The Role of Sumoylation in Senescence.

Cellular senescence is a program initiated by many stress signals including aberrant activation of oncogenes, DNA damage, oxidative lesions and telomere attrition. Once engaged senescence irreversibly limits cellular proliferation and potently prevents tumor formation in vivo. The precise mechanisms driving the onset of senescence are still not completely defined, although the pRb and p53 tumor suppressor pathways converge with the SUMO cascade to regulate cellular senescence.

The MAPK pathway functions as a redundant survival signal that reinforces the PI3K cascade in c-Kit mutant melanoma.

Stimulation of the c-Kit receptor tyrosine kinase has a critical role in the development and migration of melanocytes, and oncogenic c-Kit mutants contribute to the progression of some melanomas. c-Kit signalling activates the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways and their relative contribution to the activities of oncogenic and ligand-dependent c-Kit remains uncertain. We show that PI3K is a major regulator of MAPK activation in response to c-Kit activity and the dominant effector of c-Kit-driven melanocyte proliferation and melanoma survival.

Absence of distinguishing senescence traits in human melanocytic nevi.

Cellular senescence permanently restricts the replicative capacity of cells in response to various stress signals, including aberrant activation of oncogenes. The presence of predictive senescence markers in human premalignant lesions suggests that senescence may function as a genuine tumor suppressor. These markers are not exclusive to the senescence program, however, and it is possible that their expression in vivo does not discriminate irreversible from reversible forms of proliferative arrest.

P53 in human melanoma fails to regulate target genes associated with apoptosis and the cell cycle and may contribute to proliferation.

Background: Metastatic melanoma represents a major clinical problem. Its incidence continues to rise in western countries and there are currently no curative treatments. While mutation of the P53 tumour suppressor gene is a common feature of many types of cancer, mutational inactivation of P53 in melanoma is uncommon; however, its function often appears abnormal.

IGFBP7 is not required for B-RAF-induced melanocyte senescence.

Induction of senescence permanently restricts cellular proliferation after oncogenic stimulation thereby acting as a potent barrier to tumor development. The relevant effector proteins may therefore be fundamental to cancer development. A recent study identified IGFBP7 as a secreted factor mediating melanocyte senescence induced by oncogenic B-RAF, which is found commonly in cutaneous nevi.

The relative contributions of the p53 and pRb pathways in oncogene-induced melanocyte senescence.

Oncogene-induced senescence acts as a barrier against tumour formation and has been implicated as the mechanism preventing the transformation of benign melanocytic lesions that frequently harbour oncogenic B-RAF or N-RAS mutations. In the present study we systematically assessed the relative importance of the tumour suppressor proteins p53, p21(Waf1), pRb and p16(INK4a) in mediating oncogene-induced senescence in human melanocytes. We now show that oncogenic N-RAS induced senescence in melanocytes is associated with DNA damage, a potent DNA damage response and the activation of both the p16(INK4a)/pRb and p53/p21(Waf1) tumour suppressor pathways.

Oncogene-induced senescence does not require the p16(INK4a) or p14ARF melanoma tumor suppressors.

Oncogene-induced senescence is considered to act as a potent barrier to cell transformation, and has been seen in vivo during the early stages of tumor development. Human nevus cells frequently express oncogenic N-RAS or B-RAF, and are thought to be permanently growth arrested. Many studies have suggested that the p16(INK4a) and, to a lesser extent, the p14ARF tumor suppressor proteins act as critical triggers of oncogene-induced senescence in nevi, and thus these proteins represent major inhibitors of progression to melanoma.

The chromatin remodelling factor BRG1 is a novel binding partner of the tumor suppressor p16INK4a.

Background: CDKN2A/p16INK4a is frequently altered in human cancers and it is the most important melanoma susceptibility gene identified to date. p16INK4a inhibits pRb phosphorylation and induces cell cycle arrest, which is considered its main tumour suppressor function. Nevertheless, additional activities may contribute to the tumour suppressor role of p16INK4a and could help explain its specific association with melanoma predisposition.

Ankyrin repeat domain 1, ANKRD1, a novel determinant of cisplatin sensitivity expressed in ovarian cancer.

Purpose: The standard of care for ovarian cancer includes platinum-based chemotherapy. It is not possible, however, to predict clinical platinum sensitivity or to design rational strategies to overcome resistance. We used a novel approach to identify altered gene expression associated with high sensitivity to cisplatin, to define novel targets to sensitize tumor cells to platins and ultimately improve the effectiveness of this widely used class of chemotherapeutics.

p16INK4a expression and absence of activated B-RAF are independent predictors of chemosensitivity in melanoma tumors.

Metastatic cutaneous melanoma is highly resistant to cytotoxic drugs, and this contributes to poor prognosis. In vivo studies on the chemosensitivity of metastatic melanoma are rare and hampered by poor response rates to systemic chemotherapeutics. Patients who undergo isolated limb infusion (ILI) with cytotoxic drugs show high response rates and are, therefore, a good cohort for studying chemosensitivity in vivo.

p16INK4a-induced senescence is disabled by melanoma-associated mutations.

The p16(INK4a)-Rb tumour suppressor pathway is required for the initiation and maintenance of cellular senescence, a state of permanent growth arrest that acts as a natural barrier against cancer progression. Senescence can be overcome if the pathway is not fully engaged, and this may occur when p16(INK4a) is inactivated. p16(INK4a) is frequently altered in human cancer and germline mutations affecting p16(INK4a) have been linked to melanoma susceptibility.

