Expression of FAK and Its Involvement in the Progression of B-Cell Chronic Lymphocytic Leukemia

INTRODUCTION

B-cell chronic lymphocytic leukemia (B-CLL) is a disorder characterized by the accumulation of clonal CD5+ B lymphocytes, due to uncontrolled growth and resistance to apoptosis. Although the prognosis and clinical outcome has dramatically improved by recent innovative therapies, B-CLL still remains an incurable disease. Since signaling events downstream the BCR engagement are important for the progression of B cells, BCR signaling has been investigated in B-CLL in order to design new agents to specifically treat this disease. We demonstrated that Lyn, one of the first kinases involved in BCR signaling pathway, is overexpressed, constitutively active and anomalously distributed in malignant B cells, as compared to normal B lymphocytes. The Focal adhesion kinase (FAK), a non-receptor protein tyrosine kinase, is the primary enzyme involved in the engagement of integrins and assembly of Focal Adhesion. FAK is regulated primarily through tyrosine phosphorylation by Lyn after BCR engagement and was found to be overexpressed in many kinds of human cancers. However, a downmodulation of FAK expression and its association to poor prognosis have also been reported. The aim of this study was to investigate the role of FAK in CLL patients.

METHODS

Blood samples were collected from 5 controls and 50 B-CLL patients. Informed consent was obtained according to the Declaration of Helsinki. Untouched peripheral blood B cells were purified using the RosetteSep for human B cells isolation kit. The samples that were used had at least 95% of normal CD19+ or neoplastic CD5+/CD19+ cells, as assessed by flow-cytometry. Level of FAK protein was evaluated by Western blotting (Wb) and Flow Cytometry assay (FC). Levels of FAK were correlated to clinical parameters of patients.

RESULTS

We observed that FAK was downmodulated in 56% of analyzed patients with respect to healthy subjects (respectively, Wb: 0.28±0.25 vs 0.85±0.32, p<0.001; FC: 35%±29 vs 60%±16, p<0.05). We also identified that lower levels of FAK expression were related to the prognostic markers of poor outcome (the expression of ZAP70, CD38 and an unmutated-IGHV genes status, p<0.05) and to a shorter Treatment Free Survival (p<0.05). Moreover, patients (n=6) who had an indolent course and were responsive to the standard treatment, showed normal expression of this kinase already at diagnosis. In contrast, patients (n=6) with a more aggressive disease, had a lower expression of FAK, that was further downmodulated during the progression of disease, irrespective of how the patients were treated.

CONCLUSIONS

From the data presented in this report we propose that FAK downmodulation could be considered as a new marker of poor prognosis and as a putative predictor for high-risk subgroups of CLL, even in early-stage disease.