Current Molecular Medicine - Volume 13, Issue 1, 2013

Signaling pathways play a critical role in the maintenance of cellular structure and function. These pathways can act together with synergistic or antagonistic outcome. Cooperative and integrative cellular communication networks, otherwise known as crosstalk can amplify signaling cascades. Here, we focus on receptor crosstalk in the context of cardiovascular pathologies, mainly involving the epidermal growth factor receptor (EGFR), a critical mediator of multiple receptor pathways in normal physiological and pathophysiological processes. Considerable experimental evidence suggests that the uncontrolled expression of EGFR contributes to tumorigenesis through inhibition of apoptosis, angiogenesis, anchorage-independent growth and tumor-associated inflammation. Abnormal activation of the intrinsic tyrosine kinase of EGFR through mutation or overexpression is observed in various human cancer types. On the other hand, the role of EGFR in vascular biology is not well understood. In cardiovascular pathologies, such as atherosclerosis and restenosis, vascular smooth muscle cells (SMCs) migrate and proliferate, contributing to neointima formation, whilst apoptosis may cause plaque instability. EGFR can be transactivated by numerous pathologic stimuli that regulate SMC behaviour. This review describes our current understanding of the role of EGFR in SMC biology and pathology.

Podocyte loss plays a key role in the progression of glomerular disorders towards glomerulosclerosis and chronic kidney disease. Podocytes form unique cytoplasmic extensions, foot processes, which attach to the outer surface of the glomerular basement membrane and interdigitate with neighboring podocytes to form the slit diaphragm. Maintaining these sophisticated structural elements requires an intricate actin cytoskeleton. Genetic, mechanic, and immunologic or toxic forms of podocyte injury can cause podocyte loss, which causes glomerular filtration barrier dysfunction, leading to proteinuria. Cell migration and cell division are two processes that require a rearrangement of the actin cytoskeleton; this rearrangement would disrupt the podocyte foot processes, therefore, podocytes have a limited capacity to divide or migrate. Indeed, all cells need to rearrange their actin cytoskeleton to assemble a correct mitotic spindle and to complete mitosis. Podocytes, even when being forced to bypass cell cycle checkpoints to initiate DNA synthesis and chromosome segregation, cannot complete cytokinesis efficiently and thus usually generate aneuploid podocytes. Such aneuploid podocytes rapidly detach and die, a process referred to as mitotic catastrophe. Thus, detached or dead podocytes cannot be adequately replaced by the proliferation of adjacent podocytes. However, even glomerular disorders with severe podocyte injury can undergo regression and remission, suggesting alternative mechanisms to compensate for podocyte loss, such as podocyte hypertrophy or podocyte regeneration from resident renal progenitor cells. Together, mitosis of the terminally differentiated podocyte rather accelerates podocyte loss and therefore glomerulosclerosis. Finding ways to enhance podocyte regeneration from other sources remains a challenge goal to improve the treatment of chronic kidney disease in the future.

The S100 protein family consists of 24 members functionally distributed into three main subgroups: those that only exert intracellular regulatory effects, those with intracellular and extracellular functions and those which mainly exert extracellular regulatory effects. S100 proteins are only expressed in vertebrates and show cell-specific expression patterns. In some instances, a particular S100 protein can be induced in pathological circumstances in a cell type that does not express it in normal physiological conditions. Within cells, S100 proteins are involved in aspects of regulation of proliferation, differentiation, apoptosis, Ca2+ homeostasis, energy metabolism, inflammation and migration/invasion through interactions with a variety of target proteins including enzymes, cytoskeletal subunits, receptors, transcription factors and nucleic acids. Some S100 proteins are secreted or released and regulate cell functions in an autocrine and paracrine manner via activation of surface receptors (e.g. the receptor for advanced glycation end-products and toll-like receptor 4), G-protein-coupled receptors, scavenger receptors, or heparan sulfate proteoglycans and N-glycans. Extracellular S100A4 and S100B also interact with epidermal growth factor and basic fibroblast growth factor, respectively, thereby enhancing the activity of the corresponding receptors. Thus, extracellular S100 proteins exert regulatory activities on monocytes/macrophages/microglia, neutrophils, lymphocytes, mast cells, articular chondrocytes, endothelial and vascular smooth muscle cells, neurons, astrocytes, Schwann cells, epithelial cells, myoblasts and cardiomyocytes, thereby participating in innate and adaptive immune responses, cell migration and chemotaxis, tissue development and repair, and leukocyte and tumor cell invasion.

