Abstract
BackgroundDiffuse large B-cell lymphomas (DLBCLs) are aggressive lymphomas accounting for approximately a third of non-Hodgkin lymphomas. Prohibitin 1 (PHB1) and prohibitin 2 (PHB2) are scaffold proteins that promote mitochondria homeostasis and consequently cell survival, but biological functions of cytoplasmic PHBs remain largely unknown in DLBCL.MethodsPHB expression was analyzed in 82 DLBCL biopsies and five DLBCL cell lines by immunohistochemistry (IHC) and Western blotting. Pharmacological inhibition of PHB using the synthetic flavagline FL3 was realized in vitro to gain insight PHB cellular functions. Effects of FL3 on DLBCL cell line viability, apoptosis, C-Raf-ERK–MNK–eIF4E signaling pathway and eIF4F complex formation and activity were evaluated by XTT assay, annexin V-FITC/PI dual staining and Western blotting respectively. Subcutaneous DLBCL xenograft model in SCID mice was also performed to determine in vivo FL3 effect.ResultsAs in DLBCL cell lines, PHB1 and PHB2 were expressed in germinal center B-cell–like (GCB) and activated B-cell–like (ABC) subtypes. In patient samples, high PHB levels were associated with higher serum LDH (PHB1 and PHB2), IPIaa (PHB2), and Ki-67 (PHB2) expression. Higher PHB1 expression tends to be associated with shorter event-free survival (EFS) in patients, especially in male patients. FL3 induced apoptosis of DLBCL cell lines that was associated with inhibition of the ERK-MNK-eIF4E signaling pathway, including aggressive double/triple-hit DLBCL cell lines. This resulted in altered eIF4F complex formation and activity leading to a reduction of Bcl-2 and c-Myc expression levels. Moreover, FL3 strongly downregulated DLBCL cellular levels of Akt protein and AKT mRNA. FL3 antitumor activity was also confirmed in vivo in a murine xenograft model.ConclusionOur data indicate that PHB overexpression is associated with markers of tumor aggressiveness in DLBCL, and that targeting PHBs may be a therapeutic option, notably in aggressive subtypes.
Highlights
Diffuse large B-cell lymphomas (DLBCLs) are aggressive lymphomas accounting for approximately a third of non-Hodgkin lymphomas
Expression of Prohibitin 1 (PHB1) and prohibitin 2 (PHB2) in DLBCL cell lines and tumor cells from patients PHB1 and PHB2 expression was analyzed in germinal center B-cell (GCB) (SUDHL4, SUDHL6 cell lines) and activated B-cell (ABC) (OCI-LY3, OCI-LY10 cell lines) subtypes of DLBCL
The PHB ligand, FL3, induced apoptosis in DLBCL cell lines associated with nuclear translocation of PHB1 and Apoptosis activating factor (AIF) We evaluated the anti-tumor effect of FL3, a synthetic flavagline and ligand of PHBs that was shown to interfere with membrane localization of PHB [17, 30, 34]
Summary
Diffuse large B-cell lymphomas (DLBCLs) are aggressive lymphomas accounting for approximately a third of non-Hodgkin lymphomas. Diffuse large B-cell lymphomas (DLBCLs) are highly aggressive non-Hodgkin lymphomas for which the incidence increases with age (median age at diagnosis is 70 years). Double-hit (DHL) and more rarely triple-hit (THL) lymphomas are subgroups of very aggressive lymphomas with both MYC and BCL-2 and/or BCL6 gene rearrangements characterized by a rapidly progressing clinical course that is refractory to treatment and poor outcome after standard R-CHOP therapy. These groups of patients represent a huge therapeutic challenge [4, 5]
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