Liprin-α1 contributes to oncogenic MAPK signaling by counteracting ERK activity.

PTPRF interacting protein alpha 1 (PPFIA1) encodes for liprin-α1, a member of the leukocyte common antigen-related protein tyrosine phosphatase (LAR-RPTPs)-interacting protein family. Liprin-α1 localizes to adhesive and invasive structures in the periphery of cancer cells, where it modulates migration and invasion in head and neck squamous cell carcinoma (HNSCC) and breast cancer. To study the possible role of liprin-α1 in anticancer drug responses, we screened a library of oncology compounds in cell lines with high endogenous PPFIA1 expression. The compounds with the highest differential responses between high PPFIA1-expressing and silenced cells across cell lines were inhibitors targeting mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinases (ERK) signaling. KRAS proto-oncogene, GTPase (KRAS)-mutated MDA-MB-231 cells were more resistant to trametinib upon PPFIA1 knockdown compared with control cells. In contrast, liprin-α1-depleted HNSCC cells with low RAS activity showed a context-dependent response to MEK/ERK inhibitors. Importantly, we showed that liprin-α1 depletion leads to increased p-ERK1/2 levels in all our studied cell lines independent of KRAS mutational status, suggesting a role of liprin-α1 in the regulation of MAPK oncogenic signaling. Furthermore, liprin-α1 depletion led to more pronounced redistribution of RAS proteins to the cell membrane. Our data suggest that liprin-α1 is an important contributor to oncogenic RAS/MAPK signaling, and the status of liprin-α1 may assist in predicting drug responses in cancer cells in a context-dependent manner.

Immunoglobulin superfamily member 3 is required for the vagal neural crest cell migration and enteric neuronal network organization.

The immunoglobulin (Ig) superfamily members are involved in cell adhesion and migration, complex multistep processes that play critical roles in embryogenesis, wound healing, tissue formation, and many other processes, but their specific functions during embryonic development remain unclear. Here, we have studied the function of the immunoglobulin superfamily member 3 (IGSF3) by generating an Igsf3 knockout (KO) mouse model with CRISPR/Cas9-mediated genome engineering. By combining RNA and protein detection methodology, we show that during development, IGSF3 localizes to the neural crest and a subset of its derivatives, suggesting a role in normal embryonic and early postnatal development. Indeed, inactivation of Igsf3 impairs the ability of the vagal neural crest cells to migrate and normally innervate the intestine. The small intestine of Igsf3 KO mice shows reduced thickness of the muscularis externa and diminished number of enteric neurons. Also, misalignment of neurons and smooth muscle cells in the developing intestinal villi is detected. Taken together, our results suggest that IGSF3 functions contribute to the formation of the enteric nervous system. Given the essential role of the enteric nervous system in maintaining normal gastrointestinal function, our study adds to the pool of information required for further understanding the mechanisms of gut innervation and etiology behind bowel motility disorders.

Liprin-α1 Expression in Tumor-Infiltrating Lymphocytes Associates with Improved Survival in Patients with HPV-Positive Oropharyngeal Squamous Cell Carcinoma.

BACKGROUND: Liprin-α1 is a scaffold protein involved in cell adhesion, motility, and invasion in malignancies. Liprin-α1 inhibits the expression of metastatic suppressor CD82 in cancers such as oral carcinoma, and the expression of these proteins has been known to correlate negatively. The role of these proteins has not been previously studied in human papillomavirus (HPV)-related head and neck cancers. Our aim was to assess the clinical and prognostic role of liprin-α1 and CD82 in HPV-positive oropharyngeal squamous cell carcinoma (OPSCC) in comparison to HPV-negative OPSCC. METHODS: The data included 139 OPSCC patients treated at the Helsinki University Hospital (HUS) during 2012-2016. Immunohistochemistry was utilized in HPV determination and in biomarker assays. Overall survival (OS) was used in the survival analysis. RESULTS: Stronger expression of liprin-α1 in tumor-infiltrating lymphocytes (TILs) was linked to lower cancer stage (p < 0.001) and HPV positivity (p < 0.001). Additionally, we found an association between elevated expression of liprin-α1 and weak expression of CD82 in tumor cells (p = 0.029). In survival analysis, we found significant correlation between favorable OS and stronger expression of liprin-α1 in TILs among the whole patient cohort (p < 0.001) and among HPV-positive patients (p = 0.042). CONCLUSIONS: Increased liprin-α1 expression in the TILs is associated with favorable prognosis in OPSCC, especially among HPV-positive patients.

