PROGINS-polymorphism in the human progesterone receptor gene: a potential genetic risk factor for prostate cancer? [Elektronische Ressource] / Christian Freund

Christian Freund

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1Baylor College of Medicine, Houston, TexasBetreuung durch: Prof. Dr. med. D. G. Kieback(jetzt: Universitäts-Frauenklinik Maastricht, Niederlande)PROGINS-polymorphism in the human progesteronereceptor gene: a potential genetic risk factor forprostate cancer ?Dissertationzur Erlangung des Doktorgrades der Medizinder Medizinischen Fakultät derUniversität UlmChristian FreundStuttgart20022Amtierender Dekan: Professor Dr. R. Marre1. Berichterstatter: Professor Dr. D. Kieback2. Berichterstatter: Professor Dr. R. HautmannTag der Promotion: 14.6.20023Table of contents:1. Introduction page 5-132. Materials & Methods page 14-203. Results page 21-234. Discussion page 24-325. Conclusion page 336. Summary page 347. References page 35-478. Acknowledgements page 484Abbreviations used:BP base pairBPH benign prostatic hyperplasiaCAT chloramphenicol acetyltransferaseDHT dihydrotestosteroneDNA deoxyribonucleic acidMRNA messenger-ribonucleic acidPCR polymerase chain reactionPROGINS progesterone receptor gene insertion in intron GPSA prostate-specific antigenPSM prostate-specific membrane antigenTUR-P transurethral resection of the prostate51. Introduction:1.1. Prostate cancer and risk factorsThe prostate gland is a fibromuscular and glandular organ lying just inferior to the bladder(see Fig.1). In the United States, prostate cancer has become the second most commonlydiagnosed cancer in men (19).

Informations

• Publié par: universitat_ulm
• Publié le: 01 janvier 2002
• Nombre de lectures: 4
• Langue: English

Extrait

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Baylor College of Medicine, Houston, Texas Betreuung durch: Prof. Dr. med. D. G. Kieback (jetzt: Universitäts-Frauenklinik Maastricht, Niederlande)

PROGINS-polymorphism in the human progesterone receptor gene: a potential genetic risk factor for prostate cancer ?

Dissertation zur Erlangung des Doktorgrades der Medizin der Medizinischen Fakultät der Universität Ulm

Christian Freund Stuttgart 2002

Amtierender Dekan:

1. Berichterstatter:

2. Berichterstatter:

Tag der Promotion:

2

Professor Dr. R. Marre

Professor Dr. D. Kieback

Professor Dr. R. Hautmann

14.6.2002

Table of contents:

1. 2. 3.

4.

5. 6. 7. 8.

Introduction Materials & Methods Results

Discussion

Conclusion Summary References Acknowledgements

page 5-13 page 14-20 page 21-23

page 24-32

page 33 page 34 page 35-47 page 48

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Abbreviations used:

BP BPH CAT DHT DNA MRNA PCR PROGINS PSA PSM TUR-P

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base pair benign prostatic hyperplasia chloramphenicol acetyltransferase dihydrotestosterone deoxyribonucleic acid messenger-ribonucleic acid polymerase chain reaction progesterone receptor gene insertion in intron G prostate-specific antigen prostate-specific membrane antigen transurethral resection of the prostate

1.Introduction:

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1.1. Prostate cancer and risk factors The prostate gland is a fibromuscular and glandular organ lying just inferior to the bladder (see Fig.1). In the United States, prostate cancer has become the second most commonly diagnosed cancer in men (19). In 1995, prostate cancer was diagnosed in approximatley 317.000 U.S. males and an estimated 41.400 Americans succumbed to prostate cancer (158). The incidence of prostate cancer has risen dramatically over the last decade and even more as can be explained by increased longevity (41). This may be partially explained by stage-migration as use of PSA has revolutionized prostate cancer diagnosis in many asymptomatic patients (30,90).

