Id1 enhances Angptl7 release from BMSCs to promote AML progression. (A) The proteomics analysis strategy of BMSF from Id1^+/+ and Id1^−/− AML recipients. (B) The heat map analysis of differentially expression proteins in tandem mass tag–based proteomic analysis of BMSF from wild-type and Id1^−/− AML mice. (C) The qPCR analysis of the differentially expressed proteins in BMSF proteomics. (D) The ELISA analysis of ANGPTL7 levels in the BM fluid derived from healthy individuals (n = 3) and patients with AML (M2, n = 2; M5, n = 2). (E) The western blotting analysis of ANGPTL7 levels in the MSCs derived from healthy individuals (n = 2) and patients with AML (M2, n = 2; M5, n = 2). (F) The ELISAs showed that ID1 knockout in HS-5 cells significantly decreases the ANGPTL7 protein level in CM. Overexpression of HA-ID1 in HS-5 cells significantly upregulates the level of ANGPTL7 in CM. (G) The MTT assays showed that ANGPTL7 recombinant protein significantly promotes the proliferation of Kasumi-1 and THP-1 cells. (H) CFU assays analyzing the AE9a LSKs or MLL-AF9 L-GMP cells. Average number of colonies generated from 800 cells (n = 3). (I-K) Cell cycle analysis on Kasumi-1 and THP-1 cells with vehicle or ANGPTL7 during coculture with ID1^+/+ or ID1^−/− HS-5 cells (n = 3). (L-N) Cell cycle analysis on AE9a-LSKs and MLL-AF9-L-GMP cells with vehicle or Angptl7 during coculture with Id1^ctrl or Id1^kd MS-5 cells (n = 3). (O) The western blot analysis of lentivirus-mediated ID1 silencing in patient-derived AML subtype M2 and M5 MSCs. Anti-ID1, anti-SP1, anti-ANGPTL7, and anti-GAPDH antibodies were used. (P-Q) The MTT proliferation analysis on patient-derived AML subtype M2 and M5 CD34⁺ leukemia blast cells with vehicle or ANGPTL7 treatment during coculture with matched ID1^+/+ or ID1^−/− MSCs. ∗P < .05; ∗∗P < .01; ∗∗∗P < .005; ∗∗∗∗P < .001. FC, fold change; WT, wild-type.