Functional links between Snail-1 and Cx43 account for the recruitment of Cx43-positive cells into the invasive front of prostate cancer.

Suppressive function of connexin(Cx)43 in carcinogenesis was recently contested by reports that showed a multifaceted function of Cx43 in cancer progression. These studies did not attempt to model the dynamics of intratumoral heterogeneity involved in the metastatic cascade. An unorthodox look at the phenotypic heterogeneity of prostate cancer cells in vitro enabled us to identify links between Cx43 functions and Snail-1-regulated functional speciation of invasive cells. Incomplete Snail-1-dependent phenotypic shifts accounted for the formation of phenotypically stable subclones of AT-2 cells. These subclones showed diverse predilection for invasive behavior. High Snail-1 and Cx43 levels accompanied high motility and nanomechanical elasticity of the fibroblastoid AT-2_Fi2 subclone, which determined its considerable invasiveness. Transforming growth factor-ß and ectopic Snail-1 overexpression induced invasiveness and Cx43 expression in epithelioid AT-2 subclones and DU-145 cells. Functional links between Snail-1 function and Cx43 expression were confirmed by Cx43 downregulation and phenotypic shifts in AT-2_Fi2, DU-145 and MAT-LyLu cells upon Snail-1 silencing. Corresponding morphological changes and Snail-1 downregulation were seen upon Cx43 silencing in AT-2_Fi2 cells. This indicates that feedback loops between both proteins regulate cell invasive behavior. We demonstrate that Cx43 may differentially predispose prostate cancer cells for invasion in a coupling-dependent and coupling-independent manner. When extrapolated to in vivo conditions, these data show the complexity of Cx43 functions during the metastatic cascade of prostate cancer. They may explain how Cx43 confers a selective advantage during cooperative invasion of clonally evolving, invasive prostate cancer cell subpopulations.

Functional heterogeneity of non-small lung adenocarcinoma cell sub-populations.

The morphological and functional heterogeneity of solid tumour cells can be observed in cancer cell lines cultured in vitro. We have combined analyses of microclones developed from single cells with micropore transmigration assays to demonstrate the co-existence of cellular subsets differing in morphology and motile activity, as well as Cx43 (connexin 43) and N-cadherin expression within lung carcinoma A549 populations. 'Fibroblastoid' cells, characterized by high motility, polarized morphology and plasmalemmal localization of Cx43, displayed the strongest aptitude for transmigration through narrow obstacles. Due to high mitotic activity, they maintain the whole population but can also give rise to a sub-population of quiescent and immobile 'epithelioid' cells. Our observations indicate that phenotypic transitions between the fibroblastoid and epithelioid phenotype account for the heterogeneity of metastable A549 cell populations.

DU-145 prostate carcinoma cells that selectively transmigrate narrow obstacles express elevated levels of Cx43.

The formation of aqueous intercellular channels mediating gap junctional intercellular coupling (GJIC) is a canonical function of connexins (Cx). In contrast, mechanisms of GJIC-independent involvement of connexins in cancer formation and metastasis remain a matter of debate. Because of the role of Cx43 in the determination of carcinoma cell invasive potential, we addressed the problem of the possible Cx43 involvement in early prostate cancer invasion. For this purpose, we analysed Cx43-positive DU-145 cell subsets established from the progenies of the cells most readily transmigrating microporous membranes. These progenies displayed motile activity similar to the control DU-145 cells but were characterized by elevated Cx43 expression levels and GJIC intensity. Thus, apparent links exist between Cx43 expression and transmigration potential of DU-145 cells. Moreover, Cx43 expression profiles in the analysed DU-145 subsets were not affected by intercellular contacts and chemical inhibition of GJIC during the transmigration. Our observations indicate that neither cell motility nor GJIC determines the transmigration efficiency of DU-145 cells. However, we postulate that selective transmigration of prostate cancer cells expressing elevated levels of Cx43 expression may be crucial for the "leading front" formation during cancer invasion.

The role of connexins in prostate cancer promotion and progression.

Prostate cancer is a prevalent disease that is characterized by a presumably long latency period and a moderate propensity to metastasize. Although a range of mechanisms have been implicated in prostate carcinogenesis, the factors determining the initiation of metastasis remain obscure. The synchronized function of prostate cells depends on their metabolic and electrical coupling; disturbance of these functions has long been suggested to be integral to prostate carcinogenesis. However, although connexins form intercellular channels involved in gap-junction-mediated intercellular coupling (GJIC), whether these proteins also have GJIC-independent roles in cancer progression and metastasis remains a matter of debate. Some data indicate a correlation between connexin expression and the invasive potential of prostate cancer cells, which points to stage-specific functions of connexins during prostate cancer development. For example, restoration of connexin expression seems to be crucial for the formation of invasive cell subsets within heterogeneous prostate cancer cell populations that have undergone aberrant differentiation. Consequently, the clinical application of therapeutic and prophylactic approaches focused on the modulation of connexin expression in prostate cancer cells should be reconsidered.

