Silencing of caveolin-1 in fibroblasts as opposed to epithelial tumor cells results in increased tumor growth rate and chemoresistance in a human pancreatic cancer model

Identification of Germinal Neurofibromin Hotspots

Neurofibromin is engaged in many cellular processes and when the proper protein functioning is impaired, it causes neurofibromatosis type 1 (NF1), one of the most common inherited neurological disorders. Recent advances in sequencing and screening of the NF1 gene have increased the number of detected variants. However, the correlation of these variants with the clinic remains poorly understood. In this study, we analyzed 4610 germinal NF1 variants annotated in ClinVar and determined on exon level the mutational spectrum and potential pathogenic regions. Then, a binomial and sliding windows test using 783 benign and 938 pathogenic NF1 variants were analyzed against functional and structural regions of neurofibromin. The distribution of synonymous, missense, and frameshift variants are statistically significant in certain regions of neurofibromin suggesting that the type of variant and its associated phenotype may depend on protein disorder. Indeed, there is a negative correlation between the pathogenic fraction prediction and the disorder data, suggesting that the higher an intrinsically disordered region is, the lower the pathogenic fraction is and vice versa. Most pathogenic variants are associated to NF1 and our analysis suggests that GRD, CSRD, TBD, and Armadillo1 domains are hotspots in neurofibromin. Knowledge about NF1 genotype–phenotype correlations can provide prognostic guidance and aid in organ-specific surveillance.

Stromal Fibroblasts Counteract the Caveolin-1-Dependent Radiation Response of LNCaP Prostate Carcinoma Cells

In prostate cancer (PCa), a characteristic stromal–epithelial redistribution of the membrane protein caveolin 1 (CAV1) occurs upon tumor progression, where a gain of CAV1 in the malignant epithelial cells is accompanied by a loss of CAV1 in the tumor stroma, both facts that were correlated with higher Gleason scores, poor prognosis, and pronounced resistance to therapy particularly to radiotherapy (RT). However, it needs to be clarified whether inhibiting the CAV1 gain in the malignant prostate epithelium or limiting the loss of stromal CAV1 would be the better choice for improving PCa therapy, particularly for improving the response to RT; or whether ideally both processes need to be targeted. Concerning the first assumption, we investigated the RT response of LNCaP PCa cells following overexpression of different CAV1 mutants. While CAV1 overexpression generally caused an increased epithelial-to-mesenchymal phenotype in respective LNCaP cells, effects that were accompanied by increasing levels of the 5′-AMP-activated protein kinase (AMPK), a master regulator of cellular homeostasis, only wildtype CAV1 was able to increase the three-dimensional growth of LNCaP spheroids, particularly following RT. Both effects could be limited by an additional treatment with the SRC inhibitor dasatinib, finally resulting in radiosensitization. Using co-cultured (CAV1-expressing) fibroblasts as an approximation to the in vivo situation of early PCa it could be revealed that RT itself caused an activated, more tumor-promoting phenotype of stromal fibroblats with an increased an increased metabolic potential, that could not be limited by combined dasatinib treatment. Thus, targeting fibroblasts and/or limiting fibroblast activation, potentially by limiting the loss of stromal CAV1 seems to be absolute for inhibiting the resistance-promoting CAV1-dependent signals of the tumor stroma.

Caveolae-Associated Molecules, Tumor Stroma, and Cancer Drug Resistance: Current Findings and Future Perspectives

Simple Summary

Cell membranes contain small invaginations called caveolae. They are a specialized lipid domain and orchestrate cellular signaling events, mechanoprotection, and lipid homeostasis. Formation of the caveolae depends on two classes of proteins, the caveolins and cavins, which form large complexes that allow their self-assembly into caveolae. Loss of either of these two proteins leads to distortion of the caveolae structure and disruption of many physiological processes that affect diseases of the muscle, metabolic states governing lipids, and the glucose balance as well as cancers. In cancers, the expression of caveolins and cavins is heterogenous, and they undergo alterations both in the tumors and the surrounding tumor microenvironment stromal cells. Remarkably, their expression and function has been associated with resistance to many cancer drugs. Here, we summarize the current knowledge of the resistance mechanisms and how this knowledge could be applied into the clinic in future.