Exome sequencing reveals candidate mutations implicated in sinonasal carcinoma and malignant transformation of sinonasal inverted papilloma.

We explored somatic mutations in dysplastic sinonasal inverted papilloma (SNIP), SNIP with concomitant sinonasal squamous cell carcinoma (SNSCC), and SNSCC without preceding SNIP. Ten SNIP and SNSCC samples were analyzed with exome sequencing and tested for human papillomavirus. The identified mutations were compared to the most frequently mutated genes in head and neck squamous cell carcinoma (HNSCC) in the COSMIC database. Exome sequencing data were also analyzed for mutations not previously linked to SNSCC. Seven of the most commonly mutated genes in HNSCC and SNSCC in COSMIC harbored mutations in our data. In addition, we identified mutations in 23 genes that are likely to contribute to SNIP and SNSCC oncogenesis.

Compressive stress-mediated p38 activation required for ERα + phenotype in breast cancer.

Breast cancer is now globally the most frequent cancer and leading cause of women's death. Two thirds of breast cancers express the luminal estrogen receptor-positive (ERα + ) phenotype that is initially responsive to antihormonal therapies, but drug resistance emerges. A major barrier to the understanding of the ERα-pathway biology and therapeutic discoveries is the restricted repertoire of luminal ERα + breast cancer models. The ERα + phenotype is not stable in cultured cells for reasons not fully understood. We examine 400 patient-derived breast epithelial and breast cancer explant cultures (PDECs) grown in various three-dimensional matrix scaffolds, finding that ERα is primarily regulated by the matrix stiffness. Matrix stiffness upregulates the ERα signaling via stress-mediated p38 activation and H3K27me3-mediated epigenetic regulation. The finding that the matrix stiffness is a central cue to the ERα phenotype reveals a mechanobiological component in breast tissue hormonal signaling and enables the development of novel therapeutic interventions. Subject terms: ER-positive (ER + ), breast cancer, ex vivo model, preclinical model, PDEC, stiffness, p38 SAPK.

Liprins in oncogenic signaling and cancer cell adhesion.

Liprins are a multifunctional family of scaffold proteins, identified by their involvement in several important neuronal functions related to signaling and organization of synaptic structures. More recently, the knowledge on the liprin family has expanded from neuronal functions to processes relevant to cancer progression, including cell adhesion, cell motility, cancer cell invasion, and signaling. These proteins consist of regions, which by prediction are intrinsically disordered, and may be involved in the assembly of supramolecular structures relevant for their functions. This review summarizes the current understanding of the functions of liprins in different cellular processes, with special emphasis on liprins in tumor progression. The available data indicate that liprins may be potential biomarkers for cancer progression and may have therapeutic importance.

The expression and prognostic relevance of CDH3 in tongue squamous cell carcinoma.

P-cadherin (CDH3) is a cell-to-cell adhesion molecule that regulates several cellular homeostatic processes in normal tissues. Lack of CDH3 expression is associated with aggressive behavior in oral squamous cell carcinoma (OSCC). Previous studies have shown that CDH3 is downregulated in high-grade OSCC and its reduced expression is predictive for poorer survival. The aim of this study was to evaluate the expression and prognostic relevance of CDH3 in tongue squamous cell carcinoma (TSCC). A retrospective series of 211 TSCC and 50 lymph node samples were stained immunohistochemically with polyclonal antibody (anti-CDH3). CDH3 expression was assessed semi-quantitatively with light microscopy. Fisher's exact test was used to compare patient and tumor characteristics, and the correlations were tested by Spearman correlation. Survival curves were drawn by the Kaplan-Meier method and analyzed by the log-rank test. Univariate and multivariate Cox regression was used to estimate the association between CDH3 expression and survival. CDH3 expression did not affect TSCC patient's disease-specific survival or overall survival. Strong CDH3 expression in the primary tumor predicted poor disease-specific and overall survival in patients with recurrent disease. CDH3 expression in lymph nodes without metastasis was negative in all cases. CDH3 expression was positive in all lymph node metastases with extranodal extension. In contrast to previous report about the prognostic value of CDH3 in OSCC, we were not able to validate the result in TSCC.

