Haploinsufficient tumor suppressor PRP4K is negatively regulated during epithelial-to-mesenchymal transition.

The pre-mRNA processing factor 4 kinase (PRP4K, also known as PRPF4B) is an essential gene. However, reduced PRP4K expression is associated with aggressive breast and ovarian cancer phenotypes including taxane therapy resistance, increased cell migration and invasion in vitro, and cancer metastasis in mice. These results are consistent with PRP4K being a haploinsufficient tumor suppressor. Increased cell migration and invasion is associated with epithelial-to-mesenchymal transition (EMT), but how reduced PRP4K levels affect normal epithelial cell migration or EMT has not been studied. Depletion of PRP4K by small hairpin RNA (shRNA) in non-transformed mammary epithelial cell lines (MCF10A, HMLE) reduced or had no effect on 2D migration in the scratch assay but resulted in greater invasive potential in 3D transwell assays. Depletion of PRP4K in mesenchymal triple-negative breast cancer cells (MDA-MB-231) resulted in both enhanced 2D migration and 3D invasion, with 3D invasion correlated with higher fibronectin levels in both MDA-MB-231 and MCF10A cells and without changes in E-cadherin. Induction of EMT in MCF10A cells, by treatment with WNT-5a and TGF-ß1, or depletion of eukaryotic translation initiation factor 3e (eIF3e) by shRNA, resulted in significantly reduced PRP4K expression. Mechanistically, induction of EMT by WNT-5a/TGF-ß1 reduced PRP4K transcript levels, whereas eIF3e depletion led to reduced PRP4K translation. Finally, reduced PRP4K levels after eIF3e depletion correlated with increased YAP activity and nuclear localization, both of which are reversed by overexpression of exogenous PRP4K. Thus, PRP4K is a haploinsufficient tumor suppressor negatively regulated by EMT, that when depleted in normal mammary cells can increase cell invasion without inducing full EMT.

Author Correction: A novel mechanism of plasminogen activation in epithelial and mesenchymal cells.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Quantitative Proteome Responses to Oncolytic Reovirus in GM-CSF- and M-CSF-Differentiated Bone Marrow-Derived Cells.

The efficacy of oncolytic viruses (OVs), such as reovirus, is dictated by host immune responses, including those mediated by the pro- versus anti-inflammatory macrophages. As such, a detailed understanding of the interaction between reovirus and different macrophage types is critical for therapeutic efficacy. To explore reovirus-macrophage interactions, we performed tandem mass tag (TMT)-based quantitative temporal proteomics on mouse bone marrow-derived macrophages (BMMs) generated with two cytokines, macrophage colony stimulating factor (M-CSF) and granulocytic-macrophage colony stimulating factor (GM-CSF), representing anti- and proinflammatory macrophages, respectively. We quantified 6863 proteins across five time points in duplicate, comparing M-CSF (M-BMM) and GM-CSF (GM-BMM) in response to OV. We find that GM-BMMs have lower expression of key intrinsic proteins that facilitate an antiviral immune response, express higher levels of reovirus receptor protein JAM-A, and are more susceptible to oncolytic reovirus infection compared to M-BMMs. Interestingly, although M-BMMs are less susceptible to reovirus infection and subsequent cell death, they initiate an antireovirus adaptive T cell immune response comparable to that of GM-BMMs. Taken together, these data describe distinct proteome differences between these two macrophage populations in terms of their ability to mount antiviral immune responses.

A novel mechanism of plasminogen activation in epithelial and mesenchymal cells.

Cancer dissemination is initiated by the movement of cells into the vasculature which has been reported to be triggered by EMT (epithelial to mesenchymal transition). Cellular dissemination also requires proteases that remodel the extracellular matrix. The protease, plasmin is a prominent player in matrix remodeling and invasion. Despite the contribution of both EMT and the plasminogen activation (PA) system to cell dissemination, these processes have never been functionally linked. We reveal that canonical Smad-dependent TGFß1 signaling and FOXC2-mediated PI3K signaling in cells undergoing EMT reciprocally modulate plasminogen activation partly by regulating the plasminogen receptor, S100A10 and the plasminogen activation inhibitor, PAI-1. Plasminogen activation and plasminogen-dependent invasion were more prominent in epithelial-like cells and were partly dictated by the expression of S100A10 and PAI-1.

S100A10, a novel biomarker in pancreatic ductal adenocarcinoma.

Pancreatic cancer is arguably the deadliest cancer type. The efficacy of current therapies is often hindered by the inability to predict patient outcome. As such, the development of tools for early detection and risk prediction is key for improving outcome and quality of life. Here, we introduce the plasminogen receptor S100A10 as a novel predictive biomarker and a driver of pancreatic tumor growth and invasion. We demonstrated that S100A10 mRNA and protein are overexpressed in human pancreatic tumors compared to normal ducts and nonductal stroma. S100A10 mRNA and methylation status were predictive of overall survival and recurrence-free survival across multiple patient cohorts. S100A10 expression was driven by promoter methylation and the oncogene KRAS. S100A10 knockdown reduced surface plasminogen activation, invasiveness, and in vivo growth of pancreatic cancer cell lines. These findings delineate the clinical and functional contribution of S100A10 as a biomarker in pancreatic cancer.

