The human cyclin B1 protein modulates sensitivity of DNA mismatch repair deficient prostate cancer cell lines to alkylating agents

The role of cyclins in the development and progression of prostate cancer

The role of cyclins in hormone-dependent neoplasms is crucial in the development of the disease that is resistant to first-line therapy, as the example of breast cancer shows. However, in prostate cancer, cyclins are studied to a lesser extent. There are some well-described molecular pathways, including cyclins A1 and D1 signaling, however the role of other cyclins, e.g., D2, D3, E, and H, still requires further investigation. Recent studies indicate that cyclins regulate various cellular processes, not only the cell cycle. Furthermore, they remain in cross-talk with many other signaling pathways, e.g., MAPK/ERK, PI3K/Akt, and Notch. The androgen signaling axis, which is pivotal in prostate cancer progression, interferes with cyclin pathways at many levels. This article summarizes current knowledge on the influence of cyclins on prostate cancer progression by describing interactions between the androgen receptor and cyclins, as well as mechanisms underlying the development of resistance to currently used therapies.

Functional genomic analysis of CAF-1 mutants in Arabidopsis thaliana

Duplication of chromatin following DNA replication requires spatial reorganization of chromatin domains assisted by chromatin assembly factor CAF-1. Here, we tested the genomic consequences of CAF-1 loss and the function of chromatin assembly factor CAF-1 in heterochromatin formation. Genes located in heterochromatic regions are usually silent, and we found that this transcriptional repression persists in the absence of CAF-1 in Arabidopsis. However, using microarrays we observed that genes that are active during late S-phase, when heterochromatin is duplicated, were up-regulated in CAF-1 mutants. Arabidopsis CAF-1 mutants also have reduced cytological heterochromatin content; however, DNA methylation of pericentromeric repeats was normal, demonstrating that CAF-1 is not required for maintenance of DNA methylation. Instead, hypomethylation of the genome, which has only mild effects on the development of wild-type plants, completely arrested development of CAF-1 mutants. These results suggest that CAF-1 functions in heterochromatin formation. CAF-1 and DNA methylation, which is also needed for heterochromatin formation, have partially redundant functions that are essential for cell proliferation. Interestingly, transcriptional repression and heterochromatin compaction can be genetically separated, and CAF-1 is required only for the complete compaction of heterochromatin but not to maintain transcriptional repression of heterochromatic genes.

Induction of apoptosis and G2/M arrest by N-methyl-N′-nitro-N-nitrosoguanidine in human prostate carcinoma cells

We have investigated the effects of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a well known DNA alkylating agent, on the growth and cell cycle progression in human prostate carcinoma PC-3 and DU145 cells, which are lacking both p53 alleles and having mutated p53, respectively. It was found that MNNG could inhibit the cell growth in a dose-dependent manner, which was associated with dendrite-like morphological change and induction of apoptotic cell death. Flow cytometry showed that MNNG could cause an arrest at the G2/M phase of the cell cycle, which is closely correlated to inhibition of cyclin-dependent kinase (Cdk) 2 and Cdc2 kinase activities. Furthermore, this compound induced Cdk inhibitor p21WAF1/CIP1 expression at both the transcription and protein levels in a p53-independent manner. MNNG also activated the reporter construct of a p21 promoter. Present results indicate that the up-regulation of p21 by MNNG is likely responsible for the inhibition of Cdks kinase activity rather than the down-regulation of cyclins and Cdks expression.

Cyclin D1 expression and cell cycle response in DNA mismatch repair-deficient cells upon methylation and UV-C damage

We have evaluated cell survival, apoptosis, and cell cycle responses in a panel of DNA mismatch repair (MMR)-deficient colon and prostate cancer cell lines after alkylation and UV-C damage. We show that although these MMR-deficient cells tolerate alkylation damage, they are as sensitive to UV-C-induced damage as are the MMR-proficient cells. MMR-proficient cells arrest in the S-G2 phase of the cell cycle and initiate apoptosis following alkylation damage, whereas MMR-deficient cells continue proliferation. However, two prostate cancer cell lines that are MMR-deficient surprisingly arrest transiently in S-G2 after alkylation damage. Progression through G1 phase initially depends on the expression of one or more of the D-type cyclins (D1, D2, and/or D3). Analysis of cyclin D1 expression shows an initial MMR-independent decrease in the protein level after alkylation as well as UV-C damage. At later time points, however, only DNA damage-arrested cells showed decreased cyclin D1 levels irrespective of MMR status, indicating that reduced cyclin D1 could be a result of a smaller fraction of cells being in G1 phase rather than a result of an intact MMR system. Finally, we show that cyclin D1 is degraded by the proteasome in response to alkylation damage.

