Role of MacMARCKS in integrin-dependent macrophage spreading and tyrosine phosphorylation of paxillin

Identification of Inflammatory Proteomics Networks of Toll-like Receptor 4 through Immunoprecipitation-Based Chemical Cross-Linking Proteomics

Toll-like receptor 4 (TLR4) is a receptor on an immune cell that can recognize the invasion of bacteria through their attachment with bacterial lipopolysaccharides (LPS). Hence, LPS is a pro-immune response stimulus. On the other hand, statins are lipid-lowering drugs and can also lower immune cell responses. We used human embryonic kidney (HEK 293) cells engineered to express HA-tagged TLR-4 upon treatment with LPS, statin, and both statin and LPS to understand the effect of pro- and anti-inflammatory responses. We performed a monoclonal antibody (mAb) directed co-immunoprecipitation (CO-IP) of HA-tagged TLR4 and its interacting proteins in the HEK 293 extracted proteins. We utilized an ETD cleavable chemical cross-linker to capture weak and transient interactions with TLR4 protein. We tryptic digested immunoprecipitated and cross-linked proteins on beads, followed by liquid chromatography–mass spectrometry (LC-MS/MS) analysis of the peptides. Thus, we utilized the label-free quantitation technique to measure the relative expression of proteins between treated and untreated samples. We identified 712 proteins across treated and untreated samples and performed protein network analysis using Ingenuity Pathway Analysis (IPA) software to reveal their protein networks. After filtering and evaluating protein expression, we identified macrophage myristoylated alanine-rich C kinase substrate (MARCKSL1) and creatine kinase proteins as a potential part of the inflammatory networks of TLR4. The results assumed that MARCKSL1 and creatine kinase proteins might be associated with a statin-induced anti-inflammatory response due to possible interaction with the TLR4.

Murine Renal Transcriptome Profiles Upon Leptospiral Infection: Implications for Chronic Kidney Diseases

Background

Leptospirosis caused by pathogenic Leptospira spp leads to kidney damage that may progress to chronic kidney disease. However, how leptospiral infections induced renal damage is unclear.

Methods

We apply microarray and next-generation sequencing technologies to investigate the first murine transcriptome-wide, leptospires-mediated changes in renal gene expression to identify biological pathways associated with kidney damage.

Results

Leptospiral genes were detected in renal transcriptomes of mice infected with Leptospira interrogans at day 28 postinfection, suggesting colonization of leptospires within the kidney with propensity of chronicity. Comparative differential gene expression and pathway analysis were investigated in renal transcriptomes of mice infected with pathogens and nonpathogens. Pathways analysis showed that Toll-like receptor signaling, complements activation, T-helper 1 type immune response, and T cell-mediated immunity/chemotaxis/proliferation were strongly associated with progressive tubulointerstitial damage caused by pathogenic leptospiral infection. In addition, 26 genes related with complement system, immune function, and cell-cell interactions were found to be significantly up-regulated in the L interrogans-infected renal transcriptome.

Conclusions

Our results provided comprehensive knowledge regarding the host transcriptional response to leptospiral infection in murine kidneys, particularly the involvement of cell-to-cell interaction in the immune response. It would provide valuable resources to explore functional studies of chronic renal damage caused by leptospiral infection.

MARCKS-related protein regulates cytoskeletal organization at cell-cell and cell-substrate contacts in epithelial cells

Treatment of epithelial cells with interferon-γ and TNF-α (IFN/TNF) results in increased paracellular permeability. To identify relevant proteins mediating barrier disruption, we performed proximity-dependent biotinylation (BioID) of occludin and found that tagging of MARCKS-related protein (MRP; also known as MARCKSL1) increased ∼20-fold following IFN/TNF administration. GFP-MRP was focused at the lateral cell membrane and its overexpression potentiated the physiological response of the tight junction barrier to cytokines. However, deletion of MRP did not abrogate the cytokine responses, suggesting that MRP is not required in the occludin-dependent IFN/TNF response. Instead, our results reveal a key role for MRP in epithelial cells in control of multiple actin-based structures, likely by regulation of integrin signaling. Changes in focal adhesion organization and basal actin stress fibers in MRP-knockout (KO) cells were reminiscent of those seen in FAK-KO cells. In addition, we found alterations in cell-cell interactions in MRP-KO cells associated with increased junctional tension, suggesting that MRP may play a role in focal adhesion-adherens junction cross talk. Together, our results are consistent with a key role for MRP in cytoskeletal organization of cell contacts in epithelial cells.

Migration and Phagocytic Ability of Activated Microglia During Post-natal Development is Mediated by Calcium-Dependent Purinergic Signalling

