Neuroblastoma and hepatocyte coculture conditioned media alter apoptosis

Expression of VEGF receptors in cocultured neuroblastoma cells

BACKGROUND

VEGF is best known for its angiogenic properties. We have found that VEGF expression is increased in neuroblastoma cells cocultured with hepatocytes. In addition, we have previously shown that neuroblastoma cells cultured with exogenous VEGF have an increase in the expression of VEGF receptors. Therefore, we hypothesized that the expression of VEGF receptors would be up-regulated in neuroblastoma cells grown in the coculture environment.

MATERIALS AND METHODS

Two neuroblastoma cell lines (IMR-32 or SK-N-DZ) are used. These cells are cultured alone and in a coculture system with hepatocytes. Message for VEGF and the VEGF receptors KDR, flt-1, flt-4, neuropilin 1 (NRP-1), and neuropilin 2 (NRP-2) are measured with RT-PCR. Flt-4, NRP-1, and NRP-2 protein expression is measured with Western blot.

RESULTS

The receptors KDR and flt-1 are not detected in either cell line in either control or coculture conditions. Message for VEGF and flt-4 is significantly increased in the cocultured IMR-32 cells, while that for NRP-1 and NRP-2 is unchanged in these cells. VEGF and its receptors are unchanged in cocultured SK-N-DZ cells.

CONCLUSIONS

Neuroblastoma cells express specific VEGF receptors that are differentially regulated in the different cell lines. These findings suggest that the heterogeneity of neuroblastomas may limit the utility of targeting VEGF and its receptors as sole treatments for the tumor, and that successful therapies will be dependent upon the specific biology of the tumor.

VEGF receptors are differentially expressed by neuroblastoma cells in culture

BACKGROUND/PURPOSE

Vascular endothelial growth factor (VEGF) is best known for its angiogenic properties, but its mitogenic capacity may be more important for tumorigenesis. The ability of VEGF to induce specific biologic activities may be dependent on the amount and type of VEGF receptors present. The authors hypothesize that neuroblastoma cells express specific VEGF receptors and that their expression may be altered when the cells are exposed to differing cytokines and culture environments.

METHODS

Four groups of human neuroblastoma cells (IMR-32) are studied. (1) Control cells: cultured in standard media. (2) VEGF cells: VEGF added to the media. (3) Tumor necrosis factor alpha (TNF-alpha) cells: TNF-alpha added to the media. (4) Serum starved cells: cultured in serum-depleted media. Reverse transcriptase polymerase chain reaction (RT-PCR) is utilized to measure the VEGF receptors flt-1, KDR/flk-1, flt-4, neuropilin 1 (NRP-1), and neuropilin 2 (NRP-2).

RESULTS

Flt-1 and KDR are not detected in any groups. Flt-4, NRP-1, and NRP-2 are present in the IMR-32 cells, and their expression is significantly increased by the administration of VEGF. Neuroblastoma cells cultured with TNF-alpha or in serum-depleted media have a significant decrease in the expression of these receptors.

CONCLUSIONS

The authors show that neuroblastoma cells express specific VEGF receptors that may be altered by mitogenic or apoptotic stimuli. Specifically targeting VEGF and its receptors may be another therapeutic strategy for the treatment of neuroblastoma.

Differential expression of Bcl-2 and Bax may enhance neuroblastoma survival

BACKGROUND/PURPOSE

Aggressive tumors may alter their expression of Bcl-2 proteins to decrease apoptosis and increase survival. The authors reported previously that neuroblastoma cells have diminished apoptosis when placed in coculture with hepatocytes to stimulate a metastatic environment. It was hypothesized that the expression of proapoptotic (Bax) and prosurvival (Bcl-2 and Mcl-1) proteins would be altered in neuroblastoma cells grown in a cell culture model of metastatic neuroblastoma.

