Dipeptidyl-peptidase IV secreted by Aspergillus fumigatus, a fungus pathogenic to humans.

A dipeptidyl-peptidase IV was purified from the culture medium of the human-pathogenic fungus Aspergillus fumigatus. The enzyme has an apparent molecular mass of 95 kDa and contained approximately 10 kDa of N-linked carbohydrate. This glycoprotein is antigenic and has all characteristics of the class IV dipeptidyl-peptidases: removal of Xaa-Pro and to a lesser extent Xaa-Ala dipeptides from the N termini of peptides, including bioactive peptides such as neuropeptide Y, [des-Arg1] bradykinin, and glucagon-like peptide 1, activity at neutral pH, and presence in the amino acid sequence of the Gly-X-Ser-X-Gly consensus motif of the serine-hydrolases and the putative catalytic triad (Ser613, Asp690, His725) of the dipeptidyl-peptidases. Moreover, the last 200 amino acids displayed 60 to 65% similarity with the other dipeptidyl-peptidases IV from rat, mouse, human, and yeast. However, unlike the other dipeptidyl-peptidases, the dipeptidyl-peptidase IV of A. fumigatus is a secreted enzyme with a cleavable signal peptide. Expression of a recombinant dipeptidyl-peptidase IV of A. fumigatus has been attained in the yeast Pichia pastoris.

Interleukin 4 down-regulates expression of c-kit and autocrine stem cell factor in human colorectal carcinoma cells.

Stem cell factor (SCF) is a cytokine which plays an important role in the development of precursor cells. We have investigated the expression of SCF and its receptor, the c-kit proto-oncogene, in human colorectal carcinoma cell lines. Using reverse transcription-PCR, we confirmed the expression of c-kit in two lines (LS174T and LS1034) and of SCF in 9 of 11 cell lines tested. In a Northern blot, a single transcript of 6.6 kb was detected for SCF mRNA. In addition, two lines (LS174T and HT29) synthesized SCF protein, as detected by Western blot analysis. SCF stimulated proliferation and colony formation of LS174T in a dose-dependent manner up to 160%. A half-maximal effect was obtained with about 5.5 ng/ml of SCF under both growth conditions. LS174T cells expressed the M(r) 145,000 c-kit protein on the cell surface and a neutralizing anti-c-kit mAb inhibited colony formation of LS174T by 40%. Interleukin 4 (IL-4) completely inhibited SCF-induced proliferation of LS174T cells. Interestingly, IL-4 induced an almost complete down-regulation of both c-kit and SCF expression in LS174T. Our findings suggest that in LS174T cells, an SCF-mediated autocrine loop is functional and that IL-4 down-regulates the expression of both the receptor and the ligand of this circuit.

Growth inhibition of human colorectal-carcinoma cells by interleukin-4 and expression of functional interleukin-4 receptors.

The growth-inhibitory effect of interleukin-4 (IL-4) was investigated in a panel of 7 human colorectal-carcinoma cell lines. In 5 cell lines (HT29, WiDr, LS411N, LS513, LS1034) a dose-dependent reduction of proliferation was documented. At 100 U/ml, IL-4 inhibited thymidine incorporation between 45 and 75% and MTT conversion (26 to 41%). The ability of LS513 and WiDr cells to form colonies after IL-4 treatment was reduced by 85 and 62% respectively. LS513 was the most sensitive cell line, with IL-4 inducing half-maximal inhibition at 5 to 6 U/ml. The inhibitory effect of IL-4 was completely neutralized by anti-IL-4 antibodies. Northern-blot analysis revealed the presence of IL-4-receptor (IL-4R) mRNA in all cell lines. The membrane expression of the 130-kDa IL-4R was assessed by FACS, utilizing an anti-IL-4R monoclonal antibody and was confirmed by biotinylated IL-4 binding. Our results attribute an important role for IL-4 as a negative regulator of colorectal-carcinoma cell growth, thus indicating a possible avenue for intervention in this disease.

Blockade of the insulin-like growth-factor-I receptor inhibits growth of human colorectal cancer cells: evidence of a functional IGF-II-mediated autocrine loop.

Insulin-like growth factors (IGFs) are potent proliferation stimulators for numerous tumor cells and often function as autocrine growth factors. We have previously shown that exogenous IGF-I and IGF-II enhance proliferation of colorectal carcinoma cells. The biological signal of both factors is transmitted through the IGF-I receptor (IGF-I-R). This receptor was expressed in 12/12 colorectal carcinoma cell lines tested. alpha IR3, a neutralizing monoclonal antibody (MAb) directed against the human IGF-I-R, inhibited proliferation in 7/12 lines (Caco-2, HT-29, LS411N, LS513, LS1034, WiDr and SW620), as reflected by a reduction of MTT conversion (19 to 42%), a decrease in cell number (39 to 72%) and an increase in doubling time (up to 2-fold). In addition, in 4 cell lines (Caco-2, LS513, LS1034, WiDr) alpha IR3 suppressed colony formation in methylcellulose (40 to 84%). Excess of exogenous IGF completely neutralized alpha IR3-mediated inhibitory effects. Northern blot analysis revealed abundant expression of 2 IGF-II transcripts of 5.0 and 4.3 kb in LS1034 cells. In addition, we observed that growth inhibition by alpha IR3 was correlated with a more differentiated phenotype. Our results suggest that growth of many colorectal carcinoma cell lines is regulated by autocrine IGF-II-mediated stimulation of the IGF-I-R.

Secretion of bioactive granulocyte-macrophage colony-stimulating factor by human colorectal carcinoma cells.

Secretion of several cytokines by colorectal carcinoma cells has been substantiated. These do not include granulocyte-macrophage colony-stimulating factor (GM-CSF) thus far. We show that the supernatant of two human colorectal carcinoma cell lines, LS1034 and SW480, stimulates proliferation of GM-CSF-dependent M07e cells. The activity was constitutively secreted by LS1034 cells and could be induced by serum-free culture conditions in SW480 cells. Addition of a neutralizing anti-GM-CSF antibody completely inhibited this activity. Preabsorption with anti-GM-CSF antibody removed all M07e growth-stimulating activity from LS1034 and SW480 supernatant. Western blot analysis revealed the presence of GM-CSF in LS1034 supernatant. Our results indicate that human colorectal carcinoma cells secrete indeed biologically active GM-CSF.