TNFAIP3 is required for FGFR1 activation-promoted proliferation and tumorigenesis of premalignant DCIS.COM human mammary epithelial cells

Although ductal carcinoma in situ (DCIS) is a non-invasive breast cancer, many DCIS lesions may progress to invasive cancer and the genes and pathways responsible for its progression are largely unknown. FGFR1 plays an important role in cell proliferation, differentiation and carcinogenesis. The purpose of this study is to examine the roles of FGFR1 signaling in gene expression, cell proliferation, tumor growth and progression in a non-invasive DCIS model.

DCIS.COM cells were transfected with an empty vector to generate DCIS-Ctrl cells. DCIS-iFGFR1 cells were transfected with an AP20187-inducible iFGFR1 vector to generate DCIS-iFGFR1 cells. iFGFR1 consists of the v-Src myristoylation membrane-targeting sequence, FGFR1 cytoplasmic domain and the AP20187-inducible FKBP12 dimerization domain, which simulates FGFR1 signaling. The CRISPR/Cas9 system was employed to knockout ERK1, ERK2 or TNFAIP3 in DCIS-iFGFR1 cells. Established cell lines were treated with/without AP20187 and with/without FGFR1, MEK, or ERK1/2 inhibitor. The effects of these treatments were determined by Western blot, RNA-Seq, real-time RT-PCR, cell proliferation, mammosphere growth, xenograft tumor growth, and tumor histopathological assays.

Activation of iFGFR1 signaling in DCIS-iFGFR1 cells enhanced ERK1/2 activities, induced partial epithelial-to-mesenchymal transition (EMT) and increased cell proliferation. Activation of iFGFR1 signaling promoted DCIS growth and progression to invasive cancer derived from DCIS-iFGFR1 cells in mice. Activation of iFGFR1 signaling also altered expression levels of 946 genes involved in cell proliferation, migration, cancer pathways, and other molecular and cellular functions. TNFAIP3, a ubiquitin-editing enzyme, is upregulated by iFGFR1 signaling in a FGFR1 kinase activity and in an ERK2-dependent manner. Importantly, TNFAIP3 knockout not only inhibited the AP20187-induced proliferation and tumor growth of DCIS-iFGFR1 cells, but also further reduced baseline proliferation and tumor growth of DCIS-iFGFR1 cells without AP20187 treatment.

Activation of iFGFR1 promotes ERK1/2 activity, EMT, cell proliferation, tumor growth, DCIS progression to invasive cancer, and altered the gene expression profile of DCIS-iFGFR1 cells. Activation of iFGFR1 upregulated TNFAIP3 in an ERK2-dependent manner and TNFAIP3 is required for iFGFR1 activation-promoted DCIS.COM cell proliferation, mammosphere growth, tumor growth and progression. These results suggest that TNFAIP3 may be a potential target for inhibiting DCIS growth and progression promoted by FGFR1 signaling.