Fig 2: Modulation of Postn expression by FGFR and TGFß signaling. A NeuNDL cells were treated in the presence of MEGS with or without 10 ng/ml of TGFß-1 for 0.5 and 24 h and assessed for Postn protein levels. pSMAD2 (S465/467) was used as a control for the activation of the TGFßR. B Postn protein levels monitored in NeuNDL cells were treated with 5 µg/ml TGFßR inhibitor SB431542 or DMSO in either MEGS-depleted (PBS) or MEGS-supplemented medium for 0.5 and 24 h. pSMAD2 (S465/467) was used as a control for TFGßR inhibition. C MEGS-depleted (PBS) and BPE-supplemented media were pretreated with bFGF neutralizing antibody (nAb) or control IgG for 1 h at 4 °C prior to addition to the NeuNDL cultures and western blotting for Postn. D Immunofluorescence for SMAD2 nuclear localization was performed following a 24-h treatment with PBS, 10 ng/ml bFGF or 10 ng/ml TGFß-1 of MEGS-depleted cultures. Manual counting of representative images was conducted to assess localization. Data are represented as mean ± SEM. N = 10, ***P = 0.001 (D)

Fig 3: Epithelial Postn is acquired in a subset of breast cancers. A Immunohistochemistry for the expression of Postn was performed on mammary tumors from a panel of Neu-driven murine breast cancer models and on human tissue microarrays (TMAs). The models used were the MMTV-NeuNDL model (n = 9), MMTV-NIC (n = 10) and MMTV-PyMT (n = 8). The human TMA contained 72 cores with various levels of HER2 expression. Scale bar = 200 µm. B Tumors were classified as acquired or non-acquired according to their epithelial expression of Postn and were represented as a proportion of the total number in a bar graph. C Clustered UMAP embedding of scRNA-seq data of 24,271 cells from five triple-negative breast cancer tumors. Data and cell-type annotations were acquired from Wu et al. [1]. D Identical UMAP showing the distribution of POSTN expression across the cell types comprised in the tumor. Expression values correspond to log-transformed counts per 10 k transcripts.) Summary of the average POSTN expression (Z-score) in each cell type and the percentage of cells with POSTN detection for each patient (P1-5)

Fig 4: Postn gene expression is regulated by both bFGF and TGFß. Schematic summarizing the regulation of Postn by TGFß and FGF2. PI3K/AKT is the main drive of Postn expression. Although the exact effectors remain to be identified, FGFR signaling can repress Postn expression by acting on the PI3K/AKT pathway at one or multiple levels. TGFß signaling is shown to activate PI3K to promote AKT activation and the expression of Postn. Other growth factor receptors and surface integrins shown to activate Postn through AKT are also represented

Fig 5: PI3K/AKT pathway activity is required for the induction of Postn by bFGF removal and TGFß activation. A NeuNDL cells were treated with 25 µM LY294004 or DMSO control in both PBS and 10 ng/ml bFGF supplemented medium in the absence of MEGS for 0.5 and 24 h. pAKT (S473) was used as a control for the inhibition of PI3K. B NeuNDL cells were treated the exact same way as in (A) but with 10 µM of MK-2206 instead of LY294004. C NeuNDL cells were treated with or without 10 ng/ml TGFß-1 in combination with either 10 µM MK-2206 or DMSO controls. pSMAD2 (S465/467) and pAKT (S473) were used as control for TGFßR activation and AKT inhibition, respectively. D Medium was pretreated with bFGF neutralizing antibody or control IgG in combination with either DMSO or 10 µM MK-2206. pAKT (S473) was used as control for AKT inhibition. In all panel PBS designates MEGS-depleted conditions