Anitta Pulkka

Production, purification, and functional analysis of recombinant human and mouse 17β-hydroxysteroid dehydrogenase type 7 ☆

17beta-Hydroxysteroid dehydrogenases (17HSDs) have a central role in the regulation of the biological activity of sex steroid hormones. There is increasing evidence that in addition to their importance in gonads, these hormones also have substantial metabolic roles in a variety of peripheral tissues. In the present study, the cDNA of human 17HSD type 7 was cloned. In silico, the gene corresponding to the cDNA was localized on chromosome 1q23, close to the locus of hereditary prostate cancer 1 (HPC1) (1q24-25) and primary open-angle glaucoma (GLC1A) (1q23-25). Further, a pseudogene was found on chromosome 1q44, close to the locus of predisposing for early-onset prostate cancer (PCaP) (1q42.2-43). Both human (h17HSD7) and mouse 17HSD type 7 (m17HSD7) were for the first time produced as recombinant proteins and purified for functional analyses. Further, kinetic parameters and specific activities were described. h17HSD7 converted estrone (E1) to a more potent estrogen, estradiol (E2), and dihydrotestosterone (DHT), a potent androgen, to an estrogenic metabolite 5alpha-androstane-3beta, 17beta-diol (3betaA-diol) equally, thereby catalyzing the reduction of the keto group in either 17- or 3-position of the substrate. Minor 3betaHSD-like activity towards progesterone (P) and 20-hydroxyprogesterone (20-OH-P), leading to the inactivation of P by h17HSD7, was also detected. m17HSD7 efficiently catalyzed the reaction from E1 to E2 and moderately converted DHT to an inactive metabolite 5alpha-androstane-3alpha,17beta-diol (3alphaA-diol) and to an even lesser degree 3betaA-diol. The mouse enzyme did not metabolize P or 20-OH-P. The expression of 17HSD type 7 was observed widely in human tissues, most distinctly in adrenal gland, liver, lung, and thymus. Based on the enzymatic characteristics and tissue distribution, we conclude that h17HSD7 might be an intracrine regulator of steroid metabolism, fortifying the estrogenic milieu in peripheral tissues.

Sex steroid hormone metabolism and prostate cancer

The growth and function of the prostate is dependent on androgens. The two predominant androgens are testosterone, which is formed in the testis from androstenedione and 5alpha-dihydrotestosterone, which is formed from testosterone by 5alpha-reductases and is the most active androgen in the prostate. Prostate cancer is one of the most common cancers among men and androgens are involved in controlling the growth of androgen-sensitive malignant prostatic cells. The endocrine therapy used to treat prostate cancer aims to eliminate androgenic activity from the prostatic tissue. Most prostate cancers are initially responsive to androgen withdrawal but become later refractory to the therapy and begin to grow androgen-independently. Using LNCaP prostate cancer cell line we have developed a cell model to study the progression of prostate cancer. In the model androgen-sensitive LNCaP cells are transformed in culture conditions into more aggressive, androgen-independent cells. The model was used to study androgen and estrogen metabolism during the transformation process. Our results indicate that substantial changes in androgen and estrogen metabolism occur in the cells during the process. A remarkable decrease in the oxidative 17beta-hydroxysteroid dehydrogenase activity was seen whereas the reductive activity seemed to increase. The changes suggest that during transformation estrogen influence is increasing in the cells. This is supported by the cDNA microarray screening results which showed over-expression of several genes up-regulated by estrogens in the LNCaP cells line representing progressive prostate cancer. Since local steroid metabolism controls the bioavailability of active steroid hormones in the prostate, the variations in steroid-metabolizing enzymes during cancer progression may be crucial in the regulation of the growth and function of the organ.

17β-hydroxysteroid dehydrogenases: their role in pathophysiology

Abstract 17β-Hydroxysteroid dehydrogenases (17HSDs) regulate the biological activity of sex steroid hormones in a variety of tissues by catalyzing the interconversions between highly active steroid hormones, e.g. estradiol and testosterone, and corresponding less active hormones, estrone and androstenedione. Epidemiological and endocrine evidence indicates that estrogens play a role in the etiology of breast cancer, while androgens are involved in mechanisms controlling the growth of normal and malignant prostatic cells. Using LNCaP prostate cancer cell lines, we have developed a cell model to study the progression of prostate cancer. In the model LNCaP cells are transformed in culture condition into more aggressive cells. Our data suggest that substantial changes in androgen and estrogen metabolism occur in the cells, leading to increased production of active estrogens during the process. In breast cancer, the reductive 17HSD type 1 activity is predominant in malignant cells, while the oxidative 17HSD type 2 mainly seems to be present in non-malignant breast epithelial cells. Deprivation of an estrogen response by using specific 17HSD type 1 inhibitors is a tempting approach in treating estrogen-dependent breast cancer. Our recent studies demonstrate that in addition to sex hormone target tissues, estrogens may be important in the development of cancer in some other tissues previously not considered to be estrogen target tissues, such as the gastrointestinal tract.

