Glycoprotein non-metastatic melanoma protein B promotes tumor growth and is a biomarker for lymphangioleiomyomatosis.

Lymphangioleiomyomatosis (LAM) is a rare, progressive cystic lung disease affecting almost exclusively female-sexed individuals. The cysts represent regions of lung destruction caused by smooth muscle tumors containing mutations in one of the two tuberous sclerosis (TSC) genes. mTORC1 inhibition slows but does not stop LAM advancement. Furthermore, monitoring disease progression is hindered by insufficient biomarkers. Therefore, new treatment options and biomarkers are needed. LAM cells express melanocytic markers, including glycoprotein non-metastatic melanoma protein B (GPNMB). The function of GPNMB in LAM is currently unknown; however, GPNMB's unique cell surface expression on tumor versus benign cells makes GPNMB a potential therapeutic target, and persistent release of its extracellular ectodomain suggests potential as a serum biomarker. Here, we establish that GPNMB expression is dependent on mTORC1 signaling, and that GPNMB regulates TSC2-null tumor cell invasion in vitro. Further, we demonstrate that GPNMB enhances TSC2-null xenograft tumor growth in vivo, and that ectodomain release is required for this xenograft growth. We also show that GPNMB's ectodomain is released from the cell surface of TSC2-null cells by proteases ADAM10 and 17, and we identify the protease target sequence on GPNMB. Finally, we demonstrate that GPNMB's ectodomain is present at higher levels in LAM patient serum compared to healthy controls and that ectodomain levels decrease with mTORC1 inhibition, making it a potential LAM biomarker.

Glucocorticoid Receptor Activation in Lobular Breast Cancer Is Associated with Reduced Cell Proliferation and Promotion of Metastases.

Estrogen receptor-positive (ER+) invasive lobular breast cancer (ILC) comprises about ~15% of breast cancer. ILC's unique genotypic (loss of wild type E-cadherin expression) and phenotypic (small individual round cancer cells that grow in discontinuous nests) are thought to contribute to a distinctive pattern of metastases to serosal membranes. Unlike invasive ductal carcinoma (IDC), ILC metastases often intercalate into the mesothelial layer of the peritoneum and other serosal surfaces. While ER activity is a known driver of ILC proliferation, very little is known about how additional nuclear receptors contribute to ILC's distinctive biology. In ER+ IDC, we showed previously that glucocorticoid receptor (GR) activity inhibits pro-proliferative gene expression and cell proliferation. Here we examined ER+ ILC models and found that GR activation similarly reduces S-phase entry gene expression and ILC proliferation. While slowing tumor growth rate, our data also suggest that GR activation results in an enhanced metastatic phenotype through increasing integrin-encoding gene expression, extracellular matrix protein adhesion, and mesothelial cell clearance. Moreover, in an intraductal mouse mammary gland model of ILC, we found that GR expression is associated with increased bone metastases despite slowed primary mammary tumor growth. Taken together, our findings suggest GR-mediated gene expression may contribute to the unusual characteristics of ILC biology.

Estradiol Augments Tumor-Induced Neutrophil Production to Promote Tumor Cell Actions in Lymphangioleiomyomatosis Models.

Lymphangioleiomyomatosis (LAM) is a rare cystic lung disease caused by smooth muscle cell-like tumors containing tuberous sclerosis (TSC) gene mutations and found almost exclusively in females. Patient studies suggest LAM progression is estrogen dependent, an observation supported by in vivo mouse models. However, in vitro data using TSC-null cell lines demonstrate modest estradiol (E2) responses, suggesting E2 effects in vivo may involve pathways independent of direct tumor stimulation. We previously reported tumor-dependent neutrophil expansion and promotion of TSC2-null tumor growth in an E2-sensitive LAM mouse model. We therefore hypothesized that E2 stimulates tumor growth in part by promoting neutrophil production. Here we report that E2-enhanced lung colonization of TSC2-null cells is indeed dependent on neutrophils. We demonstrate that E2 induces granulopoiesis via estrogen receptor α in male and female bone marrow cultures. With our novel TSC2-null mouse myometrial cell line, we show that factors released from these cells drive E2-sensitive neutrophil production. Last, we analyzed single-cell RNA sequencing data from LAM patients and demonstrate the presence of tumor-activated neutrophils. Our data suggest a powerful positive feedback loop whereby E2 and tumor factors induce neutrophil expansion, which in turn intensifies tumor growth and production of neutrophil-stimulating factors, resulting in continued TSC2-null tumor growth.

