Expression of MacMARCKS restores cell adhesion to ICAM-1-coated surface

Sex Differences and Bone Metastases of Breast, Lung, and Prostate Cancers: Do Bone Homing Cancers Favor Feminized Bone Marrow?

Sex-associated differences in bone metastasis formation from breast, lung, and prostate cancer exist in clinical studies, but have not been systematically reviewed. Differences in the bone marrow niche can be attributed to sexual dimorphism, to genetic variations that affect sex hormone levels, or to the direct effects of sex hormones, natural or exogenously delivered. This review describes the present understanding of sex-associated and sex hormone level differences in the marrow niche and in formation of bone metastasis during the transition of these three cancers from treatable disease to an often untreatable, lethal metastatic one. Our purpose is to provide insight into some underlying molecular mechanisms for hormonal influence in bone metastasis formation, and to the potential influence of sexual dimorphism, genetic differences affecting sex assignment, and sex hormone level differences on the bone niche and its favorability for metastasis formation. We reviewed publications in PubMed and EMBASE, including full length manuscripts, case reports, and clinical studies of relevance to our topic. We focused on bone metastasis formation in breast, lung, and prostate cancer because all three commonly present with bone metastases. Several clear observations emerged. For breast cancer bone metastasis formation, estrogen receptor (ER) signaling pathways indicate a role for ER beta (ERβ). Estrogen influences the bone microenvironment, creating and conditioning a favorable niche for colonization and breast cancer progression. For lung cancer, studies support the hypothesis that females have a more favorable bone microenvironment for metastasis formation. For prostate cancer, a decrease in the relative androgen to estrogen balance or a “feminization” of bone marrow favors bone metastasis formation, with a potentially important role for ERβ that may be similar to that in breast cancer. Long-term estrogen administration or androgen blockade in males may feminize the bone marrow niche to one more favorable for bone metastases in prostate cancer. Administration of androgens in females, especially combined with mastectomy, may reduce risk of developing bone metastatic breast cancer. We conclude that it should be considered that females, those with female-leaning genetic variations, or hormonal states that feminize the bone marrow, may offer favorable sites for bone metastases.

In Vitro Co-Culture Models of Breast Cancer Metastatic Progression towards Bone

Advanced breast cancer frequently metastasizes to bone through a multistep process involving the detachment of cells from the primary tumor, their intravasation into the bloodstream, adhesion to the endothelium and extravasation into the bone, culminating with the establishment of a vicious cycle causing extensive bone lysis. In recent years, the crosstalk between tumor cells and secondary organs microenvironment is gaining much attention, being indicated as a crucial aspect in all metastatic steps. To investigate the complex interrelation between the tumor and the microenvironment, both in vitro and in vivo models have been exploited. In vitro models have some advantages over in vivo, mainly the possibility to thoroughly dissect in controlled conditions and with only human cells the cellular and molecular mechanisms underlying the metastatic progression. In this article we will review the main results deriving from in vitro co-culture models, describing mechanisms activated in the crosstalk between breast cancer and bone cells which drive the different metastatic steps.

Suppression of the lipopolysaccharide-induced expression of MARCKS-related protein (MRP) affects transmigration in activated RAW264.7 cells

The molecular action mechanism of MRP, one of the protein kinase C (PKC) substrates, has been under intense investigation, but reports on its role in macrophage function remain controversial. The treatment of macrophage cell lines with bacterial lipopolysaccharide (LPS) induced a high level of MRP expression suggesting that MRP plays a role in the function of activated macrophages. In order to investigate the role of MRP in activated RAW264.7 cells, we stably transfected MRP-specific shRNA expression constructs and tested for alterations in macrophage-related functions. The down-regulation of MRP expression resulted in a marked reduction in chemotaxis toward MCP-1 or extracellular matrix proteins. Furthermore, pharmacological inhibitors of PKC significantly inhibited the chemotaxis in RAW264.7 cells. These data reveals the pivotal role of MRP in the transmigration of activated RAW264.7 cells.

