CD44 was identified as a novel translocation partner of IGH in mature B-cell NHLs. (A) Ethidium bromide–stained gel showing the IGHSμ/CD44 translocation product resulting from illegitimate switch recombination (indicated by the arrow) and a self-rearrangement band (indicated by the arrowhead) resulting from the fusion of Sμ to Sγ3 of IGH (functional CSR) in a representative case (gastric GCB-type DLBCL; GL47) with an IGHSμ/CD44 translocation detected by inverse PCR. A vertical white line has been inserted to indicate a repositioned gel lane. (B) Ideogram showing that IGHSμ/CD44 translocations detected in mature B-cell lymphomas result in a classic promoter substitution. The positions and orientations of the primers (SAE/JXE followed by SAI/JXI) used for inverse PCR are indicated. The CD44ΔEx1 mRNA transcripts were activated from derivative 11. The intron/exon map of human CD44 is based on GenBank sequences (accession no. NT009237, DNA; and NM_000610, mRNA).²¹  Exons 1 to 5 and 15 to 18 (shown as black boxes) are the constitutive exons that code for CD44s (standard from). Exons 6 to 14 correspond to the alternatively spliced variant exons within the extracellular domain (shown as blue boxes). Exon 1 encodes the leader peptide (LP), exon 17 encodes the transmembrane domain (TM), and exon 18 encodes a short cytoplasmic domain. The open arrowhead indicates the coding initiation start site. (C) Interphase FISH confirmed breakage at the CD44 locus in IGHSμ/CD44 translocation-positive cases identified by inverse PCR. Break-apart FISH was performed using 2 BAC clones as probes: clone RP4-607I7 (151 kb) included the 5′ portion of intron 1 of CD44, whereas clone RP4-683L5 (135 kb) was approximately 64.5 kb away from the 3′ end of CD44 (top panel). Representative nuclei from cases with (GL47) or without (GL2) breakage of the CD44 locus are shown, exhibiting one orange, one green, and one yellow (colocalized orange and green) fusion signal pattern (1O1G1F). Vertical and horizontal white lines have been inserted to indicate different nuclei repositioned images. The images were captured by the Leica DMRBE (Leica Microsystem Wetzler GmbH) fluorescence microscope (100×/0.7 NA oil objective). The fluorescent images were imported and created by Cytovision software (Applied Imaging). (D) The IGHSμ/CD44 translocation breakpoints were located within small regions of IGHSμ and at the 5′ end of intron 1 of CD44 in mature B-cell lymphomas. The sequences shown are from GenBank (IGHSμ accession no. NG_001019.3; CD44: accession no. AL356215.11).²¹  The relative position of the 2 sets of seminested PCR primers used to confirm IGHSμ/CD44 translocations by direct PCR is shown. (E) Chromosomal locations of all IGH translocation partners (annotated genes only) reported in B-cell lymphomas. The CD44 gene (shown in bold) located at 11p13 was identified in this study as the first cell adhesion molecule²²  involved in IGH chromosomal translocations in B-cell lymphomas. GL indicates gastric lymphoma; ENL, nongastric extranodal lymphoma; and NL, nodal DLBCL. *Gastric mucosa-associated lymphoid tissue (MALT) lymphoma. **Gastric composite DLBCL with residual MALT lymphoma (DLCLML).