Cyclin E and chromosome instability in colorectal cancer cell lines

Targeting cyclin-dependent kinase 2 (CDK2) interactions with cyclins and Speedy 1 (Spy1) for cancer and male contraception

The review discusses progress in discovering cyclin-dependent kinase 2 (CDK2) inhibitors for cancer treatment and their potential for male contraception. It summarizes first-, second-, and third-generation CDK inhibitors and selective CDK2 inhibitors currently in clinical trials for cancer. Novel strategies to discover allosteric inhibitors, covalent inhibitors, and degraders are also discussed.

The crosstalk between ubiquitin-conjugating enzyme E2Q1 and p53 in colorectal cancer: An in vitro analysis

Colorectal cancer (CRC) is a prevalent gastrointestinal neoplasm that ranks fourth in terms of cancer-related deaths worldwide. In the process of CRC progression, multiple ubiquitin-conjugating enzymes (E2s) are involved; UBE2Q1 is one of those newly identified E2s that is markedly expressed in human colorectal tumors. Since p53 is a well-known tumor suppressor and defined as a key factor to be targeted by the ubiquitin-proteasome system, we hypothesized that UBE2Q1 might contribute to CRC progression through the modulation of p53. Using the lipofection method, the cultured SW480 and LS180 cells were transfected with the UBE2Q1 ORF-containing pCMV6-AN-GFP vector. Then, quantitative RT-PCR was used to assay the mRNA expression levels of p53's target genes, i.e., Mdm2, Bcl2, and Cyclin E. Moreover, Western blot analysis was performed to confirm the cellular overexpression of UBE2Q1 and assess the protein levels of p53, pre- and post-transfection. The expression of p53's target genes were cell line-dependent except for Mdm2 that was consistent with the findings of p53. The results of Western blotting demonstrated that the protein levels of p53 were greatly lower in UBE2Q1-transfected SW480 cells compared to the control SW480 cells. However, the reduced levels of p53 protein were not remarkable in the transfected LS180 cells compared to the control cells. The suppression of p53 is believed to be the result of UBE2Q1-dependent ubiquitination and its subsequent proteasomal degradation. Furthermore, the ubiquitination of p53 can act as a signal for degradation-independent functions, such as nuclear export and suppressing the p53's transcriptional activities. In this context, the decreased Mdm2 levels can moderate the proteasome-independent mono-ubiquitination of p53. The ubiquitinated p53 modulates the transcriptional levels of target genes. Therefore, the up-modulation of UBE2Q1 may influence the transcriptional activities depending on p53, and thereby contributes to CRC progression through regulating the p53.

Colon cancer transcriptome

Over the last four decades, methodological innovations have continuously changed transcriptome profiling. It is now feasible to sequence and quantify the transcriptional outputs of individual cells or thousands of samples using RNA sequencing (RNA-seq). These transcriptomes serve as a connection between cellular behaviors and their underlying molecular mechanisms, such as mutations. This relationship, in the context of cancer, provides a chance to unravel tumor complexity and heterogeneity and uncover novel biomarkers or treatment options. Since colon cancer is one of the most frequent malignancies, its prognosis and diagnosis seem to be critical. The transcriptome technology is developing for an earlier and more accurate diagnosis of cancer which can provide better protectivity and prognostic utility to medical teams and patients. A transcriptome is a whole set of expressed coding and non-coding RNAs in an individual or cell population. The cancer transcriptome includes RNA-based changes. The combined genome and transcriptome of a patient may provide a comprehensive picture of their cancer, and this information is beginning to affect treatment decision-making in real-time. A full assessment of the transcriptome of colon (colorectal) cancer has been assessed in this review paper based on risk factors such as age, obesity, gender, alcohol use, race, and also different stages of cancer, as well as non-coding RNAs like circRNAs, miRNAs, lncRNAs, and siRNAs. Similarly, they have been examined independently in the transcriptome study of colon cancer.