Tumor cells release microvesicles (MVs) that may remain in the extracellular space in proximity to the cell of origin, or that may migrate to distant sites by entering biological fluids. Increasing evidence indicates that MVs are mediators of cell-to-cell communication which are able to deliver specific signals, both within the tumor microenvironment and in the long-range. MVs are able to transfer bioactive lipids and proteins, including oncogene products and receptors, from the cell of origin to recipient cell. In addition, MVs may induce epigenetic changes in recipient cells by transferring genetic information in the form of mRNA, microRNA and oncogenes. Several changes in the phenotype and function that occur in stromal cells within the cancer microenvironment have been ascribed to tumor cell-derived MVs. In this review we discuss the various biological actions of tumor-derived MVs and their potential role in tumor biology.

Numerous reviews in the field of NK cell biology dictate the pivotal role that NK cells play in tumor rejection. Although these cell types were originally described based on their cytotoxic ability, we now know that NK cells are not naturally born to kill. Both cellular interactions and the local environment in which the NK cell resides in may influence its cytotoxic functions. Just as organ specific NK cells have distinct phenotypic and functional differences, the tumor is a unique microenvironment in itself. The NK cells originally recruited to the tumor site are able to stimulate immune responses and aid in tumor destruction but eventually become persuaded otherwise by mechanisms of immunosuppression. Here, we review potential mechanisms and players involved in NK cell immunosuppression. In particular the effects of another innate immune player, macrophages, will be addressed in augmenting immunosuppression of NK cells within tumors. Tumorassociated macrophages (TAMs) are the main regulatory population of myeloid cells in the tumor and are characterized by their ability to promote tumor cell proliferation and metastasis. In addition, they express/release immunoregulatory factors which have been shown to directly inhibit NK cell function. Understanding how these two cell types interact in the distinct tumor microenvironment will allow us to consider therapies that target TAMs to promote enhanced NK cell activity.

This review describes the key role of the serine-threonine kinase like protein Tribbles-1 in health as well as in diverse human pathologies. Tribbles-1 is a homolog protein of the Drosophila Tribbles. In Drosophila, the Tribbles protein is involved in the cell-cycle progression during mitosis and in mammals initial data showed TRIB1 to be involved in cell proliferation. In mammals, TRIB1 lacks a catalytic domain and thus acts as an adaptor protein by interacting with several partners. The activity of TRIB1 seems to be very specific to the environment and the cells type in which it is expressed, and a role for this molecule has been mainly described in several pathological states including various cancers such as acute myeloid leukemia and ovarian cancer. Further evidence has also linked TRIB1 to the control of plasmalipid homeostasis thus indicating the role of this molecule as a risk factor for myocardial infarction. Finally, TRIB1 is shown to be up-regulated during inflammatory events such as chronic inflammation of atherosclerotic arteries or chronic antibody-mediated rejection of transplanted organs. Here we provide a review of the current state of the scientific literature for TRIB1, highlighting its role in diverse pathologies and inflammatory states. A better understanding of the role of this protein as both a target as well as a biological marker in diseases should drive the development of new therapeutic strategies.

