Research / Clinical Summary

Dwayne Stupack, PhD Assistant Adjunct Professor, Pathology Tumor Growth, Invasion & Metastasis Program Contact by Email

The overall objective of Dr. Stupack's laboratory is to understand the basic cell biology associated with the malignant phenotype of neuroblastoma.

Neuroblastoma is the most common pediatric solid tumor, accounting for 7-10% of all childhood cancer. Malignant stage IV NB manifests as an aggressive, disseminated disease characterized by widespread dissemination of the tumor in vivo. These events are thought to be facilitated by changes that occur in the NB tumors associated with stage IV status. Among these, caspase 8 expression is known to be absent in the majority (~90%) of stage IV, MycN-amplified neuroblastoma.

Caspase 8 is a cysteine protease which plays a critical role in triggering programmed cell death in response to extrinsic cues. Stupack and his colleagues have linked this loss of caspase 8 to the altered function of cellular integrins.

The integrins are family of 24 heterodimeric cell surface adhesion molecules that mediate cell binding to the extracellular matrix, or ECM. Each integrin will bind one or more ECM components, and cells tend to express at least a half dozen different integrins. Most cells, including stage I, II and III neuroblastoma, are dependent upon this substrate ECM for survival. This phenomenon is known as “anchorage dependence.” Importantly, their studies have shown that the simple expression of unligated (or antagonized) cell surface integrins can trigger programmed cell death via a caspase 8-dependent mechanism. Interestingly, this form of cell death (termed Integrin-mediated death) even occurs among ECM-attached cells, provided that a threshold population of cell surface integrins remain unligated. Thus, when a cell invades an inappropriate tissue, such as during metastasis, a default “death pathway” is triggered if the integrin expression on the invading cell is not appropriate to the new ECM.

They believe that this pathway is an important checkpoint regulating tissue homeostasis and metastasis suppression. The loss of caspase 8 that is common in malignant neuroblastom also results in a loss of integrin-mediated death. Caspase 8 is best known for its role in triggering apoptosis downstream of “Death receptors” such as Fas, Trail and the Tumor Necrosis Factor Receptor, and these pathways exhibit dramatically impaired function when caspase 8 is absent.

Surprisingly, genetic reconstitution of caspase 8 expression into the malignant neuroblastoma cells is insufficient to restore apoptosis induced by death receptors. However, re-expression of caspase 8 does completely restore death induced when neuroblastoma are cultured in an inappropriate ECM. Death receptor-induced apoptosis could be restored in the presence of inhibitors of protein translation, suggesting that other inhibitory factors (such as cFLIP) also contribute to resistance to Death Receptor-induced apoptosis. Most importantly, reconstitution of caspase 8 alone was sufficient to induce apoptosis among tissue invasive cell in vivo, and to block spontaneous metastasis in an avian model of tumor dissemination.

Intriguingly, the expression of caspase 8 was also observed to regulate integrin function, leading to the acquisition of a more adherent phenotype without any increases in integrin expression, providing a second mechanism by which expression of caspase 8 might influence neuroblastoma dissemination.

To better understand how the loss of caspase 8 promotes neuroblastoma malignancy, their ongoing studies are focused on investigations of ECM attachment and survival, two factors that are critical for NB dissemination. Our understanding of neuroblastoma biology is limited, and current treatments remain inadequate, especially among patients over 1 year of age where the mortality exceeds 70%. These studies in the Stupack laboratory will provide basic insights into the cell biology behind NB malignant behavior.

Aside from ongoing validation of caspase 8 expression as a prognostic or therapeutic indicator in NB, the studies should provide new insight into the design of existing and emerging treatments that target this disease. In particular, approaches that reactivate caspase 8 expression may be useful in combination with integrin-targeted therapies and/or chemotherapies.

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