Abstract

The discovery of small, “cave-like” invaginations at the plasma membrane, called caveola, has opened up a new and exciting research area in health and diseases revolving around this cellular ultrastructure. Caveolae are rich in cholesterol and orchestrate cellular signaling events. Within caveola, the caveola-associated proteins, caveolins and cavins, are critical components for the formation of these lipid rafts, their dynamics, and cellular pathophysiology. Their alterations underlie human diseases such as lipodystrophy, muscular dystrophy, cardiovascular disease, and diabetes. The expression of caveolins and cavins is modulated in tumors and in tumor stroma, and their alterations are connected with cancer progression and treatment resistance. To date, although substantial breakthroughs in cancer drug development have been made, drug resistance remains a problem leading to treatment failures and challenging translation and bench-to-bedside research. Here, we summarize the current progress in understanding cancer drug resistance in the context of caveola-associated molecules and tumor stroma and discuss how we can potentially design therapeutic avenues to target these molecules in order to overcome treatment resistance.

Retrospective Cohort Study of Caveolin-1 Expression as Prognostic Factor in Unresectable Locally Advanced or Metastatic Pancreatic Cancer Patients

Caveolin-1 (Cav-1) plays a key role in various neoplastic diseases and is upregulated in different cancers, including pancreatic ductal adenocarcinoma (PDAC). Furthermore, Cav-1 is critical for the uptake of albumin as well as nab-paclitaxel in PDAC cells. Here, we investigated the prognostic impact of Cav-1 expression in a cohort of 39 metastatic PDAC patients treated with different first-line chemotherapy regimens. We also assessed the predictive value of Cav-1 in patients treated with gemcitabine and nab-paclitaxel. Cav-1 expression was evaluated by immunohistochemistry staining in neoplastic and stromal cells, using metastatic sites or primary tumor tissue specimens. Higher levels of Cav-1 expression were associated with significantly worse overall survival (OS) and progression-free survival (PFS). No differences in OS were found between patients treated with gemcitabine + nab-paclitaxel vs. other chemotherapy options. Multivariate analysis for OS and PFS confirmed the independent prognostic role of Cav-1 expression. Our study evidenced a negative prognostic role of Cav-1 in patients affected by metastatic/locally advanced unresectable PDAC. Moreover, Cav-1 expression seems not to predict different response rates to different types of first-line treatment. Future prospective trials will be necessary to confirm the prognostic role of Cav-1 and explore Cav-1 specific inhibitors as a therapeutic option for advanced PDAC patients.

Morphological Heterogeneity in Pancreatic Cancer Reflects Structural and Functional Divergence

Simple Summary

Pancreatic cancer has a poor prognosis, which is largely due to resistance to treatment. Tumor heterogeneity is a known cause for treatment failure and has been studied at the molecular level. Morphological heterogeneity is common but has not been investigated, despite the fact that pathology examination is an integral part of clinical diagnostics. This study assessed whether morphological heterogeneity reflects structural and functional diversity in key cancer biological processes. Using archival tissues from resected pancreatic cancer, we selected four common and distinct morphological phenotypes and demonstrated that these differed significantly for a panel of 26 structural and functional features of the cancer-cell and stromal compartments. The strong link between these features and morphological phenotypes allowed prediction of the latter based on the results for the panel of features. The findings of this study indicate that morphological heterogeneity reflects biological diversity and that its assessment may potentially provide clinically relevant information.

