ABSTRACTgpl30 is a ubiquitously expressed signaltransducing receptor component shared by interleukin 6, interleukin 11, leukemia inhibitory factor, oncostatin M, ciliary neurotrophic factor, and cardiotrophin 1. To investigate physiological roles of gpl30 and to examine pathological consequences of a lack of gpl30, mice deficient for gpl30 have been prepared. Embryos homozygous for the gpl30 mutation progressively die between 12.5 days postcoitum and term. On 16.5 days postcoitum and later, they show hypoplastic ventricular myocardium without septal and trabecular defect. Cytokine signals are mediated through specific receptor complexes, whose components belong, in most cases, to a large group of proteins called the cytokine receptor family (1). These receptor complexes are usually composed of a ligandspecific receptor chain and a signal transducer common to multiple cytokines. gp130 was initially identified as a signal transducing receptor component that associates with the interleukin 6 receptor (IL-6R) when the receptor binds interleukin 6 (IL-6) (2). gp130 is also utilized as a critical signaling component in the receptor complexes for interleukin 11, leukemia inhibitory factor (LIF), oncostatin M, ciliary neurotrophic factor (CNTF), and cardiotrophin 1 (CT-1) (refs. 1 and 3 and references therein). The discovery of this shared signal transducer, gpI30, helps to explain how these different cytokines mediate overlapping biological functions. IL-6 binding to IL-6R induces homodimerization of gp130 (4), whereas stimulation by LIF, CNTF, oncostatin M, and CT-1 leads to heterodimerization of gpl 30 with a closely related protein, LIF receptor (3, 5). Homo-or heterodimerization of gpl30 triggers the activation of JAKI, JAK2, and TYK2, members of the JAK family of cytoplasmic tyrosine kinases that are associated with gpl30 (6-8). This leads to subsequent tyrosine phosphorylation and functional activation of a latent cytoplasmic transcription factor,

During B-cell development the surrogate light (SL) chain is selectively expressed in progenitor and precursor B cells during the developmental stages of D(H) to J(H) and V(H) to D(H)J(H) rearrangements. Approximately half of all muH chains produced by these rearrangements cannot pair with SL chains and cannot form a pre-B-cell receptor (pre-BCR). A spectrum of affinities between VpreB and individual V(H) domains generates preB cells with pre-BCR of different fitness which, in turn, determines the extent of the pre-B II-cell proliferation and the fidelity of allelic exclusion of the H chain locus. Once pre-BCR is expressed, SL chain expression is turned off. As pre-B II cells proliferate, SL is diluted out, thus limiting pre-BCR formation. As a consequence, pre-B II cells stop proliferating, become small and resting and begin to rearrange the L chain loci. Multiple rearrangements of the kappaL chain alleles are often detected in wild-type small pre-B II cells. Around 20% of the muH chain-expressing small pre-B II cells also express L chains but do not display the Ig on the surface. Hence, it is likely that not all L chains originally generated in resting pre-B II cells can pair with the muH chain previously present in that cell. The best fitting ones are selected preferentially to generate sIg+ B cells. Furthermore, the transition of immature B cells from the bone marrow to spleen and their development to mature cells appear as two separate steps controlled by different genes.