Fig.1: Male human anatomy: localization of the prostate gland (143)

Despite the high incidence of prostate cancer, there is surprisingly little knowledge about the etiology and pathogenesis of prostate cancer (88,161). Prostate cancer represents a heterogeneous disease entity with varying degrees of behavior, aggressiveness, patterns of metastasis and response to therapy (55). The cause of prostate cancer is likely to be a combination of environmental and genetic factors (18). Several factors have been found to correlate with an increased incidence of prostate cancer:

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1.1.1. Family history and genetic factors: There are substantial differences in the prevalence of prostate cancer among populations (115). Having a family history of prostate cancer increases a mans own risk of developing prostate cancer (17). Among men with a positive family history for prostate cancer, there is a two- to threefold elevation in terms of relative prostate cancer risk (27,141). The relative risk was greater if a brother had prostate cancer (relative risk of 4.5) than if the father had prostate cancer (relative risk of 2.3). A family history of breast and/or ovarian cancer in a mother or sister was also positively associated with prostate cancer risk (relative risk of 1.7). Men with a family history of both prostate and breast/ovarian cancer were at an even increased risk of prostate cancer (relative risk of 5.8) (31). Genetic factors are especially important in younger patients as familial and inheritable forms of prostate cancer exist, too. These forms of prostate cancer may account for up to 43% of early-onset disease, but make up only a rather small proportion (9%) of all prostate cancer occurrences (28,74).

Therefore, the existence of prostate cancer susceptibility genes is likely. Genetic alterations involve changes in DNA sequence that may lead to aberrant gene products or proteins. Although accurate definitions are somewhat controversial, the term mutation as opposed to polymorphism is used by many to refer to changes in sequence which are not present in most individuals of a species and either have been associated with risk of disease or have resulted from damage inflicted by external agents. In contrast to mutations, which occur typically in less than one percent of the test population,  polymorphisms are more frequently observed alterations (62,116).

A number of techniques are available for mapping and identifying genes involved in modifying susceptibility to prostate cancer (109). Genes identified as canditates either from mapping data or through knowledge of their function can be screened for polymorphisms, and, if polymorphisms are present, these can be tested for association with disease (160). If a disease gene is tightly linked to a genetic marker, then the alleles of the disease gene and marker may be associated with each other and a particular marker allele may be found more frequently among affected subjects than in the general population. These association studies are generally carried out by measuring the frequency of marker alleles in a group of cases and matched controls.

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No single genetic locus appears to be responsible for a large proportion of hereditary prostate cancer cases (52,109). Rare, highly penetrant prostate cancer susceptibility genes (BRCA1/2) have been described (120). Familial susceptibility genes may be associated with a much lower risk but may be responsible for a greater proportion of cases (76). Penetrance is variable in these cases and environmental factors may be much more important (52). Polymorphisms in the prostate cancer susceptibility gene HPC2/ELAC2 have been shown to increase prostate cancer risk (117). Other polymorphismsms in candidate genes, e.g. those which are not sufficient to cause prostate cancer on their own, have been shown to influence the development of prostate cancer and are risk factors in an epidemiological sense. Among these are the genes encoding for the vitamin D receptor (37), androgen receptor (111,133), IGF (insulin-like growth factor) (42,132), and genes for various enzymes involved in androgen metabolism (89). Furthermore, changes like hypermethylation of the GSTP1 gene promoter (91), mutations in the helix-loop-helix- leucine zipper gene MXI1 (46), mutations of PI3 kinase regulator gene PTEN (24,44), hypermethylation of cell-cell-adhesion molecule E-cadherin gene CDH1 (108,150), mutations of tumor suppressor gene p53 (15), possible overexpression of the HER-2/neu receptor tyrosine kinase gene in prostate cancer (151) and decreased expression of the metastasis suppressor gene KAI1 (43) have all been implicated with increased risk of prostate cancer.

