FMNL-1 (Formin-Like 1) Gene in Chronic Lymphocytic Leukemia (CLL) Is Overexpressed in Young Patients with Adverse Prognostic Factors and Poor Outcome.

Prognosis of patients with CLL has been traditionally assessed by using clinical parameters. Although useful, such parameters are a mere reflection of the biological diversity of CLL. In this regard, the mutational status of VH genes or ZAP-70 expression separates CLL into two clinical forms with different presenting features and outcome. Formins are multidomain proteins characterized by the presence of two conserved prolin-rich regions, namely formin homology 1 and 2. These proteins are implicated in a wide range of processes, including regulation of the cytoskeleton and in the regulation of the signal for cell survival. Formin is normally expressed in spleen, lymph node, and bone marrow cells, and it has been recently found to be overexpressed in T-cell lymphomas. The aim of this study was to analyze the expression of FMNL-1 in normal B-cell subsets and in a series of 73 patients (median age, 59 years; male/female 40/33; Binet A: 90.2%) with CLL. FMNL-1 expression was analyzed by Western Blot in separate subpopulations and by quantitative RT-PCR using expression in Jurkat as baseline. Among normal lymphocytes, FMNL-1 was only expressed in memory (CD19+CD27+) B-cells and in T-cells. In CLL cases with a low percentage of T-cells, mean of FMNL-1 expression was 2.18 AU (SD, 1.01 AU). Using an arbitrary cut-off of 3.2 AU, cases with increased expression of FMNL-1 were associated with a younger age at diagnosis (< 50 yrs), elevated lymphocyte count, high serum β2-microglobulin (β2-m) levels, increased ZAP-70 and CD38 expression, shorter time to progression, and shorter survival as compared to cases with low FMNL-1 expression. No relationship was observed with genetic abnormalities (table). In summary, among B-cell lymphoproliferative disorders, FMNL-1, a gene that regulates cell survival, is found only in CLL and its overexpression correlates with adverse clinical and biological parameters, particularly in young patients.