Androgens, through their actions on the androgen receptor (AR), are required for the development of the prostate and contribute to the pathologic growth dysregulation observed in prostate cancers. Consequently, androgen ablation has become an essential component of the pharmacotherapy of prostate cancer. In this study, we explored the utility of targeting processes downstream of AR as an alternate approach for therapy. Specifically, we show that the serum and glucocorticoid-regulated kinase 1 (SGK1) gene is an androgenregulated target gene in cellular models of prostate cancer. Furthermore, functional serum-and glucocorticoid-regulated kinase 1 (SGK1) protein, as determined by the phosphorylation of its target Nedd4-2, was also increased with androgen treatment. Importantly, we determined that RNA interference-mediated knockdown of SGK1 expression attenuates the androgen-mediated growth of the prostate cancer cell line LNCaP. Given these findings, we explored the utility of SGK1 as a therapeutic target in prostate cancer by developing and evaluating a small-molecule inhibitor of this enzyme. From these studies emerged GSK650394, a competitive inhibitor that quantitatively blocks the effect of androgens on LNCaP cell growth. Thus, in addition to androgen ablation, inhibition of pathways downstream of AR is likely to have therapeutic utility in prostate cancer. [Cancer Res 2008;68(18):7475-83]
The effects of vasopressin (AVP) and vasopressin antagonists on lumen diameters of cortical afferent and efferent arterioles isolated from rabbit kidneys were examined. Over a concentration range of 10(-14) to 10(-7) M, AVP had no effect on lumen diameters of afferent arterioles, although the arterioles were responsive to norepinephrine. Similarly, addition of 10(-8) M AVP to the lumen of afferent arterioles or to the bath of arterioles pretreated with indomethacin had no effect. In contrast, AVP caused a concentration-dependent reduction of lumen diameters of efferent arterioles. AVP was approximately 100-fold more potent than norepinephrine in producing contraction of efferent arterioles. The V1-selective antagonist, [d(CH2)5Tyr(Me)]AVP, and the V1/V2-antagonist, d(CH2)5D-Tyr(Et) desGlyVAVP, inhibited the vasoconstriction produced by AVP in a concentration-dependent but noncompetitive manner. The V2-selective antagonist, [d(CH2)5D-Ile]VAVP, had no significant effect on AVP-induced vasoconstriction. We conclude that, under the in vitro conditions used, AVP selectively contracts efferent arterioles. The results provide direct evidence for a postglomerular vascular effect of AVP in the renal cortex. This activity, together with its previously described effects on the glomerulus, suggests that AVP may produce changes in glomerular function and/or peritubular forces that are involved in tubular reabsorption.
A highly purified suspension of rabbit proximal tubules was cultured in a hormone-supplemented serum-free medium. This primary culture yielded a homogeneous population of cells that demonstrated functional and morphological polarity in mono-layers. The characteristics of the Na-dependent glucose transporter in the luminal membrane were studied by measuring the uptake of alpha-methylglucoside (AMG). The kinetics of Na-dependent AMG uptake were consistent with a single saturable system with an apparent Km of 0.8 mM and Jmax of 0.14 nmol X mg-1 X min-1. AMG permeability was 0.10 microliter X mg-1 X min-1. Uptake was inhibited 95% by 0.1 mM phlorizin and by removal of sodium. The stoichiometry of Na/glucose interaction with the carrier was 2:1. These characteristics are typical of the characteristics described for the late proximal tubule. To examine whether the glucose that enters the cell across the luminal membrane is incorporated into the metabolic pool of the cell, we studied the oxidation of [14C]glucose to 14CO2 in the absence and presence of phlorizin. Significant decarboxylation of [1-14C]glucose and [6-14C]glucose was observed, consistent with the existence of aerobic metabolism and a hexose monophosphate shunt. In the presence of 0.1 mM phlorizin, uptake and oxidation of D-glucose were inhibited to an identical degree, suggesting that luminal uptake is a rate-limiting step in the oxidation of glucose by these proximal tubular cells. These studies indicate that proximal tubular cells in primary culture utilize glucose as an energy source and that the glucose derived from transport across the luminal membrane is incorporated into the metabolic pool of the cell.
The effects of endothelin 1, 2, and 3 (ET-1, -2, -3) on lumen diameter of individual afferent and efferent arterioles dissected from rabbit kidney were examined. ET-1 produced concentration-dependent and long-lasting decreases in lumen diameter in both arterioles. The 50% maximum response (EC50) values were 1.4 +/- 0.41 and 0.9 +/- 0.65 nM for afferent and efferent arterioles, respectively. In afferent arterioles, ET-2 produced decreases in lumen diameter (EC50 = 3.3 +/- 1.75 nM) that were indistinguishable from ET-1. However, ET-3 was considerably less potent (EC50 = 21.9 +/- 6.0 nM, P less than 0.05) than ET-1 or ET-2. Similar results were obtained in the efferent arteriole in which the EC50 for ET-2 (0.25 +/- 0.1 nM) was similar to ET-1, but ET-3 was significantly less potent (EC50 = 2.6 +/- 0.4 nM, P less than 0.05). Nicardipine (0.01-1 microM) produced concentration-dependent shifts in the ET-1 concentration-response curve in afferent arterioles. Verapamil (1 microM) also caused a significant shift in the ET-1 response curve. The contractile response to ET-1 was significantly more sensitive to nicardipine than was the response to norepinephrine. In contrast, the response of efferent arterioles to ET-1 and norepinephrine was unaffected by nicardipine or verapamil. The results demonstrate that ETs are potent vasoconstrictors of both the pre- and postglomerular microvasculature and may play a role in the regulation of renal hemodynamics.(ABSTRACT TRUNCATED AT 250 WORDS)
The possibility that prostaglandins (PG) located in the renal medulla may influence renal excretion of sodium by a direct tubular action was examined by the addition of prostaglandins PGE2, PGF2alpha, and PGA2 to the peritubular and luminal surfaces of isolated perfused medullary thick ascending lumbs and collecting tubules from rabbit kidneys. The prostaglandins at both high (2.5 x 10(-4) M) and low (10 (-10) M, 10 (-7) M) concentrations had no effect on transepithelial potential difference and net sodium flux across these segments. Pretreatment of the animals with indomethacin did not influence the results. In vivo, both PGE2 and PGF2alpha, caused a natriuresis when infused directly into one renal artery, whereas PGA2 had no effect on sodium excretion. The prostaglandin inhibitors indomethacin, meclofenamate, and RO 20-5720 similarly had no direct effect on sodium transport in the nephron segments studied. It is concluded that the previously observed influence of prostaglandins and prostaglandin inhibitors on renal excretion of sodium in vivo are not mediated by a direct tubular action.
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