Fig. 5: ASS1 functions as a breast tumor suppressor.

a Western blot for ASS1 expression in breast cancer cell lines (top). The relative quantification of ASS1 expression in breast cancer cell lines (ASS1 expression in MDA-MB-231 cells was defined as 1) (bottom) (mean ± s.d., n = 3 biologically independent experiments). Western blot for the expression of indicated proteins in MDA-MB-231 cells transfected with ASS1 expression plasmid (ASS1-OE) or empty vector (b, top), and in MCF7 cells infected with control or ASS1 shRNA lentivirus (ASS1-KD) (c, top). Crystal violet assay for the proliferation rate of MDA-MB-231 cells transfected with ASS1 expression plasmid (ASS1-OE) or empty vector (b, bottom), and for MCF7 cells infected with control or ASS1 shRNA lentivirus (ASS1-KD) (c, bottom) (mean ± s.d., n = 3 biologically independent experiments). **P < 0.01, ***P < 0.001 from two-tailed unpaired Student’s t-tests.d Colony formation of MDA-MB-231 cells transfected with ASS1 expression plasmid (ASS1-OE) or empty vector, and of MCF7 cells infected with control or ASS1 shRNA lentivirus (ASS1-KD). 1 × 10⁶ MDA-MB-231 cells stably expressing ASS1 (ASS1-OE) or control vector (NC) were injected subcutaneously into the right flank of BALB/c nu/nu female mice. Tumor sizes were measured every 2 or 3 days (e). 36 days later mice were sacrificed, tumors were dissected and weighted (f). Data represented as mean ± s.d. (n = 7 mice per group). ***P < 0.001 from two-tailed unpaired Student’s t-tests. g Representative imagines of ASS1 immunohistochemical staining in paraffin-embedded human breast cancer tissue sections. Scale bars are 50 μm. h Comparing the expression levels of ASS1 in recurrent (n = 60) and no recurrent (n = 83) human breast cancers. **P < 0.01 from two-tailed unpaired Student’s t-tests. Source data are provided as a Source Data file.