The biphasic induction of p21 and p27 in breast cancer cells by modulators of cAMP is posttranscriptionally regulated and independent of the PKA pathway

Advances in targeting Phosphodiesterase 1: From mechanisms to potential therapeutics

Phosphodiesterase 1 (PDE1) is an enzyme entrusted with the hydrolysis of the second messengers cAMP and cGMP, thereby governing a plethora of metabolic processes, encompassing ion channel modulation and cellular apoptosis. Recent advancements in the realm of small molecule structural variations have greatly facilitated the exploration of innovative applications for PDE1. Remarkably, a recent series of PDE1 inhibitors (PDE1i) have been meticulously formulated and devised, showcasing enhanced selectivity and potency. Among them, ITI-214 has entered Phase II clinical trials, holding promise for the treatment of Parkinson's disease and heart failure. Nevertheless, the majority of current PDE1 inhibitors have encountered substantial side effects in clinical trials attributable to their limited selectivity, this predicament presents a formidable obstacle in the development of specific small molecule inhibitors targeting PDE1. This Perspective endeavors to illuminate the potential design approaches, structure-activity relationships, and biological activities of current PDE1i, aiming to offer support and insights for clinical practice and the development of novel PDE1i.

Role of phosphodiesterase 1 in the pathophysiology of diseases and potential therapeutic opportunities

Cyclic nucleotide phosphodiesterases (PDEs) are superfamily of enzymes that regulate the spatial and temporal relationship of second messenger signaling in the cellular system. Among the 11 different families of PDEs, phosphodiesterase 1 (PDE1) sub-family of enzymes hydrolyze both 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) in a mutually competitive manner. The catalytic activity of PDE1 is stimulated by their binding to Ca²⁺/calmodulin (CaM), resulting in the integration of Ca²⁺ and cyclic nucleotide-mediated signaling in various diseases. The PDE1 family includes three subtypes, PDE1A, PDE1B and PDE1C, which differ for their relative affinities for cAMP and cGMP. These isoforms are differentially expressed throughout the body, including the cardiovascular, central nervous system and other organs. Thus, PDE1 enzymes play a critical role in the pathophysiology of diseases through the fundamental regulation of cAMP and cGMP signaling. This comprehensive review provides the current research on PDE1 and its potential utility as a therapeutic target in diseases including the cardiovascular, pulmonary, metabolic, neurocognitive, renal, cancers and possibly others.

Fluvastatin inhibits AGE-induced cell proliferation and migration via an ERK5-dependent Nrf2 pathway in vascular smooth muscle cells

Advanced glycation endproduct (AGE)-induced vascular smooth muscle cell (VSMC) proliferation and reactive oxygen species (ROS) production are emerging as important mechanisms of diabetic vasculopathy, but little is known about the molecular mechanism responsible for the antioxidative effects of statins on AGEs. It has been reported that statins exert pleiotropic effects on the cardiovascular system due to decreases in AGE-induced cell proliferation, migration, and vascular inflammation. Thus, in the present study, the authors investigated the molecular mechanism by which statins decrease AGE-induced cell proliferation and VSMC migration. In cultured VSMCs, statins upregulated Nrf2-related antioxidant gene, NQO1 and HO-1, via an ERK5-dependent Nrf2 pathway. Inhibition of ERK5 by siRNA or BIX02189 (a specific ERK5 inhibitor) reduced the statin-induced upregulations of Nrf2, NQO1, and HO-1. Furthermore, fluvastatin was found to significantly increase ARE promoter activity through ERK5 signaling, and to inhibit AGE-induced VSMC proliferation and migration as determined by MTT assay, cell counting, FACS analysis, a wound scratch assay, and a migration chamber assay. In addition, AGE-induced proliferation was diminished in the presence of Ad-CA-MEK5α encoding a constitutively active mutant form of MEK5α (an upstream kinase of ERK5), whereas depletion of Nrf2 restored statin-mediated reduction of AGE-induced cell proliferation. Moreover, fluvastatin suppressed the protein expressions of cyclin D1 and Cdk4, but induced p27, and blocked VSMC proliferation by regulating cell cycle. These results suggest statin-induced activation of an ERK5-dependent Nrf2 pathway reduces VSMC proliferation and migration induced by AGEs, and that the ERK5-Nrf2 signal module be viewed as a potential therapeutic target of vasculopathy in patients with diabetes and complications of the disease.

