Fiber orientation and crimp level might control the auxetic effect of biological tissues

We propose an analytical micromechanical model for studying the lamellar-composite-like structure of fibrous soft tissue. The tissue under consideration is made up of several lamellae, and is designed to resemble the annulus fibrosus (AF) tissue or media layer of arterial tissue, for example. The collagen fibers are arranged in parallel in each lamella and the fiber orientation differs from one lamella to its neighbors. The parallel fibers in each lamella of AF tissue, for example, have been observed to have a crimped microstructure. The proposed model incorporates this quality, considering fiber waviness as a sinusoidal shape and taking into account the fiber dispersion in different layers, where both fiber and matrix are considered as solid phases. We find that collagen-fiber waviness and layer orientation have a significant influence on Poisson's ratio. The effective Poisson's ratio predicted by the proposed model demonstrates that the crimped collagen fiber microstructure might weaken the auxetic effect of fibrous soft tissue, which might explain why, as the literature suggests, the auxetic behavior is more difficult to observe than large Poisson's ratios. As opposed to the many studies that use the well-known hyperelastic fiber-based constitutive model, in which out-of-plane expansion is often observed, the present work explains the auxetic response found in modeling and in experimental data from the perspective of collagen fiber microstructure.

ICAM-1 suppresses tumor metastasis by inhibiting macrophage M2 polarization through blockade of efferocytosis

Efficient clearance of apoptotic cells (efferocytosis) can profoundly influence tumor-specific immunity. Tumor-associated macrophages are M2-polarized macrophages that promote key processes in tumor progression. Efferocytosis stimulates M2 macrophage polarization and contributes to cancer metastasis, but the signaling mechanism underlying this process is unclear. Intercellular cell adhesion molecule-1 (ICAM-1) is a transmembrane glycoprotein member of the immunoglobulin superfamily, which has been implicated in mediating cell–cell interaction and outside-in cell signaling during the immune response. We report that ICAM-1 expression is inversely associated with macrophage infiltration and the metastasis index in human colon tumors by combining Oncomine database analysis and immunohistochemistry for ICAM-1. Using a colon cancer liver metastasis model in ICAM-1-deficient (ICAM-1^−/−) mice and their wild-type littermates, we found that loss of ICAM-1 accelerated liver metastasis of colon carcinoma cells. Moreover, ICAM-1 deficiency increased M2 macrophage polarization during tumor progression. We further demonstrated that ICAM-1 deficiency in macrophages led to promotion of efferocytosis of apoptotic tumor cells through activation of the phosphatidylinositol 3 kinase/Akt signaling pathway. More importantly, coculture of ICAM-1^−/− macrophages with apoptotic cancer cells resulted in an increase of M2-like macrophages, which was blocked by an efferocytosis inhibitor. Our findings demonstrate a novel role for ICAM-1 in suppressing M2 macrophage polarization via downregulation of efferocytosis in the tumor microenvironment, thereby inhibiting metastatic tumor progression.

The critical role of catalase in prooxidant and antioxidant function of p53

The tumor suppressor p53 is an important regulator of intracellular reactive oxygen species (ROS) levels, although downstream mediators of p53 remain to be elucidated. Here, we show that p53 and its downstream targets, p53-inducible ribonucleotide reductase (p53R2) and p53-inducible gene 3 (PIG3), physically and functionally interact with catalase for efficient regulation of intracellular ROS, depending on stress intensity. Under physiological conditions, the antioxidant functions of p53 are mediated by p53R2, which maintains increased catalase activity and thereby protects against endogenous ROS. After genotoxic stress, high levels of p53 and PIG3 cooperate to inhibit catalase activity, leading to a shift in the oxidant/antioxidant balance toward an oxidative status, which could augment apoptotic cell death. These results highlight the essential role of catalase in p53-mediated ROS regulation and suggest that the p53/p53R2-catalase and p53/PIG3-catalase pathways are critically involved in intracellular ROS regulation under physiological conditions and during the response to DNA damage, respectively.

