This Month in Investigative Urology

Article Outline

• Activated RhoA/Rho Kinase Impairs Erectile Function
• Cardiac Glycosides Decrease Prostate Specific Antigen Expression
• Expression of Estrogen Related Proteins in Hormone Refractory Prostate Cancer
• Inhibition of Cyclin Dependent Kinases Causes p53 Dependent Apoptosis in Renal Cell Carcinoma
• Copyright

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Activated RhoA/Rho Kinase Impairs Erectile Function 

Vascular smooth muscle contraction is dependent on Ca2+ dependent and Ca2+ sensitization mechanisms. One main pathway involves rho kinase (ROCK), which is activated by RhoA via stimulation of G protein coupled receptors. There is increasing evidence that activation of RhoA/ROCK signaling in the penis is involved in the pathogenesis of erectile dysfunction. Gratzke et al (page 2197) characterized the molecular expression profiles of RhoA/ROCK signaling in the penis after cavernous nerve injury (CNI) in the rat, testing the hypothesis that erectile dysfunction after CNI is accompanied by an up-regulation of RhoA/ROCK activity. Sham and bilateral CNI rats underwent cavernous nerve stimulation to determine erectile function at baseline and after intracavernous injection of a ROCK inhibitor (Y-27632).

Erectile function decreased in BCNI rats. Penile neuronal nitric oxide synthase protein levels decreased whereas RhoA and ROCK2 protein levels increased. ROCK1 protein expression was equivalent. ROCK immunoreactivity was qualitatively increased in the corporal smooth muscle of bilateral CNI rats. RhoA guanosine triphosphatase and ROCK activities were significantly increased in bilateral CNI vs sham rats. Intracavernous injection of Y-27632 caused a significantly greater increase in intracavernous pressure in bilateral CNI rats compared to sham rats, suggesting increased ROCK activity. The authors conclude that up-regulation of RhoA/ROCK in response to CNI contributes to penile vasculature dysfunction after CNI, and that the RhoA/ROCK pathway may represent a suitable target in the treatment of post-radical prostatectomy erectile dysfunction.

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Cardiac Glycosides Decrease Prostate Specific Antigen Expression 

Cardiac glycosides are the mainstay of congestive heart failure treatment. Early studies showed that in high concentrations cardiac glycosides can inhibit the proliferation of prostate cancer cell lines and promote apoptosis by inducing sustained Ca⁺² increases in the cells. Juang et al (page 2158) from Taiwan, Republic of China evaluated the mechanisms of clinically used cardiac glycosides on prostate specific antigen (PSA) gene expression in vitro. LNCaP cells were cultured and used to determine the effect of the drugs on prostate derived Ets factor (PDEF) and PSA expression.

Noncytotoxic concentrations (100 nM) of cardiac glycosides for 24 hours inhibited PSA secretion. The drugs significantly down-regulated the expression of PSA and PDEF, and over expression of PDEF enhanced the promoter activity of PSA. However, the promoter activities of the PSA and PDEF genes were attenuated when LNCaP cells were treated with 100 nM of cardiac glycosides. When LNCaP cells were treated with 25 nM digitoxin (within the range of therapeutic plasma concentrations) for 60 hours, PSA secretion decreased by 30%. The authors conclude that the effects of cardiac glycosides on PSA gene expression might be caused by down-regulation of PDEF gene expression. When cells were chronically treated with digoxin or digitoxin in concentrations close to or at therapeutic plasma levels, PSA secretion decreased. This phenomenon merits further study to determine whether it occurs in vivo, since the interpretation of PSA levels in patients taking cardiac glycosides could result in underestimation of prostate cancer risk and pathological stage.

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Expression of Estrogen Related Proteins in Hormone Refractory Prostate Cancer 

The progression to androgen independence in advanced prostate cancer treated with hormone deprivation involves several pathways often associated with androgen receptor (AR) signaling. Despite increasing evidence that estrogen signaling has a key role in the development and progression of prostate cancer, few studies have focused on estrogen pathway in the transition from hormone sensitive to hormone refractory tumors. Celhay et al (page 2172) studied the expression of proteins related to androgen and estrogen metabolism in paired samples of prostate cancers collected before androgen deprivation therapy and after hormonal relapse.

Compared to hormone sensitive samples, tissues collected after hormonal relapse were characterized by increased expression of Ki67, AR, phosphorylated AR and breast cancer antiestrogen resistance 1 (BCAR1), and by decreased staining for 5α-reductase 2, estrogen receptor β and aromatase. Shorter time to hormonal relapse was associated with high expression of aromatase and BCAR1 on diagnostic biopsies, and decreased staining for estrogen receptor α (ERA) on stromal cells. Overall survival was significantly shorter when tissues collected after relapse displayed both high proliferation index and low ERA expression. The authors conclude that proteins dysregulation is involved not only in androgen pathways, but also in estrogen synthesis and signaling during the development of hormone refractory prostate cancer. Molecules such as aromatase and BCAR1 associated with estrogen signaling seem to decrease the time to biochemical recurrence after androgen deprivation, whereas high ERA expression by stromal cells seems to delay recurrence and procure a survival advantage after relapse.

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Inhibition of Cyclin Dependent Kinases Causes p53 Dependent Apoptosis in Renal Cell Carcinoma 

Renal cell carcinoma (RCC) is extraordinarily resistant to conventional chemotherapy and, thus, it is important to investigate novel anticancer agents. Ishimaru et al (page 2143) evaluated the effect of roscovitine, a pharmacological inhibitor of cyclin dependent kinases (CDKs) on RCC cell lines in vitro. Roscovitine caused dose and time dependent inhibition of CDK2 autophosphorylation, and of CDK9 mediated Pol II phosphorylation in ACHN (p53-wt) and 786-O (p53-inactive) RCC cell lines. The drug also induced apoptosis in both cell lines within a narrow concentration range (approximately 10 μg/ml). Apoptosis induction was more efficient in ACHN cells than in 786-O cells and was at least partly due to the activity of p53. In ACHN cells roscovitine induced apoptosis was associated with induction of p21, and with reduced expression of Akt1, XIAP and phospho-Rb. These changes also were dependent on p53 and were either not present (p21) or showed a different dose pattern (Akt1, XIAP, phospho-Rb) in 786-O cells.

The partial restoration of roscovitine induced apoptosis in 786-O cells by the Mdm-2 inhibitor nutlin-3 suggests that the inactivating mutation of VHL in these cells, and its destabilizing effect on p53, is responsible for the decreased sensitivity to apoptosis. The authors show that the pro-apoptotic effect of roscovitine is restricted to a narrow dose range in RCC cells and is partly dependent on p53, and they conclude that these data provide insight into the role of VHL mutation and p53 in the RCC response to therapeutic CDKs. They suggest that roscovitine may be a novel potential chemotherapeutic agent in a subset of RCC patients if a narrow therapeutic window is used.