Proteomic Signature of CD34+ Cells From Chronic Myeloid Leukemia Patients

Abstract 3733

The tyrosine kinase inhibitors (TKIs) represent the successful molecular therapy for patients with chronic myeloid leukemia (CML), targeting the Bcr-Abl oncogenic product. However, this disease may remain not curable for the presence of residual refractory cells, persisting during the history of the disease treatment. Several mechanisms have been associated with resistance to TKIs, including the presence of rare quiescent leukemic stem cells, less susceptible to TKIs. Moreover, Bcr-Abl activates additional downstream pathways involved in the apoptotic and proliferation control of CML cells, such as RAS/MEK/ERK, PI3K/Akt, Wnt and STAT5 pathways, potentially contributing to CML TKIs drug resistance. Therefore, in this study we aimed to investigate, at the protein level, proliferative and apoptotic signal transduction pathways (STP) in CML CD34+ cells, as compared to normal CD34+ cells, in order to identify additional aberrant signals, potentially therapeutic targetable. CD34+ cells were purified from peripheral blood (PB) of five newly diagnosed, chronic phase (CP) CML patients, three normal cord blood (CB) and one leukapheretic product of a normal volunteer (PBSC). The phosphorylation status of 46 proteins from various STP and the expression of 32 proteins of the apoptotic machinery were assessed by using a customized direct phase proteome profiler antibody array. The resulting dots were visualised using ECL and quantified by densitometric analysis. CML samples were collected from patient in CP, with a WBC count ranging between 41900–135400 per microliter. The Sokal risk category was low (1/5) and intermediate (4/5). The comparison between normal CD34+ cells obtained from CB and PBSC showed that the first cells were characterized by a lower expression of STAT, Tyrosine-protein kinase and MAPK protein families. The phospho-proteomic profile of CD34+ cells from CML samples showed remarkably similarity when compared to normal CB CD34+ cells, while only two proteins resulted differently expressed in CP CD34+ cell vs. PBSC: CREB-S133, involved in the pro-survival/anti-apoptotic gene control (p=0.025) and p70S6K-T389, along the PI3k/Atk pathway and involved in the cell proliferation (p=0.049). The analysis of the 32 apoptotic proteins revealed that 10 of them were statistically significant lower in CML CD34+ cells compared to PBSC. Most of them were related to the Bcl-2 family and caspase inhibitors family, such as cIAP-1 (p=0.025), cIAP-2 (p=0.0003) and livin (p=0.016). The expression of the cyclin-dependent kinase inhibitors (CKI) was found significantly lower in CML CD34+ (p=0.05 and p=0.02 for p21/CIP1 and p27/Kip1, respectively). In conclusion, we have reported in this study that proteins and/or phosphoproteins controlling apoptosis and proliferation STP, such as Bcl-2, IAP, MAPK, PI3K/Akt, STATs and CKI families, are differentially expressed in CD34+ from CML CP, compared to PBSC. The understanding of these differences in the proteomic profile may confirm that additional multiple aberrant STP are involved in the CML and therefore must be taken into account for targeted therapies, especially of resistant cases.