The importance of Akt, Erk, and their downstream effectors-mediated signaling is indisputable for the proliferation of cell. Growth factor-induced activation of Akt and Erk pathways interacts with each other to regulate proliferation. However, an instructive model, wiring the crucial signaling nodes working in cellular growth and division, is still absent or controversial. Although growth factor-mediated mTORC1 regulation is defined considerably, debates still exist formTORC2. TSC1-TSC2 complex integrates both nutrient and mitogenic signals coming from growth factor receptors. Growth factor-induced PI3K/Akt- and Ras/Erk-mediated TSC2 inhibition is well defined. However, the interaction between TSC complex and new molecules such as Pin1 and DAPK requires further clarifications. Furthermore, the Wnt-β-catenin signaling pathway also intersects with the growth factor signaling at TSC1/TSC2 junction. Therefore, the aim of this perspective paper is to suggest an integrated model, linking growth factor-activated crucial signaling nodes in order to supply key molecular connections to degenerative diseases.

The notion of inhaled carbon monoxide (CO) being a toxic chemical under all circumstances is currently being challenged, as recent research has suggested that low concentrations of CO may have therapeutic value, especially in the airway. This review evaluates CO's effects on cellular functions that may result in beneficial outcomes in the settings of airway disease, inflammation, and injury. CO can modulate the stress response system of the cell by decreasing levels of reactive intermediates over time, produced by mitochondrial iNOS and NADPH oxidase. Intracellular stress-induced response factors (e.g., HIF-1 and HSP- 70) are induced in response to CO, possibly facilitating more rapid and effective defenses, in response to subsequent stressors. CO also can trigger changes in cellular functions downstream, protecting the cells from stress-associated events promoted in the airway, as a result of disease or injury, including reducing rates of apoptosis, proliferation, and inflammatory cellular infiltration, as well as preventing an imbalance in the extracellular matrix composition. CO has also been associated with maintaining homeostasis of ions essential for normal cellular functions (e.g., Na+, Fe2+,3+). CO also targets cell-specific functions of the airway, such as reduction of contractility of airway smooth muscle cells, and preservation of the innate defense mechanism of airway epithelial cells. Further understanding of CO's effects on fundamental cellular functions in the airway will likely hold significant value in future considerations of CO's role in airway therapy and health.

Diabetes is characterized by insulin deficiency concomitant with hyperglycemia due to reduced islet cell mass and/or dysfunction. Currently, insulin replacement is the first-line treatment option for patients with type 1 and a severe form of type 2diabetes. Treatment by insulin injection is generally effective but nonphysiological, and has the potential of producing chronic complications. On the other hand, islet transplantation can maintain normoglycemia without hypoglycemic side effects, potentially freeing diabetic patients of insulin dependence. In practice, islet transplantation remains hindered by the lack of organ donors and transplant rejection concerns. Recent advances in stem cell research and regenerative medicine, however, offer promise for the clinical application of islet cell transplantation. This review article offers a critical appraisal of current molecular induction approaches, such as directed differentiation, microenvironment induction, and genetic modification, which mimic islet cell development by inducing a variety of stem cells; they include embryonic stem cells, induced pluripotent stem cells, and various tissue-derived stem cells to become functional and transplantable insulin-producing islet cells. Despite good progress, several obstacles remain to be overcome before islet transplantation can be translated into a therapy for human patients, including, but are not limited to, immunogenicity and risk of tumorogenesis.

Type 2 diabetes (T2D) is a metabolic disorder characterised by the inability of β-cells to secrete enough insulin to maintain glucose homeostasis. Pancreatic β-cells secrete insulin in a biphasic manner, first and second phase insulin secretion, and loss of first phase insulin secretion is an independent predictor of T2D onset. Restoration of first phase insulin secretion has been shown to improve blood glucose in T2D by suppressing hepatic glucose production and priming insulin sensitive tissue to more readily take up glucose and has thus prompted numerous studies into its regulation. First phase insulin secretion is initiated primarily by the classical triggering pathway, a complex system comprised of multiple stimulatory signals. Recent studies have identified a number of novel regulatory factors that are crucial for first phase insulin secretion and glucose homeostasis. These include, among others, hypoxia inducible factor 1α, von Hippel-Lindau, factor inhibiting HIF, nicotinamide phospho-ribosyl-transferase, and the sirtuin family. This review will outline how first phase insulin secretion is initiated and detail some of the recent findings in its regulation.

