Rho family GTPases control cell migration and participate in the regulation of cancer metastasis. Invadopodia, associated with invasive tumor cells, are crucial for cellular invasion and metastasis. To study Rac1 GTPase in invadopodia dynamics, we developed a genetically-encoded, single-chain Rac1 Fluorescence Resonance Energy Transfer (FRET) biosensor.The biosensor shows Rac1 activity exclusion from the core of invadopodia, and higher activity when invadopodia disappear, suggesting that reduced Rac1 activity is necessary for their stability, and Rac1 activation is involved in disassembly. Photoactivating Rac1 at invadopodia confirmed this previously-unknown Rac1 function.We built an invadopodia disassembly model, where a signaling axis involving TrioGEF, Rac1, PAK1, and phosphorylation of cortactin, causing invadopodia dissolution. This mechanism is critical for the proper turnover of invasive structures during tumor cell invasion, where a balance of proteolytic activity and locomotory protrusions must be carefully coordinated to achieve a maximally invasive phenotype.

Biosensors based on FRET have been useful in deciphering the dynamics of protein activation events in living cells at subcellular resolutions and in time scales of seconds. These new systems allow observations of dynamic processes which were not possible previously using more traditional biochemical and cell biological approaches. The image data sets obtained from these sensors require careful processing in order to represent the actual protein activation events. Here, we will cover the basic approaches useful for processing the raw image data sets into relativistic ratiometric measurements, capable of depicting relative differences in the protein activation states within a single cell. We will discuss in detail the approaches for genetically encoded, single-chain biosensor systems based on FRET, as well as those that are based on intermolecular, dual-chain design. Additionally, the same analysis can be utilized for biosensor systems using solvatochromic dyes (Nalbant, Hodgson, Kraynov, Toutchkine, & Hahn, 2004), useful for detection of endogenous protein activation states.

Despite the 92% homology of the hematopoietic cell-specific Rac2 to the canonical isoform Rac1, these isoforms have been shown to play non-redundant roles in immune cells. To study isoform-specific dynamics of Rac in live cells we developed a genetically-encoded, single-chain FRET-based biosensor for Rac2. We also made significant improvements to our existing single-chain Rac1 biosensor. We optimized the biosensor constructs for facile expression in hematopoietic cells and performed functional validations in murine macrophage sublines of RAW264.7 cells. Rac2, along with Rac1and Cdc42, have been implicated in the formation of actin-rich protrusions by macrophages, but their individual activation dynamics have not been previously characterized. We found that both Rac1 and Rac2 had similar activation kinetics yet they had very distinct spatial distributions in response to the exogenous stimulus, fMLP. Active Rac1 was mainly localized to the cell periphery, while active Rac2 was distributed throughout the cell with an apparent higher concentration in the perinuclear region. We also performed an extensive morphodynamic analysis of Rac1, Rac2 and Cdc42 activities during the extension of random protrusions. We found that Rac2 appears to play a leading role in the generation of random protrusions, as we observed an initial strong activation of Rac2 in regions distal from the leading edge, followed by the activation of Rac1, a second burst of Rac2 and then Cdc42 immediately behind the leading edge. Overall, isoform-specific biosensors that have been optimized for expression should be valuable for interrogating the coordination of Rho family GTPase activities in living cells.

Bestrophin1 (BEST1) is expressed in human retinal pigment epithelium (RPE) and mutations in the BEST1 gene commonly cause retinal dysfunction and macular degeneration. BEST1 is presumed to assemble into a calcium-activated chloride channel and be involved in chloride transport but there is no direct evidence in live human RPE cells to support this idea. To test whether BEST1 functions as a chloride channel in living tissue, BEST1-mutant RPE (R218H, L234P, A243T) were generated from patient-derived induced pluripotent stem cells and compared with wild-type RPE in a retinal environment, using a biosensor that visualizes calcium-induced chloride ion flux in the cell. Calcium stimulation elicited chloride ion export in normal RPE but not in RPE derived from three patients with BEST1 mutations. These data, along with three-dimensional modeling, provide evidence that BEST1 assembles into a key calcium-sensing chloride channel in human RPE.

