High Expression of Human Leukocyte Formin Protein in T Non-Hodgkin’s Lymphomas and in CD19⁻ Cell Population of Normal Tonsils.

We recently described a new gene, denominated human leukocyte formin (hlf), which was overexpressed in lymphoid malignancies and cancer cell lines. In contrast, a low expression of the hlf protein was observed in lymph node and peripheral blood leukocytes in normal tissues. Interestingly, the hlf protein associates with Akt, a protein kinase of an important pathway for cell survival. In order to better characterize the expression of the hlf protein we performed Western blotting in the lymphocytes isolated from 4 tonsils from adult patients obtained during routine tonsillectomy, at the Department of Hematology, Clinic Hospital, Barcelona. Results demonstrated that the CD19⁻ cell population of the tonsil displayed a higher expression of this protein when compared with CD19⁺ cells. In addition, CD19⁺ cells were separated into two subpopulations: CD27⁺ (memory cells) and CD27⁻ (naïve cells), and the CD19⁺/CD27⁺ cell presented a higher expression when compared with naïve B cells. Furthermore, we performed Western blotting analysis in frozen biopsies of non-Hodgkin’s lymphoma (NHL) patients obtained from the Department of Pathology, Purpan Hospital (Toulouse, France). The lymph node biopsies were performed at the time of clinical diagnosis and the initial diagnosis was confirmed by immunohistochemical analysis and classified according to REAL classification. Fifty-four patients were studied with ages ranging between 28 and 93 years (median 57 years). The histologic types were: 22 follicular NHL, 15 diffuse large B-cell NHL, 17 T cell NHL (non-otherwise specified). Five reactive lymph nodes were also studied. The expression of the hlf protein was detected in all lymphoma samples studied and also in the 5 reactive lymph nodes. The hlf expression, however, was higher in T cell NHL when compared with the others NHL and reactive lymph nodes (T cell NHL vs reactive lymph node, p=0.002; T cell NHL vs follicular NHL, p=0.0001; T cell NHL vs diffuse large B-cell, p=0.012; Mann Whitney test). The hlf protein may be involved in the anti-apoptosis mechanisms, as it is expressed in all types of lymphoproliferative samples and it is associated with Akt, a pathway that is constitutively activated in some hematologic malignancies. Indeed, the ortholog protein described in mice, presents a role in the protection of the cells from apoptosis, but the pathway is unknown. This report provides a more detailed description of the expression of hlf protein in normal lymphocytes and supports the hypothesis that the hlf protein has a role in the cancer molecular pathology of hematologic malignancies.