Photosensitized rose Bengal-induced phototoxicity on human melanoma cell line under natural sunlight exposure

Rose Bengal (RB) is an anionic water-soluble xanthene dye, which used for many years to assess eye cornea and conjunctiva damage. RB showed strong absorption maxima (λmax) under visible light followed by UV-B and UV-A. RB under sunlight exposure showed a time-dependent photodegradation. Our results show that photosensitized RB generates (1)O2 via Type-II photodynamic pathway and induced DNA damage under sunlight/UV-R exposure. 2'dGuO degradation, micronuclei formation, and single- and double-strand breakage were the outcome of photogenotoxicity caused by RB. Quenching studies with NaN3 advocate the involvement of (1)O2 in RB photogenotoxicity. RB induced linoleic acid photoperoxidation, which was parallel to (1)O2-mediated DNA damage. Oxidative stress in A375 cell line (human melanoma cell line) was detected through DCF-DA assay. Photosensitized RB decreased maximum cellular viability under sunlight followed by UV-B and UV-A exposures. Apoptosis was detected as a pattern of cell death through the increased of caspase-3 activity, decreased mitochondrial membrane potential, and PS translocation through inner to outer plasma membrane. Increased cytosolic levels of Bax also advocate the apoptotic cell death. We propose a p53-mediated apoptosis via increased expression of Bax gene and protein. Thus, the exact mechanism behind RB phototoxicity was the involvement of (1)O2, which induced oxidative stress-mediated DNA and membrane damage, finally apoptotic cell death under natural sunlight exposure. The study suggests that after the use of RB, sunlight exposure may avoid to prevent from its harmful effects.

Defective Myb Function Ablates Cyclin E1 Expression and Perturbs Intestinal Carcinogenesis

Cyclin E1 is essential for the reentry of quiescent cells into the cell cycle. When hypomorphic mutant Myb mice (Myb(Plt4)) were examined, it was noted that Cyclin E1 (Ccne1) expression was reduced. Furthermore, the induction of Ccne1 in recovering intestinal epithelia following radiation-induced damage was ablated in Myb-mutant mice. These data prompted us to investigate whether Myb directly regulated Ccne1 and to examine whether elevated Myb in colorectal cancer is responsible for Cyclin E1-driven tumor growth. Here, it was found that Myb/MYB and Ccne1/CCNE1 expressions were coupled in both mouse and human adenomas. In addition, the low molecular weight Cyclin E1 was the predominant form in intestinal crypts and adenomatous polyposis coli (Apc)-mutant adenomas. Chromatin immunoprecipitation (ChIP) analysis confirmed that Myb bound directly to the Ccne1 promoter and regulated its endogenous expression. In contrast, Myb(Plt4) served as a dominant-negative factor that inhibited wild-type Myb and this was not apparently compensated for by the transcription factor E2F1 in intestinal epithelial cells. Myb(Plt4/Plt4) mice died prematurely on an Apc(Min/) (+) background associated with hematopoietic defects, including a myelodysplasia; nevertheless, Apc(Min/) (+) mice were protected from intestinal tumorigenesis when crossed to Myb(Plt4/) (+) mice. Knockdown of CCNE1 transcript in murine colorectal cancer cells stabilized chromosome ploidy and decreased tumor formation. These data suggest that Cyclin E1 expression is Myb dependent in normal and transformed intestinal epithelial cells, consistent with a cell-cycle progression and chromosome instability role in cancer.

IMPLICATIONS

This study demonstrates that Myb regulates Cyclin E1 expression in normal gastrointestinal tract epithelial cells and is required during intestinal tumorigenesis.

