Heme Oxygenase-1 in Leukemia Cells Promotes Cancer Associated Fibroblasts Mediating Progression of Acute Lymphoblastic Leukemia

Backgroud and objective: Recurrence and resistance is still the biggest challenges for Acute lymphoblastic leukemia (ALL). In recent years, a new concept has been proposed that the interaction between bone marrow microenvironment and leukemia cells could reduce the sensitivity of leukemia cells to chemotherapy. As an important matric element of the bone marrow microenvironment, Cancerassociated fibroblasts (CAFs) can mediate changes in bone marrow microenvironment to promote tumor proliferation and infiltration, but its role in ALL has not been described. Heme Oxygenase-1 (HO-1) is a rate-limiting enzyme in the process of heme catabolism, which is highly expressed in leukemia cells and can promote chemo-resistance by regulating the preservation of hematopoietic stem progenitor cells in the bone marrow microenvironment according to the recent research. In this article, we explored that HO-1 may be a key factor for promoting cancer associated fibroblasts to mediated chemo-resistance of ALL in the bone marrow microenvironment.

Methods: For clinical sample analysis, Bone marrow nucleated cells of 16 ALL patients with complete remission (ALL-CR), 12 ALL with relapse/refractory (ALL-R/R) and 10 normal controls were btained from bone marrow puncture. The expression of HO-1 and CAFs markers which includes α-SMA, FAP and FSP-1 was examined by quantitative reverse transcription-PCR (RT-PCR) and Western blot. In vitro cell experiments, CAFs was obtained from transfusion of bone marrow-derived mesenchymal stem cells (BM-MSCs) with recombinant human TGF-β1 (rhTGF-β1) stimulating. We used ALL primary cells and ALL cell lines (Nalm-6/Super-B15) to culture alone or co-culture with CAFs to detect proliferation, apoptosis and cell cycle of leukemia cells. In addition, we transfected ALL cell lines by constructing siHO-1 lentiviral vector, and co-cultured with CAFs or cultured separately to detect the above index changes in leukemia cells.

Results: The expressions of α-SMA, FAP, FSP-1 and HO-1 were significantly higher in ALL-R/R patients than in ALL-CR group and normal control group (P<0.05), which suggested that CAFs and HO-1 are closely related to recurrence and resistance of ALL. In vitro tests, after rhTGF-β1 stimulated BM-MSCs for 48h, the mRNA and protein expression levels of α-SMA, FAP and FSP-1 were significantly higher than those in BM-MSCs alone (P<0.05), This step was used to obtain CAFs. Then proceed to CAFs and Nalm-6/Super-B15 cell lines or ALL primary cells co-cultured tests. Results showed that CAFs can enhanced the leukemia cells proliferation and decreased apoptosis, and leukemia cells arrested in the G0/G1 phase was increased. Interestingly, this effect could be decreased by silencing HO-1 expression in Nalm-6/Super-B15 cell lines, which suggested that HO-1 may be a key factor mediating the interaction between leukemia cells and CAFs in bone marrow microenvironment.

Conclusion:As an important component of the bone marrow microenvironment, CAFs are closely related to the recurrence and resistance of ALL. HO-1 may be a key component mediating the interaction between CAFs and leukemia cells of ALL. This results may provide a new entry point for deepening the mechanism of ALL progression and finding more effective targeted therapies. But further in vitro and in vivo experiments are still needed for verification.