Protein kinase B/Akt signalling is required for palmitate-induced beta-cell lipotoxicity.

AIM: This study was conducted to clarify cell death and survival signals in pancreatic beta-cell lipotoxicity. METHODS: Rat insulinoma INS-1 cells, with or without expression of dominant-negative mutant of Akt (K179M), were cultured with palmitate (C16:0) or oleate (C18:1) and cell numbers were determined by 0.2% eosin dye exclusion assay. The Akt activity was determined by anti-3'-phospho-inositide-dependent protein kinase (Akt)/protein kinase B (PKB) or anti-phospho-Akt (Serine 473) immunoblotting, and nuclear protein nuclear factor-kB (NF-kappaB)-binding activity was by supershift analysis. RESULTS: Twenty-four hours treatment with palmitate increased the INS-1 cell number at 0.1-0.2 mM but decreased the cell number at 0.5-1 mM. Oleate did not affect cell number at 0.1-1.0 mM. Palmitate dose-dependently increased phosphorylation of 473th serine in Akt/PKB. The K179M form of Akt/PKB abolished palmitate-induced cell proliferation at the low dose and death at the high dose. Nuclear protein NF-kappaB binding was enhanced at 0.2 and 0.5 mM of palmitate but decreased at 1.0 mM. CONCLUSION: Results suggest that Akt/PKB signalling is involved in palmitate-induced cell death and survival of pancreatic beta cell.

Downregulation of Bim, a proapoptotic relative of Bcl-2, is a pivotal step in cytokine-initiated survival signaling in murine hematopoietic progenitors.

Two distinct signaling pathways regulate the survival of interleukin-3 (IL-3)-dependent hematopoietic progenitors. One originates from the membrane-proximal portion of the cytoplasmic domain of the IL-3 receptor (betac chain), which is shared by IL-3 and granulocyte-macrophage colony-stimulating factor and is involved in the regulation of Bcl-x(L) through activation of STAT5. The other pathway emanates from the distal region of the betac chain and overlaps with downstream signals from constitutively active Ras proteins. Although the latter pathway is indispensable for cell survival, its downstream targets remain largely undefined. Here we show that the expression of Bim, a member of the BH3-only subfamily of cell death activators, is downregulated by IL-3 signaling through either of two major Ras pathways: Raf/mitogen-activated protein kinase and the phosphatidylinositol 3-kinase/mammalian target of rapamycin. Akt/phosphokinase B does not appear to play a significant role in this regulatory cascade. Bim downregulation has important implications for cell survival, since enforced expression of this death activator at levels equivalent to those induced by cytokine withdrawal led to apoptosis even in the presence of IL-3. We conclude that Bim is a pivotal molecule in cytokine regulation of hematopoietic cell survival.

SLUG, a ces-1-related zinc finger transcription factor gene with antiapoptotic activity, is a downstream target of the E2A-HLF oncoprotein.

The E2A-HLF fusion gene transforms human pro-B lymphocytes by interfering with an early step in apoptotic signaling. In a search for E2A-HLF-responsive genes, we identified a zinc finger transcription factor, SLUG, whose product belongs to the Snail family of developmental regulatory proteins. Importantly, SLUG bears close homology to the CES-1 protein of C. elegans, which acts downstream of CES-2 in a neuron-specific cell death pathway. Consistent with the postulated role of CES-1 as an antiapoptotic transcription factor, SLUG was nearly as active as Bcl-2 or Bcl-xL in promoting the survival of IL-3-dependent murine pro-B cells deprived of the cytokine. We conclude that SLUG is an evolutionarily conserved transcriptional repressor whose activation by E2A-HLF promotes the aberrant survival and eventual malignant transformation of mammalian pro-B cells otherwise slated for apoptotic death.

Two distinct interleukin-3-mediated signal pathways, Ras-NFIL3 (E4BP4) and Bcl-xL, regulate the survival of murine pro-B lymphocytes.

Hematopoietic cells require cytokine-initiated signals for survival as well as proliferation. The pathways that transduce these signals, ensuring timely regulation of cell fate genes, remain largely undefined. The NFIL3 (E4BP4) transcription factor, Bcl-xL, and constitutively active mutants of components in Ras signal transduction pathways have been identified as key regulation proteins affecting murine interleukin-3 (IL-3)-dependent cell survival. Here we show that expression of NFIL3 is regulated by oncogenic Ras mutants through both the Raf-mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways. NFIL3 inhibits apoptosis without affecting Bcl-xL expression. By contrast, Bcl-xL levels are regulated through the membrane proximal portion in the cytoplasmic domain of the receptor (betac chain), which is shared by IL-3 and granulocyte-macrophage colony-stimulating factor. Activation of either pathway alone is insufficient to ensure cell survival, indicating that multiple independent signal transduction pathways mediate the survival of developing B-lymphoid cells.

Two candidate downstream target genes for E2A-HLF.