Microglia play an important role in synaptic pruning and controlled phagocytosis of neuronal cells during developmental stages. However, the mechanisms that regulate these functions are not completely understood. The present study was designed to investigate the role of purinergic signalling in microglial migration and phagocytic activity during post-natal brain development. One-day-old BALB/c mice received lipopolysaccharide (LPS) and/or a purinergic analogue (2-methylthioladenosine-5'-diphosphate; 2MeSADP), intracerebroventrically (i.c.v.). Combined administration of LPS and 2MeSADP resulted in activation of microglia as evident from increased expression of ionised calcium-binding adapter molecule 1 (Iba1). Activated microglia showed increased expression of purinergic receptors (P2Y2, P2Y6 and P2Y12). LPS either alone or in combination with 2MeSADP induced the expression of Na(+)/Ca(2+) exchanger (NCX-1) and P/Q-type Ca(2+) channels along with MARCKS-related protein (MRP), which is an integral component of cell migration machinery. In addition, LPS and 2MeSADP administration induced the expression of microglial CD11b and DAP12 (DNAX-activation protein 12), which are known to be involved in phagocytosis of neurons during development. Interestingly, administration of thapsigargin (TG), a specific Ca(2+)-ATPase inhibitor of endoplasmic reticulum, prevented the LPS/2MeSADP-induced microglial activation and migration by down-regulating the expression of Iba1 and MRP, respectively. Moreover, TG also reduced the LPS/2MeSADP-induced expression of CD11b/DAP12. Taken together, the findings reveal for the first time that Ca(2+)-mediated purinergic receptors regulate the migration and phagocytic ability of microglia during post-natal brain development.

c-Jun N-terminal kinase phosphorylation of MARCKSL1 determines actin stability and migration in neurons and in cancer cells

Cell migration is a fundamental biological function, critical during development and regeneration, whereas deregulated migration underlies neurological birth defects and cancer metastasis. MARCKS-like protein 1 (MARCKSL1) is widely expressed in nervous tissue, where, like Jun N-terminal protein kinase (JNK), it is required for neural tube formation, though the mechanism is unknown. Here we show that MARCKSL1 is directly phosphorylated by JNK on C-terminal residues (S120, T148, and T183). This phosphorylation enables MARCKSL1 to bundle and stabilize F-actin, increase filopodium numbers and dynamics, and retard migration in neurons. Conversely, when MARCKSL1 phosphorylation is inhibited, actin mobility increases and filopodium formation is compromised whereas lamellipodium formation is enhanced, as is cell migration. We find that MARCKSL1 mRNA is upregulated in a broad range of cancer types and that MARCKSL1 protein is strongly induced in primary prostate carcinomas. Gene knockdown in prostate cancer cells or in neurons reveals a critical role for MARCKSL1 in migration that is dependent on the phosphorylation state; phosphomimetic MARCKSL1 (MARCKSL1(S120D,T148D,T183D)) inhibits whereas dephospho-MARCKSL1(S120A,T148A,T183A) induces migration. In summary, these data show that JNK phosphorylation of MARCKSL1 regulates actin homeostasis, filopodium and lamellipodium formation, and neuronal migration under physiological conditions and that, when ectopically expressed in prostate cancer cells, MARCKSL1 again determines cell movement.

Dynamic adhesions and MARCKS in melanoma cells

Cell motility necessitates the rapid formation and disassembly of cell adhesions. We have studied adhesions in a highly motile melanoma cell line using various biochemical approaches and microscopic techniques to image close adhesions. We report that WM-1617 melanoma cells contain at least two types of close adhesion: classic focal adhesions and more extensive, irregularly shaped adhesions that tend to occur along lamellipodial edges. In contrast to focal adhesions, these latter adhesions are highly dynamic and can be disassembled rapidly via protein kinase C (PKC) activation (e.g. by eicosanoid) and MARCKS phosphorylation. MARCKS overexpression, however, greatly increases the area of close adhesions and renders them largely refractory to PKC stimulation. This indicates that nonphosphorylated MARCKS is an adhesion stabilizer. Unlike focal adhesions, the dynamic adhesions contain alpha3 integrin and MARCKS, but they do not contain the focal adhesion marker vinculin. Overall, these results begin to define the molecular and functional properties of dynamic close adhesions involved in cell motility.

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.

Comprehensive gene expression profiling of Peyer's patch M cells, villous M-like cells, and intestinal epithelial cells

Separate populations of M cells have been detected in the follicle-associated epithelium of Peyer's patches (PPs) and the villous epithelium of the small intestine, but the traits shared by or distinguishing the two populations have not been characterized. Our separate study has demonstrated that a potent mucosal modulator cholera toxin (CT) can induce lectin Ulex europaeus agglutinin-1 and our newly developed M cell-specific mAb NKM 16-2-4-positive M-like cells in the duodenal villous epithelium. In this study, we determined the gene expression of PP M cells, CT-induced villous M-like cells, and intestinal epithelial cells isolated by a novel approach using FACS. Additional mRNA and protein analyses confirmed the specific expression of glycoprotein 2 and myristoylated alanine-rich C kinase substrate (MARCKS)-like protein by PP M cells but not CT-induced villous M-like cells. Comprehensive gene profiling also suggested that CT-induced villous M-like cells share traits of both PP M cells and intestinal epithelial cells, a finding that is supported by their unique expression of specific chemokines. The genome-wide assessment of gene expression facilitates discovery of M cell-specific molecules and enhances the molecular understanding of M cell immunobiology.

