Abnormalities at 14q32.1 in T cell malignancies involve two oncogenes

Abstract

The TCL1 oncogene on human chromosome 14q32.1 is involved in the development of T cell leukemia in humans. Its expression in these leukemias is activated by chromosomal translocations and inversions at 14q32.1. Here we report the isolation and characterization of a new member of the TCL1 gene family, TCL1b, located approximately 16 kb centromeric of TCL1. The 1.2-kb TCL1b cDNA encodes a 14-kDa protein of 128 aa and shows 60% similarity to Tcl1. Expression profiles of TCL1 and TCL1b genes are very similar: both genes are expressed at very low levels in normal bone marrow and peripheral lymphocytes but are activated in T cell leukemia by rearrangements of the 14q32.1 region. Thus, translocations and inversions at 14q32. 1 in T cell malignancies involve two oncogenes.

Figure 1

Sequence comparison of Tcl1, Tcl1b, and Mtcp1. Identities are shown in black boxes, and similarities are shown in shaded boxes. For Tcl1 and Mctp1, GenBank accession numbers are X82240 and Z24459, respectively.

Figure 2

Genomic organization of the TCL1 and TCL1b genes. Vertical arrows refer to cloned 14q32.1 breakpoints (1, 10). Restriction sites are given for BssHII (B), ClaI (C), EagI (E), SfiI (F), KspI (K), MluI (M), NotI (N), NruI (R), and SalI (S). Solid boxes represent TCL1 and TCL1b exons.

Figure 3

Northern blot analysis of the TCL1 and TCL1b genes. (A) Human immune system Northern blot. Lanes 1–6: spleen, lymph node, thymus, peripheral blood leukocyte, bone marrow, and fetal liver. (B) Human cancer cell line Northern blot. Lanes 1–8: promyelocytic leukemia, HL-60; Hela cells; chronic myelogenous leukemia, K-562; T lymphoblastic leukemia, MOLT-4; Burkitt’s lymphoma Raji; colorectal adenocarcinoma, SW480; lung carcinoma, A549; and melanoma, G361. (C) Lanes 1–6: Burkitt’s lymphoma Raji, Burkitt’s lymphoma Daudi, Burkitt’s lymphoma CA-46, SupT11, bone marrow, and placenta. (D) Lane 1, bone marrow; lanes 2–7, EBV transformed lymphoblastoid cell lines (Ado-1471, Ado-1476, Ado-1701, Ado-1727, Ado-2069, Ado-2199); lane 8, CA-46. (A– D) TCL1b probe (Top), Tcl1 probe (Middle), and actin probe (Bottom).

Figure 4

RT-PCR analysis of TCL1 and TCL1b genes. (A) Normal human tissues. Lanes 1–23: heart, liver, brain, muscle, placenta, kidney, lung, pancreas, spleen, lymph node, thymus, tonsil, peripheral blood lymphocytes (PBL), bone marrow, fetal liver, fetal brain, fetal lung, fetal kidney, fetal heart, fetal skeletal muscle, fetal spleen, fetal thymus, and negative control. (B) Lanes 1–4, T cell PLL samples (3047, 3046, 3050, 3048); lanes 5–6, bone marrow, PBL. (A and B) TCL1b primers (Top), TCL1 primers (Middle), and control G3PDH primers (Bottom).