Characterization of the signaling pathways regulating alpha2beta1 integrin-mediated events by a pharmacological approach

Overcoming Chemotherapy Resistance in SCLC

SCLC is an aggressive form of lung cancer with a very poor prognosis. Although SCLC initially responds very well to platinum-based chemotherapy, it eventually recurs and at recurrence is nearly universally resistant to therapy. In light of the recent advances in understanding regarding the biology of SCLC, we review findings related to SCLC chemotherapy resistance. We discuss the potential clinical implications of recent preclinical discoveries in altered signaling pathways, transcriptional landscapes, metabolic vulnerabilities, and the tumor microenvironment.

Integrin alpha2-mediated ERK and calpain activation play a critical role in cell adhesion and motility via focal adhesion kinase signaling: identification of a novel signaling pathway

Higher levels of focal adhesion kinase (FAK) are expressed in colon metastatic carcinomas. However, the signaling pathways and their mechanisms that control cell adhesion and motility, important components of cancer metastasis, are not well understood. We sought to identify the integrin-mediated mechanism of FAK cleavage and downstream signaling as well as its role in motility in human colon cancer GEO cells. Our results demonstrate that phosphorylated FAK (tyrosine 397) is cleaved at distinct sites by integrin signaling when cells attach to collagen IV. Specific blocking antibodies (clone P1E6) to integrin alpha2 inhibited FAK activation and cell motility (micromotion). Ectopic expression of the FAK C-terminal domain FRNK attenuated FAK and ERK phosphorylation and micromotion. Calpain inhibitor N-acetyl-leucyl-leucyl-norleucinal blocked FAK cleavage, cell adhesion, and micromotion. Antisense approaches established an important role for mu-calpain in cell motility. Expression of wild type mu-calpain increased cell micromotion, whereas its point mutant reversed the effect. Further, cytochalasin D inhibited FAK phosphorylation and cleavage, cell adhesion, locomotion, and ERK phosphorylation, thus showing FAK activation downstream of actin assembly. We also found a pivotal role for FAK Tyr(861) phosphorylation in cell motility and ERK activation. Our results reveal a novel functional connection between integrin alpha2 engagement, FAK, ERK, and mu-calpain activation in cell motility and a direct link between FAK cleavage and enhanced cell motility. The data suggest that blocking the integrin alpha2/FAK/ERK/mu-calpain pathway may be an important strategy to reduce cancer progression.

Human Fibroblast Migration in Three-Dimensional Collagen Gel in Response to Noninvasive Electrical Stimulus. II. Identification of Electrocoupling Molecular Mechanisms

Cell adhesion and migration is regulated by a series of coordinated and integrated molecular mechanisms. In the accompanying article (Sun et al., Tissue Eng. 10, 1548, 2004), we demonstrate and characterize the human fibroblast movement in three-dimensional (3D) collagen gel induced by non-invasive electrical stimulus. The molecular mechanisms mediating 3D cell migration in response to physical stimuli including noninvasive electrical stimulus remain to be elucidated, however. Here we report that induced human fibroblast movement in 3D collagen gel is both integrin and Ca2+ dependent. Treatment of cells with anti-integrin antibodies prevents electrically induced cell movement. More interestingly, whereas the absence of extracellular Ca2+ suppresses cell movement, inhibition of the cell surface receptor-coupled phospholipase C (PLC) completely prevents 3D cell migration, suggesting molecular association between integrin, PLC, and intracellular Ca2+. Coupling of external electrical stimulus to PLC activation appears to be the primary event required to induce cell migration, while Ca2+ influx across the plasma membrane regulates the sustained cell movement. On the basis of the rather small strength (0.1 V/cm) of electrical stimulus used in this study, activation of the electrically operated voltage-gated Ca2+ channels is unlikely, but the mechanically operated stretch-activated cation channels appear to mediate Ca2+ influx. Elucidation of the electrocoupling molecular mechanisms involved in 3D cell movement could lead to controlled and designed manipulation of 3D cell adhesion and migration.

Integrin alpha4beta1 regulates migration across basement membranes by lung fibroblasts: a role for phosphatase and tensin homologue deleted on chromosome 10

