ID1-mediated SP1 protein levels are essential for Angptl7 transcription. (A-C) HS-5 cells were transduced with indicated sgRNAs and overexpression plasmids. Western blott and qPCR analyses were performed on these HS-5 cells after 4 days of coculture with Kasumi-1 cells. (D-F) HS-5 cells were transduced with indicated sgRNAs and overexpression plasmids. Western blot and qPCR analyses were performed on these HS-5 cells after 4 days of coculture with THP-1 cells. (G) The ELISAs showed that SP1 knockdown restricts ANGPTL7 expression and that ANGPTL7 was significantly upregulated by SP1 overexpression in HS-5 cells CM. (H) PROMO predicts the SP1 binding site on the ANGPTL7 promoter. (I) The dual-luciferase reporter assay showed that SP1 binds to site II to upregulate luciferase activity. (J) Chromatin immunoprecipitation assays showed that ANGPTL7 promoter DNA fragments were immunoprecipitated by SP1 antibodies in contrast to immunoglobulin G (IgG) in HS-5 cells cocultured with CD34⁺ HSPCs, Kasumi-1, or THP-1 cells. (K-L) The MTT assays showed that overexpression of SP1 in ID1^−/− HS-5 cells significantly promote the proliferation of Kasumi-1 and THP-1 cells. ∗P < .05; ∗∗P < .01; ∗∗∗P < .005; ∗∗∗∗P < .001.