Differential regulation of the expression of interleukin-2 receptor gamma-chain during the in vitro differentiation of human myeloid cells

IL-2 signals through Sgk1 and inhibits proliferation and apoptosis in kidney cancer cells

The interleukin-2 is a cytokine that is essential for lymphocytic survival and function. Ectopic expression of the IL-2 receptor in epithelial tissues has been reported previously, although the functional significance of this expression is still being investigated. We provided novel structural and functional information on the expression of the IL-2 receptor in kidney cancer cells and in other normal and neoplastic human epithelial tissues. In A-498 kidney cancer cells, we showed that IL-2 binding to its own receptor triggers a signal transduction pathway leading to the inhibition of proliferation and apoptosis. We found that the inhibition of proliferation is associated with Erk1/2 dephosphorylation, whereas the survival signals appear to be mediated by Sgk1 activation. This investigation focuses on the IL-2 induced regulation of Sgk1 and describes a role of the IL-2 receptor and Sgk1 in the regulation of epithelial tumor cell death and survival.

High-mobility group A1 proteins are overexpressed in human leukaemias

High-mobility group A (HMGA) proteins are non-histone nuclear proteins that bind DNA and several transcription factors. They are involved in the regulation of chromatin structure and function. HMGA protein expression is low in normal adult tissues, but abundant during embryonic development and in several human tumours. Rearrangements of the HMGA genes have been frequently detected in human benign tumours of mesenchymal origin, e.g. lipomas, lung hamartomas and uterine leiomiomas. HMGA proteins have been implicated in the control of cell growth and differentiation of the pre-adipocytic cell line 3T3-L1. In an attempt to better understand the role of HMGA1 proteins in haematological neoplasias and in the differentiation of haematopietic cells, we have investigated their expression in human leukaemias and in leukaemic cell lines induced to terminal differentiation. Here we report HMGA1 overexpression in most fresh human leukaemias of different origin and in several leukaemic cell lines. Moreover, differentiation of three cell lines towards the megakaryocytic phenotype was associated with HMGA1 protein induction, whereas induction of erythroid and monocytic differentiation generally resulted in reduced HMGA1 expression.

Identification by differential display of transcripts regulated during hematopoietic differentiation

The polymerase chain reaction-based differential display method (DDRT-PCR) was used to identify mRNAs differentially expressed during the maturation of human CD34+ progenitor cells stimulated to differentiate in vitro towards granulomonocytic or erythroid lineages with a mixture of hemopoietins (kit ligand + interleukin 3 + GM-CSF in the absence or presence of erythropoietin, respectively). Three cDNA transcripts (B32, B41, and B56) display differential expression during cytokine-induced maturation of CD34+ cells. These clones have no homology with already-described sequences. Primer extension cofirmed the presence of the corresponding mRNA. The levels of mRNA corresponding to B32 are enhanced in the later phases of the granulomonocytic as well as in the erythroid differentiation of CD34+ cells. The mRNA identified by B41 was induced by a late stage in only granulomonocytic differentiation of CD34+ cells. The mRNA corresponding to B56 was instead present in nonstimulated CD34+ cells, declined in the early stages of differentiation, and reappeared at later stages in cells treated with both combinations of cytokines. Expression of these genes was detected in a number of acute myelogenous leukemias, as well as in some leukemic cell lines. B32 and B41 were downregulated in KG-1 cells induced to differentiate towards the monocytic lineage, whereas the levels of B56 were unchanged. In K562 cells, clones B41 and B56 were downregulated only in the late phases of PMA-induced megakaryocytic differentiation and during erythroid differentiation. B32 was rapidly downregulated when K562 cells were induced to differentiate towards either megakaryocytic or erythroid phenotypes. These transcripts represent novel hematopoietic cDNAs that should prove of value for the study of human blood cells and their disorders.

Abnormal Myelocytic Cell Development in Interleukin-2 (IL-2)–Deficient Mice: Evidence for the Involvement of IL-2 in Myelopoiesis

Mice lacking interleukin-2 (IL-2) developed a severe hematopoietic disorder characterized by the abnormal development of myeloid cells and neutropenia. Analysis of the bone marrow of IL-2–deficient (IL-2−/−) mice showed that the number of mature polymorphonuclear cells was decreased by 65% to 75%, and granulocyte/macrophage precursor cells were reduced by 50%. Bone marrow cells from IL-2−/− mice were unable to sustain myelopoiesis in lethally irradiated mice and in long-term bone marrow cultures (LTBMC). The addition of exogenous IL-2 to LTBMC of IL-2−/− cells partially restored hematopoietic progenitor activity. In the bone marrow of wild-type mice, immature (Mac-1lo) myeloid cells, including myeloblasts and promyelocytes, constitutively expressed the β-chain of the IL-2R, and the number of Mac-1loIL-2Rβ+ cells was increased by twofold to threefold in IL-2−/− mice. During culture in the presence of IL-2 and the absence of stromal cells, Mac-1loIL-2Rβ+ immature myeloid cells proliferated and gave rise to mature granulocytes and macrophages. Collectively, these observations indicate that defective myelopoiesis in IL-2−/− mice is at least in part a consequence of their direct dependency on IL-2, and by regulating the growth of immature myeloid cells, IL-2 plays an important role in the homeostatic regulation of myelocytic cell generation.

Growth inhibition signalled through the interleukin-4/interleukin-13 receptor complex is associated with tyrosine phosphorylation of insulin receptor substrate-1

Induction of growth inhibition in human colorectal carcinoma cell lines by interleukin (IL)-4 and IL-13 was associated with the neophosphorylation of a 170 kDa cellular protein, identified as insulin receptor substrate-1 (IRS-1) by immunoprecipitation. Tyrosine phosphorylation of IRS-I was also induced by insulin and insulin-like growth factor I. Sublines of colorectal carcinoma cells unresponsive to growth modulation by IL-4, IL-13 or insulin-like growth factor I-induced growth did not phosphorylate IRS-1. A functional, multimeric IL-4 receptor complex was present on all carcinoma cell lines with a subunit composition of 65 kDa, 75 kDa and the previously characterized 130 kDa band as demonstrated by affinity cross-link with 126I labelled IL-4. The 65 kDa subunit is novel whereas the 75 kDa band represents the common IL-2 receptor gama-chain the novel 65 kDa receptor was present as a double band and bound primarily 125I-labelled IL-13. The present study demonstrates the involvement of a novel chain other than the gama-chain in the receptor complexes of IL-4 and IL-13 and and post-receptor tyrosine phosphorylation of IRS-1. The association of IRS-1 with growth inhibitory signals in carcinoma cells suggests a novel mechanism of tumour growth control.