Our goal is to better understand the biologic basis for lung cancer metastasis, which could potentially have a tremendous public health impact because lung cancer is the primary cause of cancer-related death in Western countries, and metastasis is the primary cause of death from lung cancer. On the basis of our previous reports, we believe that the extracellular signals that repress microRNA-200 (miR-200) levels in lung cancer cells are key drivers of metastasis and are targets for metastasis prevention. Here we show that metastasis-prone tumor cells from mice that develop lung adenocarcinomas owing to expression of mutant K-ras and p53 express both Notch and Notch ligands, and the Notch ligand jagged2 promotes tumor sphere formation, EMT, invasion, and metastasis. Jagged2 increases the expression of all six GATA transcription factor family members, and GATA3 promotes tumor cell EMT and metastasis by suppressing miR-200 levels. We posit that each of the GATA factors regulated by jagged2 plays a distinct transcriptional role and collectively mediate the diverse biologic effects of jagged2 in this tumor model. This hypothesis is innovative because it links the Notch axis to a microRNA that is central to EMT and metastasis, and it opens a new area of investigation into the role of GATA factors as promoters, rather than repressors, of metastasis. The experimental approaches we have proposed are innovative; the mouse model is based on one we created that closely recapitulates biologic and transcriptional features of human lung adenocarcinoma, and the cell micropatterning techniques we have developed are at the forefront of the interface between bioengineering and cell biology. We propose two Specific Aims.
The first Aim i s to determine whether inactivation of Jagged2 abrogates metastasis in a mouse model of lung adenocarcinoma. For this Aim, we will create mice that conditionally inactivate jagged2 and express oncogenic K-ras and p53 in the lung; we will examine whether jagged2/Notch-dependent interactions between tumor cells are required for polarized sphere formation and EMT using cell micro-patterning techniques we have developed; and we will determine whether high jagged2 levels correlate with low microRNA-200 family member expression in human lung adenocarcinoma biopsy samples and whether this expression pattern correlates with disease recurrence and short duration of survival.
The second Aim i s to examine whether the GATA transcription factor family members up-regulated by jagged2 are required for tumor cell polarization, sensitivity to TGF2-induced EMT, and metastasis. For this Aim, we will use genetic approaches to deplete GATA factors individually from lung adenocarcinoma cells; we will study the biologic and transcriptional properties of those cells in culture; and we will examine their tumorigenicity and metastatic potential in an orthotopic lung tumor model we have developed. Our long-term goal is to develop novel approaches to identify those patients who are at high risk for recurrence following treatment of early-stage disease and to use pharmacologic approaches to target key mediators of metastasis in those patients.
Lung cancer is the primary cause of cancer-related death in western countries, and metastasis is the primary cause of death from lung cancer, which demonstrates a crucial need to better understand the biologic underpinnings of metastasis. On the basis of the findings presented here, we postulate that tumor cells bind to each other in a lock-and-key fashion through a receptor (Notch) that binds to its ligand (jagged2) on adjacent tumor cells; Notch then suppresses the levels of a small RNA called miR-200, inducing a change in cell shape and detachment from neighboring cells, an early event in metastasis. If proven true, these findings would warrant studies to determine whether drugs that inhibit Notch receptors, which are currently in clinical trials, prevent lung cancer metastasis and do so most effectively for tumors that have high levels of jagged2 and Notch.
