Expression of the cap-mediated translation pathway in non-Hodgkins lymphomas: diagnostic and therapeutic implications

Abstract

8595 Background: The eukaryotic initiation factor (eIF) complex controls cap-mediated mRNA translation. This plays a key role in cancer by mediating expression of proteins critical for cell growth, transformation and tumorigenesis (e.g., cyclin D1, survivin, c-myc, Bcl-2 and VEGF). eIF4 complex (eIF4E, eIF4G and eIF4A) activity is inhibited by eIF4E binding protein-1 (4E-BP1) which thus has tumor suppressor activity. Hyper-phosphorylated 4E-BP1 is unable to bind eIF4E and promotes translation initiation and protein synthesis. Methods: We analyzed eIF complex expression in B-cell non-Hodgkins lymphomas (NHL) using immunohistochemistry (IHC) for total 4E-BP1 and Western immunoblotting (WB) for eIF4G (total), eIF4E and 4E-BP1 (total and phosphorylated). IHC was performed on 37 NHL (9 follicular [FL], 9 diffuse large cell [DLCL], 2 Burkitt’s, 5 mantle cell, 5 extranodal marginal zone/lymphoplasmacytoid, 7 small lymphocytic) and 8 reactive tissues (6 nodes, 2 tonsils). Staining intensity was graded from 0 to 3+. WB was performed on 6 NHL (2 FL, 4 DLCL) and 2 reactive tissues. Results: IHC showed a consistently high level (2–3+) of cytoplasmic 4E-BP1 expression in malignant cells in 36 of 37 NHL samples. In contrast, there was marked regional specificity of cytoplasmic expression in reactive tissues (3+ in the mantle and marginal zone cells but absent/minimal (0- 1+) in germinal centers and T cells). Nuclear expression was seen in 4 NHL samples but not in reactive tissues. Incipient/focal involvement by FL showed 3+ staining in neoplastic follicles. WB showed that phosphorylated:total 4E-BP1 ratio was increased (2-fold over reactive samples) in 3 of 4 DLCL, but not in FL. The levels of expression of eIF4G, total and phospho-eIF4E and total 4E-BP1 were comparable in reactive and NHL samples, as expected in whole tissue lysates. Conclusion: (1) 4E-BP1 detection by IHC offers a sensitive diagnostic tool for distinguishing reactive follicles from neoplastic B-cell proliferations. (2) 4E-BP1 hyper-phosphorylation may be a mechanism that can increase expression of growth and proliferation inducing proteins in aggressive NHL. (3) These findings provide the rationale for evaluating cap-dependent translation inhibition as a novel therapeutic strategy in NHL. No significant financial relationships to disclose.