Fig. 7

The SIRT1-PRRX1-KLF4 axis regulates breast cancer metastasis. a Silencing PRRX1 or forced expression of KLF4 increases metastatic capacity of non-tumorigenic basal-like BT549 cells. b Immunofluorescence staining of E-Cadherin, CK5, CK8, and ALDH1 in lung metastases. Scale bar, 50 µm. c Immunohistochemistry analysis of SIRT1 and PRRX1 in consecutive sections of a human breast cancer array. Of note, PRRX1 was predominantly localized in the nucleus (right and middle right), and SIRT1 was found in both nucleus (right and middle right) and cytoplasm (middle left). Scale bar, 100 µm. d Correlation between SIRT1 and PRRX1 protein levels in human breast tumors. Statistical significance was determined by a χ2 test. R is the correlation coefficient. e Percent specimens that are SIRT1-negative-in-nucleus according to clinical parameter of malignant tissues and lymph node metastases (** P<0.001, χ2 test). f Percent specimens with high expression (++/+++; red columns) and low expression (+, green columns) and absence (−, white columns) of PRRX1 according to clinical parameter of malignant tissues and lymph node metastases (** P<0.001, χ2 test). g Percent SIRT1-PRRX1 axis levels in indicated tissues. Of note, almost 94% lymph node metastases were stained with low-low SIRT1-PRRX1 (P<0.001). h Correlation between SIRT1 and KLF4 levels in human breast tumors. Statistical significance was determined by a χ2 test. R is the correlation coefficient. i Immunohistochemistry analysis of KLF4 in malignant tissues with or without distant metastases and lymph node metastases. Scale bar, 100 µm. Lower panel, percent of specimens with high expression (++/+++; red columns) and low expression (−/+, white columns) of KLF4 according to the distant metastases (** P<0.001, χ2 test). j A working model for SIRT1-PRRX1-KLF4-ALDH1 circuitry. SIRT1 deacetylates and thus stabilizes PRRX1; PRRX1 inhibits the transcription of KLF4; KLF4 activates transcription of ALDH1, which induces and marks CSCs