XBP1 and breast carcinoma: However, only the four transcription factors in this list (FOXA1; AR; XBP1 and GATA3) were shown to be upregulated in ER+ versus ER- tumors and in the ER+ MCF7 and T-47D luminal breast cancer cell lines relative to the ER- MDA-MB231, MDA-MB435 and SK-BR-3 cell lines [49].Nevertheless, none of the genes that correlated best with POLR3G expression were found in gene expression signatures of basal-like tumors.