E3 Ligase CHIP and Androgen Receptor Degradation

Edited by:Mohammad  Hezarkhani  MD,Urologist

Board-Certified of Urology,Tehran  University ,The Member  of  Iranian  Urological  Association

[e-mail]

04/January/2013

The androgen receptor (AR) has a vital role in the onset and progression of prostate cancer by promoting G1-S progression, possibly by functioning as a licensing factor for DNA replication.

 We here report that low dose 2-methoxyestradiol (2-ME), an endogenous estrogen metabolite, induces mitotic arrest in prostate cancer cells involving activation of the E3 ligase CHIP (C-terminus of Hsp70-interacting protein) and degradation of the AR.

The 70 kilodalton heat shock proteins (Hsp70s) are a family of ubiquitously expressed heat shock proteins. Proteins with similar structure exist in virtually all living organisms. The Hsp70s are an important part of the cell's machinery for protein folding, and help to protect cells from stress.

The Hsp70 proteins have three major functional domains:

N-terminal ATPase domain – binds ATP (Adenosine triphosphate) and hydrolyzes it to ADP (Adenosine diphosphate). The exchange of ATP drives conformational changes in the other two domains.

Substrate binding domain – contains a groove with an affinity for neutral, hydrophobic amino acid residues. The groove is long enough to interact with peptides up to seven residues in length.

C-terminal domain – rich in alpha helical structure acts as a 'lid' for the substrate binding domain. When an Hsp70 protein is ATP bound, the lid is open and peptides bind and release relatively rapidly. When Hsp70 proteins are ADP bound, the lid is closed, and peptides are tightly bound to the substrate binding domain.

When not interacting with a substrate peptide, Hsp70 is usually in an ATP bound state. Hsp70 by itself is characterized by a very weak ATPase activity, such that spontaneous hydrolysis will not occur for many minutes. As newly synthesized proteins emerge from the ribosomes, the substrate binding domain of Hsp70 recognizes sequences of hydrophobic amino acid residues, and interacts with them. This spontaneous interaction is reversible, and in the ATP bound state Hsp70 may relatively freely bind and release peptides. However, the presence of a peptide in the binding domain stimulates the ATPase activity of Hsp70, increasing its normally slow rate of ATP hydrolysis. When ATP is hydrolyzed to ADP the binding pocket of Hsp70 closes, tightly binding the now-trapped peptide chain. Further speeding ATP hydrolysis are the so-called J-domain cochaperones: primarily Hsp40 in eukaryotes, and DnaJ in prokaryotes. These cochaperones dramatically increase the ATPase activity of Hsp70 in the presence of interacting peptides.

By binding tightly to partially synthesized peptide sequences (incomplete proteins), Hsp70 prevents them from aggregating and being rendered nonfunctional. Once the entire protein is synthesized, a nucleotide exchange factor (BAG-1 and HspBP1 are among those which have been identified) stimulates the release of ADP and binding of fresh ATP, opening the binding pocket. The protein is then free to fold on its own, or to be transferred to other chaperones for further processing. HOP (the Hsp70/Hsp90 Organizing Protein) can bind to both Hsp70 and Hsp90 at the same time, and mediates the transfer of peptides from Hsp70 to Hsp90.^[6]

Hsp70 also aids in transmembrane transport of proteins, by stabilizing them in a partially folded state.

Hsp70 proteins can act to protect cells from thermal or oxidative stress. These stresses normally act to damage proteins, causing partial unfolding and possible aggregation. By temporarily binding to hydrophobic residues exposed by stress, Hsp70 prevents these partially denatured proteins from aggregating, and allows them to refold. Low ATP is characteristic of heat shock and sustained binding is seen as aggregation suppression, while recovery from heat shock involves substrate binding and nucleotide cycling. In a thermophile anaerobe (Thermotoga maritima) the Hsp70 demonstrates redox sensitive binding to model peptides, suggesting a second mode of binding regulation based on oxidative stress.

