 40% of human breast carcinomas. COX-2 is an enzyme involved in the expression of SEMA7A and production of prostaglandins, which mediate inflammation. NFkB repressed expression of SIM2, but when NFkB is suppressed, repression of SIM2 expression is negated. Loss of SIM2 resulted in aberrant PI3K/AKT/NFkB signaling leading to increased expression in COX-2 and SEMA7A. MCF7 SIM2 knockout cells lose estrogen receptor (ER), have decreased PTEN expression, and gain an epithelial to mesenchymal phenotype. Exogenous SEMA7A decreased SIM2s expression and promoter activity. MCF7 xenografts reveal reciprocal expression of SIM2s and SEMA7A. Additionally in MMTV-PyMT mice, SIM2s expression is lost as tumors transition from pre-malignant to invasive phenotypes, yet we observe maintenance of SIM2s and ER in SEMA7A-/-;PyMT mice. MCF7 SIM2 knockout cells acquire resistance to p110α inhibition but are susceptible to p110δ inhibition. These findings establish a regulatory relationship between SIM2s and SEMA7A in ER+BC suggesting a SIM2s/SEMA7A switch which may confer resistance in ER+BC via a p110 catalytic subunit switch. Thus, expression of SIM2s or SEMA7A may act as a prognostic indicator to provide therapeutic advantages in resistant and recurrent ER+BC.