Phase I biomarker modulation study of atorvastatin in women at increased risk for breast cancer

Selective estrogen receptor modulators (SERMs), tamoxifen, and raloxifene that reduce the risk of breast cancer are limited to only estrogen receptor-positive (ER(+)) breast cancer. In addition, patient acceptance of SERMs is low due to toxicity and intolerability. New agents with improved toxicity profile that reduce risk of ER-negative breast cancer are urgently needed. Observational studies show that statins can reduce breast cancer incidence and recurrence. The objective of this prospective short-term prevention study was to evaluate the effect of a lipophilic statin, atorvastatin, on biomarkers in breast tissue and serum of women at increased risk. Eligible participants included women with previous history of carcinoma in situ, or atypical hyperplasia, or 5 year breast cancer projected Gail risk >1.67 %, or lifetime breast cancer risk >20 % calculated by models including Claus, Tyrer-Cuzick, Boadicea, or BRCAPRO. Patients underwent baseline fine needle aspiration (FNA) of the breast, blood collection for biomarker analysis, and were randomized to either no treatment or atorvastatin at 10, 20, or 40 mg/day dose for 3 months. At 3 months, blood collection and breast FNA were repeated. Biomarkers included C-reactive protein (CRP), lipid profile, atorvastatin, and its metabolites, Ki-67, bcl-2, EGFR, and pEGFR. Baseline genotype for 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoAR) was also measured. Among 60 patients evaluated, a significant reduction in serum CRP, cholesterol and low-density lipoprotein (LDL), and increase in atorvastatin metabolites in serum and breast FNAs was demonstrated. No changes were observed in other tissue biomarkers. This study shows that atorvastatin and its metabolites are detectable in breast samples and may lower serum CRP among women without hyperlipidemia.

cAMP-Induced Histones H3 Dephosphorylation Is Independent of PKA and MAP Kinase Activations and Correlates With mTOR Inactivation

cAMP is a second messenger well documented to be involved in the phosphorylation of PKA, MAP kinase, and histone H3 (H3). Early, we reported that cAMP also induced H3 dephosphorylation in a variety of proliferating cell lines. Herein, it is shown that cAMP elicits a biphasic H3 dephosphorylation independent of PKA activation in cycling cells. H89, a potent inhibitor of PKA catalytic sub-unite, could not abolish this effect. Additionally, H89 induces a rapid and biphasic H3 serine 10 dephosphorylation, while a decline in the basal phosphorylation of CREB/ATF-1 is observed. Rp-cAMPS, an analog of cAMP and specific inhibitor of PKA, is unable to suppress cAMP-mediated H3 dephosphorylation, whereas Rp-cAMPS effectively blocks CREB/ATF-1 hyper-phosphorylation by cAMP and its inducers. Interestingly, cAMP exerts a rapid and profound H3 dephosphorylation at much lower concentration (50-fold lower, 0.125 mM) than the concentration required for maximal CREB/ATF-1 phosphorylation (5 mM). Much higher cAMP concentration is required to fully induce CREB/ATF-1 gain in phosphate (5 mM), which correlates with the inhibition of H3 dephosphorylation. Also, the dephosphorylation of H3 does not overlap at onset of MAP kinase phosphorylation pathways, p38 and ERK. Surprisingly, rapamycin (an mTOR inhibitor), cAMP, and its natural inducer isoproterenol, elicit identical dephosphorylation kinetics on both S6K1 ribosomal kinase (a downstream mTOR target) and H3. Finally, cAMP-induced H3 dephosphorylation is PP1/2-dependent. The results suggest that a pathway, requiring much lower cAMP concentration to that required for CREB/ATF-1 hyper-phosphorylation, is responsible for histone H3 dephosphorylation and may be linked to mTOR down regulation.

Attenuated expression of HRH4 in colorectal carcinomas: a potential influence on tumor growth and progression

BACKGROUND

Earlier studies have reported the production of histamine in colorectal cancers (CRCs). The effect of histamine is largely determined locally by the histamine receptor expression pattern. Recent evidence suggests that the expression level of histamine receptor H4 (HRH4) is abnormal in colorectal cancer tissues. However, the role of HRH4 in CRC progression and its clinical relevance is not well understood. The aim of this study is to evaluate the clinical and molecular phenotypes of colorectal tumors with abnormal HRH4 expression.

