Abstract 5458: Oncostatin M induces epithelial-mesenchymal transition and stem cell properties in senescent human mammary epithelial cells

The Interleukin-6 (IL-6) cytokine family member Oncostatin M (OSM) induces epithelial-mesenchymal transition (EMT) and cancer stem cell (CSC) properties in transformed cancer cells. Paradoxically, OSM induces a growth-inhibiting senescence response in normal human mammary epithelial cells (HMEC). Senescence is induced in normal cells by various stresses, such as aberrant oncogene signaling, and serves as a major tumor-suppressive barrier that must be bypassed for cellular transformation in vitro and tumorigenesis in vivo. Previous reports show that aberrant reactivation of EMT-inducing transcription factors (EMT-TFs) promotes senescence bypass. Thus, aberrant EMT may drive tumor initiation in addition to providing cancer cells with mesenchymal cell and stem cell properties that drive tumor progression, metastasis, and tumor recurrence. Conversely, our studies here indicate that much like aberrant oncogene signaling, aberrant EMT and CSC-properties induced by OSM may actually engage senescence in normal cells. Infecting Primary HMEC isolated from reduction mammoplasty tissue with lentivirus encoding shRNA to p16 created indefinite lifespan “Normal” HMEC. Subsequent infections with viruses encoding shRNA to p53, then constitutive expression of MYC and RAS created “Transformed” HMEC. After treating HMEC with recombinant OSM, proliferation and senescence were assessed by growth assays and qRT-PCR analysis of senescence-associated β-galactosidase (GLB1) expression. EMT and CSC-properties were assessed by western and qRT-PCR analysis of an epithelial marker E-cadherin (CDH1), a mesenchymal marker Vimentin (VIM), the EMT-TF Snail (SNAI1), and the CSC markers CD44 and HAS2. Flow cytometry examining BrdU-incorporation and CD24/CD44 surface expression also assessed proliferation and a CSC phenotype. OSM reduced growth by 80% and induced GLB1 expression in Normal HMEC, but not in Transformed HMEC. OSM-induced senescence was accompanied by Snail induction, changes in EMT-associated markers (reduced E-cadherin/increased Vimentin), and CSC marker (CD44 and HAS2) induction. Notably, OSM induced immediate SNAI1 and HAS2 expression; and a majority of the OSM-induced CD44+ population consisted of non-proliferating (BrdU-) cells. Unexpectedly, Snail and CD44 were also induced during oncogenic RAS-induced senescence; and Snail expression alone reduced growth and induced CD44 in normal HMEC. These results suggest that much like aberrant oncogene signaling, aberrantly induced EMT and CSC-properties may engage senescence in normal cells rather than promoting senescence bypass. Defining the mechanism linking senescence, EMT, and CSC-properties will identify targets for novel “pro-senescence” therapies that may inhibit metastasis and tumor recurrence, and expand our repertoire of therapies that enhance cancer patient outcomes. Citation Format: Benjamin L. Bryson, Damian J. Junk, Mark W. Jackson. Oncostatin M induces epithelial-mesenchymal transition and stem cell properties in senescent human mammary epithelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5458. doi:10.1158/1538-7445.AM2017-5458