MT1-MMP deficiency prevents transcription of niche chemokines/cytokines. (A-C) KitL, SDF-1α, and IL-7 plasma levels in MT1-MMP^+/+ and MT1-MMP^−/− plasma were measured by ELISA (n > 6). KitL, SDF-1α, and IL-7 gene expression in (D) total BM cells, (E) MS-5 control and MT1-MMP–overexpressing cells, and (F) MT1-MMP knockdown (KD) and control MS-5 cells were analyzed using real-time PCR. The results are expressed relative to expression of a β-actin. (G) KitL, SDF-1α, and IL-7 protein levels in MT1-MMP knockdown (KD) and control MS-5 cell-culture supernatants were determined by ELISA. (H) KitL, SDF-1α, and IL-7 gene expression in MT1-MMP^+/+ and MT1-MMP^−/− MEF cells was determined using real-time PCR. The results are expressed relative to expression of β-actin. (I) KitL and SDF-1α protein levels in the indicated MEF cell-culture supernatants were evaluated by ELISA. (J) Lin⁻GFP⁺ cells were cultured on MT1-MMP^+/+ and MT1-MMP^−/− MEF cells in the presence or absence of neutralizing Abs against KitL. The number of CD11b⁺Gr1⁺ cells was assessed after 7 days by FACS (n = 5). (K) Lin⁻ cells were plated in transwells. MT1-MMP^+/+ and MT1-MMP^−/− MEF cell-culture supernatants supplemented with recombinant SDF-1α were added to the lower chamber. Neutralizing Abs against SDF-1α were added to both chambers. The percentage of migrated cells was determined (n = 9 from 2 independent experiments). Errors in bar graphs are SEM; *P < .05, **P < .01. Data shown are representative of 3 to 4 independent experiments.