|Ph.D Student||Gutter-Kapon Lilach|
|Subject||Heparanase as a Mediator of Cross Talk between the|
Stroma and Tumor Compartments
|Department||Department of Medicine||Supervisor||Professor Israel Vlodavsky|
|Full Thesis text|
The role of heparanase in tumor initiation, growth, metastasis, and chemo-resistance is emerging and encourages the development of heparanase inhibitors as anti-cancer drugs. Unlike the function of heparanase in cancer cells, very little attention was given to heparanase contributed by cells comprising the tumor microenvironment.
In this thesis, we utilized genetic models of mice over-expressing (Hepa-Tg) or lacking (Hepa-KO) heparanase to reveal the role of host heparanase in tumor initiation, growth and metastasis. Hepa-Tg mice were far more sensitive to a carcinogenic agent (DMBA); Thus, while tumor development was restricted to the mammary gland of WT mice, Hepa-Tg mice developed tumors also in their lungs, liver, and other internal organs, associating with reduced survival. Moreover, Hepa-Tg mice were more prone to the development of metastases following intravenous injection of tumor cells. Consistently, tumor growth was balanced by the levels of heparanase in the host. Hence, bigger tumors were formed in Hepa-Tg mice, while smaller tumors were developed in Hepa-KO mice. In some models, this growth advantage was associated with penetration of heparanase-high host cells to the resulting tumors. However, in other models, heparanase-high host cells were not detected, leading us to suspect that the growth advantage in Hepa-Tg mice is due to systemic factors. Indeed, we found increased levels of pro-tumorigenic factors (i.e., RANKL, SPARC) in the plasma of Hepa-Tg vs. wild type (wt) and Hepa-KO mice. Furthermore, we show that plasma from Hepa-Tg mice enhances cell motility vs. control plasma.
We further utilized Hepa-KO mice to reveal the role of endogenous levels of heparanase in the function of macrophages, an important cell constituent of the tumor microenvironment. We found that heparanase is intimately engaged in the regulation of cytokine expression, macrophage motility and phagocytosis capacities. Intriguingly, inoculating WT monocytes together with Lewis lung carcinoma (LLC) cells into Hepa-KO mice resulted in a nearly complete inhibition of tumor growth. In striking contrast, inoculating LLC cells together with monocytes isolated from Hepa-KO mice did not affect tumor growth, indicating that heparanase is critically required for activation and function of macrophages.
Given that many cytokines are being regulated by heparanase, we sought for a common transcription factor that mediates cytokines gene regulation and macrophages activation. We found that c-Fos expression and DNA-binding capacities were induced by heparanase. Moreover, c-Fos induction by heparanase was markedly attenuated by a JNK inhibitor and to a lesser extent by a p38 inhibitor, signaling pathways that were significantly enhanced by heparanase. Notably, c-Fos expression was increased in parallel with the induction of cytokine expression when LLC cells were inoculated together with control macrophages. These results suggest a linear cascade by which heparanase activates Erk, p38 and JNK signaling, leading to increased c-Fos levels and induction of cytokines expression, resulting in macrophage activation.
Taken together, the results strongly suggest that endogenous heparanase is critically important for cytokine expression and macrophage activation. We further put forward the possibility that heparanase can stimulate tumor growth by elevating pro-tumorigenic factors that act systemically, and possibly modify distant tissues to accommodate metastatic cells.