Hepsin regulates TGFß signaling via fibronectin proteolysis.

Transforming growth factor-beta (TGFß) is a multifunctional cytokine with a well-established role in mammary gland development and both oncogenic and tumor-suppressive functions. The extracellular matrix (ECM) indirectly regulates TGFß activity by acting as a storage compartment of latent-TGFß, but how TGFß is released from the ECM via proteolytic mechanisms remains largely unknown. In this study, we demonstrate that hepsin, a type II transmembrane protease overexpressed in 70% of breast tumors, promotes canonical TGFß signaling through the release of latent-TGFß from the ECM storage compartment. Mammary glands in hepsin CRISPR knockout mice showed reduced TGFß signaling and increased epithelial branching, accompanied by increased levels of fibronectin and latent-TGFß1, while overexpression of hepsin in mammary tumors increased TGFß signaling. Cell-free and cell-based experiments showed that hepsin is capable of direct proteolytic cleavage of fibronectin but not latent-TGFß and, importantly, that the ability of hepsin to activate TGFß signaling is dependent on fibronectin. Altogether, this study demonstrates a role for hepsin as a regulator of the TGFß pathway in the mammary gland via a novel mechanism involving proteolytic downmodulation of fibronectin.

High-throughput compound screening identifies navitoclax combined with irradiation as a candidate therapy for HPV-negative head and neck squamous cell carcinoma.

Conventional chemotherapeutic agents are nonselective, often resulting in severe side effects and the development of resistance. Therefore, new molecular-targeted therapies are urgently needed to be integrated into existing treatment regimens. Here, we performed a high-throughput compound screen to identify a synergistic interaction between ionizing radiation and 396 anticancer compounds. The assay was run using five human papillomavirus (HPV)-negative head and neck squamous cell carcinoma (HNSCC) cell lines cultured on the human tumor-derived matrix Myogel. Our screen identified several compounds with strong synergistic and antagonistic effects, which we further investigated using multiple irradiation doses. Navitoclax, which emerged as the most promising radiosensitizer, exhibited synergy with irradiation regardless of the p53 mutation status in all 13 HNSCC cell lines. We performed a live cell apoptosis assay for two representative HNSCC cell lines to examine the effects of navitoclax and irradiation. As a single agent, navitoclax reduced proliferation and induced apoptosis in a dose-dependent manner, whereas the navitoclax-irradiation combination arrested cell cycle progression and resulted in substantially elevated apoptosis. Overall, we demonstrated that combining navitoclax with irradiation resulted in synergistic in vitro antitumor effects in HNSCC cell lines, possibly indicating the therapeutic potential for HNSCC patients.

Cancer-Associated Fibroblasts Modulate Transcriptional Signatures Involved in Proliferation, Differentiation and Metastasis in Head and Neck Squamous Cell Carcinoma.

Cancer-associated fibroblasts (CAFs) are known to increase tumor growth and to stimulate invasion and metastasis. Increasing evidence suggests that CAFs mediate response to various treatments. HNSCC cell lines were co-cultured with their patient-matched CAFs in 2D and 3D in vitro models, and the tumor cell gene expression profiles were investigated by cDNA microarray and qRT-PCR. The mRNA expression of eight candidate genes was examined in tumor biopsies from 32 HNSCC patients and in five biopsies from normal oral tissue. Differences in overall survival (OS) were tested with Kaplan-Meier long-rank analysis. Thirteen protein coding genes were found to be differentially expressed in tumor cells co-cultured with CAFs in 2D and 81 in 3D when compared to tumor cells cultured without CAFs. Six of these genes were upregulated both in 2D and 3D (POSTN, GREM1, BGN, COL1A2, COL6A3, and COL1A1). Moreover, two genes upregulated in 3D, MMP9 and FMOD, were significantly associated with the OS. In conclusion, we demonstrated in vitro that CAF-derived signals alter the tumor cell expression of multiple genes, several of which are associated with differentiation, epithelial-to-mesenchymal transition (EMT) phenotype, and metastasis. Moreover, six of the most highly upregulated genes were found to be overexpressed in tumor tissue compared to normal tissue.

