Interphase and metaphase detection of the breakpoint of 14q32 translocations in B-cell malignancies by double-color fluorescence in situ hybridization

Abstract

The breakpoint of 14q32 translocations found in B-cell malignancies was delineated specifically in both metaphase spreads and interphase nuclei by double-color fluorescence in situ hybridization (FISH) using bacteriophage clones containing the human immunoglobulin gamma chain gene locus (Igγ) and a cosmid clone, CY24-68, containing V(H) segments. CY24-68 is more telomeric than Igγ, separated by approximately 1 megabase (Mb), FISH studies were performed on four patients with non-Hodgkin's lymphoma (NHL), one with acute lymphoblastic leukemia (ALL), one with plasma cell leukemia (PCL), and three cell lines. In each patient with t(8;14), t(14;18), and t(3;14), the signal of Igγ gene was observed on der(14) and that of CY24-68 at respective partner sites of these translocations, 8q24.1, 18q21.3, and 3q27. Interphase nuclei with a signal of Igγ clearly separated from that of CY24-68 were more frequently encountered in all of the patients (45% to 74%) than those in normal controls (4% to 5%). Even in cases where only interphase nuclei were available for FISH studies, 14q32 translocations are detected as shown in two patients each with NHL and t(11;14)-carrying PCL. In two cell lines, HS-1 derived from ALL carrying t(8;14) and FR4 derived from a plasmacytoma carrying a complex form of t(8;14), the signal of Igγ was observed at the breakpoint region 8q24.1 of the der(8) in addition to the der(14), indicating that translocation event occurred within the Igγ locus. Intense Igγ signal was found at the breakpoint region on the der(14)t(11; 14) in HBL-2 derived from NHL, indicating amplification of the Igγ gene, and presumably the resultant chimeric DNA between Igγ and DNA sequences at 11q13. The present approach allowed us to unequivocally detect tumor-specific breakpoints of 14q32 translocations. Furthermore, interphase FISH provides a rapid diagnostic procedure to detect 14q32 translocations in B-cell malignancies.