Caveolin-1 (P132L), a common breast cancer mutation, confers mammary cell invasiveness and defines a novel stem cell/metastasis-associated gene signature

Caveolin-1 promotes pancreatic cancer cell differentiation and restores membranous E-cadherin via suppression of the epithelial-mesenchymal transition

Pancreatic cancer is one of the deadliest cancers due to early rapid metastasis and chemoresistance. Recently, epithelial to mesenchymal transition (EMT) was shown to play a key role in the pathogenesis of pancreatic cancer. To understand the role of caveolin-1 (Cav-1) in EMT, we over-expressed Cav-1 in a pancreatic cancer cell line, Panc 10.05, that does not normally express Cav-1. Here, we show that Cav-1 expression in pancreatic cancer cells induces an epithelial phenotype and promotes cell-cell contact, with increased expression of plasma membrane bound E-cadherin and beta-catenin. Mechanistically, Cav-1 induces Snail downregulation and decreased activation of AKT, MAPK and TGF-beta-Smad signaling pathways. In vitro, Cav-1 expression reduces cell migration and invasion, and attenuates doxorubicin-chemoresistance of pancreatic cancer cells. Importantly, in vivo studies revealed that Cav-1 expression greatly suppresses tumor formation in a xenograft model. Most interestingly, Panc/Cav-1 tumors displayed organized nests of differentiated cells that were totally absent in control tumors. Confirming our in vitro results, these nests of differentiated cells showed reexpression of E-cadherin and beta-catenin at the cell membrane. Thus, we provide evidence that Cav-1 functions as a crucial modulator of EMT and cell differentiation in pancreatic cancer.

The role of caveolin-1 in human breast cancer

Caveolin-1 is the essential constituent protein of specialised plasma membrane invaginations called caveolae. The unique topology of caveolin-1 facilitates the role of caveolae as molecular hubs, integrating the activity of a multitude of signalling molecules. Despite improvements in our understanding of caveolin-1 interactions and the function of caveolae, the relationship between dysfunctional caveolin-1 and tumourigenesis remains contentious. Perhaps most intriguing has been the demonstration of both oncogenic and tumour suppressor function within particular tumour types, including breast cancer. In this review, the biological and clinical relevance of caveolin-1 in human breast cancer are considered. Evidence is systematically presented for the potential tumour suppressor and oncogenic functions of caveolin-1. Specific reference is made to interactions between caveolin-1 and signalling pathways in the clinical and biological subtypes of breast cancer. Areas of controversy are discussed and technical considerations are highlighted. Translational implications and potential for specific therapeutic manipulation of caveolin-1 are evaluated in the context of evidence from in vitro and in vivo studies.

The role of breast cancer stem cells in metastasis and therapeutic implications

Cancer stem cells (CSCs) possess the capacity to self-renew and to generate heterogeneous lineages of cancer cells that comprise tumors. A substantial body of evidence supports a model in which CSCs play a major role in the initiation, maintenance, and clinical outcome of cancers. In contrast, analysis of the role of CSCs in metastasis has been mainly conceptual and speculative. This review summarizes recent data that support the theory of CSCs as the source of metastatic lesions in breast cancer, with a focus on the key role of the microenvironment in the stemness-metastasis link.

Constitutive recycling of the store-operated Ca2+ channel Orai1 and its internalization during meiosis

The egg's competency to activate at fertilization and transition to embryogenesis is dependent on its ability to generate a fertilization-specific Ca(2+) transient. To endow the egg with this capacity, Ca(2+) signals remodel during oocyte maturation, including inactivation of the primary Ca(2+) influx pathway store-operated Ca(2+) entry (SOCE). SOCE inactivation is coupled to internalization of the SOCE channel, Orai1. In this study, we show that Orai1 internalizes during meiosis through a caveolin (Cav)- and dynamin-dependent endocytic pathway. Cav binds to Orai1, and we map a Cav consensus-binding site in the Orai1 N terminus, which is required for Orai1 internalization. Furthermore, at rest, Orai1 actively recycles between an endosomal compartment and the cell membrane through a Rho-dependent endocytic pathway. A significant percentage of total Orai1 is intracellular at steady state. Store depletion completely shifts endosomal Orai1 to the cell membrane. These results define vesicular trafficking mechanisms in the oocyte that control Orai1 subcellular localization at steady state, during meiosis, and after store depletion.

Reverse phase protein microarrays advance to use in clinical trials

Individualizing cancer therapy for molecular targeted inhibitors requires a new class of molecular profiling technology that can map the functional state of the cancer cell signal pathways containing the drug targets. Reverse phase protein microarrays (RPMA) are a technology platform designed for quantitative, multiplexed analysis of specific phosphorylated, cleaved, or total (phosphorylated and non-phosphorylated) forms of cellular proteins from a limited amount of sample. This class of microarray can be used to interrogate tissue samples, cells, serum, or body fluids. RPMA were previously a research tool; now this technology has graduated to use in research clinical trials with clinical grade sensitivity and precision. In this review we describe the application of RPMA for multiplexed signal pathway analysis in therapeutic monitoring, biomarker discovery, and evaluation of pharmaceutical targets, and conclude with a summary of the technical aspects of RPMA construction and analysis.

