Cyclin D-cdk6 complex is targeted by p21(WAF) in growth-arrested lymphoma cells

Potential Pathways Involved in Elaidic Acid Induced Atherosclerosis in Human Umbilical Vein Endothelial Cells

Researches have demonstrated that trans-fatty acids are related to the progression of atherosclerosis, but the underlying mechanism is not clear till now. In the presented study, two-dimensional electrophoresis based proteomics was used to discover the role of elaidic acid in atherosclerosis. In human umbilical vein endothelial cells (HUVEC), twenty-two and twenty-three differentially expressed proteins were identified in low (50 μmol/L) and high (400 μmol/L) concentration elaidic acid simulated groups, respectively, comparing with the control group. The expressions of some selected proteins (PSME3, XRCC5, GSTP1, and GSTO1) were validated by qRT-PCR analysis. Western blotting analysis further confirmed that elaidic acid downregulated the expression of PSME3and XRCC5. Moreover, P53, the downstream protein of PSME3, was further investigated. Results demonstrated that a variety of proteins, many of which were related to oxidative stress, apoptosis, and DNA damage, were involved in the elaidic acid induced atherosclerosis. Furthermore, P53 was demonstrated to regulate the atherosclerosis through cell cycle arrest and apoptosis pathway.

Repo-man at the intersection of chromatin remodelling, DNA repair, nuclear envelope organization, and cancer progression

Nuclear structure and chromatin changes are very useful biomarkers in cancer diagnosis. Despite this, their biological significance and relevance to cancer progression are still not well understood. The identification of new proteins that link the nuclear envelope to chromatin organization and the understanding of the molecular mechanisms underlying these connections have begun to provide some important clues. This review discusses the role of the nuclear protein Repo-Man (CDCA2) in the maintenance of genome stability. Repo-Man (CDCA2) is a targeting subunit for the protein phosphatase 1 involved in the dephosphorylation of histone H3 during mitotic exit. In this role, it is important for the chromatin organization in post-mitotic nuclei. Repo-Man (CDCA2) is also essential for proper nuclear envelope reformation and the regulation of DNA damage responses. The relevance of this complex for cancer biology is also corroborated by emerging evidence that provides a correlation between Repo-Man (CDCA2) expression levels and cancer progression; several studies now suggest that Repo-Man (CDCA2) represents a very strong prognostic marker for poor patient survival.

Overexpression of CDCA2 in human squamous cell carcinoma: correlation with prevention of G1 phase arrest and apoptosis

Cell division cycle associated 2 (CDCA2) recruits protein phosphatase 1 to chromatin to antagonize activation of ataxia telangiectasia mutated (ATM)-dependent signal transduction. ATM kinase plays a critical role in the DNA damage response and its phosphorylation cascade to inhibit the p53-MDM2 interaction, which releases p53 to induce p21 and G1 cell-cycle arrest. However, the relevance of CDCA2 to human malignancy including oral squamous cell carcinoma (OSCC) is unknown. In the current study, we found that CDCA2 expression was up-regulated in OSCC cell lines. Functional studies with shRNA system showed that knockdown of CDCA2 significantly (P<0.05) inhibited cellular proliferation compared with the control cells by arresting cell-cycle progression at the G1 phase and up-regulating the cyclin-dependent kinase inhibitors (p21^Cip1, p27^Kip1, p15^INK4B, and p16^INK4A). CDCA2 knockdown also promoted apoptosis after treatment with the DNA damage reagent, cisplatin. In clinical samples, the CDCA2 protein expression level in primary OSCCs was significantly (P<0.05) greater than in matched normal oral tissues (67/85, 79%). Furthermore, CDCA2-positive cases were correlated significantly (P<0.05) with high cancer progression. Our results showed for the first time that CDCA2 frequently is overexpressed in OSCCs and might be associated closely with OSCC progression by preventing cell-cycle arrest and apoptosis.