Investigation into the mechanism regulating MRP localization

The major PKC substrates MARCKS and MacMARCKS (MRP) are membrane-binding proteins implicated in cell spreading, integrin activation and exocytosis. According to the myristoyl-electrostatic switch model the co-operation between the myristoyl moiety and the positively charged effector domain (ED) is an essential mechanism by which proteins bind to membranes. Loss of the electrostatic interaction between the ED and phospholipids, such as Ptdins(4,5)P2, results in the translocation of such proteins to the cytoplasm. While this model has been extensively tested for the binding of MARCKS far less is known about the mechanisms regulating MRP localization. We demonstrate that after phosphorylation, MRP is relocated to the intracellular membranes of late endosomes and lysosomes. MRP binds to all membranes via its myristoyl moiety, but for its localization at the plasma membrane the ED is also required. Although the ED of MRP can bind to Ptdins(4,5)P2 in vitro, this binding is not essential for its retention at or targeting to the plasma membrane. We conclude that the co-operation between the myristoyl moiety and the ED is not required for the binding to membranes in general but that it is essential for the targeting of MRP to the plasma membrane in a Ptdins(4,5)P2-independent manner.

The regulation of MacMARCKS expression by integrin β3

Integrin-mediated adhesion regulates multiple signaling pathways. Our group previously showed that ectopic expression of different integrin beta-subunits in the neuroepithelial cell line GE11, has distinct effects on cell morphology, actin cytoskeletal organization, and on focal contact distribution. In this report we have investigated changes in gene transcription levels resulting from overexpression of the integrin beta3 subunit. We found that beta3 overexpression leads to the transcriptional downregulation of MARCKS related protein (MRP) resulting in a decreased expression of the MRP protein. Furthermore, we show that the Ras/MAPK pathway controls the basal level of MRP expression but beta3 overexpression bypasses this pathway downstream of ERK to downregulate MRP. Further studies indicate that a region of the cytoplasmic tail of beta3 containing part of the NITY motif is responsible for increased cell spreading and MRP downregulation. However, MRP overexpression failed to inhibit the beta3-induced increase in cell spreading while the knock down of MRP expression in GE11 cells did not increase cell spreading. We suggest that the downregulation of MRP by beta3 is not required for increased cell spreading but instead that MRP downregulation is a secondary effect of increased cell spreading.

Myristoylated, alanine-rich C-kinase substrate phosphorylation regulates growth cone adhesion and pathfinding

Repellents evoke growth cone turning by eliciting asymmetric, localized loss of actin cytoskeleton together with changes in substratum attachment. We have demonstrated that semaphorin-3A (Sema3A)-induced growth cone detachment and collapse require eicosanoid-mediated activation of protein kinase C epsilon (PKC epsilon) and that the major PKC epsilon target is the myristoylated, alanine-rich C-kinase substrate (MARCKS). Here, we show that PKC activation is necessary for growth cone turning and that MARCKS, while at the membrane, colocalizes with alpha3-integrin in a peripheral adhesive zone of the growth cone. Phosphorylation of MARCKS causes its translocation from the membrane to the cytosol. Silencing MARCKS expression dramatically reduces growth cone spread, whereas overexpression of wild-type MARCKS inhibits growth cone collapse triggered by PKC activation. Expression of phosphorylation-deficient, mutant MARCKS greatly expands growth cone adhesion, and this is characterized by extensive colocalization of MARCKS and alpha3-integrin, resistance to eicosanoid-triggered detachment and collapse, and reversal of Sema3A-induced repulsion into attraction. We conclude that MARCKS is involved in regulating growth cone adhesion as follows: its nonphosphorylated form stabilizes integrin-mediated adhesions, and its phosphorylation-triggered release from adhesions causes localized growth cone detachment critical for turning and collapse.

Protein kinase C and the regulation of the actin cytoskeleton

Protein kinase C (PKC) isoforms are central components in intracellular networks that regulate a vast number of cellular processes. It has long been known that in most cell types, one or more PKC isoforms influences the morphology of the F-actin cytoskeleton and thereby regulates processes that are affected by remodelling of the microfilaments. These include cellular migration and neurite outgrowth. This review focuses on the role of classical and novel PKC isoforms in migration and neurite outgrowth, and highlights some regulatory steps that may be of importance in the regulation by PKC of migration and neurite outgrowth. Many studies indicate that integrins are crucial mediators both upstream and downstream of PKC in inducing morphological changes. Furthermore, a number of PKC substrates, directly associated with the microfilaments, such as MARCKS, GAP43, adducin, fascin, ERM proteins and others have been identified. Their potential role in PKC effects on the cytoskeleton is discussed.

The bi-directional translocation of MARCKS between membrane and cytosol regulates integrin-mediated muscle cell spreading

The regulation of the cytoskeleton is critical to normal cell function during tissue morphogenesis. Cell-matrix interactions mediated by integrins regulate cytoskeletal dynamics, but the signaling cascades that control these processes remain largely unknown. Here we show that myristoylated alanine-rich C-kinase substrate (MARCKS) a specific substrate of protein kinase C (PKC), is regulated by alpha5beta1 integrin-mediated activation of PKC and is critical to the regulation of actin stress fiber formation during muscle cell spreading. Using MARCKS mutants that are defective in membrane association or responsiveness to PKC-dependent phosphorylation, we demonstrate that the translocation of MARCKS from the membrane to the cytosol in a PKC-dependent manner permits the initial phases of cell adhesion. The dephosphorylation of MARCKS and its translocation back to the membrane permits the later stages of cell spreading during the polymerization and cross-linking of actin and the maturation of the cytoskeleton. All of these processes are directly dependent on the binding of alpha5beta1 integrin to its extracellular matrix receptor, fibronectin. These results demonstrate a direct biochemical pathway linking alpha5beta1 integrin signaling to cytoskeletal dynamics and involving bi-directional translocation of MARCKS during the dramatic changes in cellular morphology that occur during cell migration and tissue morphogenesis.

