Mactinin treatment promotes wound-healing-associated inflammation in urokinase knockout mice

Mechanisms of antitumor and immune-enhancing activities of MUC1/sec, a secreted form of mucin-1

Mucin 1 (MUC1) is a polymorphic type 1 transmembrane protein found on the apical surface of normal cells lining the lumen of ducts and glands. Mucins are thought to provide mucosal protection from environmental exposures and carcinogens. An altered form of the MUC1 glycoprotein, which is hypoglycosylated, is expressed in several types of human cancers. In our laboratory, we have found that transfection of a murine mammary tumor cell line with a human secreted isoform of MUC1 rendered these DA-3 cells (DA-3/sec) incapable of growing in intact BALB/c mice. In contrast, implantation of DA-3 cells transfected with the human transmembrane isoform of MUC1 (DA-3/TM), resulted in tumor formation and ultimately death of the animals, similar to the DA-3 parental line. Importantly, inoculation of the DA-3/sec cells in immunodeficient nude mice resulted in tumor formation, indicating that the MUC1/sec molecule's antitumor activity is immunologically controlled. In this review, we summarize the studies we have performed to elucidate possible mechanisms for the immune-mediated antitumor effect of MUC1/sec and/or a unique peptide present in this mucin. Understanding these mechanisms may provide new immunotherapeutic approaches that could be used to target different types of cancer.

Hepatitis B virus inhibits liver regeneration via epigenetic regulation of urokinase-type plasminogen activator

Liver regeneration after liver damage caused by toxins and pathogens is critical for liver homeostasis. Retardation of liver proliferation was reported in hepatitis B virus (HBV) X protein (HBx)-transgenic mice. However, the underlying mechanism of the HBx-mediated disturbance of liver regeneration is unknown. We investigated the molecular mechanism of the inhibition of liver regeneration using liver cell lines and a mouse model. The mouse model of acute HBV infection was established by hydrodynamic injection of viral DNA. Liver regeneration after partial hepatectomy was significantly inhibited in the HBV DNA-treated mice. Mechanism studies have revealed that the expression of urokinase-type plasminogen activator (uPA), which regulates the activation of hepatocyte growth factor (HGF), was significantly decreased in the liver tissues of HBV or HBx-expressing mice. The down-regulation of uPA was further confirmed using liver cell lines transiently or stably transfected with HBx and the HBV genome. HBx suppressed uPA expression through the epigenetic regulation of the uPA promoter in mouse liver tissues and human liver cell lines. Expression of HBx strongly induced hypermethylation of the uPA promoter by recruiting DNA methyltransferase (DNMT) 3A2.

CONCLUSION

Taken together, these results suggest that infection of HBV impairs liver regeneration through the epigenetic dysregulation of liver regeneration signals by HBx.

Suppression of uPA and uPAR blocks radiation-induced MCP-1 mediated recruitment of endothelial cells in meningioma

Chemokines play a vital role in recruiting various cell types in the process of tissue repair. Radiation, a major therapeutic modality in cancer treatment, has been described to induce inflammatory response that might lead to the expression of several chemokines. In the present study, we investigated the mechanism of monocyte chemoattractant protein-1 (MCP-1) induction by radiation in meningioma cell lines and the paracrine effect on human microvascular endothelial cells (HMEC). After radiation, meningioma cell lines (IOMM Lee and SF-3061) showed an increased expression of MCP-1. In addition, irradiated meningioma cancer cell conditioned medium (CM) showed an increased ability to attract HMEC and to stimulate MCP-1-induced protein (MCPIP), VEGF and angiogenin expression in HMEC. This chemotactic activity and angiogenic stimulator effect on HMEC were almost abrogated by depleting MCP-1 from the irradiated cancer cell CM. Further, inhibition of either ERK activation/expression or NF-κB nuclear translocation hindered radiation-induced MCP-1 expression in both meningioma cell lines. Further, supplementing cancer cells with exogenous ATF-uPA (with and without radiation) activated ERK phosphorylation, nuclear translocation of the NF-κB p65 sub-unit (Rel-A), and MCP-1 expression. Downregulation of uPA and uPAR, simultaneously by transfecting the cancer cells with bi-cistronic siRNA-expressing plasmid (pU) inhibited radiation-induced ERK activation, nuclear translocation of Rel-A, NF-κB DNA binding activity, and MCP-1 expression. In addition, pU-transfected cancer cells (with or without radiation) reduced radiation-induced MCP-1 and blocked the recruitment of other cell types during the inflammatory process induced by radiation both in in vitro and in vivo conditions.

Urokinase-type plasminogen activator increases hepatocyte growth factor activity required for skeletal muscle regeneration

The plasminogen system plays a crucial role in the repair of a variety of tissues, including skeletal muscle. We hypothesized that urokinase-type plasminogen activator (uPA) promotes muscle regeneration by activating hepatocyte growth factor (HGF), which, in turn, stimulates proliferation of myoblasts required for regeneration. In our studies, levels of active HGF and phosphorylation of the HGF receptor c-met were increased after muscle injury in wild-type mice. Compared with wild-type animals, mice deficient in uPA (uPA(-/-)) had markedly reduced HGF levels and c-met activation after muscle damage. This reduced HGF activity in uPA(-/-) animals was associated with decreased cell proliferation, myoblast accumulation, and new muscle fiber formation. On the other hand, HGF activity was enhanced at early time points in PAI-1(-/-) mice compared with wild-type mice and the PAI-1(-/-) animals exhibited accelerated muscle fiber regeneration. Furthermore, administration of exogenous uPA rescued HGF levels and muscle regeneration in uPA(-/-) mice, and an HGF-blocking antibody reduced HGF activity and muscle regeneration in wild-type mice. We also found that uPA promotes myoblast proliferation in vitro through its proteolytic activity, and this process was inhibited by an HGF-blocking antibody. Together, our findings demonstrate that uPA promotes muscle regeneration through HGF activation and subsequent myoblast proliferation.

