Defining Mechanisms for Anomalous Expression of Estrogen Receptor in LAM

Lymphangioleiomyomatosis (LAM) is a rare but often fatal disease, characterized by the abnormal proliferation of smooth muscle cells of the lung. LAM occurs primarily in women of childbearing age and its pathology correlates with mutations in the tuberous sclerosis 2 (TSC2) gene and expression of the hormone estrogen. Over the past decade major breakthroughs have been made with respect to our understanding of how estrogens might be directly linked to cellular proliferation, how mutations in the TSC2 gene might result in cellular proliferation and how estrogen signaling might be linked to the activities of the TSC2 gene product tuberin. In spite of these major advances, it is still unclear why smooth muscle cells of the lung are susceptible to LAM and why these same cells become responsive to the proliferation pathway of estrogens. One of the hallmarks of proliferating smooth muscle cells in LAM lesions is the anomalous expression of the intracellular receptor for estrogens, ERa. Although there appears to a very strong correlation between LAM and the loss of a functional TSC2 gene, the distinct gender specificity of LAM support the hypothesis that overexpression of ERa also plays an essential role in the pathology of LAM. Our previous studies have defined a direct link between the TSC2 gene product tuberin and estrogen signaling through ERa. In the studies proposed here we propose a set of investigations that are designed to address 2 of the major unanswered questions with respect to LAM, those being; 'why is it restricted to women' and 'why is it primarily relegated to smooth muscle cells of the lung?' The hypothesis that we will be investigating is that loss of tuberin results in cis and trans changes at the estrogen receptor alpha (ERa) promoter that permit smooth muscle-specific upregulation of ERa gene expression, and subsequent upregulation of estrogen-modulated genomic and non genomic signaling pathways. To investigate this hypothesis 2 specific aims are proposed including: 1) investigation of the mechanism for ERa promoter usage in LAM and 2) investigation of the trans . mechanisms for tuberin-associated repression of ERn expression. The proposed studies will employ a variety of sophisticated DNA and protein technologies to investigate regulation of ERn expression in LAM and the consequence to this regulation when lung smooth muscle cells lose tuberin function. Accomplishment of these specific aims will help define why smooth muscle cells of the lung lacking a functional tuberin molecule are susceptible to estrogen-stimulated proliferation events, and might also generate new targets for designing LAM and perhaps TSC-specific therapeutics.