Abstract

Inter- and intratumor heterogeneity is an important cause of treatment failure. In human pancreatic cancer (PC), heterogeneity has been investigated almost exclusively at the genomic and transcriptional level. Morphological heterogeneity, though prominent and potentially easily assessable in clinical practice, remains unexplored. This proof-of-concept study aims at demonstrating that morphological heterogeneity reflects structural and functional divergence. From the wide morphological spectrum of conventional PC, four common and distinctive patterns were investigated in 233 foci from 39 surgical specimens. Twenty-six features involved in key biological processes in PC were analyzed (immuno-)histochemically and morphometrically: cancer cell proliferation (Ki67) and migration (collagen fiber alignment, MMP14), cancer stem cells (CD44, CD133, ALDH1), amount, composition and spatial arrangement of extracellular matrix (epithelial proximity, total collagen, collagen I and III, fibronectin, hyaluronan), cancer-associated fibroblasts (density, αSMA), and cancer-stroma interactions (integrins α2, α5, α1; caveolin-1). All features differed significantly between at least two of the patterns. Stromal and cancer-cell-related features co-varied with morphology and allowed prediction of the morphological pattern. In conclusion, morphological heterogeneity in the cancer-cell and stromal compartments of PC correlates with structural and functional diversity. As such, histopathology has the potential to inform on the operationality of key biological processes in individual tumors.

Tumor-stroma biomechanical crosstalk: a perspective on the role of caveolin-1 in tumor progression

Tumor stiffening is a hallmark of malignancy that actively drives tumor progression and aggressiveness. Recent research has shed light onto several molecular underpinnings of this biomechanical process, which has a reciprocal crosstalk between tumor cells, stromal fibroblasts, and extracellular matrix remodeling at its core. This dynamic communication shapes the tumor microenvironment; significantly determines disease features including therapeutic resistance, relapse, or metastasis; and potentially holds the key for novel antitumor strategies. Caveolae and their components emerge as integrators of different aspects of cell function, mechanotransduction, and ECM-cell interaction. Here, we review our current knowledge on the several pivotal roles of the essential caveolar component caveolin-1 in this multidirectional biomechanical crosstalk and highlight standing questions in the field.

Positive feedback in Cav-1-ROS signalling in PSCs mediates metabolic coupling between PSCs and tumour cells

Caveolin-1 (Cav-1) is the principal structural component of caveolae, and its dysregulation occurs in cancer. However, the role of Cav-1 in pancreatic cancer (PDAC) tumorigenesis and metabolism is largely unknown. In this study, we aimed to investigate the effect of pancreatic stellate cell (PSC) Cav-1 on PDAC metabolism and aggression. We found that Cav-1 is expressed at low levels in PDAC stroma and that the loss of stromal Cav-1 is associated with poor survival. In PSCs, knockdown of Cav-1 promoted the production of reactive oxygen species (ROS), while ROS production further reduced the expression of Cav-1. Positive feedback occurs in Cav-1-ROS signalling in PSCs, which promotes PDAC growth and induces stroma-tumour metabolic coupling in PDAC. In PSCs, positive feedback in Cav-1-ROS signalling induced a shift in energy metabolism to glycolysis, with up-regulated expression of glycolytic enzymes (hexokinase 2 (HK-2), 6-phosphofructokinase (PFKP) and pyruvate kinase isozyme type M2 (PKM2)) and transporter (Glut1) expression and down-regulated expression of oxidative phosphorylation (OXPHOS) enzymes (translocase of outer mitochondrial membrane 20 (TOMM20) and NAD(P)H dehydrogenase [quinone] 1 (NQO1)). These events resulted in high levels of glycolysis products such as lactate, which was secreted by up-regulated monocarboxylate transporter 4 (MCT4) in PSCs. Simultaneously, PDAC cells took up these glycolysis products (lactate) through up-regulated MCT1 to undergo OXPHOS, with down-regulated expression of glycolytic enzymes (HK-2, PFKP and PKM2) and up-regulated expression of OXPHOS enzymes (TOMM20 and NQO1). Interrupting the metabolic coupling between the stroma and tumour cells may be an effective method for tumour therapy.

