Scavenger Receptor Type B1 Is Essential for High Density Lipoprotein Nanoparticle Induced B-Cell Lymphoma Cell Death

Introduction:

We recently reported that biomimetic, synthetic high-density lipoprotein nanoparticles (HDL NP), similar to natural HDL in size, shape, charge, and composition potently induce apoptosis in human B cell lymphoma cell lines in vitro, and in vivo, without adversely affecting primary hepatocytes or macrophages (Yang et al. 2013. PNAS 110(7): 2511-6).  We showed that HDL NPs bind to the high-affinity HDL receptor, scavenger receptor type B-1 (SR-B1), expressed by lymphoma cells, and may play a functional role in apoptosis of B cell lymphomas.  

Methods:

We analyzed tissue microarrays (TMAs) from patients with non-Hodgkin’s lymphoma (NHL) for SR-B1 expression.  In silicoanalyses of gene microarray datasets from the publicly available database Oncomine were conducted to investigate SR-B1 expression in lymphoma at the mRNA level.  The B cell lymphoma cell lines Ramos (Burkitt’s lymphoma), SUDHL4 (diffuse large B cell lymphoma) and HF-1 (transformed follicular lymphoma) were used to investigate the requirement for SR-B1 in HDL NP induced cell death.  A blocking antibody, and stably expressed shRNA targeting SR-B1 expression were used to inhibit HDL NP interactions with SR-B1.

Results:

SR-B1 was overexpressed in a subpopulation of NHL represented in available TMAs. At the mRNA level, SR-B1 was up-regulated in 20% of lymphoma data sets (6 of 30). These data further confirm SR-B1 as a potential target of therapeutic intervention in B cell lymphomas.

Antibody blockade of SR-B1 in the SR-B1⁺cell lines Ramos, SUDHL4, and HF-1 prevented HDL NP induced cell death in a dose dependent manner (Figure 1A).  Stable knockdown of SR-B1 by shRNA in Ramos cells also protected against HDL NP induced cell death compared with wild type and scrambled shRNA controls (Figure 1B). HDL NP induced cholesterol efflux in Ramos, SUDHL4, and HF-1 cells was reduced by the SR-B1 blocking antibody, or SR-B1 knockdown, further supporting that the HDL NP binds SR-B1. 

Conclusion:

SR-B1 is expressed in primary B cell lymphomas, and interference of HDL NP interaction with SR-B1, through antibody blockade or knockdown of SR-B1, abrogated HDL NP induced cell death in multiple B cell lymphoma cell lines.  Taken together, our data demonstrate the requirement of SR-B1 in HDL NP induced lymphoma cell death, and provide a rationale to pursue HDL NPs as potent therapy for B cell lymphomas in cases that express SR-B1.

Figure 1:Antibody blockade (A) and shRNA knockdown (B) of SR-B1 prevents HDL NP induce cell death.