Idiopathic pulmonary fibrosis is a disease that is characterized by fibroblast accumulation and activation in the distal airspaces of the lung. We hypothesized that fibrotic lung fibroblasts migrate/invade across basement membranes by integrin-mediated mechanisms as a means of entering alveoli. We demonstrate that in lung fibroblasts derived from patients with idiopathic pulmonary fibrosis, fibronectin signaling is both necessary and sufficient for basement membrane migration/invasion across basement membranes. This effect is mediated through the alpha5beta1 integrin because blockade of fibronectin-alpha5 integrin ligation attenuated this response. In contrast, ligation of alpha4beta1 integrin inhibits basement membrane invasion by normal lung fibroblasts but not by fibrotic lung fibroblasts. This phenotypic difference is not related to surface expression of the alpha4beta1 integrin, as demonstrated by flow cytometry. In normal lung fibroblasts but not in fibrotic lung fibroblasts, we show that ligation of alpha4beta1 integrin induces a significant increase in phosphatase and tensin homologue deleted on chromosome 10 (PTEN) activity. Fibrotic lung fibroblasts express constitutively less PTEN mRNA and protein as well as phosphatase activity in comparison to normal lung fibroblasts. Together, these data suggest that a loss of alpha4beta1 signaling via PTEN confers a migratory/invasive phenotype to fibrotic lung fibroblasts. Furthermore, this study implicates a loss of PTEN function in the pathophysiology of idiopathic pulmonary fibrosis.

Beta1 and beta2 integrins mediate adhesion during macrophage fusion and multinucleated foreign body giant cell formation

An in vitro system of interleukin (IL)-4-induced human monocyte-derived macrophage fusion was used to investigate the cell/substrate adhesive mechanisms that support multinucleated foreign body giant cell (FBGC) formation. Monocytes were cultured for 3 days and IL-4 was added to induce macrophage fusion and FBGC formation by day 7. Functionally defined anti-integrin antibodies demonstrated that initial monocyte adhesion is mediated by beta2 integrins, whereas during the induction of macrophage fusion by IL-4, an additional dependence on beta1 integrins is acquired. The combination of anti-beta1 plus anti-beta2 was most effective, reducing macrophage/FBGC adhesion to 10% of controls. Consistent with integrin-mediated signaling, the tyrosine kinase inhibitor genistein and the phosphatidylinositol-3-kinase inhibitors wortmannin and LY294002 also attenuated macrophage/FBGC adhesion. Confocal microscopic analysis revealed that beta2 integrins are present on monocytes after initial adhesion and are strongly expressed on fusing macrophages, particularly in peripheral cell areas, and on FBGCs. In contrast, beta1 integrins are not detected on monocytes but begin to appear during macrophage development and are strongly expressed on fusing macrophages and FBGCs. For the first time, these results demonstrate the IL-4-induced acquisition of cooperation between beta1 and beta2 integrins in the cell/substrate adhesive interactions that are required for multinucleated FBGC formation.

Establishment of two new human bladder carcinoma cell lines, CAL 29 and CAL 185. Comparative study of cell scattering and epithelial to mesenchyme transition induced by growth factors

We describe here two new human urothelial carcinoma cell lines, CAL 29 and CAL 185, established from two patients with high-grade tumours and which display very different properties in vitro. We have shown that CAL 29 cells were tumorigenic in mice and expressed characteristic features of both cell scattering and transition from epithelial to mesenchymal phenotype (EMT) after triggering by the EGF receptor ligands, TGFalpha and EGF. At the opposite, the CAL 185 cells were not tumorigenic in mice and neither scattered nor expressed vimentin intermediary filaments in the presence of growth factors. We further demonstrated that CAL 29 cell scattering was reversible after growth factor removal and that both scattering and EMT were markedly impaired after treatment with MEK, Src and PI3-kinase inhibitors suggesting that these kinases might be important components of the cellular responses to EGF and TGF-alpha leading to scattering and EMT. These agents could help to understand the intracellular pathways involved in invasiveness and to find new targets for limiting metastasis. In conclusion, these two new cell lines could be good models to dissect the molecular mechanisms involved in invasion and metastasis development in human bladder cancer.

Phosphorylation of tyrosine residues 31 and 118 on paxillin regulates cell migration through an association with CRK in NBT-II cells

Identification of signaling molecules that regulate cell migration is important for understanding fundamental processes in development and the origin of various pathological conditions. The migration of Nara Bladder Tumor II (NBT-II) cells was used to determine which signaling molecules are specifically involved in the collagen-mediated locomotion. We show here that paxillin is tyrosine phosphorylated after induction of motility on collagen. Overexpression of paxillin mutants in which tyrosine 31 and/or tyrosine 118 were replaced by phenylalanine effectively impaired cell motility. Moreover, stimulation of motility by collagen preferentially enhanced the association of paxillin with the SH2 domain of the adaptor protein CrkII. Mutations in both tyrosine 31 and 118 diminished the phosphotyrosine content of paxillin and prevented the formation of the paxillin-Crk complex, suggesting that this association is necessary for collagen-mediated NBT-II cell migration. Other responses to collagen, such as cell adhesion and spreading, were not affected by these mutations. Overexpression of wild-type paxillin or Crk could bypass the migration-deficient phenotype. Both the SH2 and the SH3 domains of CrkII are shown to play a critical role in this collagen-mediated migration. These results demonstrate the important role of the paxillin-Crk complex in the collagen-induced cell motility.