Expression of cyclin E in stage III colorectal carcinoma

Carcinogenesis is characterized by an abnormal regulation of the cell cycle. Regulators of the cell cycle such as cyclin E play an important role in neoplasia and may be correlated with prognosis. The clinical significance of the expression of cyclin E in stage III colorectal carcinoma has not yet been investigated. The expression of cyclin E was evaluated in 49 patients. Using a multivariate analysis, the expression of cyclin E in the tumor at diagnosis was compared with various clinicopathological variables, including age, gender, tumor site, tumor size, tumor differentiation and lymph node involvement. There were more node-positive cases in the cyclin E-negative group than in the cyclin E-positive group (P=0.003). However, there was no correlation between the degree of cyclin E expression and the clinical data. In conclusion, our data suggest that overexpression of cyclin E does not predict the clinical outcome in colorectal cancer stage III. Negative cyclin E staining may be associated with lymph node involvement.

Assessment of chromosomal imbalances in CIMP-high and CIMP-low/CIMP-0 colorectal cancers

Data presented in a number of recent studies have revealed a negative correlation between CpG island methylator phenotype (CIMP) and chromosomal instability (CIN) measured by a loss of heterozygosity (LOH) of selected loci, suggesting that CIN and CIMP represent two independent mechanisms in sporadic colorectal cancer (CRC) carcinogenesis. However, CIN is a heterogeneous phenomenon, which may be studied not only by employing LOH analysis but also by observing chromosomal imbalances (gains and deletions). The current study aimed to investigate the relationship between CIMP and chromosomal gains and deletions (assessed by comparative genomic hybridization) in a group of 20 CIMP-high and 79 CIMP-low/CIMP-0 CRCs. Our results revealed that the mean numbers of gains and of total chromosomal imbalances were significantly greater (p = 0.004 and p = 0.007, respectively) in the CIMP-low/CIMP-0 group compared to the CIMP-high group, while no significant difference was observed between the mean numbers of losses (p = 0.056). The analysis of copy number changes of 41 cancer-related genes by multiplex ligation-dependent probe amplification showed that CRK gene was exclusively deleted in CIMP-low/CIMP-0 tumors (p = 0.02). Given that chromosomal losses play an important role in tumor suppressor inactivation and chromosomal gains, in the activation of proto-oncogenes, we hypothesize that tumor suppressor inactivation plays similar roles in both CIMP-high and CIMP-low/CIMP-0 CRCs, while the predominance of chromosomal gains in CIMP-low/CIMP-0 tumors may suggest that the activation of proto-oncogenes is the underlying mechanism of CIMP-low/CIMP-0 CRC progression.

Advances in understanding the relationship between cyclin E and human colorectal cancer

Cell cycle deregulation is one of important mechanisms leading to human colorectal cancer. It has been revealed that cyclin E is the most important regulatory factor for cell cycle control and plays an important role in the occurrence and development of human colorectal cancer. Detection of cyclin E expression can be used to assess the prognosis of colorectal cancer.

Characterization of nuclear localization signal in the N terminus of CUL4B and its essential role in cyclin E degradation and cell cycle progression

CUL4A and CUL4B, which are derived from the same ancestor, CUL4, encode scaffold proteins that organize cullin-RING ubiquitin ligase (E3) complexes. Recent genetic studies have shown that germ line mutation in CUL4B can cause mental retardation, short stature, and other abnormalities in humans. CUL4A was observed to be overexpressed in breast and hepatocellular cancers, although no germ line mutation in human CUL4A has been reported. Although CUL4A has been known to be involved in a number of cellular processes, including DNA repair and cell cycle regulation, little is known about whether CUL4B has similar functions. In this report, we tested the functional importance of CUL4B in cell proliferation and characterized the nuclear localization signal (NLS) that is essential for its function. We found that RNA interference silencing of CUL4B led to an inhibition of cell proliferation and a prolonged S phase, due to the overaccumulation of cyclin E, a substrate targeted by CUL4B for ubiquitination. We showed that, unlike CUL4A and other cullins that carry their NLS in their C termini, NLS in CUL4B is located in its N terminus, between amino acid 37 and 40, KKRK. This NLS could bind to importin alpha1, alpha3, and alpha5. NLS-deleted CUL4B was distributed in cytoplasm and failed to promote cell proliferation. Therefore, the nuclear localization of CUL4B mediated by NLS is critical for its normal function in cell proliferation.

