Phosphoinositide metabolism in human prostate cancer cells in vitro

PI5P4Kα supports prostate cancer metabolism and exposes a survival vulnerability during androgen receptor inhibition

Phosphatidylinositol (PI)regulating enzymes are frequently altered in cancer and have become a focus for drug development. Here, we explore the phosphatidylinositol-5-phosphate 4-kinases (PI5P4K), a family of lipid kinases that regulate pools of intracellular PI, and demonstrate that the PI5P4Kα isoform influences androgen receptor (AR) signaling, which supports prostate cancer (PCa) cell survival. The regulation of PI becomes increasingly important in the setting of metabolic stress adaptation of PCa during androgen deprivation (AD), as we show that AD influences PI abundance and enhances intracellular pools of PI-4,5-P2. We suggest that this PI5P4Kα-AR relationship is mitigated through mTORC1 dysregulation and show that PI5P4Kα colocalizes to the lysosome, the intracellular site of mTORC1 complex activation. Notably, this relationship becomes prominent in mouse prostate tissue following surgical castration. Finally, multiple PCa cell models demonstrate marked survival vulnerability following stable PI5P4Kα inhibition. These results nominate PI5P4Kα as a target to disrupt PCa metabolic adaptation to castrate resistance.

Androgen-independent prostate cancer: potential role of androgen and ErbB receptor signal transduction crosstalk

In prostate cancer (PC), increasing evidence suggests that androgen receptor (AR) signalling is functional under conditions of maximal androgen blockade. PC cells survive and proliferate in the altered hormonal environment possibly by interactions between growth factor-activated pathways and AR signalling. The present review article summarizes the current evidence of this crosstalk and focuses on the interactions among the ErbB receptor network, its downstream pathways, and the AR. The potential role of this crosstalk in the development of androgen independence and in relation to antiandrogen therapy is discussed. Such interactions provide insight into possible complementary or additional strategies in the management of PC.

Identification of the phosphatidic acid phosphatase type 2a isozyme as an androgen-regulated gene in the human prostatic adenocarcinoma cell line LNCaP

Differential display was used to identify novel androgen-regulated genes in the human prostatic adenocarcinoma cell line LNCaP. A 322-base pair cDNA fragment that was consistently induced by the synthetic androgen R1881 revealed 100% homology with the human phosphatidic acid phosphatase type 2a isozyme very recently reported by Kai et al. (PAP-2a; Kai., M., Wada, I., Imai, S.-i., Sakane, F., and Kanoh, H. (1997) J. Biol. Chem. 272, 24572-24578). The fragment was used to clone the corresponding cDNA from a human prostate library. The deduced amino acid sequence confirmed the identity with human PAP-2a. The inducibility of PAP-2a mRNA by androgens was confirmed by Northern blot hybridization. The effect was time- and dose-dependent with a maximal stimulation (4-fold) after 24 h of treatment with 10(-9) M R1881. The steroid specificity of PAP-2a mRNA regulation was found to be in agreement with the aberrant ligand specificity of the mutated androgen receptor in LNCaP cells, supporting the involvement of the androgen receptor in the induction process. Furthermore, low basal levels of PAP-2a mRNA and absence of androgen inducibility were observed in the poorly differentiated and androgen receptor-negative cell lines PC-3 and DU-145. Induction of PAP-2a mRNA was not affected by the protein synthesis inhibitor cycloheximide and was accompanied by a marked increase in PAP-2 activity as measured by the conversion of phosphatidic acid into diacylglycerol in membrane fractions of LNCaP. Comparison of the expression of PAP-2a mRNA in 50 different human tissues revealed ubiquitous expression. The highest levels, however, were observed in the prostate. Since PAP-2 plays a pivotal role in the control of signal transduction by lipid mediators such as phosphatidate, lysophosphatidate, and ceramide-1-phosphate, the ability of androgens to stimulate the expression and activity of this enzyme in prostatic cells may provide an important opportunity for cross-talk between signaling pathways involving lipid mediators and androgens.