SIRT1 and PGC-1α are two nutrient sensing master regulators of cellular metabolism and their upregulation is often linked to increased lifespan. SIRT1 and PGC-1α modulate the expression of a set of nuclear genes controlling many metabolic pathways. In recent years mounting evidence has indicated the implication of these proteins in several mitochondrial diseases including neurodegenerative disorders, myopathies and Type II diabetes mellitus. Recently, these proteins have been localized in cytoplasm and mitochondria wherein they target novel substrates opening new insight into their possible function in modulating extranuclear genes and proteins. This review will firstly summarize the nuclear function of SIRT1 and PGC-1α. Then, data from papers demonstrating the presence of SIRT1 and PGC-1α in the cytoplasm and in mitochondria will be outlined so that these extranuclear forms do not remain out of sight. Finally, very recent evidence of the alteration of the pathways governed by SIRT1 and PGC-1α in human mitochondrial diseases will be described and the possible role of their mitochondrial forms will be briefly discussed.

Aging is one of the greatest risk factors in vascular diseases (VDs). During aging, there are structural and functional changes in the vasculature, including dilated lumen, altered intimal-medial thickness (IMT), vascular stiffness, endothelial dysfunction, increased endothelial apoptosis, matrix metalloproteinase (MMP) dysregulation, increased expression of inflammatory molecules, aggravated oxidative stress and shortened telomere length. These changes leave the body more susceptible to primary hypertension, stroke and coronary artery disease. Molecules that suppress these age-related changes would provide an excellent medical intervention for VDs. Mammalian Sir2 (SIRT1, a NAD+-dependent deacetylase), previously shown to extend the lifespan of lower organisms, is a promising target molecule to influence some aspects of vascular aging. In this review, we summarized roles of SIRT1 in various pathophysiological processes of vascular aging and proposed that SIRT1 and its activators can become novel therapeutic targets for age-related VDs.

The premise of targeted therapy was born from an intimate understanding of the unique biological pathways and endpoints which are implicated in the development of different disease states and conditions. In addition, the identification of the most appropriate drugs to use for targeted drug therapy has aided in growing interest of the pharmaceutical industry to allocate more resources to monoclonal antibody (mAb) therapeutics. This being the case, it is important to understand antibody based therapeutics, some of the currently Food and Drug Administration (FDA)-approved mAbs in different disease states, as well as the future direction of mAb therapies. In this article, we will provide a critical overview, and discuss a selection of antibody based therapeutics, including their bioengineered structural and functional elements. Furthermore, a segment of the currently FDA-approved mAb antibody therapies, those in research, or in investigation for disease states and conditions ranging from autoimmune disease, inflammatory response, immunosuppression, cancer, including antibody-drug conjugates, immunotherapy, and exciting prospects for antiplatelet and antithrombotic monoclonal antibody therapeutics will be reviewed. Finally, we will discuss our predictions and aspirations for the future directions of mAb-based therapeutic interventions.

Inspite of demanding research that has been undertaken for cancer treatment, cancer is a major cause of mortality. Available conventional treatment options of solid tumor are associated with serious side effects. Nanomedicines mediated fascinating approach may be effectively utilized for efficient tumor targeting by avoiding all the problems associated with conventional chemotherapy. Polymeric nanomedicines such as polymer micelles, polymeric nanoparticles, polymersomes and polymer conjugates currently developed for solid tumor treatment have proved to be efficacious cancer therapeutics. These polymeric nanostructures are able to reach tumor tissue or angiogenic endothelial cells either passively or actively. To date, more advancement in the tumor targeting field includes stimuli sensitive polymeric nanocarriers that pass through the intracellular delivery barriers and release the bioactives in response to the microenvironmental trigger of tumor cell. This review discusses the molecular aspects of solid tumor pathophysiology and its dramatic impact on research for innovative and novel therapeutic approaches linked with tumor-targeting polymeric nanomedicines.