The E2A-HLF fusion gene, formed by the t(17;19)(q22;p13) chromosomal translocation, is thought to drive the leukemic transformation of early B-cell precursors by repressing an evolutionarily conserved apoptotic pathway. To test this hypothesis, we sought to identify downstream targets of E2A-HLF in t(17;19)+ pro-B leukemia cells (UOC-B1) that had been transfected with a zinc-inducible vector encoding a dominant-negative suppressor (E2A-HLF[dn]) of the oncoprotein. Representational difference analysis of mRNAs from E2A-HLF(dn)+ UOC-B1 cells grown with (E2A-HLF inactive) or without (E2A-HLF active) the addition of zinc yielded several differentially expressed cDNA fragments that were individually subcloned. Two of the clones, designated F-5 and G-4, hybridized with mRNAs that were upregulated by E2A-HLF. Levels of both transcripts declined sharply within 8 to 12 hours after suppression of E2A-HLF DNA-binding activity, becoming undetectable after 96 hours. The F-5 cDNA was identified as a portion of ANNEXIN VIII, whose product was expressed in promyelocytic leukemia cells and UOC-B1 cells, but not in other leukemic cell lines. A novel full-length cDNA cloned with the G-4 fragment encoded a protein that we have named SRPUL (sushi-repeat protein upregulated in leukemia). It is normally expressed in heart, ovary, and placenta, but could not be detected in leukemic cell lines other than UOC-B1. Neither protein prevented apoptosis in interleukin-3-dependent murine pro-B cells, suggesting that they have paraneoplastic roles in leukemias that express E2A-HLF, perhaps in the disseminated intravascular coagulopathy and hypercalcemia that characterize these cases.

Association of HTLV-I with autoimmune thyroiditis in patients with adult T-cell leukaemia (ATL) and in HTLV-I carriers.

OBJECTIVE: Human T-lymphotrophic virus type I (HTLV-I) is a retrovirus that causes adult T-cell leukaemia (ATL). This virus is associated with a variety of autoimmune disorders. The possible association between HTLV-I Infection and autoimmune thyroiditis has not been fully studied. We therefore evaluated anti-thyroid peroxidase antibodies (TPOAb) and anti-thyroglobulin antibodies (TGAb) in the sera of patients with ATL, carriers of HTLV-I, and in healthy control subjects to investigate the possible association between such infection and auto-immune thyroiditis. PATIENTS AND METHODS: Fifty-two ATL patients (21 males, 31 females; mean age 56.4 years) and 50 HTLV-I carriers (18 males, 32 females; mean age 56.7 years) were studied. The control subjects were 877 healthy adults (271 males, 606 females; mean age 54.8 years) who were negative for HTLV-I antibody. TPOAb, TGAb, thyroxine (T4) and thyrotrophin (TSH) were measured in serum using a radioimmunoassay kit. RESULTS: Positivity for thyroid autoantibodies (TPOAb and/or TGAb) was found in 21 of 52 ATL patients (40.4%), 15 of 50 HTLV-I carriers (30.0%), and 120 of 877 control subjects (13.7%). The difference between the HTLV-I-Infected and the control subjects was statistically significant (P < 0.005). Female control subjects had a significantly higher prevalence of positivity for thyroid autoantibodies than the males (17.3 vs 5.5%, P < 0.001). Carriers of HTLV-I and patients with ATL of each sex showed an equally high prevalence of positivity for thyroid autoantibodies. Of the subjects who were positive for thyroid autoantibody, 7.5% of control subjects, 19.0% of ATL patients, and 40.0% of HTLV-I carriers had hypothyroidism. A significant difference in this respect was noted between the HTLV-I infected subjects and the control subjects (P < 0.005). CONCLUSIONS: This study demonstrates a high prevalence of positivity for thyroid autoantibodies (TPOAb and/ or TGAb) in the adult T-cell leukaemia patients and the HTLV-I carriers. The adult T-cell leukaemia patients and the HTLV-I carriers each had a high prevalence of hypothyroidism. There was an association between HTLV-I infection and autoimmune thyroiditis.

Islet-cell cytoplasmic antibodies in Japanese diabetics.

Islet Cell-Cytoplasmic Antibodies (ICA) in serum samples obtained from 616 Japanese diabetics were examined. The patients included 296 subjects with insulin-dependent diabetes (IDDM) and 320 with noninsulin dependent diabetes (NIDDM). The number of ICA-positive cases found in 96 subjects in whom the duration of IDDM was under one year was found to be 50% (48/96), though in subjects with a duration over one year, it was only 14.5% (29/200). The prevalence of ICA-positive cases in the NIDDM group was 2.2% (7/320), and none of the nondiabetics had ICA in their serum. Moreover, none of 45 first-degree relatives of 19 patients with IDDM of whom 5 were positive and others were negative for ICA had ICA. Concerning the relationship between HLA-type and ICA in IDDM, there was a tendency for the prevalence of BW54, DR4 and MT3 of HLA to be higher in the ICA-negative group than in the ICA-positive group or the non-diabetic group. In 28 patients with IDDM, both ICA and ICSA were checked. Of 21 patients positive for ICA, only 3 had ICSA, although 3 out of 7 patients with negative ICA were positive for ICSA. Therefore no correlation was found between ICA and ICSA.