Enzymes as modulators in malignant transformation

Experimental data suggest that sex steroids have a role in the development of breast and prostate cancers. The biological activity of sex steroid hormones in target tissues is regulated by several enzymes, including 17beta-hydroxysteroid dehydrogenases (17HSD). Changes in the expression patterns of these enzymes may significantly modulate the intracellular steroid content and play a pathophysiological role in malignant transformation. To further clarify the role of 17HSDs in breast cancer, we analyzed the mRNA expressions of the 17HSD type 1, 2, and 5 enzymes in 794 breast carcinoma specimens. Both 17HSD type 1 and 2 mRNAs were detected in normal breast tissue from premenopausal women but not in specimens from postmenopausal women. Of the breast cancer specimens, 16% showed signals for 17HSD type 1 mRNA, 25% for type 2, and 65% for type 5. No association between the 17HSD type 1, 2, and 5 expressions was detected. The patients with tumors expressing 17HSD type 1 mRNA or protein had significantly shorter overall and disease-free survival than the other patients. The expression of 17HSD type 5 was significantly higher in breast tumor specimens than in normal tissue. The group with 17HSD type 5 overexpression had a worse prognosis than the other patients. Cox multivariate analyses showed that 17HSD type 1 mRNA, tumor size, and ERalpha had independent prognostic significance. Using an LNCaP prostate cancer cell line, we developed a cell model to study the progression of prostate cancer. In this model, androgen-sensitive LNCaP cells are transformed in culture conditions into more aggressive, androgen-independent cells. The model was used to study androgen and estrogen metabolism during the transformation process. Our results indicate that substantial changes in androgen and estrogen metabolism occur in the cells during the process. A remarkable decrease in oxidative 17HSD activity was seen, whereas reductive activity seemed to increase. Since local steroid metabolism controls the bioavailability of active steroid hormones of target tissues, the variations in steroid-metabolizing enzymes during cancer progression may be crucial in the regulation of the growth and function of organs.

17β-Hydroxysteroid dehydrogenases and cancers☆

Abstract 17β-Hydroxysteroid dehydrogenases (17HSDs) catalyze the interconversions between active 17β-hydroxysteroids and less-active 17-ketosteroids thereby affecting the availability of biologically active estrogens and androgens in a variety of tissues. The enzymes have different enzymatic properties and characteristic cell-specific expression patterns, suggesting differential physiological functions for the enzymes. Epidemiological and endocrine evidence indicate that estrogens play a key role in the etiology of breast cancer while androgens are involved in mechanisms controlling the growth of prostatic cells, both normal and malignant. Recently, we have developed, using LNCaP prostate cancer cell lines, a cell model to study the progression of prostate cancer. In the model LNCaP cells are transformed in culture condition to more aggressive cells, able to grow in suspension cultures. Our results suggest that substantial changes in androgen and estrogen metabolism occur in the cells during the process. These changes lead to increased production of active estrogens during transformation of the cells. Data from studies of breast cell lines and tissues suggest that the oxidative 17HSD type 2 may predominate in human non-malignant breast epithelial cells, while the reductive 17HSD type 1 activity prevails in malignant cells. Deprivation of an estrogen response by using specific 17HSD type 1 inhibitors is a tempting approach to treat estrogen-dependent breast cancer. Our recent studies demonstrate that in addition to sex hormone target tissues, estrogens may be important in the development of cancer in some other tissues previously not considered as estrogen target tissues such as colon. Our data show that the abundant expression of 17HSD type 2 present in normal colonic mucosa is significantly decreased during colon cancer development.

17β-Hydroxysteroid dehydrogenase type 2: independent prognostic significance and evidence of estrogen protection in female patients with colon cancer

Abstract The mRNA expression of 17β-hydroxysteroid dehydrogenase (17HSD) types 1 and 2 enzymes catalyzing opposite reaction of estrogen metabolism was investigated in colon cancer. Further, the significance of the 17HSD type 2 enzyme as a possible marker of colorectal cancer (CRC) prognosis was studied. In the normal mucosa, 17HSD type 2 mRNA was predominantly expressed in the surface epithelium and in the upper parts of the crypts. In the lamina propria expression was seen in endothelial cells and mononuclear phagocytes. In colorectal tumors, 17HSD type 2 expression was in most cases downregulated. Female patients had significantly more cancers with high 17HSD type 2 mRNA expression ( n =11/35; 31%) than male patients ( n =3/39; 8%) ( P =0.02). We observed a significant impact of 17HSD type 2 mRNA expression on survival in female patients with distal colorectal cancer ( n =24), with an overall cumulative 5-year survival rate of 54% in those with low 17HSD type 2 mRNA expression. None of the female patients with high 17HSD type 2 mRNA expression survived ( n =11; P =0.0068; log rank 7.32). In male patients, no significant association with survival was observed. Our data provide evidence suggesting that low 17HSD type 2 mRNA expression is an independent marker of favorable prognosis in females with distal colorectal cancer, supporting the presence of gender- and location-related differences in the pathogenesis of colon cancer.