METHODS

Immunoblotting, real-time PCR, immunofluorescence and immunohistochemistry assays were adopted to examine HRH4 expression in case-matched CRC samples (n = 107) and adjacent normal tissues (ANTs). To assess the functions of HRH4 in CRC cells, we established stable HRH4-transfected colorectal cells and examined cell proliferation, colony formation, cell cycle and apoptosis in these cells.

RESULTS

The protein levels of HRH4 were reduced in most of the human CRC samples regardless of grade or Dukes classification. mRNA levels of HRH4 were also reduced in both early-stage and advanced CRC samples. In vitro studies showed that HRH4 over-expression caused growth arrest and induced expression of cell cycle proteins in CRC cells upon exposure to histamine through a cAMP -dependent pathway. Furthermore, HRH4 stimulation promoted the 5-Fu-induced cell apoptosis in HRH4-positive colorectal cells.

CONCLUSION

The results from the current study supported previous findings of HRH4 abnormalities in CRCs. Expression levels of HRH4 could influence the histamine-mediated growth regulation in CRC cells. These findings suggested a potential role of abnormal HRH4 expression in the progression of CRCs and provided some new clues for the application of HRH4-specific agonist or antagonist in the molecular therapy of CRCs.

Low-energy laser irradiation promotes synovial fibroblast proliferation by modulating p15 subcellular localization

BACKGROUND AND OBJECTIVE

Low-energy laser irradiation (low-level laser therapy) (LELI/LLLT/photobiomodulation) has been found to modulate various biological effects, especially those involved in promoting cell proliferation. Synovial fibroblasts are important in maintaining the homeostasis of articular joints and have strong chondrogenetic capacity. Here, we investigated the effect and molecular basis of LELI on synovial fibroblast proliferation.

STUDY DESIGN/MATERIALS AND METHODS

HIG-82 rabbit synovial fibroblasts were cultured, and laser irradiation (660 nm) was applied at the power density of 40 mW/cm(2) for 2 minutes, corresponding to laser fluence of 4.8 J/cm(2). The effect of LELI on cell proliferation, cell cycle progression, and expression of cyclin-dependent kinase inhibitors (CKIs) were investigated. We also examined whether the effects of LELI on HIG-82 cell proliferation were affected by cAMP content, which is known to influence the cell cycle via inducing CKIs.

RESULTS

LELI promoted HIG-82 synovial fibroblast proliferation and induced cytoplasmic localization of cyclin-dependent kinase inhibitor p15 (INK4B/CDKN2B). Moreover, the proliferation of HIG-82 synovial fibroblasts was reduced by cAMP, while cAMP inhibitor, SQ22536, induced p15 cytoplasmic localization and as a result, elevated synovial fibroblast proliferation was observed. In addition, the promotive effect of LELI-induced HIG-82 synovial fibroblast proliferation was abolished by cAMP treatment. Our findings suggest that cAMP may be involved in the effect of LELI on synovial fibroblast proliferation.

CONCLUSION

We revealed the effect and molecular link involved in synovial fibroblast proliferation induced by 660-nm LELI. Our study provides new insights into the mechanisms by which LELI has biological effects on synovial fibroblast proliferation. These insights may contribute to further investigation on biological effects and application of LELI in regenerative medicine.

Activation of FoxO transcription factors contributes to the antiproliferative effect of cAMP

cAMP is a potent inhibitor of cell proliferation in a variety of cell lines. Downregulation of cyclin D1 and upregulation of the cell cycle inhibitor p27Kip1 are two mechanisms by which cAMP may induce a G1-arrest. Here we show that cAMP inhibits proliferation of cells that constitutively express cyclin D1 or are deficient for Rb, demonstrating that changes in these cell cycle regulators do not account for the cAMP-induced growth effects in mouse embryo fibroblasts (MEFs). Interestingly, the antiproliferative effect of cAMP mimics the effect previously observed for FoxO transcription factors. These transcription factors are under negative control of protein kinase B (PKB). We show that in MEFs cAMP strongly induces transcriptional activation of FoxO4 through the inhibition of PKB. Accordingly, not only p27Kip1 but also the FoxO target MnSOD is upregulated by cAMP. Importantly, introduction of dominant-negative FoxO partially rescues cAMP-induced inhibition of proliferation. From these results we conclude that inhibition of PKB and subsequent activation of FoxO transcription factors mediates an antiproliferative effect of cAMP.

