Specificity protein 1 induces the expression of angiomotin in response to IL-6/STAT3 activation to mediate YAP-dependent growth of breast cancer cells

Abstract

Chronic inflammation is a major driver of tumor progression in over fifty percent of breast cancers. Tumors activate inflammatory processes by secreting factors that recruit and trigger inflammatory cells to release cytokines such as Interleukin 6 (IL-6). IL-6 stimulates the activity of signal transducers and activators of transcription 3 (STAT3), a transcription factor that has been extensively studied for its role in promoting breast cancer. Recently, downregulated HIPPO signaling was shown to drive the pro-growth effects of IL 6. Reduced HIPPO signaling allows for the nuclear translocation of transcriptional co-activator yes associated protein (YAP), implicating IL-6 in the co-activation of several transcription factors such as the TEADs that trigger pro growth programs. While IL-6/STAT3 stimulation has been shown to increase YAP activity, the mechanism driving this remains undocumented. The Angiomotins (Amots) are adapters of the HIPPO pathway that directly bind and regulate YAP activity. Molecular characterization of Amot transcriptional regulation unexpectedly revealed a single promoter controlling the expression of its two major isoforms: Amot 130 and Amot 80. Through immunofluorescent analysis, this study found that total Amot levels were elevated across multiple breast tumor subtypes and highest in samples with increased presence of stromal inflammatory cells. Further, the induction of total Amot expression by IL 6 was found to be essential for YAP dependent growth of breast cancer cells. The activation of Amot transcription by IL-6 was found to be through Specificity Protein 1 (Sp1), a transcription factor that is activated by STAT3. This work connects the activation of YAP1 by IL-6/STAT3 through the elevation of Amot expression by Sp1. Taken together, this explains a new avenue whereby breast cancer cells acquire enhanced oncogenic properties in response to inflammatory signaling.