The E3 ubiquitin ligase EDD is an adverse prognostic factor for serous epithelial ovarian cancer and modulates cisplatin resistance in vitro.

Despite a high initial response rate to first-line platinum/paclitaxel chemotherapy, most women with epithelial ovarian cancer relapse with recurrent disease that becomes refractory to further cytotoxic treatment. We have previously shown that the E3 ubiquitin ligase, EDD, a regulator of DNA damage responses, is amplified and overexpressed in serous ovarian carcinoma. Given that DNA damage pathways are linked to platinum resistance, the aim of this study was to determine if EDD expression was associated with disease recurrence and platinum sensitivity in serous ovarian cancer.

p14ARF regulates E2F-1 ubiquitination and degradation via a p53-dependent mechanism.

Alterations in the ARF tumor suppressor protein (also known as p14ARF in humans and p19ARF in the mouse) occur frequently in cancer and are associated with susceptibility to melanoma, pancreatic cancer and nervous system tumors. ARF proteins interact with the E2F-1, -2 and -3 transcription activators to inhibit their transcriptional activity and induce their degradation via the 26S proteasome pathway. The impact of ARF on the E2F proteins may provide a mechanism for p53-independent ARF activity on cell cycle progression and tumor susceptibility.

Physical and functional interaction of the p14ARF tumor suppressor with ribosomes.

Alterations in the p14(ARF) tumor suppressor are frequent in many human cancers and are associated with susceptibility to melanoma, pancreatic cancer, and nervous system tumors. In addition to its p53-regulatory functions, p14(ARF) has been shown to influence ribosome biogenesis and to regulate the endoribonuclease B23, but there remains considerable controversy about its nucleolar role. We sought to clarify the activities of p14(ARF) by studying its interaction with ribosomes.

Focal subnuclear distribution of progesterone receptor is ligand dependent and associated with transcriptional activity.

The progesterone receptor (PR) is a critical mediator of progesterone action in the female reproductive system. Expressed in the human as two proteins, PRA and PRB, the receptor is a ligand-activated nuclear transcription factor that regulates transcription by interaction with protein cofactors and binding to specific response elements in target genes. We previously reported that PR was located in discrete subnuclear foci in human endometrium.

Retinal light damage: structural and functional effects of the antioxidant glutathione peroxidase-1.

Purpose: The role of the antioxidant enzyme glutathione peroxidase-1 (GPx1) in protecting the retina against photo-oxidative damage was investigated in GPx1-deficient and wild-type mice.

Method: Albino GPx1-deficient and age-matched wild-type mice were examined. Baseline electroretinograms (ERGs) were recorded.

Kidney expression of glutathione peroxidase-1 is not protective against streptozotocin-induced diabetic nephropathy.

In many diseases, including progressive renal disorders, tissue injury and pathological intracellular signaling events are dependent on oxidative stress. Glutathione peroxidase-1 (Gpx1) is an antioxidant enzyme that is highly expressed in the kidney and removes peroxides and peroxynitrite that can cause renal damage. Therefore, we examined whether this abundant renal antioxidant enzyme limits renal damage during the development of type 1 diabetic nephropathy.

Inhibition of antigen and calcium ionophore induced secretion from RBL-2H3 cells by phosphatase inhibitors.

The role of serine/threonine protein phosphatases PP1 and PP2A in mast cell secretion was investigated using the phosphatase inhibitors okadaic acid and calyculin A. Calyculin A (5-25 nm) inhibited antigen-induced secretion from a rat mucosal mast cell line (RBL-2H3) when added in conjunction with the activator. Okadaic acid (250-1000 nm) inhibited secretion only when added before activation and did so in a time- and concentration-dependent manner.

Induction of interleukin-4 and interleukin-5 expression in mast cells is inhibited by glucocorticoids.

Inflammation in asthma and other allergic diseases is characterized by excessive production of immunoglobulin E (IgE) and the influx of leukocytes, especially eosinophils. Interleukin 4 (IL-4) and IL-5 are essential for IgE production and eosinophilia, respectively, and are produced by mast cells in allergic conditions, for which glucocorticoids are widely used therapeutically. We assessed the effect of glucocorticoids on IL-4 and IL-5 mRNA production by the RBL-2H3 cell line, an analog of mucosal mast cells.

Calcium ionophore-induced secretion from mast cells correlates with myosin light chain phosphorylation by protein kinase C.

Rat basophilic leukemia mast cells (RBL-2H3) secrete histamine when activated by Ag. This secretion correlates with increased phosphorylation of myosin light chain by protein kinase C (PKC). Calcium ionophores (A23187) also elicit secretion, which is enhanced by PMA.

Calcium-independent secretion by ATP gamma S from a permeabilized rat basophilic leukaemia cell line (RBL-2H3).

Activation of rat basophilic leukaemia cells (RBL-2H3) leads to the secretion of allergic and inflammatory mediators. These cells can be permeabilized, yet still retain their ability to secrete in response to antigen. Secretion can also be induced in permeabilized cells by the addition of the ATP analogue, ATP gamma S [adenosine-5'-O-(3-thiotriphosphate)], which is relatively resistant to phosphatase activity.