Characterization of human exonuclease 1 in complex with mismatch repair proteins, subcellular localization and association with PCNA

Human exonuclease 1 (hEXO1) has been implicated in DNA mismatch repair (MMR), replication, and recombination, but the nature of its interaction with these cellular processes is still ambiguous. We show that hEXO1 colocalizes with proliferating cell nuclear antigen (PCNA) at DNA replication sites and that the C-terminal region of hEXO1 is sufficient for this localization. We also show that both hMLH1-hPMS2 (MutLalpha) and hMLH1-hEXO1 complexes are formed in a reaction mixture containing all three proteins. Moreover, hEXO1 5' double-stranded exonuclease activity on a homoduplex substrate but not on a substrate containing a G/T mismatch was inhibited by complex formation with hMSH2-hMSH6 (MutSalpha) or MutLalpha. Taken together, the results support a model in which hEXO1 plays a role in events at the replication sites as well as a functional role in the MMR and/or recombination processes.

Perillyl alcohol mediated radiosensitization via augmentation of the Fas pathway in prostate cancer cells

BACKGROUND

The management of hormone-insensitive locally advanced prostate cancer is difficult and complex and there is an urgent need for the development of effective chemotherapeutic agents intended for combination with currently available treatment modalities.

METHODS

The present paper demonstrates the effectiveness of the monoterpene perillyl alcohol (POH) as potent radiosensitizer on DU145 and PC3 cell lines by performing clonogenic survival assays, cycle analysis, and assays to detect viability, apoptosis, and Fas receptor/ligand by flow cytometry.

RESULTS

POH pretreatment resulted in a dose dependent sensitization to kill cell by radiation. Furthermore, POH treatment induced a transient G(2)/M arrest, enhanced the expression of the membrane bound form of the Fas ligand and sensitized the cells to Fas mediated apoptosis.

CONCLUSIONS

The unique manner of radiosensitization in addition to its low toxicity profile makes POH a promising new agent for preclinical evaluation as a potential radiosensitizer in the treatment of prostate cancer.

Reduced expression of hMSH2 and hMLH1 and risk of prostate cancer: a case-control study

BACKGROUND

Although prostate cancer is the most common incident cancer in men, not much is known about its etiology. We tested the hypothesis that expression levels of hMSH2 and hMLH1 in unaffected (normal) tissue play a role in the etiology of prostate cancer.

METHODS

Total RNA was extracted from peripheral blood lymphocytes of subjects ascertained by a case-control study (70 patients and 97 age- and ethnicity-matched controls). A multiplex reverse transcription-polymerase chain reaction assay was used to simultaneously evaluate the relative expression of hMSH2 and hMLH1, using beta-actin as the internal control.

RESULTS

The relative gene expression levels of hMSH2 and hMLH1 were significantly lower in cases than in controls (P < 0.05 for both genes). When compared with the highest tertile of the controls, low expression levels (the middle and lowest tertiles) of hMLH1 were associated with significantly increased risk of prostate cancer in a dose-response relationship (ORs = 2.68, and 4.31; 95% confidence interval = 1.00-7.23 and 1.64-11.30, respectively) after adjustment for age, ethnicity, smoking status, and family history of prostate cancer.

CONCLUSIONS

These results suggest that reduced expression of hMLH1 in peripheral lymphocytes may be a risk factor for prostate cancer. However, it cannot be ruled out that the reduced expression we observed may be caused by the disease status. Our findings and the factors that may affect the expression of hMLH1 need further confirmation in larger prospective studies.