Iosla Finn

Establishing the Mechanosensitive Response of SP1 Phosphorylation in Breast Cancer

Faculty PI: Ryan Stowers

Breast cancer progression is accompanied by dynamic remodeling of the extracellular matrix (ECM), altering tissue mechanics and promoting invasive cell behavior through mechanotransductive pathways including PI3K and ERK1/2. Sp1 is a transcription factor highly expressed in aggressive cancers and has been shown to respond to changes in ECM mechanics in breast cancer. Mechanosensitive PI3K and ERK1/2 pathways can phosphorylate Sp1 at T453 and T739 in other cancers, however, it is unclear whether these activation sites are similarly regulated by breast tissue mechanics in vitro and in vivo. We hypothesized that tumor-mimicking conditions of increased stiffness and stress relaxation would drive the greatest nuclear pSp1-T739 and pSp1-T453 expression. To investigate pSp1-T739 in vitro, we cultured breast epithelial cells (MCF10A) in alginate-Matrigel hydrogels that mimic the mechanics of healthy and diseased tissue, followed by immunostaining and confocal imaging. In vivo, nuclear localization of pSp1-T453 and pSp1-T739 were evaluated across disease progression using mechanically characterized mammary tissue from healthy, early-, and late-stage carcinoma MMTV-PyMT mice. Expression of both pSp1-T453 and pSp1-T739 was greatest in the mammary epithelium of tissues in early carcinoma and lowest in late carcinoma. In vitro, pSp1-T739 showed no significant differences in nuclear localization across matrix conditions, indicating that this phosphorylation site may not be similarly regulated via mechanotransduction in engineered matrices. Conversely, elevated pSp1-T453/T739 in early murine carcinomas may indicate roles in early disease progression. Future studies will determine whether these sites are directly regulated by PI3K/ERK1/2 and what downstream transcriptional programs they activate.