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.

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.

Sequential activation of individual PKC isozymes in integrin-mediated muscle cell spreading: a role for MARCKS in an integrin signaling pathway

To understand how muscle cell spreading and survival are mediated by integrins, we studied the signaling events initiated by the attachment of muscle cells to fibronectin (FN). We have previously demonstrated that muscle cell spreading on FN is mediated by alpha5beta1 integrin, is associated with rapid phosphorylation of focal adhesion kinase and is dependent on activation of protein kinase C (PKC). Here we investigated the role of individual PKC isozymes in these cellular processes. We show that alpha, delta and epsilonPKC are expressed in muscle cells and are activated upon integrin engagement with different kinetics - epsilonPKC was activated early, whereas alpha and deltaPKC were activated later. Using isozyme-specific inhibitors, we found that the activation of epsilonPKC was necessary for cell attachment to FN. However, using isozyme-specific activators, we found that activation of each of three isozymes was sufficient to promote the spreading of alpha5-integrin-deficient cells on FN. To investigate further the mechanism by which integrin signaling and PKC activation mediate cell spreading, we studied the effects of these processes on MARCKS, a substrate of PKC and a protein known to regulate actin dynamics. We found that MARCKS was localized to focal adhesion sites soon after cell adhesion and that MARCKS translocated from the membrane to the cytosol during the process of cell spreading. This translocation correlated with different phases of PKC activation and with reorganization of the actin cytoskeleton. Using MARCKS-antisense cDNA, we show that alpha5-expressing cells in which MARCKS expression is inhibited fail to spread on FN, providing evidence for the crucial role of MARCKS in muscle cell spreading. Together, the data suggest a model in which early activation of epsilonPKC is necessary for cell attachment; the later activation of alpha or deltaPKC may be necessary for the progression from attachment to spreading. The mechanism of PKC-mediated cell spreading may be via the phosphorylation of signaling proteins, such as MARCKS, that are involved in the reorganization of the actin cytoskeleton.

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.

Shigella invasion of macrophage requires the insertion of IpaC into the host plasma membrane. Functional analysis of IpaC

Shigella infects residential macrophages via the M cell entry, after which the pathogen induces macrophage cell death. The bacterial strategy of macrophage infection, however, remains largely speculative. Wild type Shigella flexneri (YSH6000) invaded macrophages more efficiently than the noninvasive mutants, where YSH6000 induced large scale lamellipodial extension including ruffle formation around the bacteria. When macrophages were infected with the noninvasive ipaC mutant, the invasiveness and induction of membrane extension were dramatically reduced as compared with that of YSH6000. J774 macrophages infected with YSH6000 showed tyrosine phosphorylation of several proteins including paxillin and c-Cbl, and this pattern was distinctive from those stimulated by Salmonella typhimurium or phorbol ester. Upon addition of IpaC into the external medium of macrophages, membrane extensions were rapidly induced, and this promoted uptake of Escherichia coli. The exogenously added IpaC was found to be integrated into the host cell membrane as detected by immunostaining. The IpaC domain required for the induction of membrane extension from J774 was narrowed down within the region of residues 117-169, which contains a putative membrane-spanning sequence. Our data indicate that Shigella directs its own entry into macrophages, and the IpaC domain which is required for the association with its host membrane is crucial.

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.

A single amino acid in the cytoplasmic domain of the beta 2 integrin lymphocyte function-associated antigen-1 regulates avidity-dependent inside-out signaling

The leukocyte-specific beta(2) integrin lymphocyte function-associated antigen-1 (LFA-1) (alpha(L)/beta(2)) mediates activation-dependent adhesion to intercellular adhesion molecule (ICAM)-1. In leukocytes, LFA-1 requires activation by intracellular messengers to bind ICAM-1. We observed malfunctioning of LFA-1 activation in leukemic T cells and K562-transfected cells. This defective inside-out integrin activation is only restricted to beta(2) integrins, since beta(1) integrins expressed in K562 readily respond to activation signals, such as phorbol 12-myristate 13-acetate. To unravel these differences in inside-out signaling between beta(1) and beta(2) integrins, we searched for amino acids in the beta(2) cytoplasmic domain that are critical in the activation of LFA-1. We provide evidence that substitution of a single amino acid (L732R) in the beta(2) cytoplasmic DLRE motif, creating the DRRE motif, is sufficient to completely restore PMA responsiveness of LFA-1 expressed in K562. In addition, an intact TTT motif in the C-terminal domain is necessary for the acquired PMA responsiveness. We observed that restoration of the PMA response altered neither LFA-1 affinity nor the phosphorylation status of LFA-1. In contrast, strong differences were observed in the capacity of LFA-1 to form clusters, which indicates that inside-out activation of LFA-1 strongly depends on cytoskeletal induced receptor reorganization that was induced by activation of the Ca(2+)-dependent protease calpain.