ANO1 Expression Orchestrates p27Kip1/MCL1-Mediated Signaling in Head and Neck Squamous Cell Carcinoma.

Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous group of tumors that derive from the mucosal epithelium of the upper aerodigestive tract and present high mortality rate. Lack of efficient targeted-therapies and biomarkers towards patients' stratification are caveats in the disease treatment. Anoctamin 1 (ANO1) gene is amplified in 30% of HNSCC cases. Evidence suggests involvement of ANO1 in proliferation, migration, and evasion of apoptosis; however, the exact mechanisms remain elusive. Aim of this study was to unravel the ANO1-dependent transcriptional programs and expand the existing knowledge of ANO1 contribution to oncogenesis and drug response in HNSCC. We cultured two HNSCC cell lines established from primary tumors harboring amplification and high expression of ANO1 in three-dimensional collagen. Differential expression analysis of ANO1-depleted HNSCC cells demonstrated downregulation of MCL1 and simultaneous upregulation of p27Kip1 expression. Suppressing ANO1 expression led to redistribution of p27Kip1 from the cytoplasm to the nucleus and associated with a cell cycle arrested phenotype. ANO1 silencing or pharmacological inhibition resulted in reduction of cell viability and ANO1 protein levels, as well as suppression of pro-survival BCL2 family proteins. Collectively, these data provide insights of ANO1 involvement in HNSCC carcinogenesis and support the rationale that ANO1 is an actionable drug target.

The critical effects of matrices on cultured carcinoma cells: Human tumor-derived matrix promotes cell invasive properties.

The interaction between squamous cell carcinoma (SCC) cells and the tumor microenvironment (TME) plays a major role in cancer progression. Therefore, understanding the TME is essential for the development of cancer therapies. We used four (primary and metastatic) head and neck (HN) SCC cell lines and cultured them on top of or within 5 matrices (mouse sarcoma-derived Matrigel®, rat collagen, human leiomyoma-derived Myogel, human fibronectin and human fibrin). We performed several assays to study the effects of these matrices on the HNSCC behavior, such as proliferation, migration, and invasion, as well as cell morphology, and molecular gene profile. Carcinoma cells exhibited different growth patterns depending on the matrix. While fibrin enhanced the proliferation of all the cell lines, collagen did not. The effects of the matrices on cancer cell migration were cell line dependent. Carcinoma cells in Myogel-collagen invaded faster in scratch wound invasion assay. On the other hand, in the spheroid invasion assay, three out of four cell lines invaded faster in Myogel-fibrin. These matrices significantly affected hundreds of genes and a number of pathways, but the effects were cell line dependent. The matrix type played a major role in HNSCC cell phenotype. The effects of the ECMs were either constant, or cell line dependent. Based on these results, we suggest to select the most suitable matrix, which provides the closest condition to the in vivo TME, in order to get reliable results in in vitro experiments.

Human Tumor-Derived Matrix Improves the Predictability of Head and Neck Cancer Drug Testing.

In vitro cancer drug testing carries a low predictive value. We developed the human leiomyoma-derived matrix "Myogel" to better mimic the human tumor microenvironment (TME). We hypothesized that Myogel could provide an appropriate microenvironment for cancer cells, thereby allowing more in vivo-relevant drug testing. We screened 19 anticancer compounds, targeting the epidermal growth factor receptor (EGFR), MEK, and PI3K/mTOR on 12 head and neck squamous cell carcinoma (HNSCC) cell lines cultured on plastic, mouse sarcoma-derived Matrigel (MSDM), and Myogel. We applied a high-throughput drug screening assay under five different culturing conditions: cells in two-dimensional (2D) plastic wells and on top or embedded in Matrigel or Myogel. We then compared the efficacy of the anticancer compounds to the response rates of 19 HNSCC monotherapy clinical trials. Cancer cells on top of Myogel responded less to EGFR and MEK inhibitors compared to cells cultured on plastic or Matrigel. However, we found a similar response to the PI3K/mTOR inhibitors under all culturing conditions. Cells grown on Myogel more closely resembled the response rates reported in EGFR-inhibitor monotherapy clinical trials. Our findings suggest that a human tumor matrix improves the predictability of in vitro anticancer drug testing compared to current 2D and MSDM methods.

Liprin-α1 modulates cancer cell signaling by transmembrane protein CD82 in adhesive membrane domains linked to cytoskeleton.