Prolactin is Expressed in Uterine Leiomyomas and Promotes Signaling and Fibrosis in Myometrial Cells.

Uterine leiomyomas are benign, estrogen-sensitive, fibrotic smooth muscle cell tumors occurring in the uterine myometrium. Leiomyomas are a considerable health burden, with a lifetime prevalence of 80% and limited treatment options. Estrogen and progesterone have positive effects on leiomyoma growth, but little is known about the roles of other hormones. One hormone of interest is prolactin, as it has been described to be present and functional in leiomyomas. The current study investigates prolactin production within leiomyomas and its effects on myometrial cells. RNA isolation and quantitative-PCR of human leiomyoma samples relative to matched adjacent myometrium confirms significant expression of prolactin and dopamine receptor D2, a known regulator of prolactin production and release in the pituitary, with no difference in prolactin receptor expression. Immunohistochemistry confirms increased prolactin in leiomyomas compared to adjacent myometrium and uteri from women without leiomyomas. These results suggest that leiomyomas contain cells that produce prolactin, which may then promote signaling in leiomyoma cells to regulate leiomyoma development/growth. Accordingly, we find that prolactin robustly activates STAT5 and MAPK signaling in rat and human myometrial cell lines. Furthermore, prolactin stimulates expression of myofibroblast markers in rat myometrial cells. Our findings suggest that local prolactin production in leiomyomas may stimulate trans-differentiation of myometrial cells to myofibroblasts, which in turn contributes to the fibrotic nature of leiomyomas.

Neutrophil elastase from myeloid cells promotes TSC2-null tumor growth.

Chronic inflammation promotes progression of many cancers, with circulating myeloid-derived suppressor cell (MDSC) levels correlating with poor prognosis. Here we examine effects of MDSCs on lymphangioleiomyomatosis (LAM), a rare disease occurring almost exclusively in women whereby estrogen-sensitive metastatic TSC2-null tumors grow throughout the lungs, markedly reducing pulmonary function. The LAM cell origin remains unknown; however, previous work demonstrated that Tsc2 inactivation in the mouse uterus induced estrogen-dependent myometrial tumors with nearly all features of LAM. Half of these animals developed metastatic myometrial tumors in the lungs, suggesting that LAM cells might originate from the myometrium, possibly explaining its overwhelming female prevalence and estrogen-sensitivity. Here we report that MDSC levels, and in particular granulocytic myeloid cell levels, are elevated in the periphery and in tumors of uterine-specific Tsc2-null mice. Importantly, MDSC depletion or inhibition of their recruitment impairs myometrial tumor growth. RNA and protein analysis of Tsc2-null myometrial tumors and xenografts demonstrate high expression and activity of the serine protease neutrophil elastase (NE), with selective qPCR studies indicating a stromal origin of the NE. Notably, treatment with sivelestat, a known NE inhibitor already approved for human use in some countries, reduces tumor growth similar to MDSC depletion. Furthermore, NE promotes Tsc2-null tumor cell growth, migration, and invasion in vitro. Finally, NE-expressing myeloid cells are present throughout the lungs of LAM patients but not controls. These data suggest that NE derived from granulocytic myeloid cells might directly promote LAM tumor cell progression and could be a novel therapeutic target for LAM.

Glycoprotein Non-Metastatic Melanoma Protein B (GPNMB) and Cancer: A Novel Potential Therapeutic Target.