PTEN expression in ovine granulosa cells increases during terminal follicular growth

In the present paper, we have studied the expression of the Phosphatase and TENsin homolog deleted on chromosome 10 (PTEN) and its putative biological role in the sheep ovary. We found by Northern-blot, immunohistochemistry and immunoblot that PTEN is highly expressed in granulosa cells from large differentiated follicles (LF) in comparison with small proliferating follicles (SF) (P < 0.001), with no clear effect of follicle quality. Moreover, the PTEN lipid phosphatase activity is also higher in LF than in SF (P < 0.01). In contrast, levels of the phosphorylated form of AKT (pAKT) are lower in LF than in SF (P < 0.0001). IGF-I and insulin but not FSH, LH or forskolin are able to stimulate the expression of PTEN mRNA (P < 0.001) and protein by ovine granulosa cells after 48 h of culture in vitro. An IGF-1 time course analysis showed that expression of PTEN protein appeared after 12h of culture, concomitant with the fall of the pAKT levels, which peaked after 6h of stimulation with IGF-I. Moreover, transfection experiments showed that overexpression of PTEN in ovine granulosa cells induced a decrease and an increase in E2F and p27 promoter activity, respectively (P < 0.05). Overall, our present data show for the first time that the expression of PTEN increases during terminal follicular growth. This increase, that might be induced by IGF-I but not FSH, would participate in the proliferation/differentiation transition of ovine granulosa cells in differentiating follicles.

Cyclooxygenase-2 Inhibits Novel Ginseng Metabolite-Mediated Apoptosis

Recently, a novel intestinal bacterial metabolite of ginseng protopanaxadiol saponins, i.e., 20-O-(beta-D-glucopyranosyl)-20(S)-protopanaxadiol (IH-901), has been reported to induce apoptosis in a variety of cancer cells. Here we show a differential effect of IH-901 on several cell types. Exposure to IH-901 for 48 hours at a supposedly subapoptotic concentration of 40 mumol/L led to both apoptotic cell death and G1 arrest in Hep3B cells, but only resulted in G1 arrest in MDA-MB-231, Hs578T, and MKN28 cells. Additionally, the treatment of MDA-MB-231, but not of Hep3B, with IH-901 up-regulated cyclooxygenase-2 (COX-2) mRNA (2 hours) and protein (6 hours), and enhanced the production of prostaglandin E2. In MDA-MB-231 cells, IH-901 induced the sustained activation of extracellular signal-regulated kinase (ERK), whereas inhibition of mitogen-activated protein/ERK kinase blocked IH-901-mediated COX-2 induction and resulted in apoptosis, suggesting the involvement of an ERK-COX-2 pathway. Combined treatment with IH-901 and nonsteroidal anti-inflammatory drugs inhibited COX-2 enzyme and induced apoptosis in MDA-MB-231 and Hs578T cells. Adenovirus-mediated COX-2 small interfering RNAs also effectively inhibited COX-2 protein expression and enhanced IH-901-mediated apoptosis without inhibiting ERK 1/2 phosphorylation, thus providing direct evidence that COX-2 is an antiapoptotic molecule. Moreover, IH-901-mediated G1 arrest resulted from an increase in p27Kip1 mRNA and protein expression followed by a decrease in CDK2 kinase activity that was concurrent with the hypophosphorylation of Rb and p130. In conclusion, IH-901 induced both G1 arrest and apoptosis, and this apoptosis could be inhibited by COX-2 induction.