BACKGROUND: PPFIA1 is located at the 11q13 region commonly amplified in cancer. The protein liprin-α1 encoded by PPF1A1 contributes to the adhesive and invasive structures of cytoskeletal elements and is located at the invadosomes in cancer cells. However, the precise mechanism of liprin-α1 function in cancer progression has remained elusive. METHODS: Invasion regulating activity of liprin-α1 was examined by analyzing the functions of squamous cell carcinoma of head and neck (HNSCC) cell lines in three-dimensional collagen I after RNAi mediated gene knockdown. Transcriptome profiling and Gene Set Enrichment Analysis from HNSCC and breast cancer cells were used to identify expression changes relevant to specific cellular localizations, biological processes and signaling pathways after PPFIA1 knockdown. The significance of the results was assessed by relevant statistical methods (Wald and Benjamini-Hochberg). Localization of proteins associated to liprin-α1 was studied by immunofluorescence in 2D and 3D conditions. The association of PPFIA1 amplification to HNSCC patient survival was explored using The Cancer Genome Atlas data. RESULTS: In this study, we show that liprin-α1 regulates biological processes related to membrane microdomains in breast carcinoma, as well as protein trafficking, cell-cell and cell-substrate contacts in HNSCC cell lines cultured in three-dimensional matrix. Importantly, we show that in all these cancer cells liprin-α1 knockdown leads to the upregulation of transmembrane protein CD82, which is a suppressor of metastasis in several solid tumors. CONCLUSIONS: Our results provide novel information regarding the function of liprin-α1 in biological processes essential in cancer progression. The results reveal liprin-α1 as a novel regulator of CD82, linking liprin-α1 to the cancer cell invasion and metastasis pathways.

Drug-Sensitivity Screening and Genomic Characterization of 45 HPV-Negative Head and Neck Carcinoma Cell Lines for Novel Biomarkers of Drug Efficacy.

There is an unmet need for effective targeted therapies for patients with advanced head and neck squamous cell carcinoma (HNSCC). We correlated gene expression, gene copy numbers, and point mutations in 45 human papillomavirus-negative HNSCC cell lines with the sensitivity to 220 anticancer drugs to discover predictive associations to genetic alterations. The drug response profiles revealed diverse efficacy of the tested drugs across the cell lines. Several genomic abnormalities and gene expression differences were associated with response to mTOR, MEK, and EGFR inhibitors. NOTCH1 and FAT1 were the most commonly mutated genes after TP53 and also showed some association with response to MEK and/or EGFR inhibitors. MYC amplification and FAM83H overexpression associated with sensitivity to EGFR inhibitors, and PTPRD deletion with poor sensitivity to MEK inhibitors. The connection between high FAM83H expression and responsiveness to the EGFR inhibitor erlotinib was validated by gene silencing and from the data set at the Cancer Cell Line Encyclopedia. The data provide several novel genomic alterations that associated to the efficacy of targeted drugs in HNSCC. These findings require further validation in experimental models and clinical series. Mol Cancer Ther; 17(9); 2060-71. ©2018 AACR.

Liprin-α1 is a regulator of vimentin intermediate filament network in the cancer cell adhesion machinery.

PPFIA1 is located at the 11q13 region, which is one of the most commonly amplified regions in several epithelial cancers including head and neck squamous cell carcinoma and breast carcinoma. Considering the location of PPFIA1 in this amplicon, we examined whether protein encoded by PPFIA1, liprin-α1, possesses oncogenic properties in relevant carcinoma cell lines. Our results indicate that liprin-α1 localizes to different adhesion and cytoskeletal structures to regulate vimentin intermediate filament network, thereby altering the invasion and growth properties of the cancer cells. In non-invasive cells liprin-α1 promotes expansive growth behavior with limited invasive capacity, whereas in invasive cells liprin-α1 has significant impact on mesenchymal cancer cell invasion in three-dimensional collagen. Current results identify liprin-α1 as a novel regulator of the tumor cell intermediate filaments with differential oncogenic properties in actively proliferating or motile cells.

Identification of several potential chromatin binding sites of HOXB7 and its downstream target genes in breast cancer.