The adhesion signaling molecule p190 RhoGAP is required for morphogenetic processes in neural development

Rho GTPases direct actin rearrangements in response to a variety of extracellular signals. P190 RhoGAP (GTPase activating protein) is a potent Rho regulator that mediates integrin-dependent adhesion signaling in cultured cells. We have determined that p190 RhoGAP is specifically expressed at high levels throughout the developing nervous system. Mice lacking functional p190 RhoGAP exhibit several defects in neural development that are reminiscent of those described in mice lacking certain mediators of neural cell adhesion. The defects reflect aberrant tissue morphogenesis and include abnormalities in forebrain hemisphere fusion, ventricle shape, optic cup formation, neural tube closure, and layering of the cerebral cortex. In cells of the neural tube floor plate of p190 RhoGAP mutant mice, polymerized actin accumulates excessively, suggesting a role for p190 RhoGAP in the regulation of +Rho-mediated actin assembly within the neuroepithelium. Significantly, several of the observed tissue fusion defects seen in the mutant mice are also found in mice lacking MARCKS, the major substrate of protein kinase C (PKC), and we have found that p190 RhoGAP is also a PKC substrate in vivo. Upon either direct activation of PKC or in response to integrin engagement, p190 RhoGAP is rapidly translocated to regions of membrane ruffling, where it colocalizes with polymerized actin. Together, these results suggest that upon activation of neural adhesion molecules, the action of PKC and p190 RhoGAP leads to a modulation of Rho GTPase activity to direct several actin-dependent morphogenetic processes required for normal neural development.

MARCKS-related protein binds to actin without significantly affecting actin polymerization or network structure. Myristoylated alanine-rich C kinase substrate

Actinis a 42-kDa protein which, due to its ability to polymerize into filaments (F-actin), is one of the major constituents of the cytoskeleton. It has been proposed that MARCKS (an acronym for myristoylated alanine-rich C kinase substrate) proteins play an important role in regulating the structure and mechanical properties of the actin cytoskeleton by cross-linking actin filaments. We have recently reported that peptides corresponding to the effector domain of MARCKS proteins promote actin polymerization and cause massive bundling of actin filaments. We now investigate the effect of MARCKS-related protein, a 20-kDa member of the MARCKS family, on both filament structure and the kinetics of actin polymerization in vitro. Our experiments document that MRP binds to F-actin with micromolar affinity and that the myristoyl chain at the N-terminus of MRP is not required for this interaction. In marked contrast to the effector peptide, binding of MRP is not accompanied by an acceleration of actin polymerization kinetics, and we also could not reliably observe an actin cross-linking activity of MRP.

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.

Interaction between actin and the effector peptide of MARCKS-related protein. Identification of functional amino acid segments

It is widely assumed that the members of the MARCKS protein family, MARCKS (an acronym for myristoylated alanine-rich C kinase substrate) and MARCKS-related protein (MRP), interact with actin via their effector domain, a highly basic segment composed of 24-25 amino acid residues. To clarify the mechanisms by which this interaction takes place, we have examined the effect of a peptide corresponding to the effector domain of MRP, the so-called effector peptide, on both the dynamic and the structural properties of actin. We show that in the absence of cations the effector peptide polymerizes monomeric actin and causes the alignment of the formed filaments into bundle-like structures. Moreover, we document that binding of calmodulin or phosphorylation by protein kinase C both inhibit the actin polymerizing activity of the MRP effector peptide. Finally, several effector peptides were synthesized in which positively charged or hydrophobic segments were deleted or replaced by alanines. Our data suggest that a group of six positively charged amino acid residues at the N-terminus of the peptide is crucial for its interaction with actin. While its actin polymerizing activity critically depends on the presence of all three positively charged segments of the peptide, hydrophobic amino acid residues rather modulate the polymerization velocity.

Macrophage-enriched myristoylated alanine-rich C kinase substrate and its phosphorylation is required for the phorbol ester-stimulated diffusion of beta 2 integrin molecules

An early event of beta(2) integrin activation is the increased diffusion rate of this molecule on the cell surface, thereby providing integrin molecules with a better chance to meet the ligands. The activation of protein kinase C (PKC) stimulates integrin diffusion by releasing the cytoskeletal constraint on integrin molecules. We report here that macrophage-enriched myristoylated alanine-rich C kinase substrate (MacMARCKS), a membrane-associated PKC substrate involved in integrin activation, is required for this PKC-stimulated diffusion of integrin molecules. Using the single-particle tracking technique, we observed that the activation of PKC stimulated an 11-fold increase in the diffusion rate of beta(2) integrins in wild type J774 macrophage cells but not in those expressing mutant MacMARCKS. Further evidence is provided from a MacMARCKS-deficient cell line in which phorbol esters failed to stimulate the diffusion of integrin. Transfection of wild type MacMARCKS into these cells restored the rapid diffusion rate of the beta(2) integrins. The phosphorylation of MacMARCKS is important because transfection of a nonphosphorylatable MacMARCKS mutant or the addition of staurosporine eliminates the rapid diffusion rate of integrin. Furthermore, adding cytochalasin D bypasses the MacMARCKS deficiency and stimulates beta(2) integrin diffusion, suggesting that MacMARCKS's involvement in integrin activation is prior or at the site of cytoskeleton. Therefore, we conclude that MacMARCKS is required for releasing the cytoskeletal constraint on integrin molecules during PKC-mediated integrin activation.

