Abstract:
Acute myeloid leukemia (AML) is the most common aggressive type of leukemia in adults. It 
originates in immature white blood cells in the bone marrow and can spread into the 
bloodstream, migrating to secondary sites such as the brain, liver, and the spleen. Recent 
research from our lab has demonstrated that AML cell migration is partly regulated by the 
interaction between CD34, a hematopoietic stem cell marker and surface glycoprotein expressed 
on AML cells, and its corresponding receptor, E-selectin, expressed on tissue cells that AML 
cells migrate towards. Our findings further showed that CD34 binding to E-selectin stimulates 
the phosphorylation of ezrin at the Thr-567 site, enabling ezrin to link actin filaments to the 
plasma membrane and potentially promote the formation of membrane projection (i.e. 
microvilli)—key structures in cell motility. Given the crucial role of Rho-associated coiled-coil 
kinase (ROCK) in regulating actin dynamics and microvilli formation, we sought to investigate 
its involvement in the ezrin signaling pathway. Treatment with the ROCK inhibitor (Y-27632) 
led to a significant reduction in ezrin phosphorylation at Thr-567, suggesting a disruption in the 
linkage between actin and the plasma membrane, and consequently impairing cell migration due 
to altered microvilli formation. Beyond its effect on ezrin, CD34 was also suspected to influence 
the localization and spatial organization of other E-selectin ligands, including PSGL-1, CD44, 
CD43, during cell interaction with E-selectin under flow conditions. Using a microfluidics-based 
chamber assay coupled with super-resolution imaging (TIRF and STORM), we observed notable 
changes in the clustering patterns of these E-selectin ligands and ezrin before and after CD34 
knockdown. Altogether, our findings highlight the potential role of ROCK in CD34 downstream 
signaling and underscore the regulatory function of CD34 in orchestrating the spatial 
organization of other E-selectin ligands–effects that are critical to the process of cellular 
migration.

Bio:
Abdulrahman Alharthi is a master's student in Bioscience at King Abdullah University of Science and Technology (KAUST). He earned a Bachelor of Science degree in Biomedical Laboratory Science from Michigan Sate University. At KAUST, under the supervision of Professor Jasmeen Merzaban, his research is focused on understanding the role of hematopoietic stem cell marker CD34 in the migration process of acute myeloid leukemic cells.