Author/Authors :
El-Tounsi, Iman Menoufeya University - Faculty of medicine - Department of clinical pathology, Egypt , Alenzi, Faris Q B King Faisal University - college of applied biomedical sciences - Department of clinical laboratory sciences, section of immunology, Saudi Arabia , Gafari, Maha Ain Shams University - Faculty of medicine - Department of community medicine, Egypt
Abstract :
The Fas/FasL pathway is one of the most investigated systems involved in regulating apoptosis through ligation of the Fas (CD95/ApoJ) Death Receptor (DR). In AML, coexpression of DRs and their ligands on leukemic cells is not always accompanied by apoptosis, suggesting that the apoptotic death receptor signaling path way is disrupted. The prognostic value of the expression of molecules in-volved in DR-mediated apoptosis pathways has been less studied. TOSO is one surface molecule de-scribed to regulate the Fas pathway. Little is known about its effect in AML primary cells. We meas-ured the expression of Fas and TOSO in some AML cell lines, 12 adult AML primary samples as well as in 5 normal CD34+ (NCD34+) samples as control cells. TOSO was constitutively expressed in all samples with variable degrees. Apoptosis through ligation of Fas by anti-Fas antibody (CHI 1) with and without Ara-C was investigated after 24hrs culture. CHI 1 at 100ng/ml induced a small but sig-nificant decrease in viable cells in AML samples compared to control cells (6.26±1.6%, 7.33±1.7, re-spectively, p=0.01). Apoptosis was enhanced by the addition of Ara-C at 6uM. We observed marked heterogeneity among primary AML samples. While 7 samples showed variable response to CHI 1 kill-ing, 5 samples were resistant. In our study, mean fluorescence intensity ratio (MFIR) of CD95 was higher in NCD34+ cells than in leukemic ones, correlating with Fas induction of cell death. Although, Fas was variably expressed in all AML samples, yet not all samples were sensitive to Fas death path-way. There was a significant negative correlation between CD95 MFIR and TOSO expression in AML CD34+ cells. Moreover, there was a negative correlation between induction of death by CHl1 and TOSO expression with borderline significance in these cells. We conclude that the majority of AML cells exhibit variable expression of Fas, and apoptosis could be induced by ligation of Fas with, a less toxic, specific monoclonal antibody (MoAb) CHI 1 in some cases. Our results suggest that TOSO may be an important player in regulation of the Fas pathway, yet further functional studies, on a larger scale, are required to identify at which step of the pathway does, TOSO interact, and to withdraw sta-tistical prognostic correlations regarding treatment outcome. TOSO may be considered as a potential target for investigation, as an alternate mechanism of resistance to Fas pathway in AML.