Mactinin, a fragment of cytoskeletal alpha-actinin, is a novel inducer of heat shock protein (Hsp)-90 mediated monocyte activation

Background

Monocytes, their progeny such as dendritic cells and osteoclasts and products including tumor necrosis factor (TNF)-α, interleukin (IL)-1α and IL-1β play important roles in cancer, inflammation, immune response and atherosclerosis. We previously showed that mactinin, a degradative fragment of the cytoskeletal protein α-actinin, is present at sites of monocytic activation in vivo, has chemotactic activity for monocytes and promotes monocyte/macrophage maturation. We therefore sought to determine the mechanism by which mactinin stimulates monocytes.

Results

Radiolabeled mactinin bound to a heterocomplex on monocytes comprised of at least 3 proteins of molecular weight 88 kD, 79 kD and 68 kD. Affinity purification, mass spectroscopy and Western immunoblotting identified heat shock protein (Hsp)-90 as the 88 kD component of this complex. Hsp90 was responsible for mediating the functional effects of mactinin on monocytes, since Hsp90 inhibitors (geldanamycin and its analogues 17-allylamino-17-demethoxygeldanamycin [17-AAG] and 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin [17-DMAG]) almost completely abrogated the stimulatory activity of mactinin on monocytes (production of the pro-inflammatory cytokines IL-1α, IL-1β and TNF-α, as well as monocyte chemotaxis).

Conclusion

Mactinin is a novel inducer of Hsp90 activity on monocytes and may serve to perpetuate and augment monocytic activation, thereby functioning as a "matrikine." Blockage of this function of mactinin may be useful in diseases where monocyte/macrophage activation and/or Hsp90 activity are detrimental.

Macrophage roles following myocardial infarction

Following myocardial infarction (MI), circulating blood monocytes respond to chemotactic factors, migrate into the infarcted myocardium, and differentiate into macrophages. At the injury site, macrophages remove necrotic cardiac myocytes and apoptotic neutrophils; secrete cytokines, chemokines, and growth factors; and modulate phases of the angiogenic response. As such, the macrophage is a primary responder cell type that is involved in the regulation of post-MI wound healing at multiple levels. This review summarizes what is currently known about macrophage functions post-MI and borrows literature from other injury and inflammatory models to speculate on additional roles. Basic science and clinical avenues that remain to be explored are also discussed.

Urokinase-type plasminogen activator plays essential roles in macrophage chemotaxis and skeletal muscle regeneration

Although macrophages are thought to play important roles in tissue repair, the molecular mechanisms involved remain to be elucidated. Mice deficient in urokinase-type plasminogen activator (uPA-/-) exhibit decreased accumulation of macrophages following muscle injury and severely impaired muscle regeneration. We tested whether macrophage-derived uPA plays essential roles in macrophage chemotaxis and skeletal muscle regeneration. Macrophage uPA was required for chemotaxis, even when invasion through matrix was not necessary. The mechanism by which macrophage uPA promoted chemotaxis was independent of receptor binding but appeared to depend on proteolytic activity. Exogenous uPA restored chemotaxis to uPA-/- macrophages and rescued muscle regeneration in uPA-/- mice. Macrophage depletion in wild-type (WT) mice using clodronate liposomes resulted in impaired muscle regeneration, confirming that macrophages are required for efficient healing. Furthermore, transfer of WT bone marrow cells to uPA-/- mice restored macrophage accumulation and muscle regeneration. In this rescue, transferred WT cells appeared to contribute to IGF-1 expression but did not fuse to regenerating fibers. These data indicate that WT leukocytes, including macrophages, that express uPA were sufficient to rescue muscle regeneration in uPA-/- mice. Overall, the results indicate that uPA plays a fundamental role in macrophage chemotaxis and that macrophage-derived uPA promotes efficient muscle regeneration.

uPA deficiency exacerbates muscular dystrophy in MDX mice

Duchenne muscular dystrophy (DMD) is a fatal and incurable muscle degenerative disorder. We identify a function of the protease urokinase plasminogen activator (uPA) in mdx mice, a mouse model of DMD. The expression of uPA is induced in mdx dystrophic muscle, and the genetic loss of uPA in mdx mice exacerbated muscle dystrophy and reduced muscular function. Bone marrow (BM) transplantation experiments revealed a critical function for BM-derived uPA in mdx muscle repair via three mechanisms: (1) by promoting the infiltration of BM-derived inflammatory cells; (2) by preventing the excessive deposition of fibrin; and (3) by promoting myoblast migration. Interestingly, genetic loss of the uPA receptor in mdx mice did not exacerbate muscular dystrophy in mdx mice, suggesting that uPA exerts its effects independently of its receptor. These findings underscore the importance of uPA in muscular dystrophy.