To clarify whether the expression of the WT1 gene in leukemic cells is aberrant or merely reflects that in normal counterparts, the expression levels of the WT1 gene were quantitated for normal hematopoietic progenitor cells. Bone marrow (BM) and umbilical cord blood (CB) cells were fluorescence-activated cell sorting (FACS)-sorted into CD34+ and CD34− cell populations, and the CD34+ cells into nine subsets (CD34+CD33−, CD34+CD33+, CD34+CD38−, CD34+CD38+, CD34+HLA-DR−, CD34+HLA-DR+, CD34+c-kithigh, CD34+c-kitlow, and CD34+c-kit−) according to the expression levels of CD34, CD33, CD38, HLA-DR, and c-kit. Moreover, acute myeloid leukemic cells were also FACS-sorted into four populations (CD34+CD33−, CD34+CD33+, CD34− CD33+, and CD34− CD33−). FACS-sorted normal hematopoietic progenitor and leukemic cells and FACS-unsorted leukemic cells were examined for the WT1 expression by quantitative reverse transcriptase-polymerase chain reaction. The WT1 expression in the CD34+ and CD34− cell populations and in the nine CD34+ subsets of BM and CB was at either very low (1.0 to 2.4 × 10−2) or undetectable (<10−2) levels (the WT1 expression level of K562 cells was defined as 1.0), whereas the average levels of WT1 expression in FACS-sorted and -unsorted leukemic cells were 2.4 to 9.3 × 10−1. Thus, the WT1 expression levels in normal hematopoietic progenitor cells were at least 10 times less than those in leukemic cells. Therefore, we could not find any normal counterparts of BM or CB that expressed the WT1 at levels comparable with those in leukemic cells. These results indicate an aberrant overexpression of the WT1 gene in leukemic cells and imply the involvement of this gene in human leukemogenesis.

IntroductionWilms tumor gene, WT1, is responsible for the tumorigenesis of a childhood renal neoplasm, Wilms tumor, which is thought to arise as a result of the inactivation of both alleles of the WT1 gene. 1,2 The WT1 gene has been considered a tumor-suppressor gene on the basis of findings such as intragenic deletions or mutations in Wilms tumor, germline mutations in patients with leukemia predisposition syndromes, and WT1-mediated growth suppression of Wilms tumor cells. [3][4][5][6][7] This gene encodes a zinc finger transcription factor involved in tissue development, in cell proliferation and differentiation, and in apoptosis. 8 The WT1 gene product represses the transcription of growth factor (platelet-derived growth factor ␣ chain, 9 colony-stimulating factor-1, 10 and insulinlike growth factor-II [IGF-II] 11 ) and growth factor receptor genes (IGF-IR 12 and EGFR 13 ), and the other genes (RAR-␣, 14 c-myb, 15 c-myc, 16 bcl-2, 16 ornithine decarboxylase, 17 and N-myc 18 ), whereas it activates the transcription of some genes (retinoblastoma suppressor-associated protein 46,20 and bcl-2 21 ). Unlike tumor-suppressor genes such as Rb and p53 that are ubiquitously expressed, WT1 gene expression is restricted to a limited set of tissues, including gonads, uterus, kidney, mesothelium, and hematopoietic progenitors. [22][23][24] WT1 knock-out mice have been shown to have defects in the urogenital system and to die at embryonic day 13.5, probably because of heart failure. 25 The WT1 gene was originally defined as a tumor-suppressor gene, as mentioned earlier. However, we recently proposed that the wild-type WT1 gene performs an oncogenic rather than a tumorsuppressor function in leukemogenesis and tumorigenesis in various types of solid tumors on the basis of the following findings: (1) high expression of the wild-type WT1 gene in leukemias [26][27][28][29][30][31] and various types of solid tumors, including ovarian tumors, Leydig cell tumors, mesothelioma, gastric cancer, colon cancer, lung cancer, and breast cancer 23,[32][33][34][35][36][37][38][39][40][41][42][43] ; (2) growth inhibition of leukemic 44,45 and solid tumor cells 41 by treatment with WT1 antisense oligomers; (3) promotion of cell growth, but blocking of cell differentiation, in the myeloid progenitor cell line 32D 46 and in normal bone marrow myeloid cells 47 as a result of constitutive WT1 gene expression caused by transfection with the wild-type WT1 gene; and (4) WT1 expression detected in most 7,12-dimethylbenzanthracene-induced erythroblastic leukemias and a tendency for cells with high levels of WT1 expression to develop into leukemias. 48 Stimulation in vitro of HLA-A2.1-positive or -A24.2-positive peripheral blood mononuclear cells with 9-mer WT1 peptides containing major histocompatibility complex (MHC) class 1 binding anchor motifs elicited WT1-specific cytotoxic T lymphocytes (CTLs). [49][50][51] These CTLs specifically killed WT1-expressing tumor cells in an HLA class 1-restricted manner and inhibited colony (1) cancer-testis ant...