B cell precursor acute lymphoblastic leukemia (B-ALL) is the most common childhood malignancy. A subset of children with B-ALL are at high risk for relapse and death. Gene expression profiles in these high-risk B-ALLs is similar to that of Philadelphia chromosome positive ALL. Approximately half of these Ph-like B-ALL are characterized by genetic alterations that result in overexpression of CRLF2. CRLF2, together with the IL-7 receptor α chain, forms a receptor complex for the cytokine, TSLP. When TSLP binds, the receptor initiates downstream JAK2/STAT5 and PI3/AKT/mTOR pathway activation. The activating JAK mutations found in some CRLF2 B-ALL led to speculation that TSLP stimulation is not a factor in this disease. However, we find that TSLP increases phosphorylation of STAT5, AKT and S6 (downstream of mTOR) in CRLF2 B-ALL cells, including those with JAK defects. Activation of these pathways has been associated with oncogenesis and chemoresistance and their downstream targets include members of the Bcl2 family. The Bcl2 family pro-survival molecule Bcl-XL is a down stream target of STAT5 in Ph+ B-ALL. Mcl-1, another BCL2 family pro-survival molecule is known to be upregulated by mTOR activation via post-translational mechanisms in B cell lymphoma. We hypothesized that TSLP-induced JAK2/STAT5 and PI3/AKT/mTOR pathway activation contribute to chemoresistance in high risk CRLF2 B-ALL by upregulating the expression of Bcl-XL and Mcl-1. To test this hypothesis we cultured human CRLF2 B-ALL cell lines (MUTZ5 and CALL4) with and without TSLP and evaluated expression of the Bcl2 family pro-survival proteins, Bcl-XL, Mcl-1, and Bcl2. We found that TSLP induced significant increases in Bcl-XL and Mcl-1 proteins, but not Bcl2 in CRLF2 B-ALL cells. These cell lines have activating Jak mutations and thus reflect the ability of TSLP to increase expression of the Bcl2 family proteins in cases where activating JAK mutations are present. Next we evaluated the effect of Mcl-1 inhibitor on MUTZ5 and CALL4 cells. Preliminary data from these experiments show that cell counts in cultures treated with Mcl-1 inhibitor are reduce by >90% and this reduction is maintained in the presence of TSLP. These data provide evidence that TSLP-induced CRLF2 signals increase expression of Bcl2 pro-survival proteins, even in CRLF2 B-ALL cells with activating JAK mutations. These data also suggest that Mcl-1 inhibitors could be an effective treatment for this disease. Ongoing studies will evaluate the effect of TSLP and Mcl-1 inhibitors in primary CRLF2 B-ALL samples.

Citation Format: Cornelia Stoian, Muhammad Omair Kamal, Olivia Francis, Rhaya Johnson, Simone Montgomery, Jacqueline Coats, Hannah Choi, Shania Aponte-Paris, Micheal Reed, Shanalee Martinez, Karina Mayagoitia, Evgeny Chirshev, Chunhua Song, Sinisa Dovat, Kimberly J. Payne. TSLP regulates expression of Bcl2 family proteins in Ph-like ALL with CRLF2 alterations. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2444.