The pioneer transcriptional factors (PTFs) of the Oct3/4 network including Oct3/4, Nanog, Sox2, Sall4 (ONSS), have been associated with breast cancer. Regulation of ONSS and other factors in this network were assessed for their role in malignancy. M ethods Triple negative breast cancer cell line (MDA-MB-231) transfected with human Oct3/4-GFP promoter was sorted using FACS. Differentially expressed genes (DEGs) were identified using qPCR and microarray. 3D mammospheres (CSC) from Oct3/4(+) cells were assessed for stable Oct3/4 expression. Tumor seeding and lung metastatic potential of Oct3/4(+) cells were assessed in immunocompromised mice. DEGs in the tumors were assessed with respect to implanted tissue (SQ, lungs or brain), recurrence, and metastases. Expression of CD44+/CD24- was evaluated using flow cytometry. Resistance of Oct3/4(+) cells to paclitaxel was assessed using MTS assay.


Oct3/4-GFP expression was stable in mammospheres. Oct3/4(+) cells showed 25 DEGs and significant resistance to paclitaxel when compared to non-transfected cells. Upregulated growth and developmental genes included Gata6, FoxA2, Sall4, Zic2, H2afJ, Stc1 and Bmi1 . The Oct3/4(+) cells also showed enhanced tumorigenic potential and aggressive growth in immunocompromised mice. Additionally, this modulated transcriptome of the Oct3/4 (+) cells showed further upregulation of several genes in metastatic lung lesions in mice (> 5 fold) compared to orthotopic tumors including Oct4A, Bmi1, Ezh2, Klf5, Hox7B, Gja1, Stc1, Amigo2 and Dkk1. Serially re-implanting tumors in mice as a model of recurrence and metastasis highlighted Sall4, c-Myc, Mmp1, Mmp9 and Dkk1 genes in maintaining an upregulated expression specifically in metastatic lesions and a 2-fold higher expression of stem cell phenotype markers (CD44+/CD24-). Overall Oct3/4 expression in tumors in lungs, brain and metastases were significantly higher than orthotopic mammary fat pad tumors. Additionally, the transcriptome was most upregulated in brain except for Gja1 and H2faJ , indicating tissue-specific regulation of this transcriptome.


ONSS and other Oct3/4 related factors may drive the differentiation and maintenance of breast cancer stem cells and may promote their tumorigenic potential and resistance to drugs such as paclitaxel. However, there is tissue-specific heterogeneity in the differential upregulation of this transcriptome as well stemness phenotype of tumors in these tissues.

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