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Updated: May 5, 2026
From a 2DE-Gel Spot to Protein Function: Lesson Learned From HS1 in Chronic Lymphocytic Leukemia
Published on: October 19, 2014
Detection and characterization of human high molecular weight B cell growth factor receptors on leukemic B cells in
F M Uckun1, A S Fauci, M Chandan-Langlie
1Department of Therapeutic Radiology-Radiation Oncology, University of Minnesota, Minneapolis 55455.
Insights
Human high molecular weight-B cell growth factor (HMW-BCGF) stimulates various B cells, including those in chronic lymphocytic leukemia (CLL). This study details the HMW-BCGF receptor (R) expression and function on CLL cells, revealing its role in leukemia cell proliferation.
Area of Science:
- Hematology
- Immunology
- Molecular Biology
Background:
- Human high molecular weight-B cell growth factor (HMW-BCGF) is known to stimulate B cell proliferation.
- The specific role and receptor expression of HMW-BCGF in chronic lymphocytic leukemia (CLL) remain to be fully elucidated.
Purpose of the Study:
- To investigate the expression, function, and structure of HMW-BCGF receptors (R) on leukemic B cells in CLL.
- To determine the correlation between HMW-BCGF receptor expression and responsiveness to HMW-BCGF in CLL.
Main Methods:
- Ligand binding assays using 125I-labeled HMW-BCGF.
- Immunofluorescence/flow cytometry and Scatchard analyses with an anti-HMW-BCGF R monoclonal antibody (BA-5).
- In vitro proliferation assays ([3H]TdR incorporation and colony assays) and crosslinking studies.
Main Results:
- 60% of CLL cases constitutively expressed HMW-BCGF R and demonstrated significant proliferation in response to HMW-BCGF.
- HMW-BCGF receptors were functional on HCL, PLL, and activated normal B cells.
- Scatchard analysis revealed approximately 3,000 HMW-BCGF R/cell on responsive CLL cells, with a dissociation constant (Ka) of 4.6 X 10(7) M-1.
- A 150-kD HMW-BCGF/HMW-BCGF R complex was identified, suggesting a 90-kD receptor protein.
- The anti-HMW-BCGF R antibody BA-5 inhibited HMW-BCGF-stimulated CLL colony formation.
Conclusions:
- HMW-BCGF receptor expression is correlated with responsiveness to HMW-BCGF in CLL.
- HMW-BCGF plays a direct role in stimulating CLL cell proliferation, independent of accessory cells.
- This study provides the first detailed analysis of HMW-BCGF R expression, function, and structure on B lineage CLL cells.
Abstract:
Human high molecular weight-B cell growth factor (HMW-BCGF) (60 kD) stimulates activated normal B cells, B cell precursor acute lymphoblastic leukemia (BCP-ALL) cells, hairy cell leukemia (HCL) cells, prolymphocytic leukemia (PLL) cells, and chronic lymphocytic leukemia (CLL) cells. The expression of human high molecular weight B cell growth factor (HMW-BCGF) receptors (R) on clonal populations of leukemic B cells in CLL was studied by ligand binding assays using 125I-labeled HMW-BCGF as well as by immunofluorescence/flow cytometry and Scatchard analyses using an anti-HMW-BCGF R monoclonal antibody (MAb), designated BA-5. There was a high correlation between HMW-BCGF R expression and responsiveness to HMW-BCGF. 60% of CLL cases constitutively expressed HMW-BCGF R and showed a marked proliferative response to HMW-BCGF in [3H]TdR incorporation assays as well as colony assays. Similarly, HCL cells, PLL cells, and activated normal B cells expressed functional HMW-BCGF R, as determined by ligand binding assays using 125I-HMW-BCGF, [3H]TdR incorporation assays, and reactivity with BA-5 MAb. Scatchard analyses indicated the existence of approximately 3,000 HMW-BCGF R/cell on HMW-BCGF responsive CLL cells with an apparent Ka value of 4.6 X 10(7) M-1. The concentrations of HMW-BCGF required for maximum stimulation of CLL cells were two to three orders of magnitude lower than those needed for half maximal receptor occupancy, indicating that only a small fraction of HMW-BCGF R need to be occupied to stimulate leukemic CLL B cells. Crosslinking of surface bound 125I-HMW-BCGF (60 kD) with the bivalent crosslinker DTSSP to its binding site on fresh CLL cells identified a 150-kD HMW-BCGF/HMW-BCGF R complex, suggesting an apparent molecular weight of 90 kD for the receptor protein. The growth stimulatory effects of HMW-BCGF on clonogenic CLL cells did not depend on accessory cells or costimulant factors. The anti-HMW-BCGF R monoclonal antibody BA-5 disrupted HMW-BCGF/HMW-BCGF R interactions at the level of clonogenic CLL cells and inhibited HMW-BCGF-stimulated CLL colony formation in vitro. To our knowledge, this study represents the first detailed analysis of expression, function, and structure of HMW-BCGF R on B lineage CLL cells.