1.1.2. Hormonal factors: Hormone-related cancers account for almost 30% of all cancers diagnosed in the United States (65), including cancer of the prostate and testis in men and cancer of the endometrium, breast and ovary in women (128). Experimental evidence indicates that hormonal imbalances may be involved in tumorigenesis and/or contribute to their development (92). Steroid hormones like androgens, estrogens and progestins are involved in the development and/or progression of cancer (79). This is due to the fact that ligand- occupied steroid hormone receptors act as transcription factors thereby influencing the rate of cell division and degree of cell differentiation. The magnitude of the tissue response is correlated not only to the number of receptor-bearing cells but also to the receptor density per cell.

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Male sex hormones, most notably testosterone and dihydrotestosterone, are heavily involved in growth and maintenance of normal prostate epithelium as well as in the development of prostate cancer (11,69). High levels of circulating testosterone and low levels of sex hormone binding globulin  even though both are within normal endogenous ranges - are associated with increased risk for prostate cancer (56). Serum levels of free testosterone were higher among prostate cancer patients than in controls (40).  As prostate cancer growth depends on androgens, cancers often regress after androgen stimulation has been withdrawn (48,72) but nearly all patients ultimately develop androgen-independent prostate cancer and succumb to the disease (87).   The mechanisms by which tumor cells finally escape androgen ablation and become androgen-independent are not well understood (144). More than 80% of androgen-independent prostate tumors show high levels of androgen receptor expression. In some cancers of the prostate, androgen receptor levels are increased because of gene amplification and/or overexpression, whereas in others, the androgen receptor is mutated (162). Despite some controversy, an association between a polymorphism in the androgen receptor gene (CAG repeat) and prostate cancer has been made (60). Also, a polymorphism at codon 726 of the androgen receptor gene is six times more common in prostate cancer patients than in controls (106).

In addition to testosterone, the steroid hormones progesterone, estrogen and vitamin D as well as their cognate receptors are present and implicated in the development of normal prostate tissue and in the pathophysiology of prostate cancer (39). Nevertheless, most of the research correlating prostate cancer occurrence with hormonal factors has focused on androgens and their receptors rather than investigating the role of estrogen or progesterone.

1.1.3. Racial differences: African-Americans in the United States have the highest prostate cancer rate in the world and nearly twice that of whites in the United States (121). In African-Americans, serum concentrations of complexed and free testosterone are 15 % and 13% higher than in Caucasians. This could explain the twofold difference in prostate cancer risk (121). More interestingly, African-American men demonstrate higher serum PSA levels than white males even after adjustment for patients' age and prostate volume in men without prostate

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cancer and for cancer grade and stage in men with prostate cancer (1). The etiology of higher PSA levels in African-Americans is not understood yet and might be secondary to biological and/or environmental/ socioeconomic factors (1).

1.1.4. Dietary factors: Prostate cancer risk appears to be positively correlated with high intake of lipids of animal origin (8,119). This is judged from the observation that while native Japanese and Chinese males have a lower risk for prostate cancer, the risk observed in second- and third- generation Japanese-Americans and Chinese-Americans is similar to white American men (18). This may be secondary to changes in nutrition. Dietary lipid may be related to prostate cancer risk, although the specific lipid(s) responsible for this increased risk have not been identified (83). Given the diverse effects of fatty acids on cellular physiology and chemistry, the relationship between lipid intake and/or metabolism and cancer development is rather complex. However, an interaction between dietary factors and tumor development appears likely, as for example vitamins and minerals are acting as antioxidants and a variety of genetic factors influence lipid metabolism (83).  In addition, obesity may be associated with increased risk not only for prostate cancer but also for a variety of other cancers. Obesity may influence the cancer risk secondary to alterations in the metabolism of steroid hormones, insulin, and insulin growth factor, the distribution of body fat and changes in adiposity at different ages (25). A positive association between plasma concentrations of insulin-like growth factor-I and prostate cancer risk was observed. Men in the highest quartile of insulin-like growth factor-I concentrations had a relative prostate cancer risk of 4.3 compared with men in the lowest quartile (33). In the established prostate cancer cell line LnCaP, a close association between proliferation rate and content of the intracellular calcium pool was seen (32,93). Vitamin D has been shown to have antiproliferative effects in prostate cancerin-vitro (113). Therefore, vitamin D deficiency may increase the risk of initiation and progression of prostate cancer (148).

