Metastasis is a major obstacle that must be overcome for the successful treatment of lung cancer. Proteins secreted by cancer cells may facilitate the progression of metastasis, particularly within the phases of migration and invasion. To discover metastasis-promoting secretory proteins within cancer cells, we used the label-free quantitative proteomics approach and compared the secretomes from the lung adenocarcinoma cell lines CL1-0 and CL1-5, which exhibit low and high metastatic properties, respectively. By employing quantitative analyses, we identified 660 proteins, 68 of which were considered to be expressed at different levels between the two cell lines. Lung cancer is the leading cause of cancer death, and ϳ90% of all lung cancer deaths are attributed to metastases (1). Approximately 95% of lung cancer patients are not diagnosed until they develop symptoms, and 85% of the newly diagnosed lung cancer patients are already in the advanced stages of the disease (2, 3). Once the tumor cells have metastasized and spread throughout the lungs, the cancer is considerably more difficult to treat. Invasiveness and metastasis are major threats to successful treatment. Cancer metastasis is an intricate, multi-step process in which the tumor cells must gain both migratory and invasive properties (4). In metastasis research, there are two common in vivo models, spontaneous and experimental metastasis (5-7). In brief, spontaneous metastasis refers to primary tumor cells that are able to dissociate from the primary tumor and metastasize to the secondary organ via the circulatory system. In contrast, experimental metastasis refers to the injection of tumor cells directly into the systemic circulation. Many researchers have attempted to determine the molecular basis of these transitions in hopes of developing target-specific drugs or biomarkers for the prevention and diagnosis of metastasis. Although there have been many discoveries regarding a particular proFrom the ‡Department

Rab small GTPases are master regulators of membrane trafficking and guide vesicle targeting. Recent publications show that Rab-controlled trafficking pathways are altered during tumorigenesis. However, whether any of the Rabs plays a metastasis suppressor role is least explored. Here we address the metastasis suppressive function of human Rab37 (hRAB37) using secretomics, cell, animal and clinical analyses. We show that tissue inhibitor of metalloproteinase 1 (TIMP1), a secreted glycoprotein that inhibits extracellular matrix turnover, is a novel cargo of hRAB37. hRAB37 regulates the exocytosis of TIMP1 in a nucleotide-dependent manner to inactivate matrix metalloproteinase 9 (MMP9) migration axis in vitro and in vivo. Dysfunction of hRAB37 or TIMP1 abrogates metastasis suppression. Lung cancer patients with metastasis and poor survival show low hRAB37 protein expression coinciding with low TIMP1 in tumours. Our findings identify hRAB37 as a novel metastasis suppressor Rab that functions through the TIMP1-MMP9 pathway and has significant prognostic power.

Summary The pathophysiology of heart failure (HF) is diverse, owing to multiple etiologies and aberrations in a number of cellular processes. Therefore, it is essential to understand how defects in the molecular pathways that mediate cellular responses to internal and external stressors function as a system to drive the HF phenotype. Mass spectrometry (MS)-based proteomics strategies have great potential for advancing our understanding of disease mechanisms at the systems level because proteins are the effector molecules for all cell functions and, thus, are directly responsible for determining cell phenotype. Two MS-based proteomics strategies exist: peptide-based bottom-up and protein-based top-down proteomics—each with its own unique strengths and weaknesses for interrogating the proteome. In this review, we will discuss the advantages and disadvantages of bottom-up and top-down MS for protein identification, quantification, and the analysis of post-translational modifications, as well as highlight how both of these strategies have contributed to our understanding of the molecular and cellular mechanisms underlying HF. Additionally, the challenges associated with both proteomics approaches will be discussed and insights will be offered regarding the future of MS-based proteomics in HF research.

Intramyocardial transplantation of cardiomyocytes (CMs), endothelial cells (ECs), and smooth muscle cells (SMCs) derived from human induced pluripotent stem cells (hiPSCs) has beneficial effects on the post-infarction heart. However, the mechanisms underlying the functional improvements remain undefined. We employed large-scale label-free quantitative proteomics to identify proteins that were differentially regulated following cellular transplantation in a swine model of myocardial infarction (MI). We identified 22 proteins that were significantly up-regulated after trilineage cell transplantation compared to both MI and Sham groups. Among them, 12 proteins, including adenylyl cyclase-associated protein 1 and tropomodulin-1, are associated with positive regulation of muscular contraction whereas 11 proteins, such as desmoplakin and zyxin, are involved in embryonic and muscular development and regeneration. Moreover, we identified 21 proteins up-regulated and another 21 down-regulated in MI, but reversed after trilineage cell transplantation. Proteins up-regulated after MI but reversed by transplantation are related to fibrosis and apoptosis. Conversely, proteins down-regulated in MI but restored after cell therapy are regulators of protein nitrosylation. Our results show that the functionally beneficial effects of trilineage cell therapy are accompanied by differential regulation of protein expression in the recipient myocardium, which may contribute to the improved cardiac function.