Hsp70 seems to be able to participate in disposal of damaged or defective proteins. Interaction with CHIP (Carboxyl-terminus of Hsp70 Interacting Protein)–an E3 ubiquitin ligase–allows Hsp70 to pass proteins to the cell's ubiquitination and proteolysis pathways.

Finally, in addition to improving overall protein integrity, Hsp 70 directly inhibits apoptosis.^[8] One hallmark of apoptosis is the release of cytochrome c, which then recruits Apaf-1 and dATP/ATP into an apoptosome complex. This complex then cleaves procaspase-9, activating caspase-9 and eventually inducing apoptosis via caspase-3 activation. Hsp 70 inhibits this process by blocking the recruitment of procaspase-9 to the Apaf-1/dATP/cytochrome c apoptosome complex.

It does not bind directly to the procaspase-9 binding site, but likely induces a conformational change that renders procaspase-9 binding less favorable. Hsp70 is shown to interact with Endoplasmic reticulum stress sensor protein IRE1alpha thereby protecting the cells from ER stress - induced apoptosis. This interaction prolonged the splicing of XBP-1 mRNA thereby inducing transcriptional upregulation of targets of spliced XBP-1 like EDEM1, ERdj4 and P58IPK rescuing the cells from apoptosis. Other studies suggest that Hsp 70 may play an anti-apoptotic role at other steps, but is not involved in Fas-ligand-mediated apoptosis (although Hsp 27 is).

Therefore, Hsp 70 not only saves important components of the cell (the proteins) but also directly saves the cell as a whole. Considering that stress-response proteins (like Hsp 70) evolved before apoptotic machinery, Hsp 70’s direct role in inhibiting apoptosis provides an interesting evolutionary picture of how more recent (apoptotic) machinery accommodated previous machinery (Hsps), thus aligning the improved integrity of a cell’s proteins with the improved chances of that particular cell’s survival.

Depletion of the AR by small interfering RNA (siRNA) eliminates 2-ME-induced arrest and introducing AR into PC3-M cells confers 2-ME-induced mitotic arrest. Knockdown of CHIP or MDM2 (mouse homolog of double minute 2 protein) individually or in combination reduced AR degradation and abrogated M phase arrest induced by 2-ME.

Our data link AR degradation via ubiquitination to mitotic arrest. Targeting the AR by activating E3 ligases such as CHIP represents a novel strategy for the treatment of prostate cancer.

References:

1-Androgen receptor degradation by the E3 ligase CHIP modulates mitotic arrest in prostate cancer cells ,Oncogene , (17 December 2012) | doi:10.1038/onc.2012.561

S Sarkar, D L Brautigan, S J Parsons and J M Larner

2-Wikipedia,The Free Encyclopedia  November 23,2012

Some Men Complaint of Shortened Penis Following Prostate Cancer Treatment

Jan. 2, 2013

Complaints were more common in men treated with radical prostatectomy (surgical removal of the prostate) or male hormone-blocking drugs combined with radiation therapy, according to the study by researchers from Dana-Farber/Brigham and Women's Cancer Center (DF/BWCC). No men reported a perceived shortening of their penis following radiation therapy alone.

The study's findings, which are being published in the January issue of the journal Urology, are based on surveys completed by physicians of 948 men treated for prostate cancer and who had suffered a recurrence of the disease.

Twenty-five men (2.63 percent of the group) complained of smaller penises after treatment -- 3.73 percent for surgery, 2.67 percent for radiotherapy plus androgen deprivation therapy (ADT), and 0% for radiotherapy alone. Radiotherapy included both radiation administered by an external x-ray machine, and brachytherapy -- the implantation of radioactive seeds directly into the prostate.