Role of the ubiquitin-proteasome in protein quality control and signaling: implication in the pathogenesis of eye diseases

The ubiquitin-proteasome pathway (UPP) plays important roles in many cellular functions, such as protein quality control, cell cycle control, and signal transduction. The selective degradation of aberrant proteins by the UPP is essential for the timely removal of potential cytotoxic damaged or otherwise abnormal proteins. Conversely, accumulation of the cytotoxic abnormal proteins in eye tissues is etiologically associated with many age-related eye diseases such as retina degeneration, cataract, and certain types of glaucoma. Age- or stress-induced impairment or overburdening of the UPP appears to contribute to the accumulation of abnormal proteins in eye tissues. Cell cycle and signal transduction are regulated by the conditional UPP-dependent degradation of the regulators of these processes. Impairment or overburdening of the UPP could also result in dysregulation of cell cycle control and signal transduction. The consequences of the improper cell cycle and signal transduction include defects in ocular development, wound healing, angiogenesis, or inflammatory responses. Methods that enhance or preserve UPP function or reduce its burden may be useful strategies for preventing age-related eye diseases.

Genetic disruption of p38alpha Tyr323 phosphorylation prevents T-cell receptor-mediated p38alpha activation and impairs interferon-gamma production

T cells possess a p38 activation alternative pathway in which stimulation via the antigen receptor (T-cell receptor [TCR]) induces phosphorylation of p38alpha and beta on Tyr323. To assess the contribution of this pathway to normal T-cell function, we generated p38alpha knockin mice in which Tyr323 was replaced with Phe (p38alpha(Y323F)). TCR-mediated stimulation failed to activate p38alpha(Y323F) as measured by phosphorylation of the Thr-Glu-Tyr activation motif and p38alpha catalytic activity. Cell-cycle entry was delayed in TCR-stimulated p38alpha(Y323F) T cells, which also produced less interferon (IFN)-gamma than wild-type T cells in response to TCR-mediated but not TCR-independent stimuli. p38alpha(Y323F) mice immunized with T-helper 1 (Th1)-inducing antigens generated normal Th1 effector cells, but these cells produced less IFN-gamma than wild-type cells when stimulated through the TCR. Thus, the Tyr323-dependent pathway and not the classic mitogen-activated protein (MAP) kinase cascade is the physiologic means of p38alpha activation through the TCR and is necessary for normal Th1 function but not Th1 generation.

Prostate cancer cells tolerate a narrow range of androgen receptor expression and activity

BACKGROUND

The precise role of androgen receptor (AR) in the normal development of prostate and the progression of prostate cancer (CaP) remains controversial. While AR expression and activity is associated with growth arrest and differentiation of normal prostate cells, it is maintained in CaP cells that are characterized by continued proliferation. Our objective was to determine the importance of AR signaling for survival and growth of CaP cells, particularly those with a hormone-refractory phenotype.

METHOD

AR expression was modulated in androgen-sensitive (AS) and androgen-insensitive (AI) CaP cells using RNAi and cDNA transduction. Resulting changes in AR transcriptional activity and cell growth were quantified.

RESULTS

Interference with AR expression in both AS and AI CaP cells by shRNA transduction demonstrated a direct correlation between residual AR expression and cell viability. CaP cells lacking AR expression undergo apoptosis several days after AR down-regulation. This delayed response suggests that AR regulates apoptosis likely through an indirect mechanism. Overexpression of AR or hyper-stimulation of AR with high levels of androgen was also poorly tolerated by CaP cells. Cells with elevated AR had a growth disadvantage due to G1 cell cycle arrest and induction of p21 and GADD45 expression.

CONCLUSIONS

CaP cells expressing endogenous AR are sensitive to both increases and decreases in AR expression levels and activity. AR in CaP cells is delicately regulated to provide a balance between cell death and continued proliferation. Thus, both approaches, inhibition and over-stimulation of AR activity, may have therapeutic value for treatment of prostate cancer.