METHODS

Human neuroblastoma cells (IMR-32) were grown alone or in coculture with human hepatocytes for 2, 3, or 4 days. Bcl-2, Mcl-1, and Bax mRNA were measured with reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

Bcl-2, an antiapoptotic protein, was significantly increased in cocultured neuroblastoma cells by day 4. Bax, a proapoptotic protein, was significantly diminished by day 3. No significant change in Mcl-1 occurred in this study.

CONCLUSIONS

When neuroblastoma cells placed in coculture, the prosurvival protein, Bcl-2, is upregulated whereas the proapoptotic protein, Bax, is downregulated. The combination of these changes can maximally enhance the survival rate of neuroblastoma cells in coculture. The propensity for neuroblastoma to either metastasize or regress may be associated with its ability to differentially regulate the expression of different members of the Bcl-2 protein family.

Neuroblastoma, Apoptosis, and Growth Factors

Neuroblastoma is the most common extracranial tumor of childhood. This tumor is associated with alterations in apoptosis and is affected by various growth factors and cytokines. In this short review we will discuss recent findings in our laboratory where we have been studying a cell culture model of neuroblastoma.

Caspase 3 expression is altered in a coculture model of neuroblastoma

BACKGROUND

Previously, we demonstrated that neuroblastoma cells cocultured with hepatocytes are protected from apoptosis, while apoptosis is upregulated in the hepatocytes. The mechanisms responsible for these findings are unknown. We hypothesize that caspase 3, a cysteine protease central to the apoptotic pathway, will be altered in this coculture model that simulates metastatic neuroblastoma.

METHODS

Control human neuroblastoma cells and liver cells are plated in standard media. For the study group, a noncontact, coculture system is used. Hepatocytes are plated on cell culture inserts, placed above a growing layer of neuroblastoma cells, and incubated. Activated caspase 3 is measured after 1, 2, 3, or 4 days.

RESULTS

Activated caspase 3 levels are significantly decreased in the cocultured neuroblastoma cells on days 2, 3, and 4. Conversely, cocultured hepatocytes have a significant increase in caspase 3 activation at all time periods, with the largest difference seen after 1 day in coculture.

CONCLUSIONS

The capacity for neuroblastoma to differentially alter caspase 3 activation may provide a significant survival advantage for the neuroblastoma cells in metastatic environments. Understanding the mechanisms for this altered regulation may lead to improved and better targeted therapy for this malignancy.

VEGF is upregulated in a neuroblastoma and hepatocyte coculture model

BACKGROUND

We hypothesize that angiogenic factors are altered by the interaction between neuroblastoma cells and host tissues.

MATERIALS AND METHODS

Human Chang hepatocytes and human neuroblastoma cells are cultured separately and in a noncontact, coculture system. Immunostaining for VEGF is performed on the cells. ELISA is used to detect vascular endothelial growth factor (VEGF), basic fibroblast growth factor, and interleukin-8 in the conditioned media. Human umbilical vein endothelial cells (HUVEC) are cultured with standard medium (control) and hepatocyte, neuroblastoma, and coculture conditioned media. After 48 and 72 h, cells are counted to determine proliferation. Finally, VEGF-blocking antibody is added to the HUVEC cultures with the conditioned media.

RESULTS

VEGF is markedly elevated in the coculture medium compared to the media from hepatocytes or neuroblastoma grown alone [412.2 +/- 52 vs 235 +/- 35 or 74.5 +/- 28.5 (pg/10(6) cells), P < 0.05]. Other growth factors are almost undetectable in any of the media. Immunostaining for VEGF in the cocultured hepatocytes is decreased by almost 50%, but VEGF immunostaining is increased fourfold in the cocultured neuroblastoma cells. A significant increase in cell proliferation is seen at both 48 and 72 h when HUVEC are cultured with the coculture media. Cell proliferation is blocked with the addition of anti-VEGF antibody.

CONCLUSION

The interaction of neuroblastoma with hepatocytes results in an increased production of VEGF. It stimulates endothelial cell proliferation and may enhance the tumor's metastatic potential in an autocrine fashion.