Identification of estrogen-responsive genes involved in breast cancer metastases to the bone

Bone metastasis is the most common metastasis in breast cancer patients. Clinical observations propose strong association between estrogen receptor (ER)-positive tumors and the development of bone metastases. We hypothesized of biologically diverse sets of hormone-dependent tumors predisposed to bone metastases and of possible role of ER-signaling pathways in the development and progression of bone metastases. We developed a novel in vitro estrogen (E2)-responsive model system, in which breast cancer cells and bone cells express high levels of either ERalpha or ERbeta. Using co-culture approach and gene array technology we identified E2-responsive genes involved in the interaction between cancer cells and bone cells. We detected 13 genes that were altered solely by ERalpha and 11 genes that were regulated solely by ERbeta in cancer cells. Only 5 genes were modified by both ERalpha and ERbeta. Interestingly, the majority of genes in bone cells were altered through ERbeta. Two genes, namely MacMarcks and Muc-1, whose changes in expressions in cancer cells in response to E2 were highly significant, were selected for immunohistochemical analysis using tissue microarrays of 59 infiltrating ductal carcinomas. Our results indicated that both MacMarcks and Muc-1 were expressed at high frequency in ER-positive tumors. The correlation between ERalpha- and ERbeta-status of hormone-dependent tumors with combined expression of these two markers might suggest a more aggressive tumor phenotype associated with bone metastases. Further analysis of tissues with clinicopathological characteristics and known bone metastatic disease will indicate potential prognostic values of these and other markers in the development of bone metastases in a subgroup of "bad" hormone-dependent breast cancer.

The small GTPase R-Ras regulates organization of actin and drives membrane protrusions through the activity of PLCepsilon

R-Ras, an atypical member of the Ras subfamily of small GTPases, enhances integrin-mediated adhesion and signaling through a poorly understood mechanism. Dynamic analysis of cell spreading by total internal reflection fluorescence (TIRF) microscopy demonstrated that active R-Ras lengthened the duration of initial membrane protrusion, and promoted the formation of a ruffling lamellipod, rich in branched actin structures and devoid of filopodia. By contrast, dominant-negative R-Ras enhanced filopodia formation. Moreover, RNA interference (RNAi) approaches demonstrated that endogenous R-Ras contributed to cell spreading. These observations suggest that R-Ras regulates membrane protrusions through organization of the actin cytoskeleton. Our results suggest that phospholipase Cepsilon (PLCepsilon) is a novel R-Ras effector mediating the effects of R-Ras on the actin cytoskeleton and membrane protrusion, because R-Ras was co-precipitated with PLCepsilon and increased its activity. Knockdown of PLCepsilon with siRNA reduced the formation of the ruffling lamellipod in R-Ras cells. Consistent with this pathway, inhibitors of PLC activity, or chelating intracellular Ca2+ abolished the ability of R-Ras to promote membrane protrusions and spreading. Overall, these data suggest that R-Ras signaling regulates the organization of the actin cytoskeleton to sustain membrane protrusion through the activity of PLCepsilon.

Avidity modulation activates adhesion under flow and requires cooperativity among adhesion receptors

An early step in activation of leukocyte adhesion is a release of integrins from cytoskeletal constraints on their diffusion, leading to rearrangement and, consequently, increased avidity. Static adhesion assays using purified ligand as a substrate have demonstrated that very low doses of cytochalasin D disconnect beta2-integrins from their cytoskeletal links, allowing rearrangement and activating adhesion. The adhesion process in blood vessels is poorly simulated by these assays, however, for two reasons: leukocyte adhesion to endothelium 1), occurs in the presence of blood flow and 2), involves the simultaneous interactions of multiple sets of adhesion molecules. We investigated the effect of cytochalasin D, at concentrations that increase integrin diffusion but do not alter leukocyte shape and surface features, on adhesion of leukocytes to endothelial cells under flow. Cytochalasin D increased the number of rolling cells, the number of firmly adherent cells, and the duration of both rolling and firm adhesion. These effects required endothelial cell expression of ICAM-1, the ligand for leukocyte beta2-integrins. The beta2-integrin-ICAM-1 interaction alone was not sufficient, however. Experiments using purified substrates demonstrated that avidity effects on activation of adhesion under flow require functional cooperativity between integrins and other adhesion receptors.

