Ras effector pathways modulate scatter factor-stimulated NF-kappaB signaling and protection against DNA damage

Scatter factor (SF) (hepatocyte growth factor) is a pleiotrophic cytokine that accumulates within tumors in vivo and protects tumor cells against cytotoxicity and apoptosis due to DNA damaging agents in vitro. Previous studies have established that SF-mediated cell protection involves antiapoptotic signaling from its receptor (c-Met) to PI3 kinase --> c-Akt --> Pak1 (p21-activated kinase -1) --> NF-kappaB (nuclear factor-kappa B). Here, we found that Ras proteins (H-Ras and R-Ras) enhance SF-mediated activation of NF-kappaB and protection of DU-145 and MDCK (Madin-Darby canine kidney) cells against the topoisomerase IIalpha inhibitor adriamycin. Studies of Ras effector loop mutants and their downstream effectors suggest that Ras/PI3 kinase and Ras/Raf1 pathways contribute to SF stimulation of NF-kappaB signaling and cell protection. Further studies revealed that Raf1 positively regulates the ability of SF to stimulate NF-kappaB activity and cell protection. The ability of Raf1 to stimulate NF-kappaB activity was not due to the classical Raf1 --> MEK1/2 --> ERK1/2 pathway. However, we found that a MEK3/6 --> p38 pathway contributes to SF-mediated activation of NF-kappaB. In contrast, RalA, a target of the Ras/RalGDS pathway negatively regulated the ability of SF to stimulate NF-kappaB activity and cell protection. Ras, Raf1 and RalA modulate SF stimulation of NF-kappaB activity, in part, by regulating IkappaB kinase (IKK)-beta kinase activity. These findings suggest that Ras/Raf1/RalA pathways may converge to modulate NF-kappaB activation and SF-mediated survival signaling at the IKK complex and/or a kinase upstream of this complex.

Effect of Akt inhibition on scatter factor-regulated gene expression in DU-145 human prostate cancer cells

The cytokine scatter factor (SF) (hepatocyte growth factor) transduces various biologic actions, including cell motility, invasion, angiogenesis and apoptosis inhibition. The latter is relevant to understanding the role of SF in promoting tumor cell survival in different contexts, for example, detachment from basement membrane, growth in metastatic sites and responses to chemo- and radiotherapy. Previously, we showed that SF protects cells against apoptosis owing to DNA damage, by a mechanism involving phosphoinositol-3-kinase/c-Akt signaling. Here, we used DNA microarray assays to identify c-Akt-regulated genes that might contribute to cell protection. DU-145 human prostate cancer cells were transfected+/-a dominant-negative mutant Akt, treated+/-SF and analysed for gene expression using Affymetrix arrays. These studies identified SF-regulated genes for which induction was c-Akt-dependent vs -independent. Selected microarray findings were confirmed by semiquantitative and quantitative reverse transcription-polymerase chain reaction. We tested the contribution of four SF-inducible/c-Akt-dependent genes (AMPD3, EPHB2, MX1 and WNT4) to protection against adriamycin (a DNA topoisomerase IIalpha inhibitor) using RNA interference. Knockdown of each gene except EPHB2 caused a small but significant reduction in the SF cell protection. The lack of effect of EPHB2 knockdown may be due to the fact that DU-145 cells contain a single-mutant EPHB2 allele. A combination of three small interfering RNAs blocked most of the protection by SF in both DU-145 and T47D cells. These findings identify novel c-Akt-regulated genes, some of which contribute to SF-mediated cytoprotection.

Expression and bioactivity of recombinant human lysozyme in the milk of transgenic mice

Human milk lysozyme is an important protein for innate immunity, but human breast milk is a fairly poor source for commercial production of this enzyme. Research on the expression of recombinant human lysozyme (rHlys) is therefore potentially valuable to the dairy industry. In this study, 2 different kinds of transgenic mice, PBC-hLY and PBC-sighLY, were generated and used as system models to express rHlys. Six lines of PBC-hLY transgenic mice with human lysozyme genomic DNA-based constructs were generated, and a maximum expression level of rHlys approaching 0.154 mg/mL was achieved. Antibacterial activity of the whey from PBC-hLY female transgenic mice was determined by a turbidimetric assay. Results showed that antibacterial activity of the whey was strongly enhanced, and confirmed that rHlys retained full activity. For rHlys to be secreted efficiently into the milk of transgenic mice, 5 lines of mice were also generated, in which the signal peptide DNA of bovine beta-casein was substituted for that of lysozyme in PBC-hLY transgenic mice. Compared with PBC-hLY transgenic mice, both the expression levels of rHlys and the antibacterial activity of the whey were much higher in the PBC-sighLY transgenic mice. The concentration of rHlys in one of these mice amounted to 1.405 mg/mL-3 times higher than the level in human whey. The antibacterial activity of the whey was also 3 times higher than that of human whey. The rHlys from both PBC-hLY and PBC-sighLY transgenic mice had the same antibacterial activity as human milk lysozyme. The effect of the signal peptide and copy numbers of the transgene on expression of rHlys was also evaluated. This work will certainly permit a better understanding of how mammary gland bioreactor systems can be applied to produce rHlys in other mammals, such as cattle.

Epigenetic transfer of metastatic activity by uptake of highly metastatic B16 melanoma cell-released exosomes

AIM

To investigate potential role of highly metastatic BL6-10 tumor cell-released exosomes (EXO) in transfer of metastatic activity into poorly metastatic tumor cell line F1.

METHODS

The highly metastatic B16 melanoma cell line (BL6-10) was generated in our laboratory. EXO from this cell line were isolated and amount of exosomal recovered proteins was measured using Bradford assay. For phenotypic analysis BL6-10 and F1 melanoma cells were stained with FITC-conjugated anti-MHC I (H-2K(b)), MHC II (Ia(b)) and Met 72 antibodies and analyzed by flow cytometry. C57BL/6 mice (8 per group) were injected (i. v.) with 0.5 x 10(6) F1, BL6-10 and F1(EXO) melanoma cells. Lungs were removed 4 weeks after tumor cell injection, fixed in 10% neutral buffered formaldehyde and embedded in paraffin for histological analysis.

RESULTS

Data revealed that BL6-10 cells expressed metastasis marker (Met 72 tumor antigen), while F1 cells did not display this cell surface marker. All mice inoculated with BL6-10 melanoma cells had numerous lung tumor colonies, while mice injected with F1 tumor cells were free of lung metastatic colonies. BL6-10 tumor cells-released EXO also expressed Met 72 tumor antigen as BL6-10 tumor cells, but in less amount. F1 tumor cells can uptake EXO from BL6-10 tumor cells and express acquired exosomal Met 72 tumor antigen.

CONCLUSION

The metastatic activity of highly metastatic BL6-10 tumor cells can be transferred to poorly metastatic F1 tumor cells by uptake of highly metastatic BL6-10 tumor-released EXO.