The scientific team, led by Paul Nguyen, MD, a radiation oncologist, and medical student Arti Parekh, said it is the first study to link men's perceptions of a reduction in penis size to lowered life satisfaction, problems in emotional relationships, and misgivings about the specific form of prostate cancer treatment they chose.

Nguyen said that the potential side effect of a smaller penis is well-known among physicians and surgeons, said Nguyen, "but it's almost never discussed with patients, so it can be very upsetting to some men when it occurs. Patients can deal with almost any side effect if they have some inkling ahead of time that they may happen."

The report's authors said physicians should discuss the possibility with their patients so that they can make more-informed treatment choices.There were no direct measurements of penis size either before or after treatment, said the researchers. Nor did the patients' physicians specifically ask about this side effect; the issue was brought up by patients in conversations with their doctors. For this and other reasons, the authors of the new study suggest that the problem is likely more common than reported in the survey. 

"Prostate cancer is one of the few cancers where patients have a choice of therapies, and because of the range of possible side effects, it can be a tough choice," said Nguyen. "This study says that when penile shortening does occur, it really does affect patients and their quality of life. It's something we should be discussing up front so that it will help reduce treatment regrets."

The likelihood and magnitude of penis shortening as a consequence of treatment have not been well studied, said the researchers. However, Jim Hu, MD, a surgeon at the University of California, Los Angeles Medical Center and a co-author of the study, said "Previous studies have concluded that there is shortened penis length following prostatectomy. This is most common with non-nerve sparing surgery, as this may result in fibrosis and atrophy of erectile tissue due to damage to nerve and vascular structures." The present study did not find much difference on that score. 

The study's subjects were men enrolled in a registry called COMPARE that collects data on patients whose prostate cancer shows signs of recurring after initial treatment. Of the 948 men in the study, 22 percent were younger than 60 and the majority were in their 60s, 70s and 80s. Just over half -- 54 percent -- had undergone surgery to remove their cancerous prostate, while 24 percent received radiation therapy combined with hormone-blocking treatment, and 22 percent had radiation therapy alone. 

In an editorial comment accompanying the report, Luc Cormier, MD, PhD, of Dijon University Hospital in France said the study "is really of interest because of the number of patients and that it included other treatment methods in addition to radical prostatectomy."

The surveys of the men did not report on their sexual functioning. Cormier observed that "sexual activity needs to be thoroughly measured owing to the obvious relationship with the patients' perception of penile leng.

 Reference:

Arti Parekh, Ming-Hui Chen, Karen E. Hoffman, Toni K. Choueiri, Jim C. Hu, Charles L. Bennett, Michael W. Kattan, Oliver Sartor, Karen Stein, Powell L. Graham, Anthony V. D'Amico, Paul L. Nguyen. Reduced Penile Size and Treatment Regret in Men With Recurrent Prostate Cancer After Surgery, Radiotherapy Plus Androgen Deprivation, or Radiotherapy Alone. Urology, 2013; 81 (1): 130 DOI: 10.1016/j.urology.2012.08.068 

Bladder Cancer News

Narrated by:Dr.M.Hezarkhani   December 28, 2012 

Cancer Diagnosis Later in Life Poses Significant Risk to Offspring, Study Suggests

December 20, 2012

Relatives of family members diagnosed with cancer are still at risk of the disease even if the diagnosis came at an older age, a new paper ...

Popular Pain Relievers May Reduce Risk of Bladder Cancer

November 7, 2012

 Researchers have found that duration of ibuprofen use was associated with a reduced risk of bladder cancer in patients in northern New England, which has a high mortality rate of this

High Levels of Vitamin D in Plasma Protects Against Bladder Cancer

October 30, 2012

High levels of vitamin D are associated with protection against bladder cancer, according to a study by molecular biologists and ...

New Drug Delivery System for Bladder Cancer Using Nanoparticles

October 25, 2012

Scientists have shown in experimental mouse models that a new drug delivery system allows for administration of three times the maximum tolerated dose of a standard drug therapy for advanced bladder ...  