Cell surface protease activation during RAS transformation: Critical role of the plasminogen receptor, S100A10.

The link between oncogenic RAS expression and the acquisition of the invasive phenotype has been attributed to alterations in cellular activities that control degradation of the extracellular matrix. Oncogenic RAS-mediated upregulation of matrix metalloproteinase 2 (MMP-2), MMP-9 and urokinase-type plasminogen activator (uPA) is critical for invasion through the basement membrane and extracellular matrix. The uPA converts cell surface-bound plasminogen to plasmin, a process that is regulated by the binding of plasminogen to specific receptors on the cell surface, however, the identity of the plasminogen receptors that function in this capacity is unclear. We have observed that transformation of cancer cells with oncogenic forms of RAS increases plasmin proteolytic activity by 2- to 4-fold concomitant with a 3-fold increase in cell invasion. Plasminogen receptor profiling revealed RAS-dependent increases in both S100A10 and cytokeratin 8. Oncogenic RAS expression increased S100A10 gene expression which resulted in an increase in S100A10 protein levels. Analysis with the RAS effector-loop mutants that interact specifically with Raf, Ral GDS pathways highlighted the importance of the RalGDS pathways in the regulation of S100A10 gene expression. Depletion of S100A10 from RAS-transformed cells resulted in a loss of both cellular plasmin generation and invasiveness. These results strongly suggest that increases in cell surface levels of S100A10, by oncogenic RAS, plays a critical role in RAS-stimulated plasmin generation, and subsequently, in the invasiveness of oncogenic RAS expressing cancer cells.

Aldehyde dehydrogenase 1A3 influences breast cancer progression via differential retinoic acid signaling.

Aldehyde dehydrogenase (ALDH) 1A enzymes produce retinoic acid (RA), a transcription induction molecule. To investigate if ALDH1A1 or ALDH1A3-mediated RA signaling has an active role in breast cancer tumorigenesis, we performed gene expression and tumor xenograft studies. Analysis of breast patient tumors revealed that high levels of ALDH1A3 correlated with expression of RA-inducible genes with retinoic acid response elements (RAREs), poorer patient survival and triple-negative breast cancers. This suggests a potential link between ALDH1A3 expression and RA signaling especially in aggressive and/or triple-negative breast cancers. In MDA-MB-231, MDA-MB-468 and MDA-MB-435 cells, ALDH1A3 and RA increased expression of RA-inducible genes. Interestingly, ALDH1A3 had opposing effects in tumor xenografts, increasing tumor growth and metastasis of MDA-MB-231 and MDA-MB-435 cells, but decreasing tumor growth of MDA-MB-468 cells. Exogenous RA replaced ALDH1A3 in inducing the same opposing tumor growth and metastasis effects, suggesting that ALDH1A3 mediates these effects by promoting RA signaling. Genome expression analysis revealed that ALDH1A3 induced largely divergent gene expression in MDA-MB-231 and MDA-MB-468 cells which likely resulted in the opposing tumor growth effects. Treatment with DNA methylation inhibitor 5-aza-2'deoxycytidine restored uniform RA-inducibility of RARE-containing HOXA1 and MUC4 in MDA-MB-231 and MDA-MB-468 cells, suggesting that differences in epigenetic modifications contribute to differential ALDH1A3/RA-induced gene expression in breast cancer. In summary, ALDH1A3 induces differential RA signaling in breast cancer cells which affects the rate of breast cancer progression.

On the contribution of S100A10 and annexin A2 to plasminogen activation and oncogenesis: an enduring ambiguity.

Plasminogen receptors are becoming increasingly relevant in regulating many diseases such as cancer, stroke and inflammation. However, controversy has emerged concerning the putative role of some receptors, in particular annexin A2, in binding plasminogen. Several reports failed to account for the effects of annexin A2 on the stability and conformation of its binding partner S100A10. This has created an enduring ambiguity as to the actual function of annexin A2 in plasmin regulation. Supported by a long line of evidence, we conclude that S100A10, and not annexin A2, is the primary plasminogen receptor within the annexin A2-S100A10 complex and contributes to the plasmin-mediated effects that were originally ascribed to annexin A2.

Annexin A2 heterotetramer: structure and function.

Annexin A2 is a pleiotropic calcium- and anionic phospholipid-binding protein that exists as a monomer and as a heterotetrameric complex with the plasminogen receptor protein, S100A10. Annexin A2 has been proposed to play a key role in many processes including exocytosis, endocytosis, membrane organization, ion channel conductance, and also to link F-actin cytoskeleton to the plasma membrane. Despite an impressive list of potential binding partners and regulatory activities, it was somewhat unexpected that the annexin A2-null mouse should show a relatively benign phenotype. Studies with the annexin A2-null mouse have suggested important functions for annexin A2 and the heterotetramer in fibrinolysis, in the regulation of the LDL receptor and in cellular redox regulation. However, the demonstration that depletion of annexin A2 causes the depletion of several other proteins including S100A10, fascin and affects the expression of at least sixty-one genes has confounded the reports of its function. In this review we will discuss the annexin A2 structure and function and its proposed physiological and pathological roles.