SYK Is a Critical Regulator of FLT3 in Acute Myeloid Leukemia

Abstract

SUMMARY Cooperative dependencies between mutant oncoproteins and wild-type proteins are critical in cancer pathogenesis and therapy resistance. Although spleen tyrosine kinase (SYK) has been implicated in hematologic malignancies, it is rarely mutated. We used kinase activity profiling to identify collaborators of SYK in acute myeloid leukemia (AML) and determined that FMS-like tyrosine kinase 3 (FLT3) is transactivated by SYK via direct binding. Highly activated SYK is predominantly found in FLT3-ITD positive AML and cooperates with FLT3-ITD to activate MYC transcriptional programs. FLT3-ITD AML cells are more vulnerable to SYK suppression than FLT3 wild-type counterparts. In a FLT3-ITD in vivo model, SYK is indispensable for myeloproliferative disease (MPD) development, and SYK overexpression promotes overt transformation to AML and resistance to FLT3-ITD-targeted therapy. SIGNIFICANCE Although imatinib therapy has been paradigm shifting for treating patients with BCR-ABL-rearranged chronic myelogenous leukemia (CML), the application of targeted kinase inhibitors to treating AML has been a more complex undertaking. In this study, we identified an oncogenic partnership between the most commonly mutated kinase in AML, FLT3, and the cytoplasmic kinase SYK. SYK transactivates FLT3 by a direct physical interaction, is critical for the development of FLT3-ITD-induced myeloid neoplasia, and is more highly activated in primary human FLT3-ITD-positive AML. These studies also raise the possibility of SYK activation as a mechanism of resistance to FLT3 inhibitors, suggest FLT3 mutant AML as a subtype for SYK inhibitor testing, and nominate the clinical testing of SYK and FLT3 inhibitor combinations.

SOCS proteins in regulation of receptor tyrosine kinase signaling

“…SOCS2 has higher affinity for the motifs pY-(I/L/V)-(I/L)-(I/V)-I and SOCS4 has higher affinity for the motifs pY-(I/L/V)-X-(I/V/S/T/G)-X [60]. Signaling through RTKs is tightly regulated by interacting proteins and very often SH2-domain containing proteins are involved in this regulation [4][5][6][7][106][107][108]. Since SH2 domain of different SOCS proteins displays specificity to the different pY consensus sequence it is expected that SOCS proteins display a degree of selectively in regulation of RTK signaling.…”

Brain-Expressed X-linked (BEX) proteins in human cancers

“…Signaling downstream of FLT3 is tightly controlled by various signaling proteins which associate with FLT3 and regulate downstream signaling by propagating the signals from extracellular stimuli or diminish the signal by destabilizing the receptor. For example, association of GRB10, SLAP, SYK and CSK resulted in enhanced FLT3 signaling, while the association of SOCS6, SOCS2 and LNK suppressed FLT3 signaling by destabilizing the receptor [85][86][87][88][89][90][91][92][93][94][95]. BEX1 expression was found to be down-regulated in a group of FLT3-ITD positive AML patients [8].…”

Targeting MTHFD2 in acute myeloid leukemia

“…Sequences targeted by each of these hairpins are listed in Table S6. shRNA constructs targeting MTH FD2 with miR30 expression cassettes were designed and delivered via a TRM PVIR vector as previously described (Puissant et al, 2014). For virus production, 12 µg of the aforementioned vector with 6 µg pCMV-GAG/POL and pCMV-VSVG (for retroviral infection of human cells) or 6 µg pCMV8.9 and pCMV-VSVG (for lentiviral infection of human or murine cells, respectively) packaging vectors were transfected into the 293 packaging cell line using X-treme-GENE 9 (Roche), and the resulting viral supernatants were harvested as previously described (Banerji et al, 2012).…”

“…ssGSEA projection on the collection of 186 KEGG canonical pathways, collections of MYC target gene set signatures, MTH FD2 signatures and JQ1 treatment effect signatures was applied separately to each of the primary AML transcript datasets-TCGA_LAML and Wouters (Cancer Genome Atlas Research Network, 2013). ssGSEA projection on gene set signatures for MTH FD2 KD, CMap MTH FD2 trt-sh, MTH FD2 expression z-score, JQ1 treatment (Zuber et al, 2011), Consensus_JQ1 signature (Puissant et al, 2014), and MYC target gene signatures (MSigDB c2.v04 collection) were performed in each primary tumor dataset. A ssGSEA z-score cutoff 1 was used to assess if a tumor sample is highly enriched in any of the gene signatures.…”