The serine/threonine protein kinase paralogs ROCK1 & 2 have been implicated as essential modulators of angiogenesis; however their paralog-specific roles in endothelial function are unknown. shRNA knockdown of ROCK1 or 2 in endothelial cells resulted in a significant disruption of in vitro capillary network formation, cell polarization, and cell migration compared to cells harboring non-targeting control shRNA plasmids. Knockdowns led to alterations in cytoskeletal dynamics due to ROCK1 & 2-mediated reductions in actin isoform expression, and ROCK2-specific reduction in myosin phosphatase and cofilin phosphorylation. Knockdowns enhanced cell survival and led to ROCK1 & 2-mediated reduction in caspase 6 and 9 cleavage, and a ROCK2-specific reduction in caspase 3 cleavage. Microarray analysis of ROCK knockdown lines revealed overlapping and unique control of global transcription by the paralogs, and a reduction in the transcriptional regulation of just under 50% of VEGF responsive genes. Finally, paralog knockdown in xenograft angiosarcoma tumors resulted in a significant reduction in tumor formation. Our data reveals that ROCK1 & 2 exhibit overlapping and unique roles in normal and dysfunctional endothelial cells, that alterations in cytoskeletal dynamics are capable of overriding mitogen activated transcription, and that therapeutic targeting of ROCK signaling may have profound impacts for targeting angiogenesis.

Protein serine/threonine phosphatases are important cellular signaling molecules and play major roles in regulating many different functions including cell proliferation, senescence, programmed cell death, and oncogenic cell transformation. Among different serine/threonine phosphatases, PP-1 and PP-2A contribute to more than 90% phosphatase activities in eukaryotes. While the functions of PP-2A in cell transformation and tumorigenesis have been well established, the role of PP-1 in carcinogenesis remains to be further explored. Moreover, PP-1 exists in different isoforms, whether these isoforms have differential functions in tumorigenesis remains to be examined. In the present study, we demonstrated that in lung cancer 1299 cells, PP1α and PP- 1γ exist in an antagonizing balance. In the parent H1299 cells, PP-1γ is dominant, about 4-fold higher than that of PP-1α. Overexpression of PP-1α significantly down-regulates PP-1γ at both mRNA and protein levels. In contrast, knockdown of PP-1α leads to upregulation of PP-1γ. Moreover, overexpression of PP-1α significantly attenuates the ability of the H1299 cells in promoting tumorigenicity as tested in immuno-deficient nude mice. This attenuation is derived from the halted cell cycle progression, which is largely attributed by the changed RB-E2F activity. Together, our results demonstrate that PP-1α and PP-1γ not only antagonize each other in lung cancer cells, but also display differential functions in tumorigenicity.

The c-Jun N-terminal kinases (JNKs) constitute one of the three major types of mitogen-activated protein kinases. Previous studies showed that JNK mediates multiple signaling transduction pathways implicated in cell proliferation, differentiation, inflammation, stress response and apoptosis in mammals. In the present study, we use goldfish as a model system and demonstrate that JNK kinases are necessary to promote embryonic survival and regulate eye development in vertebrates. During goldfish development, JNK1 and JNK2 are expressed at every stage from cleavage to hatching larvae. JNK3 is turned on at the gastrulation stage and then expressed at similar level to that of JNK2. JNK1 activity remains slightly fluctuated during different developmental stages. Inhibition of JNK activity caused massive apoptosis of blastula cells and significant death of goldfish embryos, which are associated with altered expression of the anti-apoptotic regulator, Mcl-1 and the proapoptotic regulator, Bak. These results provide novel information regarding the mechanisms by which JNKs promote embryonic survival. In addition, the embryos that survived inhibition of JNK activity displayed severe phenotype in the eye with clear microphthalmia and lens coloboma. To confirm that the observed phenotype is derived from JNK activity deficiency, we expressed JNK dominant negative mutant (DNM-JNK) in goldfish. Expression of DNM-JNK also caused similar phenotypes with altered expression of pax-6, Sox-2 and β-crystallin. Together, our results demonstrate that JNKs play important roles in promoting survival of vertebrate embryos and regulating development of vertebrate eye.