Two variants of the human hepatocellular carcinoma-associated HCAP1 gene and their effect on the growth of the human liver cancer cell line Hep3B

We have cloned a cDNA from chromosome band 17p13.3, designated as HCAP1 (HCC-associated protein 1, originally named HC56). Database searches revealed that HCAP1 shares most of its open reading frame with GEMIN4. Single nucleotide polymorphism (SNP) screening revealed a high incidence of SNP in the coding region of HCAP1 (12 SNP sites). A collection of 140 controls and 22 cases from the Qidong area was genotyped at 6 SNP sites. The 22 cases exhibited higher frequencies of minor alleles than did the controls, and 2 sites revealed significant differences between the controls and the cases. We constructed 2 haplotypes, HCAP1-N (with common alleles at 5 SNP sites) and HCAP1-M (with minor alleles at 5 SNP sites), in a mammalian expression system. Both haplotypes resulted in a remarkable reduction in colony formation and suppression of cell growth after being transfected into the human hepatocellular carcinoma (HCC) cell line. The inhibitory effect of HCAP1-N was stronger than that of HCAP1-M. Different haplotypes also resulted in different gene expression profiles in the Hep3B cell line according to an examination of 588 genes on an Atlas membrane. The expression induced by HCAP1-M caused an up-regulation of genes involved in cellular proliferation and a down-regulation of genes involved in cellular apoptosis and DNA repair. These results, in addition to the statistical data, are biological evidence that the HCAP1-M variant of HCAP1 has a reduced inhibitory effect on hepatocarcinoma cell growth and an impaired DNA repair system. This suggests that HCAP1-M may be related to cancer susceptibility.

High-temporal-resolution analysis demonstrates that ICAM-1 stabilizes WEHI 274.1 monocytic cell rolling on endothelium

Leukocyte rolling, adhesion, and migration on vascular endothelium involve several sets of adhesion molecules that interact simultaneously. Each of these receptor-ligand pairs may play multiple roles. We examined the role of ICAM-1 in adhesive interactions with mouse aortic endothelial cells (MAECs) in an in vitro flow system. Average rolling velocity of the monocytic cell line WEHI 274.1 was increased on ICAM-1-deficient MAECs compared with wild-type MAECs, both with and without TNF-alpha stimulation. High-temporal-resolution analysis provided insights into the underlying basis for these differences. Without TNF-alpha stimulation, average rolling velocity was slower on wild-type than on ICAM-1-deficient endothelium because of brief (<1 s) pauses. On TNF-alpha-stimulated ICAM-1-deficient endothelium, cells rolled faster because of transient accelerations, producing "jerky" rolling. Firm adhesion to ICAM-1-deficient MAECs was significantly reduced compared with wild-type MAECs, although the number of rolling cells was similar. These results demonstrate directly that ICAM-1 affects rolling velocity by stabilizing leukocyte rolling.

Rearrangement of integrins in avidity regulation by leukocytes

Leukocyte adhesion must be tightly controlled in order for leukocytes to patrol the body as nonadherent cells, yet stop and emigrate from the blood into tissues at sites of infection or inflammation. A key element in this process is activation of beta2 integrins. While beta2 integrin activation involves conformational changes that increase affinity for ligand, evidence is accumulating that rearrangement of integrins, resulting in increases in avidity, is at least as important in regulating binding capacity. Recent work has established the importance of diffusion and rearrangement of integrins to activation of leukocyte adhesion, and has begun to unravel the molecular basis of its regulation.

Dynamitin controls Beta 2 integrin avidity by modulating cytoskeletal constraint on integrin molecules

Dynamitin, a subunit of the microtubule-dependent motor complex, was implicated in cell adhesion by binding to MacMARCKS (Macrophage-enriched myristoylated alanine-rice C kinase substrate). However, how dynamitin is involved in cell adhesion is unclear despite the fact that both MacMARCKS and microtubules regulate beta(2) integrin activation. We report that dynamitin regulates beta(2) integrin avidity toward iC3b by modulating the lateral mobility of beta(2) integrin molecules. Using the single particle tracking method, we found that integrin molecular mobility in cells expressing the fusion protein CFP (cyan fluorescent protein)-dynamitin or CFP-MB (the MacMARCKS binding domain peptide of dynamitin) increased 6-fold over the control cells, suggesting that disturbing dynamitin function dramatically altered the cytoskeletal constraint on beta(2) integrin molecules. Further mechanistic studies revealed that overexpression of dynamitin stimulated the phosphorylation of endogenous MacMARCKS protein, which lead to the enhanced tyrosine phosphorylation of paxillin. This effect of dynamitin correlates with the observation that higher concentration of PKC inhibitor is required to block beta(2) integrin mobility in dynamitin-expressing cells. Although dynamitin acts at the point of MacMARCKS phosphorylation, it is upstream of RhoA, because its effect was blocked by RhoA inhibitor. Thus, we conclude that dynamitin is a part of the cytoskeletal constraint that locks beta(2) integrin in the inactive form.