Epidermal growth factor receptor and caveolin-1 coexpression identifies adult supratentorial ependymomas with rapid unfavorable outcomes

Supratentorial ependymomas account for a minority of intracranial ependymomas, which still have uncertain prognostic markers. Among them, epidermal growth factor receptor (EGFR) overexpression correlates with a poor prognosis. In glioblastoma cells, EGFR function has been reported to be regulated by its migration from cell membrane infoldings called caveolae and by its colocalization with the caveolae-associated protein caveolin-1 (cav-1). Therefore, we decided to investigate cav-1 expression and coexpression with EGFR in a series of adult intracranial ependymomas. We analyzed 22 adult supratentorial ependymomas and compared tumor grades as determined by the WHO classification and patient survival rates with the expression of EGFR, cav-1, and p53 and the values of the proliferation marker Ki-67, all tested by immunohistochemistry; in addition, we investigated the mutational profile of cav-1. The results demonstrate that the tumor grade is directly correlated with EGFR, Ki-67, and cav-1 expression only, whereas (by univariate analysis) the expression of all the studied markers, as well as the tumor histological grade, significantly correlated with the patient's overall survival (OS). By multivariate analysis using the Cox proportional hazards model, among all variables considered, cav-1 was the only independent prognostic marker related to OS (relative risk = 13.92; P = .013). Among grade II ependymomas, only cav-1 correlated with poor OS (P = .011), distinguishing 2 distinct subgroups of tumors with different outcomes despite sharing identical grading. All the patients studied carried wild-type cav-1 sequences, demonstrating that cav-1 overexpression is not driven by activating mutations, as previously reported in other tumor types. Interestingly, after stratifying all cases into 4 distinct groups according to cav-1 and EGFR expression (cav-1+/EGFR+, cav-1-/EGFR-, cav-1+/EGFR-, and cav-1-/EGFR+), the coexpression of cav-1 and EGFR identified a subset of patients with definitively poor prognoses. Further studies are needed to support this evidence on a larger scale and to clarify how cav-1 and EGFR interaction can influence tumor aggressiveness.

The tumor-suppressive function of Connexin43 in keratinocytes is mediated in part via interaction with caveolin-1

Connexin43 (Cx43) is known to have tumor-suppressive effects, but the underlying mechanisms are still poorly understood. In keratinocytes, we previously showed that the COOH-terminal domain of Cx43 directly interacts with the tumor suppressor Cav-1. We now show that rat epidermal keratinocytes (REK) that are reduced in Cx43 present features of epithelial-to-mesenchymal transition and are more invasive than their control counterparts, whereas overexpression of Cx43 inhibited the 12-O-tetradecanoyl-phorbol-13-acetate (TPA)- and epidermal growth factor (EGF)-induced invasive properties. Carbenoxolone did not alter the inhibitory effect of Cx43 against TPA- and EGF-induced cell invasion, indicating the involvement of a gap junctional intercellular communication-independent mechanism. Interestingly, the association of Cx43 with Cav-1 was found to be reduced after TPA and EGF treatment. Accordingly, the colocalization of Cx43 with Cav-1 was diminished in cells from a human epidermal squamous cell carcinoma, as well as in sections from human keratinocyte tumors, suggesting that Cx43/Cav-1 interaction plays a protective role against keratinocyte transformation. As opposed to cells that overexpress Cx43-GFP, invasion could be induced in rat epidermal keratinocytes that overexpressed a GFP-tagged truncated mutant of Cx43 (Delta244-GFP) that we previously showed not to interact with Cav-1, as well as in cells that overexpressed Cx43-GFP but were reduced in Cav-1. Our data show that Cx43 possesses tumor-suppressive properties in keratinocytes and provide the first evidence that the Cx43/Cav-1 interaction is altered in keratinocyte transformation processes, as well as in human keratinocyte tumors, and that this association might play a role in Cx43-mediated tumor suppression.

Function of EWS-POU5F1 in sarcomagenesis and tumor cell maintenance

POU5F1 is a transcription factor essential for the self-renewal activity and pluripotency of embryonic stem cells and germ cells. We have previously reported that POU5F1 is fused to EWSR1 in a case of undifferentiated sarcoma with chromosomal translocation t(6;22)(p21;q12). In addition, the EWS-POU5F1 chimeras have been recently identified in human neoplasms of the skin and salivary glands. To clarify the roles of the EWS-POU5F1 chimera in tumorigenesis and tumor cell maintenance, we used small-interfering RNA-mediated gene silencing. Knockdown of EWS-POU5F1 in the t(6;22) sarcoma-derived GBS6 cell line resulted in a significant decrease of cell proliferation because of G1 cell cycle arrest associated with p27(Kip1) up-regulation. Moreover, senescence-like morphological changes accompanied by actin polymerization were observed. In contrast, EWS-POU5F1 down-regulation markedly increased the cell migration and invasion as well as activation of metalloproteinase 2 and metalloproteinase 14. The results indicate that the proliferative activity of cancer cells and cell motility are discrete processes in multistep carcinogenesis. These findings reveal the functional role of the sarcoma-related chimeric protein as well as POU5F1 in the development and progression of human neoplasms.