Effects of Extracellular Matrix on Cytoskeletal and Myofibrillar Organization in vitro

The distribution and three-dimensional relationship of myofibrillar and cytoskeletal components during myofibrillogenesis were examined in preparations of neonatal rat cardiac myocytes processed in parallel for scanning electron microscopy (SEM), intermediate voltage transmission electron microscopy (IVEM) and immunofluorescence (IF). Of the various methods used for processing, optimal results were achieved by pre-extraction with Triton X-100 in an actin-stabilizing buffer. This procedure effectively removed the surface membrane, as viewed by SEM images, while preserving myofibrillar and cytoskeletal structure, as evidenced by IF for actin, -actinin and vinculin. Cytoskeletons in SEM images consisted of a cortex of anastomosing filaments through which ran parallel filament bundles oriented in the long axis of the cell and attached aiong their length to the substrate by numerous fine filaments. In IVEM images, myofibrils were laterally connected at the level of the Z bands. Myocytes grown on different extracellular matrices showed different patterns and distributions of both striated myofibrils and focal adhesions, as determined by IF for -actinin and vinculin, respectively. Cells on collagen I and III contained striated myofibrils which extended to the cell perimeters where focal adhesions were predominately located. Cells on laminin and fibronectin matrices exhibited myofibrils and focal adhesions more centrally located. In addition, cells on laminin contained circumferential arcs of filaments near the cell periphery

Identification of Fibroblasts as a Major Site of Albumin Catabolism in Peripheral Tissues

Rat serum albumin has been labeledw ith dilactitollZ5I- tyramine,( 12‘I-DLT) a radioactive tracer which remains entrappedw ithin lysosomes following cellular uptake and degradation of the carrier protein. Similar kinetics of clearance from the rat circulation were observed for albumin labeled conventionally with lZsI or 12‘I-DLT-albumin, both proteinhsa ving circulating half-lives of -2.2 days. In contrast, the recovery of whole body radioactivity had half-lives of -2.2 and 5.1 days, respectively, for the two protein preparations, indicating substantial retention of degradation products derived from catabolism of ”‘I-DLT-albumin. Measurement of total and acid-soluble radioactivity in tissues 2 or 4 days after injection of ”‘1-DLTalbumin revealed that skin and muscle accounted for the largest fraction( 50-60%)o f degradation products in the body. Fibroblaswtse re identified by autoradiography as the major cell type containing radioactive degradation products in skin and muscle. Fibroblasts were isolated from skin by collagenase digestion, followed by density gradient centrifugation. The amount of acid-soluble radioactivity recovered in these cells was in excellent agreement with that predicted based on acid precipitation of solubilized wholsek in preparations. These studies demonstrate for the first time that fibroblasts are a major cell type involved in the degradation of albuminin vivo

Hypertrophic Stimulation Increases β-actin Dynamics in Adult Feline Cardiomyocytes

The myocardium responds to hemodynamic stress through cellular growth and organ hypertrophy. The impact of cytoskeletal elements on this process, however, is not fully understood. While α-actin in cardiomyocytes governs muscle contraction in combination with the myosin motor, the exact role of β-actin has not been established. We hypothesized that in adult cardiomyocytes, as in non-myocytes, β-actin can facilitate cytoskeletal rearrangement within cytoskeletal structures such as Z-discs. Using a feline right ventricular pressure overload (RVPO) model, we measured the level and distribution of β-actin in normal and pressure overloaded myocardium. Resulting data demonstrated enriched levels of β-actin and enhanced translocation to the Triton-insoluble cytoskeletal and membrane skeletal complexes. In addition, RVPO in vivo and in vitro hypertrophic stimulation with endothelin (ET) or insulin in isolated adult cardiomyocytes enhanced the content of polymerized fraction (F-actin) of β-actin. To determine the localization and dynamics of β-actin, we adenovirally expressed GFP-tagged β-actin in isolated adult cardiomyocytes. The ectopically expressed β-actin-GFP localized to the Z-discs, costameres, and cell termini. Fluorescence recovery after photobleaching (FRAP) measurements of β-actin dynamics revealed that β-actin at the Z-discs is constantly being exchanged with β-actin from cytoplasmic pools and that this exchange is faster upon hypertrophic stimulation with ET or insulin. In addition, in electrically stimulated isolated adult cardiomyocytes, while β-actin overexpression improved cardiomyocyte contractility, immunoneutralization of β-actin resulted in a reduced contractility suggesting that β-actin could be important for the contractile function of adult cardiomyocytes. These studies demonstrate the presence and dynamics of β-actin in the adult cardiomyocyte and reinforce its usefulness in measuring cardiac cytoskeletal rearrangement during hypertrophic stimulation

