ALL is the second most common hematologic malignancy of which patients with B-ALL account for 80% . Despite combination chemotherapy has achieved remarkable success on B-ALL; however, about 20 percent of patients with B-ALL still show insensitive to chemotherapy drugs . As is well-know, the ultimate goal of clinical therapy is to overcome the drug-resistance and reduce the recurrence. In this study, we demonstrated for the first time that Cyr61 can decrease the chemosensitivity of B-ALL cells to both DNR and VCR; Simultaneously, we also found that DNR can induce the production of Cyr61 in B-ALL cells through the ATM-dependent NF-κB pathway.
Cyr61 is a matrix protein and a member of CCN (Cyr61/CTGF/NOV) family. Cy61 plays an important role in maintaining the normal physiological function of the body [47–54]. Recent studies have found that Cyr61 contributes to the occurrence and development of tumors [9–13]. Our previous study has shown that the level of Cyr61 in both serum and bone marrow of ALL patients is increased, and the increasing Cyr61 can promote ALL cell survival . However, the role of Cyr61 in the chemosensitivity of B-ALL cells and the origin of Cyr61 in bone marrow remain unclear.
Although, DNR and VCR, common chemotherapy drugs for hematologic tumors, have good clinical response to B-ALL patients, however, there still remain some patients to develop drug resistance to therapy . In this study, we were surprised to find that Cyr61 could decrease chemosensitivity of B-ALL cells to DNR and VCR through regulating the cell apoptosis. Combining with our previous study , we confirmed that Cyr61 would play an important role in inducing multidrug resistance by affecting chemotherapy-induced apoptosis in B-ALL cells as well as blocking the function of Cyr61 maybe an interesting target for B-ALL.
It is well known that the regulation of cellular apoptosis is determined by the balance of anti-apoptotic and pro-apoptotic factors of Bcl-2 family proteins [55, 56]; therefore, we evaluated the effect of Cyr61 on the expression of Bcl-2, Bcl‐xL, XIAP, and Survivin; Interestingly, our data indicated that Cyr61 can increase the expression of Bcl‐2 without affecting Bcl‐xL, XIAP, and Survivin levels. Our findings reported here were consistent with our previous results in which Cyr61 can promote the survival of chronic myeloid leukemia (CML) cells by upregulating Bcl‐2 expression . Considering that Bcl-2 is the classical antiapoptotic protein of the Bcl-2 family , we propose that Cyr61 decrease the apoptosis of B-ALL cells through the Bcl‐2 pathway.
There is no doubt that Cyr61 plays an important role in decreasing the chemosensitivity of DNR and VCR in B-ALL; however, how this protein is produced in bone marrow remains enigmatic. Many studies have indicated that chemotherapy can induce drug resistance via producing a variety of cytokines, which can shelter the tumor cells from chemotherapy drugs [29, 37, 59]; Delightfully, as expected, our study showed that DNR, known as common first-line chemotherapy drug for B-ALL, could up-regulate the expression of Cyr61 in Nalm-6 cells through ATM/ NF-κB pathway. We speculated that inducing B-ALL cells to release Cyr61 by DNR might be a self-protective mechanism by tumor cells for survival; moreover, the increased Cyr61 could protect B-ALL cells from the drugs killing effects, which explained the high recurrence rate in later clinical treatment as well as the mechanism of minimal residual leukemia (MRL). In summary, our study has indicated that up-regulation of Cyr61 expression in Nalm-6 cells by DNR may proceed via ATM/NF-κB pathway and this may provide a target for us to clear the chemo-resistant remnant B-ALL cells.
DNR is one of anthracycline antibiotics and also belongs to cell cycle non-specific drug which can cause strong DNA damage respond (DDR). ATM, also known as a central molecule for DDR, can lead to a cell-cycle delay, which facilitates DNA repair prior to replication [55–57]. ATM downstream molecule NF-κB mediates the abnormal expression of anti-apoptotic genes in leukemic cells . Based on the studies presented above, we speculated that DNR may up-regulate the expression of Cyr61 in Nalm-6 cells through ATM/ NF-κB pathway. In this study, our data confirmed this assumption, and it was found that Nalm-6 cells had obvious DDR under the stimulation of DNR, the phosphorylation of ATM had been significantly increased and the expression of Cyr61 had been up-regulated after NF-κB activating
Taken together, our data showed that the Cyr61 can reduce the chemosensitivity of DNR and VCR in B-ALL cells via activating Bcl-2; moreover, DNR can induce the production of Cyr61 in B-ALL cells via an ATM-dependent NF-κB pathway. Blocking the Cyr61 expression in B-ALL cells may overcome the protection effect of therapy-induced BM niche and potentially prevent the occurrence of B-ALL relapse, which thereby significantly improve the efficacy of chemotherapeutics.