The Presence of P311 in Lymphangioleiomyomatosis Lesions May Link TGFß1 Expression with the mTOR Pathway
JM Moore, K Rao Badri, AN Husain, L Schuger. University of Chicago Medical Center, Chicago, IL
Background: Lymphangioleimyomatosis (LAM) is a rare fatal lung disease effecting women predominantly of child-bearing age. LAM is characterized by the infiltration of the lung by smooth muscle (SM)-like cells leading to cystic destruction and pulmonary insufficiency. The finding of circulating LAM cells in blood suppports the notion that extra-pulmonary involvement is due to metastasis rather than multifocal disease. LAM had been associated with mutations in the tuberous sclerosis complex gene 2 (TSC2 or tuberin) leading to activation of the mTOR (molecular target of rapamycin)/S6K1 signaling pathway. Active mTOR binds to eIF3 (eukaryotic initiation factor 3), displacing and activating S6K1, which promotes translation of cell growth-regulation genes. P311 is an 8-kDa protein found in SM cells and neurons. We recently found that p311 null mice have a severe decrease in SM TGFß1 translation. Since LAM cells exhibit SM-like differentiation, we evaluated LAM lesions for expression of P311 and TGFß1.
Design: Serial sections of FFPE lung tissue sampled from 21 patients with sporatic LAM were immunostained for LAM markers SM actin and HMB 45, P311 and TGFß1. Additional LAM lesions were laser-microdissected for P311 co-immunoprecipitation studies using a specific anti-P311 antibody, followed by mass spectrometry to identify P311 binding partners.
Results: P311 was focally positive in LAM lesions with intensity similar to or higher than that of neighboring vascular SM. LAM cells expressing P311 also showed strong staining for TGFß1, while neighboring blood vessel SM did not express TGFß1. Co-immunoprecipitation followed by mass spectrometry demonstrated that P311 interacts with eIF3.
Conclusions: - LAM lesions are focally and concomitantly positive for P311 and TGFß1. Since the lack of P311 in p311 null mice results in a decrease in TGFß1 level, we postulate that the expression of TGFß1 in LAM cells is related to the production of P311 by these cells. - Since TGFß1 promotes tumor tolerance and stimulates the production of extracellular matrix degrading proteases, the expression of TGFß1 by LAM cells is likely to contribute to the invasive nature of the disease. - Based on the fact that P311 interacts with eIF3, we propose that by such interaction P311 facilitates the binding of active mTOR to eIF3 in the tuberin-deficient LAM cells. However, since vascular SM has normal tuberin function, the mTOR pathway is inactive and is not recruited to promote translation of TGFß1.
Tuesday, March 23, 2010 2:15 PM
Platform Session: Section F, Tuesday Afternoon