NMR and mass spectrometry studies of putative interactions of cell cycle proteins pRb and CDK6 with cell differentiation proteins MyoD and ID-2

Cell growth and differentiation require precise coordination of cell cycle and differentiation proteins. This can be achieved by direct interactions between proteins, by indirect interaction in multiprotein complexes, or by modulation of gene expression levels of partner proteins. Contradictory data abound in the literature regarding the binding between some central cell cycle proteins, pRb, and CDK6, with myogenic differentiation promoting, MyoD, and inhibiting, Id-2, factors. We have tested these interactions using pure proteins and in vitro biophysical and biochemical methods, which included mass spectrometry, nuclear magnetic resonance (NMR), the affinity chromatography pull-down assays, and gel filtration chromatography. Using this multimethod approach, we were able to document interactions between pRb and HPV-E7, pRb and SV40 large T antigen, CDK6 and p19, and MyoD and DNA. Using the same methods, we could unambiguously show that there is no direct protein-protein interaction in vitro between the small pocket domain of pRb and the bHLH domain of MyoD, the small pocket domain of pRb and Id-2, and CDK6 and a 15-amino-acid peptide from the C-terminal domain of MyoD. Indirect interactions, through additional binding partners in multiprotein complexes or modulation of gene expression levels of these proteins, are therefore their probable mode of action.

Regulation of the ubiquitin proteasome pathway in human lens epithelial cells during the cell cycle

Most proliferating cells follow a series of orderly transitions from one phase to another. These transitions are usually controlled by timed degradation of cell cycle regulators by the ubiquitin-proteasome pathway (UPP). There are no published reports regarding the timing of phases of the human lens cell cycle or regarding cell cycle-related changes in UPP components. Objectives of this study were to characterize the timing of the phases of the human lens epithelial cell cycle and to explore potential functions of critical components of the UPP in controlling lens cell cycle. Human lens epithelial cells were synchronized at G0/G1 phase by contact inhibition. Cell cycle progression upon subculturing was monitored by FACS analysis. It took approximately 40 hr for HLEC to complete one cell cycle, approximately 20 hr for G1 phase, approximately 8-10 hr for S phase and approximately 10 hr for the combination of G2 and M phases. Proteasome-dependent degradation of p21WAF and p27Kip, the dominant Cdk inhibitors, was associated with the G1/S phase transition in these cells. Proteasome inhibition experiments indicate that proteolysis is the predominant process which is responsible for the variations in these regulators during the cell cycle. Levels of specific ubiquitin conjugating enzymes, Ubc7 and Ubc10, increased 6 and 2-fold at the G2/M phase and S/G2/M phases, respectively. Levels of these E2s decreased precipitously upon completion of the M phase. In contrast, levels of ubiquitin activating enzyme (E1) and Ubc3 remained constant during the cell cycle. Cul1, a component of the SCF (an E3), remained relatively constant during cell cycle. The up-regulation of Ubc7 and Ubc10 during the G2/M and S/G2/M phases suggests that these enzymes may be involved in controlling the cell cycle progression at this phase. Taken together, the data indicate that expression of key components of the UPP in the human lens epithelial cells is regulated in a cell cycle-dependent manner. Some of the variations in levels of ubiquitin conjugating enzymes are suggestive of previously undescribed functions.

Function of the ubiquitin proteolytic pathway in the eye

The ubiquitin pathway (UP) is involved in regulation of many essential cellular processes usually by the degradation of regulators of these processes. For example the UP is involved in regulation of cell cycle, proliferation, differentiation, organogenesis, development, and signal transduction in the lens and retina. A functional UP has also been documented in the cornea. Upon aging or exposure to stress there is an accumulation of damaged proteins, including ubiquitinated proteins, in the lens and retina. Some of these proteins may be cytotoxic. Thus, an active UP may be required to avoid such age and disease-related accumulation of damaged proteins. In this review we will explain the biochemistry of the UP and we will document the most important studies regarding UP function in the lens, retina and cornea.