The microtubule cytoskeleton participates in control of beta2 integrin avidity

Leukocyte avidity is regulated by cytoskeletal constraints, which keep beta(2) integrins in an inactive mode. Releasing these constraints results in increased lateral mobility and clustering of integrins, effectively activating adhesion. At least part of the constraint on beta(2) integrins is due to actin; whether other cytoskeletal components are involved has not previously been investigated. Microtubules are a candidate for control of integrin rearrangement, because they modulate focal adhesions, which are sites of interaction between integrins and the cytoskeleton. Here we report that both depolymerization of microtubules by colchicine or nocodazole and stabilization of microtubules by taxol increased the lateral mobility of beta(2) integrins, activating adhesion. Increased integrin mobility was accompanied by an increase in tyrosine phosphorylation of paxillin, a biochemical event associated with activation of beta(2) integrins. Further, C3 exoenzyme, an inhibitor of Rho, blocked induction of integrin mobility by nocodazole, but not by taxol, suggesting that there are multiple microtubule-dependent pathways to integrin rearrangement, only some of which require Rho activity. Taken together, our data suggest that a dynamic microtubule system is required to regulate integrin-cytoskeleton interactions. Furthermore, these data demonstrate that microtubules participate in control of integrin rearrangement, one of the earliest steps in activation of integrin-mediated adhesion.

In vivo interaction between dynamitin and MacMARCKS detected by the fluorescent resonance energy transfer method

Dynamitin is a subunit of the dynactin complex regulating microtubule-dependent motor functions, and MacMARCKS (Macrophage-enriched myristoylated alanine-rich protein kinase C substrate) is a major protein kinase C substrate regulating integrin activation. The interaction between dynamitin and MacMARCKS has been implicated in integrin-dependent cell spreading. However, the in vivo interaction of these two proteins in living cells has not been demonstrated. Spatial and temporal information about the interaction is also lacking. In this study, we used the fluorescent resonance energy transfer method to demonstrate in vivo interaction between MacMARCKS and dynamitin with cyan fluorescent protein (CFP)-conjugated dynamitin as the donor fluorophore and yellow fluorescent protein (YFP)-conjugated MacMARCKS as the acceptor fluorophore. The interaction of these two fusion proteins was studied both in vitro and in vivo, and typical fluorescent resonance energy transfer was observed; the CFP emission peak increased while the YFP emission peak decreased when protein interaction was abolished. Spatial and temporal information was obtained in RAW macrophage cells. In resting macrophage cells, dynamitin-MacMARCKS interaction is concentrated at the cell periphery, although the majority of dynamitin is distributed at the perinuclear region of the cells. When cells were treated with phorbol 12-myristate 13-acetate, both proteins concentrated to perinuclear regions of the cells, and yet the interaction disappeared as the cell spread. Similar events were also observed in 293 cells. Thus, we conclude that dynamitin and MacMARCKS indeed interact in living cells.

Protein kinase C-regulated dynamitin-macrophage-enriched myristoylated alanine-rice C kinase substrate interaction is involved in macrophage cell spreading

Macrophage spreading requires the microtubule cytoskeleton and protein kinase C (PKC). The mechanism of involvement of the microtubules and PKC in this event is not fully understood. Dynamitin is a subunit of dynactin, which is important for linking the microtubule-dependent motor protein dynein to vesicle membranes. We report that dynamitin is a Ca(2+)/calmodulin-binding protein and that dynamitin binds directly to macrophage-enriched myristoylated alanine-rice C kinase substrate (MacMARCKS), a membrane-associated PKC substrate involved in macrophage spreading and integrin activation. Dynamitin was found to copurify with MacMARCKS both during MacMARCKS purification with conventional chromatography and during the immunoabsorption of MacMARCKS using anti-MacMARCKS antibody. Vice versa, MacMARCKS was also found to cosediment with the 20 S dynactin complex. We determined that the effector domain of MacMARCKS is required to interact with the N-terminal domain of dynamitin. MacMARCKS and dynamitin also partially colocalized at peripheral regions of macrophages and in the cell-cell border of 293 epithelial cells. Treatment with phorbol esters abolished this colocalization. Disrupting the interaction with a short peptide derived from the MacMARCKS-binding domain of dynamitin caused macrophages to spread and flatten. These data suggest that the dynamitin-MacMARCKS interaction is involved in cell spreading. Furthermore, the regulation of this interaction by PKC and Ca(2+)/calmodulin provides a possible regulatory mechanism for cell adhesion and spreading.