Changes in gene expression in response to polyamine depletion indicates selective stabilization of mRNAs.

We used differential display analysis to identify mRNAs responsive to changes in polyamine synthesis. As an overproducing model we used the kidneys of transgenic hybrid mice overexpressing ornithine decarboxylase and S-adenosylmethionine decarboxylase, two key enzymes in polyamine biosynthesis. To identify mRNAs that respond to polyamine starvation, we treated Rat-2 cells with alpha-difluoromethylornithine, a specific inhibitor of polyamine biosynthesis. We isolated 41 partial cDNA clones, representing 37 differentially expressed mRNAs. Of these, 15 have similarity with known genes, five appear to be similar to reported expressed sequence tags and seventeen clones were novel sequences. Of the 35 mRNAs expressed differentially after alpha-difluoromethylornithine treatment, 26 were up-regulated. The expression of only three mRNAs was altered in the transgenic animals and all three were down-regulated. Determination of mRNA half-life of three of the mRNAs up-regulated in response to polyamine depletion revealed that the accumulation results from stabilization of the messages. Because most of the transcripts identified from Rat-2 cells suffering polyamine starvation were accumulated, we conclude that polyamine depletion, while blocking cell growth, is stabilizing mRNAs. This may be due to the lack of spermidine for post-translational modification of the eukaryotic initiation factor 5A, which plays a major role in mRNA turnover. The coupling of mRNA stabilization with cell-growth arrest in response to polyamine starvation provides cells with an economical way to resume growth after recovery from polyamine deficiency.

Structure and organization of the gene encoding rat S-adenosylmethionine decarboxylase

The gene for S‐adenosylmethionine decarboxylase (AdoMetDC) was isolated from a rat genomic library using AdoMetDC cDNA as a probe. Nucleotide sequence analysis shows that the rat AdoMetDC gene consists of 8 exons which encode a protein identical to that inferred by a rat AdoMetDC cDNA sequence. The exons range in length from 43 to 1964 base pairs spanning 15672 bases of chromosomal DNA. All of the exon/intronjunctions were found to conform to the consensus splice donor and acceptor sequences, Exon 8 corresponds to the 3′ noncoding region of the 2 species of AdoMetDC mRNA which are formed by alternative utilization of 2 polyadenylation signals separated from each other by 1272 nucleotides. The transcription initiation site was located by SI nuclease protection and by primer extension analysis, −325 nucleotides upstream of the translation initiation codon. The promoter region of the rat AdoMetDC gene contains a TATA box at −29 base pairs. No typical GC or CAAT boxes are located in the promoter, but six GC boxes and several putative binding sites for both tissue‐specific and non‐specific transcription factors are found in the proximal part of intron I. Southern blot analyses reveal a complex hybridization pattern suggesting that there are multiple copies of the AdoMetDC gene in the rat genome.

On the metabolism of ornithine in synaptosomal preparations.

The present results show that ornithine is metabolized to glutamate by isolated synaptosomes from mouse cerebral cortex. Under the experimental conditions used the glutamate was channelled further to the tricarboxylic acid cycle, and to a lesser degree to GABA. The possible significance of these metabolic pathways are discussed. Results of an earlier study suggest an excessive metabolism of ornithine via putrescine to GABA in synaptosomes. Those results could not be verified in the present study and a possible reason for the disagreement is demonstrated. However, the present results suggest that putrescine, which is known to be produced from ornithine elsewhere in the nervous tissue, may be metabolized to GABA in synaptosomes.

Possible Involvement of Humoral Regulation in the Effects of Elevated Cerebral 4‐Aminobutyric Acid Levels on the Polyamine Metabolism in Brain

Abstract: It has been reported in several recent studies that the manipulation of cerebral 4‐aminobutyric acid (GABA) level results in unexpected changes in the cerebral polyamine metabolism in vivo. The mechanisms behind these interactions have remained unknown. The present results show that the changes in polyamine metabolism are not limited to the brain, but are observable also in the liver, which served as a peripheral reference tissue. Different types of responses in the activities of the poiyamine‐synthesizing enzymes, ornithine decarboxylase and adenosylmethionine decarboxylase, were observed after increasing the cerebral GABA concentration of mice with varying doses of two GABA transaminase inhibitors, gabaculine and ethanolamine‐O‐sulphate. The time course of the significant changes in the enzyme activities showed significant correlation between the brain and liver. The possibility of direct effects of the drugs on liver was excluded by injecting them intracerebroventricularly, and by performing control experiments with equal doses given peripherally. It is concluded that the observed changes in the polyamine metabolism of liver are produced through centrally mediated humoral regulation, and that the corresponding changes in the brain are obviously due to the same factor or factors, since they are significantly correlated to the changes in liver.