DeltaRaf-1:ER* bypasses the cyclic AMP block of extracellular signal-regulated kinase 1 and 2 activation but not CDK2 activation or cell cycle reentry

Elevation of cellular cyclic AMP (cAMP) levels inhibits cell cycle reentry in a variety of cell types. While cAMP can prevent the activation of Raf-1 and extracellular signal-regulated kinases 1 and 2 (ERK1/2) by growth factors, we now show that activation of ERK1/2 by DeltaRaf-1:ER is insensitive to cAMP. Despite this, DeltaRaf-1:ER-stimulated DNA synthesis is still inhibited by cAMP, indicating a cAMP-sensitive step downstream of ERK1/2. Although cyclin D1 expression has been proposed as an alternative target for cAMP, we found that cAMP could inhibit DeltaRaf-1:ER-induced cyclin D1 expression only in Rat-1 cells, not in CCl39 or NIH 3T3 cells. DeltaRaf-1:ER-stimulated activation of CDK2 was strongly inhibited by cAMP in all three cell lines, but cAMP had no effect on the induction of p21(CIP1). cAMP blocked the fetal bovine serum (FBS)-induced degradation of p27(KIP1); however, loss of p27(KIP1) in response to DeltaRaf-1:ER was less sensitive in CCl39 and Rat-1 cells and was completely independent of cAMP in NIH 3T3 cells. The most consistent effect of cAMP was to block both FBS- and DeltaRaf-1:ER-induced expression of Cdc25A and cyclin A, two important activators of CDK2. When CDK2 activity was bypassed by activation of the ER-E2F1 fusion protein, cAMP no longer inhibited expression of Cdc25A or cyclin A but still inhibited DNA synthesis. These studies reveal multiple points of cAMP sensitivity during cell cycle reentry. Inhibition of Raf-1 and ERK1/2 activation may operate early in G(1), but when this early block is bypassed by DeltaRaf-1:ER, cells still fail to enter S phase due to inhibition of CDK2 or targets downstream of E2F1.

p21-dependent inhibition of colon cancer cell growth by mevastatin is independent of inhibition of G1 cyclin-dependent kinases

Mevastatin arrested HCT116 colon cancer cells at the G1/S transition and increased cellular levels of p21CIP1/WAF1. p21-deficient colon cancer cells continued to proliferate in the presence of mevastatin. Although p21 was necessary for the G1/S block, the G1 cyclin-dependent kinases (Cdks) cyclin E-Cdk2 and cyclin D-Cdk4 remained active. Despite the activity of the G1 Cdks the retinoblastoma protein was hypophosphorylated due to unknown mechanisms that were dependent on the p21 protein. The resulting decrease in cyclin A mRNA and protein led to a decrease in the activity of cyclin A-Cdk2. Therefore, although p21 was required for the G1/S arrest of HCT116 colon cancer cells by mevastatin, its mode of action was more complicated than the simple formation of a physical complex with cyclin-Cdk2. This mechanism of inhibition is different from that seen in prostate cancer cells (Ukomadu, C., and Dutta, A. (2003) J. Biol. Chem. 278, 4840-4846) where the activating phosphorylation of cyclin E-Cdk2 is suppressed and p21 is not required, suggesting the existence of cell line-specific differences in the mechanism by which statins arrest the cell cycle.

Statin use and the risk of breast and prostate cancer

BACKGROUND

Laboratory data suggest that the cholesterol-lowering "statin" drugs may have chemopreventive potential against cancer at various sites, including breast and prostate. However, in one trial of pravastatin there was a significant excess of breast cancer in the treatment group. In the present study, we assessed the relation of statin use to the risk of breast and prostate cancer in our hospital-based Case-Control Surveillance Study of Drugs and Serious Illnesses.

METHODS

Cases were 1,132 women with breast cancer and 1,009 men with prostate cancer; controls were 1,331 women and 1,387 men admitted for conditions unrelated to statin use. We used multivariate unconditional logistic regression models to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for use of statins compared with no use.

RESULTS

The OR for breast cancer among statin users was 1.5 (95% CI = 1.0-2.3), largely accounted for by an OR of 1.8 (95% CI = 0.9-3.6) among cases with carcinoma in situ. Among invasive cases, the OR was 1.2 (95% CI = 0.7-2.0). The odds ratio for prostate cancer overall was 1.2 (95% CI = 0.8-1.7), and it was 1.4 (95% CI = 0.7-2.5) for Stage A.