Knockdown of MSI2 inhibits metastasis by interacting with caveolin-1 and inhibiting its ubiquitylation in human NF1-MPNST cells

Malignant peripheral nerve sheath tumours (MPNSTs) are highly aggressive Schwann cell-derived sarcomas, and they are either associated with neurofibromatosis type 1 (NF1) or sporadic. Our previous study found that high mobility group protein A2 (HMGA2) regulates NF1-MPNST growth through Musashi-2 (MSI2); however, whether MSI2 regulates MPNST metastasis and what the mechanism is remain unclear. Here, we demonstrated that the protein caveolin-1 (CAV1) directly interacts with MSI2 in human NF1-MPNST cells. Moreover, we discovered that knockdown of MSI2 induces CAV1 protein expression by inhibiting its ubiquitylation level in NF1-MPNSTs. In addition, CAV1 mediates the suppressive function of MSI2 in epithelial-mesenchymal transition, migration and invasion in vitro and metastasis in vivo. These results help to reveal the potential mechanisms of MSI2 as a target of antimetastatic treatment for human NF1-MPNST.

Cav-1 Ablation in Pancreatic Stellate Cells Promotes Pancreatic Cancer Growth through Nrf2-Induced shh Signaling

A more comprehensive understanding of the complexity of pancreatic cancer pathobiology, especially, and understanding of the role of the tumor microenvironment (TME) in disease progression should pave the way for therapies to improve patient response rates. Previous studies reported that caveolin-1 (Cav-1) has both tumor-promoting and tumor-suppressive functions. However, the function of Cav-1 in the pancreatic cancer microenvironment remains largely unexplored. Here, we show that coinjection of Cav-1-silenced pancreatic stellate cells (PSCs) with pancreatic cancer cells increased tumor growth. To comprehensively characterize paracrine communication between pancreatic cancer cells and PSCs, PSCs were cultured with pancreatic cancer cell conditioned medium (CM) containing cytokines. We reveal that Cav-1-silenced PSCs facilitated the growth of pancreatic cancer cells via enhanced paracrine shh/MMP2/bFGF/IL-6 signaling. Specifically, Cav-1-silenced PSCs exhibited increased shh expression, which heterotypically activated the shh signaling pathway in pancreatic cancer cells. Moreover, Cav-1-deficient PSCs accumulated ROS to enhance the shh pathway and angiogenesis in pancreatic cancer cells. In addition, overexpression of Nrf2 reversed the effects of Cav-1 knockdown on PSCs, increasing ROS production and enhancing paracrine shh/MMP2/bFGF/IL-6 signaling. Together, our findings show that stromal Cav-1 may mediate different mechanisms in the complex interaction between cancer cells and their microenvironment though Nrf2-induced shh signaling activation during pancreatic cancer progression.

Progression-Related Loss of Stromal Caveolin 1 Levels Mediates Radiation Resistance in Prostate Carcinoma via the Apoptosis Inhibitor TRIAP1

Tumour resistance to chemo- and radiotherapy, as well as molecularly targeted therapies, limits the effectiveness of current cancer treatments. We previously reported that the radiation response of human prostate tumours is critically regulated by CAV1 expression in stromal fibroblasts and that loss of stromal CAV1 expression in advanced tumour stages may contribute to tumour radiotherapy resistance. Here we investigated whether fibroblast secreted anti-apoptotic proteins could induce radiation resistance of prostate cancer cells in a CAV1-dependent manner and identified TRIAP1 (TP53 Regulated Inhibitor of Apoptosis 1) as a resistance-promoting CAV1-dependent factor. TRIAP1 expression and secretion was significantly higher in CAV1-deficient fibroblasts and secreted TRIAP1 was able to induce radiation resistance of PC3 and LNCaP prostate cancer cells in vitro, as well as of PC3 prostate xenografts derived from co-implantation of PC3 cells with TRIAP1-expressing fibroblasts in vivo. Immunohistochemical analyses of irradiated PC3 xenograft tumours, as well as of human prostate tissue specimen, confirmed that the characteristic alterations in stromal-epithelial CAV1 expression were accompanied by increased TRIAP1 levels after radiation in xenograft tumours and within advanced prostate cancer tissues, potentially mediating resistance to radiation treatment. In conclusion, we have determined the role of CAV1 alterations potentially induced by the CAV1-deficient, and more reactive, stroma in radio sensitivity of prostate carcinoma at a molecular level. We suggest that blocking TRIAP1 activity and thus avoiding drug resistance may offer a promising drug development strategy for inhibiting resistance-promoting CAV1-dependent signals.