Expression of the zinc finger gene EVI-1 in ovarian and other cancers

The EVI-1 gene was originally detected as an ectopic viral insertion site and encodes a nuclear zinc finger DNA-binding protein. Previous studies showed restricted EVI-1 RNA or protein expression during ontogeny; in a kidney and an endometrial carcinoma cell line; and in normal murine oocytes and kidney cells. EVI-1 expression was also detected in a subset of acute myeloid leukaemias (AMLs) and myelodysplasia. Because EVI-1 is expressed in the urogenital tract during development, we examined ovarian cancers and normal ovaries for EVI-1 RNA expression using reverse transcription polymerase chain reaction (RT-PCR) and RNAase protection. Chromosome abnormalities were examined using karyotypes and whole chromosome 3 and 3q26 fluorescence in situ hybridisation (FISH). RNA from six primary ovarian tumours, five normal ovaries and 47 tumour cell lines (25 ovarian, seven melanoma, three prostate, seven breast and one each of bladder, endometrial, lung, epidermoid and histiocytic lymphoma) was studied. Five of six primary ovarian tumours, three of five normal ovaries and 22 of 25 ovarian cell lines expressed EVI-1 RNA. A variety of other non-haematological cancers also expressed EVI-1 RNA. Immunostaining of ovarian cancer cell lines revealed nuclear EVI-1 protein. In contrast, normal ovary stained primarily within oocytes and faintly in stroma. Primary ovarian tumours showed nuclear and intense, diffuse cytoplasmic staining. Quantitation of EVI-1 RNA, performed using RNAase protection, showed ovarian carcinoma cells expressed 0 to 40 times the EVI-1 RNA in normal ovary, and 0-6 times the levels in leukaemia cell lines. Southern analyses of ovarian carcinoma cell lines showed no amplification or rearrangements involving EVI-1. In some acute leukaemias, activation of EVI-1 transcription is associated with translocations involving 3q26, the site of the EVI-1 gene. Ovarian carcinoma karyotypes showed one line with quadruplication 3(q24q27), but no other clonal structural rearrangements involving 3q26. However, whole chromsome 3 and 3q26 FISH performed on lines with high EVI-1 expression showed translocations involving chromosome 3q26. EVI-1 is overexpressed in ovarian cancer compared with normal ovaries, suggesting a role for EVI-1 in solid tumour carcinogenesis or progression. Mechanisms underlying EVI-1 overexpression remain unclear, but may include rearrangements involving chromosome 3q26.

Roles of estrogen and SHBG in prostate physiology

Heretofore, the function of estrogen in the prostate, other than as an antiandrogen, has been unclear. In this review of a growing fund of knowledge about both estrogen and the plasma protein, sex hormone-binding globulin (SHBG), or testosterone-estradiol binding globulin (TeBG), the hypothesis is proposed that estrogen, mediated by SHBG, participates with androgen in setting the pace of prostatic growth and function. It is suggested that the estrogen not only directs stromal proliferation and secretion, but also, through IGF-I, conditions the response of the epithelium to androgen.

Phosphoinositide turnover during hepatocarcinogenesis induced by N-nitrosodiethylamine

The metabolism of phosphatidylinositol (PI) has been examined in rat liver during administration of N-nitrosodiethylamine (NDEA). The activities of PI kinase and PIP kinase were observed to be decreased as early as 7 days from the onset of NDEA administration, and remained suppressed until 60 days. PI synthetase showed a transient increase in activity at 7 days and thereafter the activity declined. The level of diacylglycerol (DAG), a key second messenger, showed a steady rise during the period of NDEA administration. A parallel increase in DAG kinase activity was also apparent. The results suggest that alterations of enzymes central to second messenger system with resulting changes in phosphoinositide turnover are important events during hepatocarcinogenesis induced by NDEA.

Effects of androgen on intracellular calcium of LNCaP cells

Mibolerone (dimethylnortestosterone) or 5 alpha-dihydrostestosterone (DHT) increase intracellular calcium (Ca2+i) of human prostate cancer cells (LNCaP) as early as 2 min after treatment. These effects were concentration-dependent (10(-6)-10(-12) M) and they were blocked by preincubation with hydroxyflutamide (10(-6) M). Verapamil (10(-6) M) also suppressed the mibolerone (10(-6) M)-induced increase in Ca2+i, in cells which were previously exposed to 1 mM CaCl2 introduced in a Ca(2+)-free media. The results indicate that androgens elicit changes in Ca2+i in LNCaP cells as a result of Ca2+ influx through L-type channels in the plasma membrane. Since androgens are involved in the regulation of prostate cell division and growth, these findings suggest that calcium is involved in metabolic and mitogenic responses to steroid hormone in target cells.