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The insulin-like growth factor type 1 receptor (IGF-1R) is now thought to have a dual function in breast cancer. Several studies have shown overexpression of the IGF-1R pathway results in increased tumor cell proliferation and survival. Recent loss-of-function models have shown decreased mammary tumorigenesis latency and increased metastasis. These recent studies correlate with analyses of human patient datasets identifying worse overall survival with low IGF-1R expression. Similarly, inhibition of IGF-1R in the clinic has had no affect or has led to worse outcomes supporting the hypothesis that the IGF-1R may have tumor suppressive properties. Our prior published studies revealed loss of IGF-1R function results in heightened tumor epithelial stress, which alters the tumor microenvironment to be permissive for metastasis. Therefore, we asked does the loss of IGF-1R inherently change the tumor epithelium or is it simply the alterations of the microenvironment that lead to a metastatic primary tumor? We first analyzed cell invasion of primary tumor epithelial cells from a mouse tumor model driven by the Wnt1 oncogene (MMTV-Wnt1) and with reduced IGF-1R signaling by expression of a dominant-negative transgene (MMTV-dnIGF-1R). Epithelial cells from the MMTV-Wnt1/dnIGF-1R (bigenic) tumors invaded at the same rate as MMTV-Wnt1 tumor epithelial cells by tail vein injection suggesting invasive capacity is unchanged with reduced IGF-1R signaling. Interestingly, size of lung micrometastases from tail vein injected bigenic tumor epithelial cells was significantly reduced and the number also decreased over time in part due to a proliferative defect determined by immunostaining for pH3. Similarly, bigenic primary tumor epithelial cells injected into the mammary gland fat pad failed to form tumors suggesting alterations in cell adhesion. Consistent with this observation, E-cadherin gene and protein expression were decreased in the bigenic tumor epithelium compared to MMTV-Wnt1 tumors. In vitro analysis of cell adhesion in MMTV-Wnt1 primary epithelial cells resulted in both K8+ (luminal) and K14+ (basal) tumor epithelial cells adherence, while only K14+ cells from bigenic tumors adhered to collagen. Similarly, the lung micrometastases from tail vein injections exhibited predominantly K14+ cells. Analysis of MMTV-Wnt1 and bigenic primary tumors using single cell RNAseq revealed alterations in both stromal and epithelial populations that may contribute to bigenic primary tumor growth and metastasis. These data support the conclusion that inhibiting IGF-1R signaling results in both alterations to the tumor epithelium (partial EMT) and microenvironment that result in metastasis, but also, that the IGF-1R deficient metastatic cells need a niche or paracine signaling to proliferate.

SAT-LB26 A Dual Role for IGF-1R in Mammary Tumorigenesis