Lymph nodes are the initial, clinically detected sites of metastasis for many solid tumors, including breast carcinoma and melanoma. The clinical record suggests a progression from lymph node metastases to distant metastases. Indeed, excision of tumor-bearing, draining lymph nodes can improve the clinical outcome for many tumor types. Surprisingly, little is known about factors in the lymph node microenvironment that may contribute to tumor metastasis. Studies from the Varner lab indicate that primary tumors induce integrin a4-mediated lymphangiogenesis in tumors and in draining and distal lymph nodes prior to metastasis. Antagonists of integrin a4 prevent both lymph node lymphangiogenesis and lymph node metastasis. The alpha4 integrin binds directly to the focal adhesion protein paxillin, an important regulator of cell migration. Paxillin acts as a scaffolding protein by bringing into close proximity signaling molecules that are crucial in promoting cell migration. As paxillin can directly associate with integrin a4, it may, therefore, play a critical role in the signaling events promoting lymphangiogenesis. Indeed, preliminary studies indicate that mice bearing a knockin mutation that prevent a4-paxillin interactions (C57BI/6 a4 Y991A) exhibit defects in lymphangiogenesis and tumor metastasis. Therefore, I propose to characterize further the role of a4-paxillin interactions in promoting lymphatic endothelial cell migration and lymphangiogenesis.
The aims of this proposal are 1) To determine whether integrin a4-paxillin interactions and paxillin phosphorylation are critical for lymphatic endothelial cell (LEC) migration, 2) To determine whether the Rac pathway is a downstream effector of a4-paxillin interactions during LEC migration, and 3) To examine the role of integrin a4 mediated paxillin signaling during lymphangiogenesis and metastasis in vivo. By characterizing the signal transduction pathways that regulate integrin a4 mediated lymphangiogenesis, the proposed studies could lead to the development of new therapies for preventing tumor metastasis.
Tumor metastases to distant organs is of significant concern as this determines the clinical outcome of the patient. Solid tumors (i.e. breast carcinomas), metastasize to the lymph nodes prior to spreading to other organs. Understanding how the lymph nodes prepare and permit for this tumor metastasis, will enable new therapies to be developed for treating and/or preventing metastases.
