The t(10;11)(p13;q14) in the U937 cell line results in the fusion of the AF10 gene and CALM, encoding a new member of the AP-3 clathrin assembly protein family.

Abstract

The translocation t(10;11)(p13;q14) is a recurring chromosomal abnormality that has been observed in patients with acute lymphoblastic leukemia as well as acute myeloid leukemia. We have recently reported that the monocytic cell line U937 has a t(10;11)(pl3;ql4) translocation. Using a combination of positional cloning and candidate gene approach, we cloned the breakpoint and were able to show that AF1O is fused to a novel gene that we named CALM (Clathrin Assembly Lymphoid Myeloid leukemia gene) located at 11ql4. AFIO, a putative transcription factor, had recently been cloned as one of the fusion partners of MLL. CALM has a very high homology in its N-terminal third to the murine ap-3 gene which is one of the clathrin assembly proteins. The N-terminal region of ap-3 has been shown to bind to clathrin and to have a high-affinity binding site for phosphoinositols. The identification of the CALM/AFIO fusion gene in the widely used U937 cell line will contribute to our understanding of the malignant phenotype of this line.

Leukaemic transformation by CALM–AF10 involves upregulation of Hoxa5 by hDOT1L

“…The observation that the OM-LZ region is retained in the CALM-AF10 fusion protein raises the possibility that hDOT1L may also function in CALM-AF10-mediated leukaemia. To examine the potential role for hDOT1L in CALM-AF10-mediated leukaemia, we first attempted to establish a causal relationship between the CALM-AF10 fusion protein and leukaemia.Previous studies have established that the human monocytic leukemia cell line U937 expresses the CALM-AF10 fusion protein 10,11 . To determine whether CALM-AF10 is relevant for cell proliferation and transformation, CALM-AF10 was knocked down in U937 cells using a vector-based RNA interference (RNAi) approach 5 .…”

Cloning and characterization of AFX, the gene that fuses to MLL in acute leukemias with a t(X;11)(q13;q23)

“…. The notion that the various fusion partners of the MLL gene are similarly important for the transformation process as the MLL gene, is supported by the recent ®nding that that AF10 gene also fuses to another gene, CALM, in cases of translocation t(10;11)(p13;q14) (Dreyling et al, 1995).…”

The cloning, mapping and expression of a novel gene, BRL, related to the AF10 leukaemia gene

“…It is interesting that the translocation breakpoints in MLL, AF10 and AF17 usually occur outside the cysteine rich regions such that these elements are lost from the critical fusion proteins . The exceptions to this include one adult case of acute myeloid leukaemia demonstrating a t(10;11) translocation (Chaplin et al, 1995a,b) and also the t(10;11) translocation of U937 cell line (Dreyling et al, 1996), in both of which the breaks in AF10 occur within the CRR. It is possible that the cysteine rich regions are important to the transcriptional regulation of myeloid cells (Saha et al, 1995) and that their loss or disruption is critical to malignant transformation in haematopoietic cells.…”

“…Despite the complexity of the AF10 translocations a consistent feature seems to be the fusion of the leucine zipper domain to MLL (Chaplin et al, 1995b). Another important feature of AF10, so far unusual for MLL partner genes, is that it has been found rearranged with genes other than MLL, namely CALM, in the U937 cell line (Dreyling et al, 1996) and HEAB in an invins(10;11)(p12;q23q12) in a 2 year old child with acute monoblastic leukaemia (Tanabe et al, 1996). AF17, the gene involved in the t(11;17) translocation (Prasad et al, 1994) encodes a protein containing a cysteine rich region and a potential leucine zipper domain, both highly homologous with the same features in AF10.…”