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

To evaluate the role of MacMARCKS, a major substrate of protein kinase C, in cell adhesion, we selected a macrophage cell line, Wehi 274.1.7. Although surface expression of beta2-integrins can be detected on these cells, they lack the phorbol ester- or chemokine-induced adhesion to ICAM-1-coated surface, an event mediated by beta2-integrins. Concomitantly, these cells lack expression of both MacMARCKS and its homologue, MARCKS. When wild type MacMARCKS was expressed in these cells, the phorbol ester-induced adhesion to ICAM-1-coated surface increased approximately 5-fold compared to vector transfected control cells. To further investigate the potential physiological role of MacMARCKS in this adhesion event, we also tested the effect of monocyte chemotactic protein-1, and a 3-fold increase in the adhesion to ICAM-1-coated surface was observed with MacMARCKS-transfected cells. Therefore, these data suggest that MacMARCKS is an essential component in regulating cell adhesion.

Phosphorylated form of MacMARCKS is essential to LFA-1-dependent cell-cell adhesion of U937 monocytic cells

MacMARCKS (MRP, F52), a protein kinase C (PKC) substrate, is involved in the activation of beta2-integrin. To determine the role of the PKC-mediated phosphorylation of MacMARCKS in this process, human U937 monocytic cells were transfected with cDNAs encoding wild type or mutant MacMARCKS. We observed that the expression of the exogenous wild type MacMARCKS greatly enhanced LFA-1-mediated cell-cell adhesion in U937 cells treated with phorbol 12-myristate 13-acetate (PMA). This MacMARCKS-stimulated adhesion depended on the phosphorylation status of MacMARCKS: whereas phosphorylated MacMARCKS enhanced adhesion, unphosphorylated MacMARCKS inhibited it. However, phosphorylated MacMARCKS alone could not induce LFA-1-mediated cell-cell adhesion unless phorbol esters were added, suggesting that the phosphorylation of other proteins might also be involved. Okadaic acid, a phosphatase inhibitor, induced LFA-1-mediated cell-cell adhesion only in the cells expressing wild type or phosphorylated MacMARCKS and not in the cells expressing unphosphorylated MacMARCKS. Therefore, we conclude that the phosphorylated form of MacMARCKS is essential to LFA-1-mediated cell-cell adhesion.

Actin cytoskeleton organization in response to integrin-mediated adhesion

Cell matrix adhesion regulates actin cytoskeleton organization through distinct steps, from formation of filopodia and lamellipodia in the early phases of cell adhesion to organization of focal adhesions and stress fibers in fully adherent cells. In this review, we follow the events induced by integrin-mediated adhesion, such as activation of GTPases Cdc42 and Rac and their effectors and their role in actin polymerization leading to formation of lamellipodia and filopodia and cell spreading. We also show that actin stress fiber and focal adhesion formation following adhesion requires cooperation between integrin-mediated signaling and additional stimuli, including activation of PKC, Rho GTPases, and PTKs such as p125Fak and Src.

MARCKS-related protein (MRP) is a substrate for the Leishmania major surface protease leishmanolysin (gp63)

Myristoylated alanine-rich C kinase substrate (MARCKS) and MARCKS-related protein (MRP; MacMARCKS) are protein kinase C substrates in diverse cell types. Activation of murine macrophages by cytokines increases MRP expression, but infection with Leishmania promastigotes during activation results in MRP depletion. We therefore examined the effect of Leishmania major LV39 on recombinant MRP. Both live promastigotes and a soluble fraction of LV39 lysates degraded MRP to yield lower molecular weight fragments. Degradation was independent of MRP myristoylation and was inhibited by protein kinase C-dependent phosphorylation of MRP. MRP was similarly degraded by purified leishmanolysin (gp63), a Leishmania surface metalloprotease. Degradation was evident at low enzyme/substrate ratios, over a broad pH range, and was inhibited by 1,10-phenanthroline and by a hydroxamate dipeptide inhibitor of leishmanolysin. Using mass spectrometric analysis, cleavage was shown to occur within the effector domain of MRP between Ser(92) and Phe(93), in accordance with the substrate specificity of leishmanolysin. Moreover, an MRP construct in which the effector domain had been deleted was resistant to cleavage. Thus, Leishmania infection may result in leishmanolysin-dependent hydrolysis of MRP, a major protein kinase C substrate in macrophages.

Integrin signalling in neutrophils and macrophages

Integrins have been characterized extensively as adhesion receptors capable of transducing signals inside the cell. In myelomonocytic cells, integrin-mediated adhesive interactions regulate different selective cell responses, such as transmigration into the inflammatory site, cytokine secretion, production or reactive oxygen intermediates, degranulation and phagocytosis. In the last few years, great progress has been made in elucidating mechanisms of signal transduction by integrins in neutrophils and macrophages. This review summarises the current information on the role of integrins in regulating myelomonocytic cell functions and highlights the signalling pathways activated by integrin engagement in these cells. Also, exploiting the current knowledge of mechanisms of integrin signal transduction in other cell types, we propose a model to explain how integrins transduce signals inside neutrophils and macrophages, and how signaling pathways leading to regulation of selective cell functions may be coordinated.