Blood vessels as targets in tumor therapy

The landmark papers published by Judah Folkman in the early 1970s on tumor angiogenesis and therapeutic implications promoted the rapid development of a very dynamic field where basic scientists, oncologists, and pharmaceutical industry joined forces to determine the molecular mechanisms in blood vessel formation and find means to exploit this knowledge in suppressing tumor vascularization and growth. A wealth of information has been collected on angiogenic growth factors, and in 2004 the first specific blood vessel-targeted cancer therapy was introduced: a neutralizing antibody against vascular endothelial growth factor (VEGF). Now (2011) we know that suppression of tumor angiogenesis may be a double-edged sword and that the therapy needs to be further refined and individualized. This review describes the hallmarks of tumor vessels, how different angiogenic growth factors exert their function, and the perspectives for future development of anti-angiogenic therapy

Cadmium Induces p53-Dependent Apoptosis in Human Prostate Epithelial Cells

Cadmium, a widespread toxic pollutant of occupational and environmental concern, is a known human carcinogen. The prostate is a potential target for cadmium carcinogenesis, although the underlying mechanisms are still unclear. Furthermore, cadmium may induce cell death by apoptosis in various cell types, and it has been hypothesized that a key factor in cadmium-induced malignant transformation is acquisition of apoptotic resistance. We investigated the in vitro effects produced by cadmium exposure in normal or tumor cells derived from human prostate epithelium, including RWPE-1 and its cadmium-transformed derivative CTPE, the primary adenocarcinoma 22Rv1 and CWR-R1 cells and LNCaP, PC-3 and DU145 metastatic cancer cell lines. Cells were treated for 24 hours with different concentrations of CdCl2 and apoptosis, cell cycle distribution and expression of tumor suppressor proteins were analyzed. Subsequently, cellular response to cadmium was evaluated after siRNA-mediated p53 silencing in wild type p53-expressing RWPE-1 and LNCaP cells, and after adenoviral p53 overexpression in p53-deficient DU145 and PC-3 cell lines. The cell lines exhibited different sensitivity to cadmium, and 24-hour exposure to different CdCl2 concentrations induced dose- and cell type-dependent apoptotic response and inhibition of cell proliferation that correlated with accumulation of functional p53 and overexpression of p21 in wild type p53-expressing cell lines. On the other hand, p53 silencing was able to suppress cadmium-induced apoptosis. Our results demonstrate that cadmium can induce p53-dependent apoptosis in human prostate epithelial cells and suggest p53 mutation as a possible contributing factor for the acquisition of apoptotic resistance in cadmium prostatic carcinogenesis

The many facets of the matricelluar protein periostin during cardiac development, remodeling, and pathophysiology

Periostin is a member of a growing family of matricellular proteins, defined by their ability to interact with components of the extracellular milieu, and with receptors at the cell surface. Through these interactions, periostin has been shown to play a crucial role as a profibrogenic molecule during tissue morphogenesis. Tissues destined to become fibrous structures are dependent on cooperative interactions between periostin and its binding partners, whereas in its absence, these structures either totally or partially fail to become mature fibrous entities. Within the heart, fibrogenic differentiation is required for normal tissue maturation, remodeling and function, as well as in response to a pathological myocardial insult. In this review, aspects related to the function of periostin during cardiac morphogenesis, remodeling and pathology are summarized