View Abstract

A7110 - Genetic Features of Metastatic Tsc2-Null Cells: Relevance to Pulmonary LAM
Author Block: K. Obraztsova1, R. Rue1, E. N. Atochina-Vasserman2, C. Guo3, A. Gow4, V. P. Krymskaya5; 1Pulmonary, Allergy, Critical care, University of Pennsylvania, Philadelphia, PA, United States, 2Pulmonary, Allergy, Critical care, Univeristy Pennsylvania, Philadelphia, PA, United States, 3Rutgers, Piscataway, NJ, United States, 4Pharmacology and Toxicology, Rutgers, Piscataway, NJ, United States, 5Pulmonary, Allergy and Critical care, University Pennsylvania, Philadelphia, PA, United States.
Introduction:
Loss of tumor suppressor Tuberous Sclerosis Complex 2 (TSC2) is associated with a rare lung disease pulmonary Lymphangioleiomyomatosis (LAM). LAM is a progressive neoplastic disease which affects predominantly women of childbearing age and is characterized by cystic lung destruction and loss of pulmonary function. To this day, there is no cure for LAM, and little is known how TSC2 loss induces LAM pathobiology, as well as what is the LAM cell of origin. It is generally believed that LAM cells have metastatic properties and travel through blood and lymphatic system before they reach the lung. In previous studies, we showed that Tsc2-null cells derived from kidney lesions (TTJ cells) of Tsc2-/+ mice with spontaneous loss of heterozygocity for Tsc2, form lung tumors in C57/BL6 mice following tail vein injection. We aimed to study and characterize unique features of Tsc2-null cells enabling them to metastasise mouse lung.
Methods:
To better understand the nature of Tsc2-null cell tumorigenicity, we searched for specific changes in gene expression in vitro and in vivo using qPCR analysis. We examined TTJ cell line gene expression, as well as different cell populations isolated from a metastatic mouse lung. Cell populations were separated using antibody-based bead sorting resulting in: CD45+, CD31+(CD45neg), EpCAM+(CD45neg, CD31neg), PDPN+(CD45neg, CD31neg, EpCAMneg) and (CD45neg, CD31neg, EpCAMneg PDPNneg) populations.
Results:
The lowest Tsc2 gene expression was found in the PDPN+(CD45neg, CD31neg, EpCAMneg) cell population of the metastatic mouse model of LAM.
In agreement with this finding we found that TTJ cells do not express any other cell surface markers but PDPN. Furthermore, TTJ cells show significant down-regulation of cell adhesion molecules expression such as Cadm1, Cdh13, Cdh5, as well as increase in expression of metalloproteinases (MMPs), namely, Mmp19 and Mmp1a.
Conclusions:
TTJ cell tumorigenicity can be attributed to the loss of cell adhesion molecules expression. In turn, high expression of MMPs may contribute to their invasiveness. High expression of PDPN appears to be a unique genetic feature of TTJ cells. It is known that tumor cells often upregulate PDPN as they undergo epithelial-mesenchymal transition, and this upregulation is correlated with increased motility and metastasis. Interestingly, PDPN induces lymphangiogenesis, which is pathologically upregulated in LAM. It has also been shown by immunohistochemical staining that LAM lesions overexpress MMPs and abundantly express PDPN. Elucidation of the spatial and temporal expression of these markers may shed light on the mechanisms of cystic remodeling in LAM.