Depression, Shortened Telomeres Increase Mortality in Bladder Cancer Patients

October 18, 2012

 Low depressive symptoms and a longer telomere length are compelling factors that contribute to a prolonged life for bladder cancer patients, according to ...   

Two Components of Red Meat Combined With Alteration in DNA Repair Increase Risk for Bladder Cancer

October 17, 2012

Two components of red meat -- dietary protein and dietary iron -- may combine to form powerful carcinogens, N-nitroso compounds, which increase risk for bladder cancer. Moreover, individuals with ...  
 

Depression and Shortened Telomeres Increased Bladder Cancer Mortality

October 17, 2012  

The combination of shortened telomeres, a biological marker of aging associated with cancer development, and elevated depression significantly impacted bladder cancer mortality, according to new

Like Prostate Cancer, Bladder Cancer Patients May Benefit from Anti-Androgen Therapy

September 24, 2012  

Bladder cancer patients whose tumors express high levels of the protein CD24 have worse prognoses than patients with lower CD24. A new study shows that CD24 expression may depend on androgens – ...  

Lack of Oxygen in Cancer Cells Leads to Growth and Metastasis

September 13, 2012  

The proteins HIF-1a and CD24 have both been implicated in the aggressive characteristics of hypoxic cancers. A new study shows that HIF-1a drives CD24 overexpression, and that CD24 then drives ...   

New Insight Into Cell Development and Cancer

        News

Dec. 27, 2012 

Long-standing research efforts have been focused on understanding how stem cells, cells capable of transforming into any type of cell in the body, are capable of being programmed down a defined path to contribute to the development of a specific organ like a heart, lung, or kidney. Research from the University of North Carolina at Chapel Hill School of Medicine has shed new light on how epigenetic signals may function together to determine the ultimate fate of a stem cell.

The study, published December 27, 2012 by the journal Molecular Cell, implicates a unique class of proteins called polycomb-like proteins, or PCL's, as bridging molecules between the "on" and "off" state of a gene. While all of these specialized types of cells share the same genetic information encoded in our DNA, it is becoming increasingly clear that information outside the genome, referred to as epigenetics, plays a central role in orchestrating the reprogramming of a stem cell down a defined path.

Although it is understood that epigenetics is responsible for turning genes "on" and "off" at defined times during cellular development, the precise mechanisms controlling this delicate process are less well understood.

"This finding has important implications for both stem cell biology and cancer development, as the same regulatory circuits controlled by PCL's in stem cells are often misregulated in tumors," said Dr. Greg Wang, senior author of the study and Assistant Professor of Biochemistry and Biophysics in the UNC School of Medicine and a member of UNC Lineberger Comprehensive Cancer Center.

The study, led by postdoctoral research fellows Drs. Ling Cai and Rui Lu in the Wang lab, and Dr. Scott Rothbart, a Lineberger postdoctoral fellow in the lab of Dr. Brian Strahl, Associate Professor of Biochemistry and Biophysics in the UNC School of Medicine and a member of UNC Lineberger Comprehensive Cancer Center, identified that PCL's interact with an epigenetic signal associated with genes that are turned on to recruit a group of proteins called the PRC2 complex which then turn genes off."In stem cells, the PRC2 complex turns genes off that would otherwise promote reprogramming into specialized cells of organs like the heart or lungs," said Wang.

In addition to its fundamental role in cellular development, elevated levels of PRC2 have been found in cancers of the prostate, breast, lung, and blood, and pharmaceutical companies are already developing drugs to target PRC2. Wang and colleagues determined that the same mechanisms controlling PRC2 function in stem cells also applies in human cancers.

"The identification of a specific PCL in controlling PRC2 in cancer cells suggests we may be able to develop drugs targeting this PCL to regulate PRC2 function in a more controlled manner that may maintain PRC2 function in stem cells while inhibiting it in the tumor," said Wang.