Signal-dependent regulation of gene expression as a target for cancer treatment: inhibiting p38alpha in colorectal tumors

In the last year, several evidences indicated that pharmacological manipulation of relevant signaling pathways could selectively affect gene expression to influence cell fate. These findings render of extreme importance the elucidation of how external stimuli are transduced to mediate chromatin modifications, resulting in a permissive or repressive environment for gene expression. These signaling cascades activate or repress the function of chromatin binding proteins that represent attractive pharmacological targets for human diseases. Actually, the closer the target is to chromatin, the more the transcriptional effect will be selective. Recent studies suggest that pharmacological manipulation of signaling pathways to modulate cell fate is indeed possible and that chromatin-associated kinases could represent an optimal target. The p38 MAPK is the prototype of this class of enzymes and its central role in the transcription process is evolutionary conserved. In this review we will focus on the possibility to inhibit p38alpha in colorectal cancer to arrest tumor progression and induce autophagic cell death.

Deregulation of Cyclin E induces chromosomal instability in human colon cancer

AIM: To study the influence of stably inducible expression of Cyclin E on the chromosomal instability in human colon cancer cell line DLD1.

METHODS: Tetracycline-responsive gene-inducible cell line DLD1tTA-cyclin E was generated. Western blot was used to examine the induction of Cyclin E expression upon removal of doxycycline. 4'-6-Diamidino-2-phenylindole (DAPI) staining was performed to detect the percentage of cells with chromosomal instability 1, 3, 5, 7 and 14 d after the induction of Cyclin E expression.

RESULTS: Western blot showed that the peak of Cyclin E expression appeared 96 h after induction. The percentage of cells with chromosomal instability in tet-off DLD1tTA-Cyclin E cells ranged from 0.97% to 1.22% (t = 3.81, P > 0.01). However, the percentages of cells with chromosomal instability were 2.41%, 3.63%, 3.92%, 6.17% and 8.34%, respectively, 1, 3, 5, 7 and 14 d after the induction of Cyclin E expression (t = 4.77, P < 0.01).

CONCLUSION: Deregulation of cyclin E can induce the formation of aneuploidy in human colon cancer cell line DLD1, and it also plays an important role in the pathway of chromosomal instability.

E- and A-type cyclins as markers for cancer diagnosis and prognosis

Cyclin-dependent kinase (CDK)2 interacting cyclins perform essential functions for DNA replication and cellular proliferation. The human genome encodes two E-type cyclins (E and E2) and two A-type cyclins (A1 and A2). Dysregulation of the CDK2-bound cyclins plays an important role in the pathogenesis of cancer. Cyclin A2 is associated with cellular proliferation and can be used for molecular diagnostics as a proliferation marker. In addition, cyclin A2 expression is associated with a poor prognosis in several types of cancer. Cyclin A1 is a tissue-specific cyclin that is highly expressed in acute myeloid leukemia and in testicular cancer. High levels of cyclin E expression are found in many types of cancer. Overexpression of cyclin E at the mRNA level can be based on gene amplification and transcriptional mechanisms. In addition, proteolytically cleaved forms of cyclin E that show oncogenic functions have been described. Cyclin E plays a critical role for G1/S transition. Its overexpression is not only associated with proliferation but rather indicates a more malignant phenotype which is likely to be linked to the induction of chromosomal instability. These biological functions of cyclin E relate to a poor prognosis when high cyclin E levels are found. The link between cyclin E and poor prognosis is well established in breast and lung cancer but is likely to be observed in other cancers as well. The second E-type cyclin, cyclin E2, has been shown to be overexpressed in breast cancers although the potential role as a diagnostic or prognostic marker is unknown. This review provides an overview of the potential of cyclins E and A as markers for diagnosis and prognosis in human cancer.