Glycoprotein non-metastatic melanoma protein B (GPNMB) is a transmembrane protein enriched on the cell surface of cancer cells, including melanoma, glioblastoma, and triple-negative breast cancer. There is growing evidence identifying GPNMB as a tumor-promoter; however, despite its biological and clinical significance, the molecular mechanisms engaged by GPNMB to promote tumorigenesis are not well understood. GPNMB promotes aggressive behaviors such as tumor cell proliferation, migration, and invasion. The extracellular domain of GPNMB shed from the cell surface interacts with integrins to facilitate in the recruitment of immune-suppressive and pro-angiogenic cells to the tumor microenvironment, thereby enhancing tumor migration and invasion. GPNMB also modulates receptor tyrosine kinases and integrin signaling in a cell autonomous fashion, leading to downstream kinase signaling that in turn triggers the expression and secretion of tumorigenic factors such as matrix metalloproteinases (MMPs) and cytokines. Therefore, GPNMB exerts its pro-tumorigenic role both intracellularly and in a paracrine fashion through shedding its extracellular domain. This review highlights the importance of GPNMB in cancer progression and discusses molecular mediators of GPNMB-induced tumor growth and invasion.

Paxillin and embryonic PolyAdenylation Binding Protein (ePABP) engage to regulate androgen-dependent Xenopus laevis oocyte maturation - A model of kinase-dependent regulation of protein expression.

Steroid-triggered Xenopus laevis oocyte maturation is an elegant physiologic model of nongenomic steroid signaling, as it proceeds completely independent of transcription. We previously demonstrated that androgens are the main physiologic stimulator of oocyte maturation in Xenopus oocytes, and that the adaptor protein paxillin plays a crucial role in mediating this process through a positive feedback loop in which paxillin first enhances Mos protein translation, ensued by Erk2 activation and Erk-dependent phosphorylation of paxillin on serine residues. Phosphoserine-paxillin then further augments Mos protein translation and downstream Erk2 activation, resulting in meiotic progression. We hypothesized that paxillin enhances Mos translation by interacting with embryonic PolyAdenylation Binding Protein (ePABP) on polyadenylated Mos mRNA. Knockdown of ePABP phenocopied paxillin knockdown, with reduced Mos protein expression, Erk2 and Cdk1 activation, as well as oocyte maturation. In both Xenopus oocytes and mammalian cells (HEK-293), paxillin and ePABP constitutively interacted. Testosterone (Xenopus) or EGF (HEK-293) augmented ePABP-paxillin binding, as well as ePABP binding to Mos mRNA (Xenopus), in an Erk-dependent fashion. Thus, ePABP and paxillin work together in an Erk-dependent fashion to enhance Mos protein translation and promote oocyte maturation.

Estrogen maintains myometrial tumors in a lymphangioleiomyomatosis model.

Lymphangioleiomyomatosis (LAM) is a rare disease in women. Patients with LAM develop metastatic smooth-muscle cell adenomas within the lungs, resulting in reduced pulmonary function. LAM cells contain mutations in tuberous sclerosis genes (TSC1 or TSC2), leading to up-regulation of mTORC1 activity and elevated proliferation. The origin of LAM cells remains unknown; however, inactivation of Tsc2 gene in the mouse uterus resulted in myometrial tumors exhibiting LAM features, and approximately 50% of animals developed metastatic myometrial lung tumors. This suggests that LAM tumors might originate from the uterine myometrium, possibly explaining the overwhelming prevalence of LAM in female. Here, we demonstrate that mouse Tsc2-null myometrial tumors exhibit nearly all the features of LAM, including mTORC1/S6K activation, as well as expression of melanocytic markers and matrix metalloproteinases (MMPs). Estrogen ablation reduces S6K signaling and results in Tsc2-null myometrial tumor regression. Thus, even without TSC2, estradiol is required to maintain tumors and mTORC1/S6K signaling. Additionally, we find that MMP-2 and -9, as well as neutrophil elastase (NE), are overexpressed in Tsc2-null myometrial tumors in an estrogen-dependent fashion. In vivo fluorescent imaging using MMP- or NE-sensitive optical biomarkers confirms that protease activity is specific to myometrial tumors. Similar to LAM cells, uterine Tsc2-null myometrial cells also overexpress melanocytic markers in an estrogen-dependent fashion. Finally, we identify glycoprotein NMB (GPNMB) as a melanocytic marker up-regulated in Tsc2-null mouse uteri and human LAM samples. Our data highlight the potential importance of estradiol in LAM cells, suggesting that anti-estrogen therapy may be a treatment modality. Furthermore, proteases and GPNMB might be useful LAM biomarkers.