Expression of Angiogenin in Normal B Lymphocytes and B-CLL Cells.

Angiogenesis is critical for the clinical progression of hematopoietic malignancies and depends on a series of angiogenic factors. Angiogenin is a potent angiogenic factor produced by the host microenvironment and certain neoplastic cells. The association between angiogenin, cancer progression and poor outcome in solid tumors has been documented, but its significance in B-CLL has not been defined. A previous study suggests that B-CLL patients in Rai stage O with higher angiogenin levels have a better clinical outcome. This is surprising in light of the association of angiogenin levels with progression in solid tumors. Therefore we analyzed angiogenin mRNA and protein expression by the leukemic cells of B-CLL patients in order to correlate the production of this molecule with disease progression in B-CLL.

Angiogenin was expressed in B-CLL cells as well as in B cells of normal donors, although the expression in the former was much higher than in the latter. Q PCR revealed a 7-fold induction in angiogenin-specific mRNA transcription in B-CLL cells (n=10) in comparison to normal B cells (n=13). In addition, angiogenin protein was identified by confocal microscopy both within and on the cell surface of B-CLL cells. All B-CLL cases, regardless of IgV gene mutation status, express angiogenin as defined by FACS. Approximately 85% of the cells that comprise B-CLL clones (n=28) display angiogenin on their surface membranes (range: 55-98%). Furthermore approximately 13% of polyclonal B cells from normal subjects (n=12) also produce angiogenin (range: 1–33%). Using enzyme immunoassay, we also measured serum angiogenin levels and detected significant differences in 66 B-CLL patients (median: 381 ng/mL; range: 185–875) versus 24 age- and sex-matched healthy controls (median: 301 ng/mL; range: 192–536) (P = 0.0056). Surprisingly, there was no correlation between surface and serum angiogenin levels and the different V gene-defined B-CLL subgroups.

Our results show for the first time that a small fraction of normal B cells and all cases of B-CLL express angiogenin transcripts as well as intracellular and surface membrane protein. Angiogenin levels do not correlate with IgV gene mutations status or expression of surface membrane CD38. The role of angiogenin in the pathogenesis and progression of B-CLL needs further study.