Lack of radiation dose or quality dependence of epithelial-to-mesenchymal transition (EMT) mediated by transforming growth factor ß.

PURPOSE: Epithelial-to-mesenchymal transition (EMT) is a phenotype that alters cell morphology, disrupts morphogenesis, and increases motility. Our prior studies have shown that the progeny of human mammary epithelial cells (HMECs) irradiated with 2 Gy undergoes transforming growth factor ß (TGF-ß)-mediated EMT. In this study we determined whether radiation dose or quality affected TGF-ß-mediated EMT. METHODS AND MATERIALS: HMECs were cultured on tissue culture plastic or in Matrigel (BD Biosciences, San Jose, CA) and exposed to low or high linear energy transfer (LET) and TGF-ß (400 pg/mL). Image analysis was used to measure membrane-associated E-cadherin, a marker of functional epithelia, or fibronectin, a product of mesenchymal cells, as a function of radiation dose and quality. RESULTS: E-cadherin was reduced in TGF-ß-treated cells irradiated with low-LET radiation doses between 0.03 and 2 Gy compared with untreated, unirradiated cells or TGF-ß treatment alone. The radiation quality dependence of TGF-ß-mediated EMT was determined by use of 1 GeV/amu (gigaelectron volt/atomic mass unit) (56)Fe ion particles at the National Aeronautics and Space Administration's Space Radiation Laboratory. On the basis of the relative biological effectiveness of 2 for (56)Fe ion particles' clonogenic survival, TGF-ß-treated HMECs were irradiated with equitoxic 1-Gy (56)Fe ion or 2-Gy (137)Cs radiation in monolayer. Furthermore, TGF-ß-treated HMECs irradiated with either high- or low-LET radiation exhibited similar loss of E-cadherin and gain of fibronectin and resulted in similar large, poorly organized colonies when embedded in Matrigel. Moreover, the progeny of HMECs exposed to different fluences of (56)Fe ion underwent TGF-ß-mediated EMT even when only one-third of the cells were directly traversed by the particle. CONCLUSIONS: Thus TGF-ß-mediated EMT, like other non-targeted radiation effects, is neither radiation dose nor quality dependent at the doses examined.

Ionizing radiation predisposes nonmalignant human mammary epithelial cells to undergo transforming growth factor beta induced epithelial to mesenchymal transition.

Transforming growth factor beta1 (TGFbeta) 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 TGFbeta activation in vivo. We now show that IR sensitizes human mammary epithelial cells (HMEC) to undergo TGFbeta-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 TGFbeta (0.4 ng/mL) or double treated. All double-treated (IR + TGFbeta) HMEC underwent a morphologic shift from cuboidal to spindle shaped. This phenotype was accompanied by a decreased expression of epithelial markers E-cadherin, beta-catenin, 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 TGFbeta alone elicited EMT, although IR increased chronic TGFbeta signaling and activity. Gene expression profiling revealed that double-treated cells exhibit a specific 10-gene signature associated with Erk/mitogen-activated protein kinase (MAPK) signaling. We hypothesized that IR-induced MAPK activation primes nonmalignant HMEC to undergo TGFbeta-mediated EMT. Consistent with this, Erk phosphorylation was transiently induced by irradiation and persisted in irradiated cells treated with TGFbeta, 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.