1.1.5. Age: The incidence of prostate cancer increases with age. The highest prevalence is found in men in their seventh and eighth decade of life. As many as 40% of 70-79 year old males

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may harbor prostate cancer (12).Increased age is a relative risk factor for advanced pathological findings in men with clinical stage B1 prostate cancer (7).

A summary of the risk factors discussed above is given in Tab.1.

Risk factor Increases individual risk References Concentration of steroid hormones in serum  unknown (11,69) Age unknown (12)

Family history two- to threefold Rac e (African-American  twofold vs. Caucasian-American) Diet, especially lipid intake unknown Table 1: Risk factors for prostate cancer

(27,141) (121) (8,119)

1.2. Clinical aspects of prostate cancer The diagnosis of prostate cancer must be made early in order to effectively decrease prostate cancer mortality (85). In principle, prostate cancer patients can be stratified according to their risk of cancer progression and assigned to one of three groups:

a.) high-risk patients who will (or may have) already progressed to metastatic prostate cancer without appropriate forms of treatment and who may not be cured b.) potentially curable patients at medium risk for disease progression and metastatic disease requiring antitumor therapy c.) low risk patients with insignificant cancers likely not needing any form of treatment (127).

As a consequence of improved screening for prostate cancer, the number of patients with small, localized tumors (group c.) has increased over time (75). Therefore, screening of whole populations with PSA remains controversial (5,9).

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It is now widely accepted that many patients with small, localized and well-differentiated tumors may never experience clinically manifest prostate cancer in their lives. Therefore, not every prostate cancer might warrant treatment. In contrast, patients falling into group b.) will have the greatest benefit from cancer screening. Nevertheless, even in patients who are at risk for cancer progression, treatment-induced morbidity may outweigh potential marginal survial benefits. This is due to the fact that many prostate cancer patients are diagnosed late in life, suffer from serious co-morbidities, and may die with instead from prostate cancer (71,99). Unfortunately, no molecular marker for biological aggressiveness and metastatic potential of prostate cancer is available to date which would allow to accurately predict the course of disease on an individual basis (47). Therefore, intense research effort is under way to determine genetic differences which could serve as individual risk predictors.

1.3. PROGINS In 1995, a polymorphism in the human progesterone receptor gene was identified and named PROGINS (100,122). This polymorphism consists of three obligate structural aberrations: (1) Alu insert, (2) silent point mutation in exon 5 and (3) functional mutation in the hinge region (exon 4). As a consequence of this mutation, PROGINS encodes for a receptor protein with increased stability (123) and increased hormone-induced transcriptional activity. PROGINS was found to be an risk factor for ovarian cancer in BRCA1 and BRCA2 mutation carriers who were never exposed to oral contraceptives (100,122,123). In contrast, PROGINS lowers the risk for breast cancer in postmenopausal women (45,154).

1.4. Steroid receptors and cancer Strong evidence for the implication of steroids and steroid receptors in oncogenesis and tumor growth exists in the female population (36,126). Estrogen-based contraceptives reduce the risk of ovarian cancer, but addition of a progestagen may counteract the increased risk of endometrial cancer (38). Estrogens used in postmenopausal hormone replacement therapy increase the risk of both breast and endometrial cancer, but addition of a progestagen may counteract the increased risk to the endometrium (38). In human breast cancer, the presence and concentration of estrogen and progesterone receptors is of prognostic and therapeutic significance: tumors with high receptor levels