Lithium Attenuates TGF-ß(1)-Induced Fibroblasts to Myofibroblasts Transition in Bronchial Fibroblasts Derived from Asthmatic Patients.

Bronchial asthma is a chronic disorder accompanied by phenotypic transitions of bronchial epithelial cells, smooth muscle cells, and fibroblasts. Human bronchial fibroblasts (HBFs) derived from patients with diagnosed asthma display predestination towards TGF-ß-induced phenotypic switches. Since the interference between TGF-ß and GSK-3ß signaling contributes to pathophysiology of chronic lung diseases, we investigated the effect of lithium, a nonspecific GSK-3ß inhibitor, on TGF-ß(1)-induced fibroblast to myofibroblast transition (FMT) in HBF and found that the inhibition of GSK-3ß attenuates TGF-ß(1)-induced FMT in HBF populations derived from asthmatic but not healthy donors. Cytoplasmically sequestrated ß-catenin, abundant in TGF-ß(1)/LiCl-stimulated asthmatic HBFs, most likely interacts with and inhibits the nuclear accumulation and signal transduction of Smad proteins. These data indicate that the specific cellular context determines FMT-related responses of HBFs to factors interfering with the TGF-ß signaling pathway. They may also provide a mechanistic explanation for epidemiological data revealing coincidental remission of asthmatic syndromes and their recurrence upon the discontinuation of lithium therapy in certain psychiatric diseases.

Fenofibrate attenuates contact-stimulated cell motility and gap junctional coupling in DU-145 human prostate cancer cell populations.

In the present study, we investigated the effects of fenofibrate on the invasive potential of DU-145 human prostate cancer cells in the context of gap junctional intercellular coupling and the formation of reactive oxygen species. Time-lapse analyses of cell motility, accompanied by tests of cell viability, membrane microviscosity, reactive oxygen species accumulation and the function of gap junctional protein connexin 43 were performed in monolayer cultures of DU-145 cells following fenofibrate administration. Fenofibrate inhibited the motility of DU-145 cells and attenuated gap junctional intercellular coupling in a manner independent of its effects on cell viability, PPARα activation and cell membrane micro-viscosity. Instead, N-acetyl-L-cysteine, a scavenger of reactive oxygen species, restored cell motility and gap junctional coupling in fenofibrate-treated DU-145 cell populations. These data indicate that two parameters crucial for cancer cell metastatic potential, i.e. cell motility and gap junctional coupling, are inhibited by fenofibrate. Thus, fenofibrate affects prostate cancer cell invasion via an orchestrated action on versatile cancer cell properties determining this process. A novel mechanism of anti-invasive activity of fenofibrate, which depends on its interference with cell motility and the function of gap junctions regulated by reactive oxygen species, is suggested.

Blood monocytes stimulate migration of human pancreatic carcinoma cells in vitro: the role of tumour necrosis factor - alpha.

In some types of cancers, tumour-infiltrating monocytes/macrophages (TIM) may be responsible for the formation of an invasive microenvironment in a manner dependent on the secretion of soluble mediators such as tumour necrosis factor-alpha (TNF). Human pancreatic carcinoma (HPC-4) cells are able to induce TNF production by monocytes. Here, the effect of human peripheral blood monocytes, precursors of TIM, on the motility of co-cultured HPC-4 cells, was directly analysed in vitro. A phenotypic transition, i.e., the appearance of rear-front polarised HPC-4 cells paralleled by their increased motility, and increased motility of monocytes, were observed. This effect was attenuated when HPC-4 cells and monocytes were co-cultured in the presence of inhibitors of TNF production and anti-TNF monoclonal antibodies, indicating the specific role of this cytokine in determining paracrine loops between monocytes and cancer cells. Moreover, exogenous TNF induced HPC-4 cell motility concomitantly to the appearance of cellular features characteristic for epithelial-mesenchymal transition (EMT) such as rear-front polarisation, rearrangements of the actin cytoskeleton characteristic for motile cells and the induction of Snail-1 expression. Since cell movement is crucial for cancer invasion and the formation of metastases, these findings demonstrate an EMT-dependent mechanism of cancer progression which acts through the phenotypic transition of pancreatic cancer cells dependent on monocyte-derived TNF.