Phagocytic and macropinocytic activity in MARCKS-deficient macrophages and fibroblasts

Macrophages express high levels of the myristoylated, alanine-rich, C kinase substrate (MARCKS), an actin cross-linking protein. To investigate a possible role of MARCKS in macrophage function, fetal liver-derived macrophages were generated from wild-type and MARCKS knockout mouse embryos. No differences between the wild-type and MARCKS-deficient macrophages with respect to morphology (Wright's stain) or actin distribution (staining with rhodamine-phalloidin, under basal conditions or after treatment with phorbol esters, lipopolysaccharide, or both) were observed. We then evaluated phagocytosis mediated by different receptors: Fc receptors tested with IgG-coated sheep red blood cells, complement C3b receptors tested with C3b-coated yeast, mannose receptors tested with unopsonized zymosan, and nonspecific phagocytosis tested with latex beads. We also studied fluid phase endocytosis in macrophages and mouse embryo fibroblasts by using FITC-dextran to quantitate this process. In most cases, there were no differences between the cells derived from wild-type and MARCKS-deficient mice. However, a minor but significant and reproducible difference in rates of zymosan phagocytosis at 45-60 min was observed, with lower rates of phagocytosis in the MARCKS-deficient cells. Our data indicate that MARCKS deficiency may lead to slightly decreased rates of zymosan phagocytosis.

Down-regulation of MARCKS-related protein (MRP) in macrophages infected with Leishmania

Leishmania, a protozoan parasite of macrophages, has been shown to interfere with host cell signal transduction pathways including protein kinase C (PKC)-dependent signaling. Myristoylated alanine-rich C kinase substrate (MARCKS) and MARCKS-related protein (MRP, MacMARCKS) are PKC substrates in diverse cell types. MARCKS and MRP are thought to regulate the actin network and thereby participate in cellular responses involving cytoskeletal rearrangement. Because MRP is a major PKC substrate in macrophages, we examined its expression in response to infection by Leishmania. Activation of murine macrophages by cytokines increased MRP expression as determined by Western blot analysis. Infection with Leishmania promastigotes at the time of activation or up to 48 h postactivation strongly decreased MRP levels. Leishmania-dependent MRP depletion was confirmed by [3H]myristate labeling and by immunofluorescence microscopy. All species or strains of Leishmania parasites tested, including lipophosphoglycan-deficient Leishmania major L119, decreased MRP levels. MRP depletion was not obtained with other phagocytic stimuli including zymosan, latex beads, or heat-killed Streptococcus mitis, a Gram-positive bacterium. Experiments with [3H]myristate labeled proteins revealed the appearance of lower molecular weight fragments in Leishmania-infected cells suggesting that MRP depletion may be due to proteolytic degradation.

MacMARCKS is not essential for phagocytosis in macrophages

MacMARCKS (also known as myristoylated alanine-rich protein kinase C substrate (MARCKS)-related protein) is a member of the MARCKS family of protein kinase C substrates. MacMARCKS contains within it a basic effector domain that contains the serine residues that are phosphorylated by protein kinase C, as well as a calcium/calmodulin and actin-binding site. Two previous reports demonstrated that a macrophage cell line expressing a mutant form of MacMARCKS that lacks the effector domain is defective in phagocytosis and cell adhesion (Zhu, Z., Bao, Z., and Li, J. (1995) J. Biol. Chem. 270, 17652-17655; Li, J., Zhu, Z., and Bao, Z. (1996) J. Biol. Chem. 271, 12985-12990). We report here that macrophages from MacMARCKS null mice phagocytose and spread normally. Thus, although MacMARCKS is recruited to phagosomes, it is not absolutely required for phagocytosis.

Lipopolysaccharide induction of MARCKS-related protein and cytokine secretion are differentially impaired in microglia from LPS-nonresponsive (C3H/HeJ) mice

Many events involved in activation of microglia and leukocytes by lipopolysaccharide (LPS) are mediated by protein kinase C (PKC), and we have recently demonstrated that a major PKC substrate, MARCKS-related protein (MRP), is selectively induced by LPS in murine microglia. In microglia from LPS-nonresponsive (C3H/HeJ) mice, induction of MRP and secretion of CSF-1 required much higher LPS concentrations (> or = 100 ng/ml) than in normal (C3H/OuJ) microglia (< or = 10 ng/ml). By contrast, TNF alpha production was not significantly increased in C3H/HeJ microglia even at 1 microgram LPS/ml. Microglia expressed PKC isoforms alpha, beta, delta, and zeta (but not gamma and epsilon); PKC isoform levels were similar in both normal and C3H/HeJ microglia and no significant change in response to LPS was noted. Our results indicate that LPS alters PKC substrate (rather than kinase) expression, and that the Lpsd mutation in C3H/HeJ mice differentially affects regulation of several gene products implicated in microglial function.

Transgenic complementation of MARCKS deficiency with a nonmyristoylatable, pseudo-phosphorylated form of MARCKS: evidence for simultaneous positive and dominant-negative effects on central nervous system development