Ribonucleotide reductase small subunit p53R2 suppresses MEK-ERK activity by binding to ERK kinase 2

The p53-dependent RR small subunit (p53R2) protein, a newly identified member of the ribonucleotide reductase family, plays a key role in the p53-dependent cellular response to DNA. Several recent studies have suggested that p53R2 also plays an important role in suppressing the invasive potential of human cancer cells. However, the cellular mechanism that regulates invasiveness remains largely unknown. In this study, we show that p53R2 interacts with MEK2 (extracellular signal-regulated kinase (ERK) kinase 2-mitogen-activated protein kinase (MAPK) kinase 2), the molecule immediately upstream of ERK in the Ras-Raf-MAPK signaling cascade. In co-immunoprecipitation and immunofluorescence analyses, we found that p53R2 and MEK2 interact physically in cultured mammalian cells, and that the p53R2 segment comprising amino acids 161-206 is critical for this interaction. Moreover, serum-induced phosphorylation of MEK1/2 and ERK1/2 was greatly augmented in human cancer cells expressing small-interfering RNA against p53R2. On the other hand, phosphorylation of MEK1/2 and ERK1/2 in human cancer cells was markedly attenuated by overexpression of p53R2. Furthermore, MEK2 was required for p53R2 knockdown-induced enhancement of the invasive ability and anchorage-independent growth of human lung cancer H1299 cells. Taken together, these findings show that p53R2 negatively modulates serum-induced MEK-ERK activity and inhibits the MEK-ERK-mediated malignancy potential of human cancer cells.

[Infection of white spot baculo-like virus(WSBV) in Penaeus chinensis: evidence from electron microscopy and DNA hybridization]

Severe epizootic causing high mortalities in cultivated Penaeus chinensis has occurred every year in mainland China since 1993 with great economic loss. Naturally diseased P. chinensis sampled in Qingdao shrimp farming regions between 1993 and 1998 were examined by electron microscopy. A similar non-occluded nuclear bacilliform virus like the white spot baculo-like virus (WSBV) reported in Taiwan was mostly found in the gill, cuticular epidermis under the exoskeleton, stomach, lymphoid organ and other tissues of ectodermal and mesodermal origin from these diseased samples. The viron was enveloped with a mean size of (125 +/- 7.6) nm x (345 +/- 16) nm. Sometimes, a nipple-like appendage could be found protruding from one extremity of the viron. Envelopes were all lost after purification from cesium chloride gradient ultracentrifugation. The cylindrical nucleocapsid in negatively staining preparations was (80 +/- 13) nm x (380 +/- 24) nm with 13-16 stripes perpendicular to the longitudinal axis of the nucleocapsid. Based on its pathogenic and morphological characteristics, this virus should be related to WSBV. A pair of primers created from information of WSBV genome DNA SalI fragment produced a 355 bp band using the WSBV isolate from P. chinensis in mainland China, as the DNA template. The specific PCR product was cloned, sequenced and labeled with digoxigenin (DIG) DNA labeling kit (Boehringer Mannherm). The sequence of the probe is identical to that of WSBV. All of the sampled diseased shrimps between 1993 and 1998 reacted with the DIG-labeled probe by dot-blot hybridization and no hybridization was observed using DNA from health shrimp as templates. These results based on electron microscopy and DNA hybridization indicated that the shrimp epizootic occurred in mainland China was related to the WSBV infection previously occurred in Taiwan early 1992.

Absence of the microsatellite mutator phenotype in human bronchial epithelial cells transformed by alpha particles

The immortalized human bronchial epithelial cell line, BEP2D, can become malignantly transformed following its irradiation with alpha particles. Exposed cells progress through a latent period of eight to ten weeks prior to exhibiting malignant properties. The molecular basis for this delay is unclear, however it is thought to involve a manifestation of genomic instability brought on by ionizing radiation. In this study we addressed whether the microsatellite mutator phenotype which arises in cells that lack mismatch repair function could have played a role in the radiation-induced transformation of BEP2D cells. Three cell lines, including BEP2D and two transformed clonal derivatives, H2BT2L and R30T1L, were examined for the presence of the microsatellite mutator phenotype using a selectable reporter system developed in our laboratory. This reporter system is based on the ability of stably transduced cells to restore the reading frame of a hygromycin B phosphotransferase transferase gene rendered out of frame by the insertion of a (CA)(13) repeat tract immediately downstream of the ATG start codon. The parental BEP2D cell line had a relatively low hygromycin B resistant colony formation frequency of 2.36 x 10(-4). This value was similar to the frequencies of two malignantly transformed derivatives H2BT2L (0.996 x 10(-4)) and R30T1L (1.87 x 10(-4)). We therefore conclude that the H2BT2L and R30T1L cell lines are not deficient in their hMSH2, hMLH1, hPMS2 or hMSH3 mismatch repair gene functions, and that other factors orchestrated the alpha particle induced malignant transformation of H2BT2L and R30T1L cells.