Despite improved prognosis of CML patients with the use of imatinib (IM), its administration is associated with extramedullary disease (EMD) occurrence. We postulate that, like in the metastatic processes, changes in migration and adherence potential may enable leukemic cells to inhabit extramedullary sites. Focal adhesion complexes linking between extracellular matrix and the cell cytoskeleton are likely to play an important role in these processes.
Pyk2 is a tyrosine kinase highly expressed in hematopoietic cells, localized to focal adhesion complexes, and known to participate in adhesion and migration processes. We have previously shown that Pyk2 participates in NB4 (an acute promyelocytic leukemia [APL] cell line) cells' adhesion and migration following exposure to the APL targeted therapy ATRA.
We postulate that similar to the effect of ATRA on NB4 cells, IM being also a targeted therapy, might also be associated with enhanced adhesion and migration abilities of the CML cell line K562.
Our objectives were to identify the effect of IM administration on pyk2 expression and on K562 cell adhesion and migration ability and to establish the role of these changes in treatment-associated EMD.
We found a 2.6-fold increase in pyk2 mRNA expression in K562 cells following exposure to IM. We also found that 30% of IM-treated K562 cells adhered to fibronectin (FN) compared to untreated cells having no adhesion ability. In addition, a 3-fold induction in migration was seen in K562 cells following treatment. Furthermore, K562 cells treated with IM demonstrated a 2-fold increase in invasion potential as compared to untreated cells. In order to assess whether Pyk2 is essential for IM-dependent adhesion and migration of K562 cells, these cells were infected with pyk2 specific shRNAs. While 30% of the non-infected NB4 cells adhered to FN following IM treatment, only 12% of the pyk2-shRNA–infected K562 cells exhibited adhesion potential (Pvalue<0.002). In addition, we witnessed over a 3-fold reduction in the ability of pyk2-shRNA–infected K562 cells to migrate following exposure to IM when compared to parental K562 cells. These data support the role of Pyk2 in IM-mediated adhesion and migration.
Finally, we found that IM treatment induced an in-vivo increase in pyk2 mRNA expression level in leukocytes derived from 3 out of 5 CML patients studied.
IM induces K562 cell adhesion, migration and invasion accompanied by increased pyk2 expression. Pyk2 is one of the key proteins regulating IM-induced cell migration and adhesion. Collectively our data suggest a critical role of Pyk2 in adhesion and migration initiated by the targeted therapy IM and a possible role in EMD development. These data support a common mechanism for the development of EMD in hematological malignancies treated by targeted therapies via pyk2 expression.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.