Glycoprotein-NMB (GPNMB) is Pro-Tumorigenic in Lymphangioleiomyomatosis (LAM)

Abstract Lymphangioleiomyomatosis (LAM) is an estrogen-sensitive lung disease found almost exclusively in women. LAM is characterized by the hyperproliferation of smooth muscle cells creating small tumors throughout the lungs, resulting in the formation of large cysts that replace normal alveolar space. Growth of these tumors and progression of the cyst development leads to pulmonary function loss, and sometimes subsequent lung transplantation. However, LAM recurs after transplantation and LAM cells can be found circulating in body fluids suggesting a metastatic nature of the disease. Due to LAM’s estrogen sensitivity, female specificity, and metastatic nature, we previously proposed that LAM cells originate from the uterine myometrium. We therefore designed a uterine-specific TSC2-null mouse model where all of the mice generate uterine tumors characteristic of LAM and half develop lung metastases. Using RNASeq analysis of uterine tissue from this mouse model, when focusing on genes regulated by estrogen and TSC2, we discovered increased expression of melanocytic markers, including Glycoprotein Non-Metastatic Melanoma Protein B (GPNMB), which is known to be oncogenic in other cancers. GPNMB was not only highly expressed in our mouse model, it was also expressed in TSC2-null cell lines, and LAM patient lungs and uteri. Interestingly, serum GPNMB is a potential biomarker, as LAM patients have higher serum GPNMB levels compared to healthy controls. Knocking down GPNMB expression by siRNA decreased proliferation, migration, and invasion in TSC2-null cells. Further, knocking out GPNMB in TSC2-null cells using CRISPR/Cas9 decreased xenograft tumor growth in mice and GPNMB is a potential therapeutic target for LAM. Supported by grants from NIH (R01 CA193583, T32HL066988), the LAM Foundation, and DOD