Tumor cell motility and invasion rely on actin cytoskeleton rearrangements mediated by the activation of RhoGTPase signaling pathways. Invadopodia are membrane-degrading protrusions that mediate extracellular matrix degradation. Here, we provide procedures for imaging RhoGTPase biosensors in tumor cells during the formation of invadopodia and matrix degradation.

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;'Insights into the molecular and immunologic pathogenesis of primary CNS lymphomas are essential for meaningful progress in therapy. Tumor-associated macrophages represent the dominant infiltrating leukocyte and there are few established insights into their phenotypes and role in this disease. While upregulation of Th2 cytokines IL-4 and IL-10 in the microenvironment has been demonstrated, the relative roles of M1 and M2 macrophages in contributing to CNS lymphoma pathogenesis has not been elucidated. To date, there is also no information regarding the relative contributions of brain resident microglia and infiltrating macrophages and their interactions with lymphoma. Additional key questions include the identification of factors that mediate both immune cell chemotaxis in CNS lymphomas, as well as the relationship between myeloid cell infiltration and T-cell mediated immune surveillance and immunosuppression. We combined analyses of clinical specimens and mechanistic studies using preclinical in vivo models and show evidence that infiltrating tumor-associated macrophages, derived from monocyte precursors, have a critical role in attenuating CNS lymphoma progression. Immunohistochemical analysis of the density and morphologic features of CD68+ tumor-associated macrophages in 62 diagnostic specimens of immunocompetent PCNSL demonstrated that smaller macrophage size and lower macrophage density correlated with significantly shorter OS. Evaluation of CD68 immunoreactivity using image analysis software (ImageJ) confirmed the heterogeneity of macrophage size and infiltrative density in PCNSL. A multivariate Cox model including age, IELSG score, receipt of consolidation and/or maintenance therapy demonstrated that tumor-associated macrophage density (both count and area) was a significant, independent predictor of favorable PFS and OS and that larger macrophage size a significant, independent predictor of OS in PCNSL treated with standard MTX-based induction (predominantly MTX, temozolomide, rituximab). Using a variety of syngeneic and non-syngeneic preclinical models, including patient-derived CNS lymphoma cells, as well as diagnostic clinical specimens, we characterized the phenotype of tumor-associated macrophages in PCNSL. Using flow-cytometry, we demonstrated that while CD45 high tumor-associated macrophages exhibit strong expression of the canonical M2 marker CD206, a scavenger receptor, these also displayed high co-expression of iNOS and MHC II, markers of classically-activated M1 macrophages. Pharmacologic inhibition of the CSF-1 receptor led to accelerated CNS lymphoma progression, attenuated T-cell infiltration and blocked rituximab efficacy. A flow-cytometric assay of phagocytosis, using Raji lymphoma transduced to express mCherry, demonstrated that infiltrating CD206+ macrophages are the dominant mediator of lymphoma phagocytosis. We applied 2P intravital imaging of a CNS lymphoma model using Cx3cr1GFP/+:Ccr2RFP/+ myeloid cell dual reporter mice and transcriptional studies to define the time-dependent infiltration and phenotypic changes in tumor-associated macrophages and microglia that correlate with disease progression. Using IFN-γ -/- mice we identified a critical role for IFN-γ in the regulation of CNS lymphoma, in the presence and absence of T-cells. We identified IFN-γ-regulated genes in tumor-associated macrophages that may contribute to direct lymphoma cytotoxicity as well as stimulation of T-cell chemotaxis and antigen processing, including TAP1 and TAP2. By IHC, we confirmed TAP1 expression in a subset of diagnostic specimens of PCNSL and determined, using Cox multivariate model, that strong TAP1 correlated with improved PFS (p<0.0006). Notably, independent of receipt of maintenance therapy, TAP1 also correlated with improved PFS in 38 patients that received only MTX-based induction, without dose-intensive chemotherapy consolidation. (Figure 1) Our results support a direct, immune-editing role for monocyte-derived macrophages in the regulation of CNS lymphoma progression, via several mechanisms, including antigenic processing and cross-presentation. We suggest that tumor-associated CD68 and TAP1 (and TAP2) be evaluated further as candidate biomarkers for risk stratification in PCNSL, particularly in trials that involve targeted immunotherapy. Supported by NCI and LLS. Figure 1 Figure 1. Disclosures Rubenstein: Kymera: Research Funding.