AML1-ETO9a is correlated with C-KIT overexpression/mutations and indicates poor disease outcome in t(8;21) acute myeloid leukemia-M2

Abstract

AML1-ETO fusion gene is generated from chromosomal translocation t(8;21) mainly in acute myeloid leukemia M2 subtype (AML-M2). Its spliced variant transcript, AML1-ETO9a, rapidly induces leukemia in murine model. To evaluate its clinical significance, AML1-ETO9a expression was assessed in 118 patients with t(8;21) AML-M2, using qualitative and nested quantitative reverse transcriptase (RT)-PCR methods. These cases were accordingly divided into the AML1-ETO9a-H group (n ¼ 86, positive for qualitative RT-PCR, with higher level of AML1-ETO9a by quantitative RT-PCR) and the AML1-ETO9a-L group (n ¼ 32, negative for qualitative RT-PCR, with lower but still detectable level of AML1-ETO9a by quantitative RT-PCR). C-KIT expression was significantly increased in the AML1-ETO9a-H group, as compared with the AML1-ETO9a-L group. Of the 36 patients harboring C-KIT mutations, 32 patients overexpressed AML1-ETO9a (P ¼ 0.0209). Clinically, AML1-ETO9a-H patients exhibited significantly elevated white blood cells count, less bone marrow aberrant myelocytes, increased CD56 but decreased CD19 expression (P ¼ 0.0451, P ¼ 0.0479, P ¼ 0.0149 and P ¼ 0.0298, respectively). Moreover, AML1-ETO9a overexpression was related to short event-free and overall survival time (P ¼ 0.0072 and P ¼ 0.0076, respectively). Taken together, these data suggest that AML1-ETO9a is correlated with C-KIT overexpression/mutations and indicates poor disease outcome in t(8;21) AML-M2.

Supraphysiologic levels of the AML1-ETO isoform AE9a are essential for transformation

“…S8 B and C). Our result that none of the 23 randomly selected t(8;21) patient samples has detectable 9a protein predicts that between 0% and 14.3% of t(8;21) patients express 9a protein (Wilson method with 95% confidence), which is significantly lower than the reported percentage (∼70%) of patients harboring the 9a transcript (binomial exact test P value < 0.05) (14,16). Collectively, these data underscore the significance of oncogene expression to disease phenotype and suggest that, whereas AE9a is a potent oncogene at high expression levels in murine transduction/transplantation assays, its contribution to t(8;21) disease requires careful verification.…”

“…Furthermore, disease relapse is significantly correlated with higher transcript levels (39)(40)(41)(42). Similarly, high transcript levels of AE9a also correlated with t(8;21) disease relapse (16,43 signals from cooperating events play a role in how AE or AE9a affect downstream signals. A number of cooperating oncogenes have been shown to promote leukemic transformation with full-length AE (6,(8)(9)(10)(11)(12)(13).…”

“…Conversely, C-terminal truncation of AE through frameshift mutation (AML1-ETOtr) or alternative splicing at exon 9 (AE9a) leads to acute myeloid leukemia (AML) transformation of murine HSPCs (14,15). The AE9a transcript is expressed in ∼70% of t(8;21) + AML patients, along with full-length AE (14,16). AE9a lacks the conserved ETO domains NHR3/4, whose interaction with corepressor proteins such as N-CoR/SMRT and HDACs is important for transcriptional repression (17)(18)(19)(20).…”

Bortezomib interferes with C-KIT processing and transforms the t(8;21)-generated fusion proteins into tumor-suppressing fragments in leukemia cells

“…S9). In t(8;21) AML, AE and AE9a are associated with C-KIT mutation/overexpression (8,11), and AE is able to up-regulate C-KIT (8). Therefore, BOR represents a C-KIT, AE/AE9a double targeting agent that triggers a positive feedback signal network to induce apoptosis, and its efficacy on the murine t(8;21) AML model suggests its potential of clinical application in t(8;21) AML as well as other C-KIT-driven cancers.…”

“…The t(8;21), which represents the most common chromosomal anomaly in AML, targets eight twenty one [ETO, also known as myeloid transforming gene on chromosome 8 (MTG8) or RUNX1T1] on chromosome 8 and acute myeloid leukemia 1 [AML1, also known as Runt-related transcription factor 1 (RUNX1), core binding factor (CBF) α2, and Phosphatidylethanolamine-binding protein (PEBP) 2αB] on chromosome 21, yielding two fusion transcripts, the AML1-ETO (AE) (9) and AML1-ETO9a (AE9a), lacking the neuralized homology repeat (NHR)3-4 domains at the C terminus of ETO moiety (10). It has been established that AE9a bears a much stronger leukemogenic activity than AE in murine system (10), and a similar situation might exist in human setting (11). Studies showed that t(8;21) AML follows a stepwise leukemogenesis (i.e., AE/AE9a represent the first, fundamental genetic hit to initiate the disease), whereas activation of the C-KIT pathway may be a second but also crucial hit for the development of a full-blown leukemia (8,12).…”