HOXB7 encodes a transcription factor that is overexpressed in a number of cancers and encompasses many oncogenic functions. Previous results have shown it to promote cell proliferation, angiogenesis, epithelial-mesenchymal transition, DNA repair and cell survival. Because of its role in many cancers and tumorigenic processes, HOXB7 has been suggested to be a potential drug target. However, HOXB7 binding sites on chromatin and its targets are poorly known. The aim of our study was to identify HOXB7 binding sites on breast cancer cell chromatin and to delineate direct target genes located nearby these binding sites. We found 1,504 HOXB7 chromatin binding sites in BT-474 breast cancer cell line that overexpresses HOXB7. Seventeen selected binding sites were validated by ChIP-qPCR in several breast cancer cell lines. Furthermore, we analyzed expression of a large number of genes located nearby HOXB7 binding sites and found several new direct targets, such as CTNND2 and SCGB1D2. Identification of HOXB7 chromatin binding sites and target genes is essential to understand better the role of HOXB7 in breast cancer and mechanisms by which it regulates tumorigenic processes.

Systems-level analysis of clinically different phenotypes of juvenile nasopharyngeal angiofibromas.

OBJECTIVES/HYPOTHESIS: To explore the molecular genetic background of juvenile nasopharyngeal angiofibromas and to identify biological processes and putative factors determining the different growth patterns of these tumors. STUDY DESIGN: By comparing copy number and gene expression level changes of two clinically different phenotypes of juvenile nasopharyngeal angiofibromas, we aimed to find processes essential in the growth and development of these tumors. Based on the results and prior knowledge of the proteins significance for growth, we studied the expression of tyrosine kinase SYK in 27 tumor samples. METHODS: Comparative genomic hybridization and gene expression analyses were performed for the two tumor samples, and protein expression of SYK was studied in 27 samples by immunohistochemical staining. RESULTS: Between low- and high-stage juvenile nasopharyngeal angiofibromas, 1,245 genes showed at least a two-fold change in expression. The corresponding proteins of these transcripts were enriched in different biological processes. Protein kinase SYK was expressed in all 27 samples, and its intensity significantly correlated with tumor stage. CONCLUSIONS: Because the molecular genetic background of juvenile nasopharyngeal angiofibroma is unknown, our aim was to investigate genomic alterations that could associate to low- and high-stage tumors. We were able to identify gene expression changes that relate to particular biological processes, but assessing clinically relevant molecular profiles still requires further characterization. Due to the low incidence of juvenile angiofibroma, in the future a combination of molecular profiling data from several studies would be useful in understanding the molecular background of the disease.

Comparative analysis of algorithms for integration of copy number and expression data.

Chromosomal instability is a hallmark of cancer, and genes that display abnormal expression in aberrant chromosomal regions are likely to be key players in tumor progression. Identifying such driver genes reliably requires computational methods that can integrate genome-scale data from several sources. We compared the performance of ten algorithms that integrate copy-number and transcriptomics data from 15 head and neck squamous cell carcinoma cell lines, 129 lung squamous cell carcinoma primary tumors and simulated data. Our results revealed clear differences between the methods in terms of sensitivity and specificity as well as in their performance in small and large sample sizes. Results of the comparison are available at http://csbi.ltdk.helsinki.fi/cn2gealgo/.

Comprehensive exon array data processing method for quantitative analysis of alternative spliced variants.

Alternative splicing of pre-mRNA generates protein diversity. Dysfunction of splicing machinery and expression of specific transcripts has been linked to cancer progression and drug response. Exon microarray technology enables genome-wide quantification of expression levels of the majority of exons and facilitates the discovery of alternative splicing events. Analysis of exon array data is more challenging than the analysis of gene expression data and there is a need for reliable quantification of exons and alternatively spliced variants. We introduce a novel, computationally efficient methodology, Multiple Exon Array Preprocessing (MEAP), for exon array data pre-processing, analysis and visualization. We compared MEAP with existing pre-processing methods, and validation of six exons and two alternatively spliced variants with qPCR corroborated MEAP expression estimates. Analysis of exon array data from head and neck squamous cell carcinoma (HNSCC) cell lines revealed several transcripts associated with 11q13 amplification, which is related with decreased survival and metastasis in HNSCC patients. Our results demonstrate that MEAP produces reliable expression values at exon, alternatively spliced variant and gene levels, which allows generating novel experimentally testable predictions.