CONCLUSIONS

The data from the present study do not support a protective effect of statins against breast or prostate cancer. Detection bias is a possible explanation for the higher ORs observed for carcinoma in situ or early-stage cancer as compared with more invasive cancer.

The cyclin-dependent kinase inhibitor p21WAF1/Cip1 is an antiestrogen-regulated inhibitor of Cdk4 in human breast cancer cells

The MCF-7 cell line is a model of estrogen-dependent, antiestrogen-sensitive human breast cancer. Antiestrogen treatment of MCF-7 cells causes dramatic decreases in both Cdk4 and Cdk2 activities, which leads to a G(1) phase cell cycle arrest. In this report, we investigate the mechanism(s) by which Cdk4 activity is regulated in MCF-7 cells. Through time course analysis, we demonstrate that changes in Cdk4 activity in response to estrogen or antiestrogen treatment do not correlate directly with cyclin D1 protein levels or association. In contrast, Cdk4 activity does correlate with changes in the level of the Cdk inhibitor p21(WAF1/Cip1). Furthermore, we show that extracts of antiestrogen-treated cells contain a factor capable of inhibiting the Cdk4 activity present in extracts of estrogen-treated cells, and immunodepletion experiments identify this factor as p21(WAF1/Cip1). These results identify p21(WAF1/Cip1) as an important physiological regulator of Cdk4 complexes in human breast cancer cells.

p27(Kip1) enhances myelin basic protein gene promoter activity

The process of oligodendrocyte differentiation is a complex event that requires cell cycle withdrawal, followed by the activation of a specific transcriptional program responsible for the synthesis of myelin genes. Because growth arrest precedes differentiation, we sought to investigate the role of cell cycle molecules in the activation of myelin gene promoters. We hypothesized that the cell cycle inhibitor p27(Kip1), which is primarily responsible for arresting proliferating oligodendrocyte progenitors, may be involved in the transcriptional regulation of myelin genes. In agreement with this hypothesis, overexpression of p27(Kip1) in the CG4 cell line, but not in 3T3 fibroblasts, enhances the expression of luciferase driven by the myelin basic protein (MBP) promoter. Interestingly, this effect is specific for p27(Kip1); overexpression of other cell cycle inhibitors had no effect. Additionally, this effect is independent of halting the cell cycle; treatment with the cell cycle blocker roscovitine did not affect MBP promoter usage. We conclude that p27(Kip1) contributes to oligodendrocyte differentiation by regulating transcription of the MBP gene.

Induction of p21WAF1 expression via Sp1-binding sites by tamoxifen in estrogen receptor-negative lung cancer cells

Although originally synthesized as an anti-estrogen, tamoxifen (Tam) was found to be able to inhibit proliferation of estrogen receptor (ER)-negative cancer cells in vitro. However, the molecular basis of such ER-independent growth inhibition is largely unknown. We have previously demonstrated that Tam induces p21WAF1 and p27KIP1 expression in human lung cancer cells which lack ER-alpha and -beta. We found that Tam induced p21WAF1 expression via transcriptional activation. In order to determine the molecular mechanism responsible for p21WAF1 induction by Tam, we performed a deletion analysis on the p21WAF1 promoter. The minimal region in the p21WAF1 promoter required for Tam-activated induction was mapped to a contiguous stretch of 10 bp located 83 bases upstream of the transcription initiation site. Our results showed that transcription factor Sp1 and Sp3 bound to this GC-rich region and mutation of Sp1-binding sites dramatically attenuated Tam-induced p21WAF1 promoter activity. We also tried to elucidate the signaling pathway that mediated the activation of p21WAF1 by Tam. Inhibition of mitogen-activated protein kinase pathways did not block Tam-induced p21WAF1. Similarly, protein kinase C inhibitor calphostin C could not suppress Tam-induced p21WAF1. Conversely, pretreatment of a specific protein kinase A inhibitor H89 significantly attenuated the induction of p21WAF1 by Tam. Furthermore, PKA activators forskolin and dibutyryl-cAMP activated p21WAFI promoter activity and increased p21wAF1 protein level in lung cancer cells. Taken together, these results demonstrate that Tam activates the p21WAF1 promoter via Sp1-binding sites and suggest that PKA may be involved in the induction of p21wAF1 by Tam in ER-negative lung cancer cells.