Ionizing Radiation Predisposes Nonmalignant Human Mammary Epithelial Cells to Undergo Transforming Growth Factor β–Induced Epithelial to Mesenchymal Transition

Abstract

Transforming growth factor B1 (TGFB) is a tumor suppressor during the initial stage of tumorigenesis, but it can switch to a tumor promoter during neoplastic progression. Ionizing radiation (IR), both a carcinogen and a therapeutic agent, induces TGFB activation in vivo. We now show that IR sensitizes human mammary epithelial cells (HMEC) to undergo TGFB-mediated epithelial to mesenchymal transition (EMT). Nonmalignant HMEC (MCF10A, HMT3522 S1, and 184v) were irradiated with 2 Gy shortly after attachment in monolayer culture or treated with a low concentration of TGFB (0.4 ng/mL) or double treated. All double-treated (IR + TGFB) HMEC underwent a morphologic shift from cuboidal to spindle shaped. This phenotype was accompanied by a decreased expression of epithelial markers E-cadherin, Bcatenin, and ZO-1, remodeling of the actin cytoskeleton, and increased expression of mesenchymal markers N-cadherin, fibronectin, and vimentin. Furthermore, double treatment increased cell motility, promoted invasion, and disrupted acinar morphogenesis of cells subsequently plated in Matrigel. Neither radiation nor TGFB alone elicited EMT, although IR increased chronic TGFB signaling and activity. Gene expression profiling revealed that double-treated cells exhibit a specific 10-gene signature associated with Erk/mitogenactivated protein kinase (MAPK) signaling. We hypothesized that IR-induced MAPK activation primes nonmalignant HMEC to undergo TGFB-mediated EMT. Consistent with this, Erk phosphorylation was transiently induced by irradiation and persisted in irradiated cells treated with TGFB, and treatment with U0126, a MAP/Erk kinase (MEK) inhibitor, blocked the EMT phenotype. Together, these data show that the interactions between radiation-induced signaling pathways elicit heritable phenotypes that could contribute to neoplastic progression. [Cancer Res 2007;67(18):8662-70]

Radiotherapy-induced plasticity of prostate cancer mobilizes stem-like non-adherent, Erk signaling-dependent cells

“…The radiationinduced phenotypic heterogeneity, we report, might reflect transient cellular plasticity as well as stress-evoked responses of preexistent subsets cells seen in the parental DU145 and PC-3 cell populations. [40][41][42][43][44][45][46][47][48][49][50][51][52] Ionizing radiation can promote traits of EMT in normal human mammary epithelium, 41 lung carcinoma 42,43 and colorectal cancer cells. 44 Furthermore, besides their role in E-cadherin repression, 45,46 Slug and Snail have been implicated in radioresistance-associated EMT.…”

Mechanism of the Mesenchymal–Epithelial Transition and Its Relationship with Metastatic Tumor Formation

“…Thus, in the absence of the EMT-inducing signals received from the activated stroma that are present in primary tumors, metastatic cancer cells may simply fall back to an epithelial state when entering into sites of dissemination (84,85). However, some studies found that the induction of an EMT seemed to be able to create a heritable state, even long after the EMT-inducing stimulus was removed (86). Furthermore, increasing evidence suggests that the EMT process is greatly associated with resistance to chemotherapy, radiotherapy, and even targeted therapy (see the "Clinical importance of EMT and MET" section).…”

Radiation induces epithelial-mesenchymal transition in colorectal cancer cells

“…Several signaling pathways are also reported to be associated with EMT, which lead to transcriptional and post-transcriptional induction of EMT transcription factors (23). In regard to the relationship between irradiation and EMT, Andarawewa et al reported that irradiation induced TGF-β-mediated EMT (24). Several studies have examined the possible role of EMT in CRC progression (25,26), and the association between chemoresistance and EMT in CRC (27)(28)(29).…”