MARCKS is a widely expressed protein kinase C substrate that is essential for normal prenatal development of the central nervous system in mice. MARCKS-deficient mice exhibit universal perinatal mortality and numerous developmental abnormalities of the brain and retina. To determine which domains of the protein were important in complementing these neurodevelopmental anomalies, we have interbred MARCKS knockout mice with transgenic mice expressing an epitope-tagged human MARCKS transgene that can completely correct the MARCKS-deficient phenotype. Previous structure-function studies showed that a nonmyristoylatable form of MARCKS could correct all of the neuroanatomical abnormalities, and resulted in approximately 25% viable pups that grew to adulthood and were fertile. The present experiment attempted a similar complementation strategy in which a nonmyristoylatable, "pseudo-phosphorylated" form of the protein was used, which has been shown to be almost completely cytosolic in cell expression studies. Surprisingly, this transgene was able to complement almost all of the cerebral anatomical abnormalities characteristic of the knockout mice. However, these mice also exhibited a universal, novel phenotype: profound retinal ectopia, in which retinal tissue was often found in the vitreous humor as well as extraocularly. Retrospective evaluation of the original MARCKS knockout phenotype revealed that this anomaly was present in about 43% of the knockout mice, and was clearly detectable as early as embryonic day 12.5, before retinal cell differentiation begins. These data suggest that a nonmyristoylatable, pseudo-phosphorylated form of MARCKS can complement most if not all cerebral aspects of the MARCKS-deficient phenotype, but that it appears to worsen a retinal phenotype, perhaps by exerting a dominant-negative effect on a coexpressed MARCKS homologue.

Modulation of hepatocyte growth factor-induced scattering of HT29 colon carcinoma cells. Involvement of the MAPK pathway

Hepatocyte growth factor (HGF)/scatter factor modulates the motility of HT29 colon carcinoma cells in vitro by inducing morphological changes that depend on the type of extra-cellular matrix (ECM) ligand; HGF-induced scattering of HT29 cells is observed if cells are grown on plastic coated with serum proteins but not laminin. The absence of scattering correlates with a lack of cell spreading on laminin and it is not due to impaired HGF induced tyrosine phosphorylation of the E-cadherin/desmosome component, (gamma)-catenin, or lack of activation of mitogen activated protein kinase (MAPK). Treatment of HT29 cells with phorbol 12-myristate, 13-acetate (PMA), but not arachidonic acid, restored the ability of the cells to spread on laminin in an integrin-dependent manner. Moreover, the addition of both PMA and HGF restored the ability of these cells to scatter on laminin in a synergistic manner. This event correlated with increased tyrosine phosphorylation of paxillin and activation of MAPK. Moreover, when the MEK (MAPK kinase)/MAPK pathway was blocked by the MEK inhibitor PD098059, HGF-induced scattering of HT29 cells was blocked. Thus, HGF modulation of HT29 cell motility is regulated by both integrin and growth factor-dependent signaling and implicates MAPK in the modulation of intercellular adhesion and epithelial cell motility.

The major myristoylated PKC substrate (MARCKS) is involved in cell spreading, tyrosine phosphorylation of paxillin, and focal contact formation

The expression of the myristoylated PKC substrate MARCKS is reduced in tumor-derived choroidal melanoma cells (OCM-1). We transfected the OCM-1 cells with MARCKS cDNA and we selected clones with stable overexpression of the protein. Tyrosine phosphorylation of paxillin, a biochemical marker of focal contact formation, was conserved upon serum starvation when MARCKS was overexpressed, while it was almost abolished in the control cells. Immunofluorescent labelling of paxillin and vinculin, another component of focal contact, revealed that these structures were conserved upon serum starvation when MARCKS was overexpressed but not in the control cells. Furthermore, the cell morphology was affected by the ectopic expression of MARCKS, leading to increased spreading and formation of membrane processes. These data suggest the involvement of MARCKS in cell spreading and focal contact formation.

A three-dimensional collagen lattice induces protein kinase C-zeta activity: role in alpha2 integrin and collagenase mRNA expression

A three-dimensional collagen lattice can provide skin fibroblasts with a cell culture environment that simulates normal dermis. Such a collagen matrix environment regulates interstitial collagenase (type I metalloproteinase [MMP-1], collagenase-1) and collagen receptor alpha2 subunit mRNA expression in both unstimulated or platelet-derived growth factor-stimulated dermal fibroblasts (Xu, J., and R.A.F. Clark. 1996. J. Cell Biol. 132:239-249). Here we report that the collagen gel can signal protein kinase C (PKC)-zeta activation in human dermal fibroblasts. An in vitro kinase assay demonstrated that autophosphorylation of PKC-zeta immunoprecipitates was markedly increased by a collagen matrix. In contrast, no alteration in PKC-zeta protein levels or intracellular location was observed. DNA binding activity of nuclear factor kappaB (NF-kappaB), a downstream regulatory target of PKC-zeta, was also increased by fibroblasts grown in collagen gel. The composition of the NF-kappaB/Rel complexes that contained p50, was not changed. The potential role of PKC-zeta in collagen gel-induced mRNA expression of collagen receptor alpha2 subunit and human fibroblast MMP-1 was assessed by the following evidence. Increased levels of alpha2 and MMP-1 mRNA in collagen gel-stimulated fibroblasts were abrogated by bisindolylmaleimide GF 109203X and calphostin C, chemical inhibitors for PKC, but retained when cells were depleted of 12-myristate 13-acetate (PMA)-inducible PKC isoforms by 24 h of pretreatment with phorbol PMA. Antisense oligonucleotides complementary to the 5' end of PKC-zeta mRNA sequences significantly reduced the collagen lattice-stimulated alpha2 and MMP-1 mRNA levels. Taken together, these data indicate that PKC-zeta, a PKC isoform not inducible by PMA or diacylglycerol, is a component of collagen matrix stimulatory pathway for alpha2 and MMP-1 mRNA expression. Thus, a three-dimensional collagen lattice maintains the dermal fibroblast phenotype, in part, through the activation of PKC-zeta.