Cooperative actions of hepatocyte growth factor and 1,25-dihydroxyvitamin D3 in osteoblastic differentiation of human vertebral bone marrow stromal cells

Bone formation and remodeling require continuous generation of osteoprogenitor cells from bone marrow stromal cells (MSC), which generate and respond to a variety of growth factors with putative roles in hematopoiesis and mesenchymal differentiation. In this study we examine the interaction of two such factors on the maturation of skeletal components. We previously reported that these factors, hepatocyte growth factor (HGF) and 1,25-dihydroxyvitamin D(3) (vitD(3)), act together to increase alkaline phosphatase in chondroblasts. We now describe the cooperative effect of these agents on MSC isolated and cultured from human vertebral bone marrow. MSC (passages 3-9) isolated from bone marrow cells of human vertebrae (T1-L5) from 22-36-year-old normal donors were first expanded in vitro and then plated in the presence or absence of 10 ng/mL HGF and/or 10 nmol/L vitD(3), for 7-18 days. HGF treatment increased cell proliferation 2.5-fold, with no effect on alkaline phosphatase activity. Whereas vitD(3) treatment inhibited cell growth by 50%, alkaline phosphatase activity was stimulated eightfold, although no mineralization was observed. HGF together with vitD(3) increased cell proliferation 1.5-fold and alkaline phosphatase activity 13-fold over untreated control. Moreover, mineralization was detected only with this combination. Our findings provide evidence that HGF in concert with vitamin D may promote growth and differentiation of human MSC into osteogenic cells.

2-Methoxyestradiol induces G2/M arrest and apoptosis in prostate cancer

Few therapeutic treatment options are available for patients suffering from metastatic androgen-independent prostate cancer. We investigated the ability of the estrogen metabolite 2-methoxyestradiol to inhibit the proliferation of a variety of human prostate cancer cell lines in vitro and to inhibit the growth of androgen-independent prostate cancer in a transgenic mouse model in vivo. Our results showed that 2-methoxyestradiol is a powerful growth inhibitor of LNCaP, DU 145, PC-3, and ALVA-31 prostate cancer cells. Cell flow cytometry of 2-methoxyestradiol-treated DU 145 cells showed a marked accumulation of cells in the G2/M phase of the cell cycle and an increase in the sub-G1 fraction (apoptotic). In addition, staining for annexin V, changes in nuclear morphology, and inhibition of caspase activity support a role for apoptosis. More importantly, we showed that 2-methoxyestradiol inhibits prostate tumor progression in the Ggamma/T-15 transgenic mouse model of androgen-independent prostate cancer without toxic side effects. These results in cell culture and an animal model support investigations into the clinical use of 2-methoxyestradiol in patients with androgen-independent prostate cancer.

Basic calcium phosphate crystals up-regulate metalloproteinases but down-regulate tissue inhibitor of metalloproteinase-1 and -2 in human fibroblasts

OBJECTIVE

To examine the effect of basic calcium phosphate (BCP) crystals on expression of tissue inhibitors of metalloproteinases (TIMP)-1 and -2 in human fibroblasts.

METHOD

Using a semi-quantitative reverse transcription-polymerase chain reaction method and phosphocitrate (PC), a specific inhibitor of the biological effects of BCP crystals, we examined the effects of BCP on the steady state transcript levels of metalloproteinase (MMP)-1, -3, -9 and -13 and TIMP-1 and -2 in human fibroblasts. DNA primers against elongation factor were used as internal controls. RNAs isolated from human fibroblasts treated with BCP crystals (50 microg/ml) in the presence or absence of PC (10(-3) M) were used as templates, and RNA from untreated control cultures and cultures treated with Interleukin-1-beta (IL-1beta) were used as negative and positive controls, respectively.

RESULTS

We observed increases in MMP-1, -3, -9 and -13 transcripts by BCP crystals. BCP crystal down-regulated TIMP-1 and -2 over untreated controls. Western blot analysis confirmed that BCP crystals down-regulate the synthesis of TIMP-1 and -2. While IL-1beta up-regulated MMP-1, -3, -9 and -13, it had no significant effect on expression of either TIMP. In all cases, PC specifically reversed the differential regulation of MMPs and TIMPs by BCP crystals but had no effect on IL-1beta induction of MMP expression.

CONCLUSION

The ability of BCP to induce the synthesis of degradative MMPs while down-regulating the synthesis of the naturally occurring counterpart TIMPs may explain the changes consistent with a role of BCP crystal in the pathogenesis of degenerative changes in osteoarthritis. The ability of PC to reverse both degradative effects of BCP crystal suggests that PC can be a potential therapeutic agent for BCP crystal deposition diseases.

Inhibition of gap-junctional communication induces the trans-differentiation of osteoblasts to an adipocytic phenotype in vitro

Osteoblasts and adipocytes are thought to differentiate from a common stromal progenitor cell. These two phenotypically mature cell types show a high degree of plasticity, which can be observed when cells are grown under specific culture conditions. Gap junctions are abundant among osteoblastic cells in vivo and in vitro, whereas they are down-regulated during adipogenesis. Gap junctional communication (GJC) modulates the expression of genes associated with the mature osteoblastic phenotype. Inhibition of GJC utilizing 18-alpha-glycyrrhetinic acid (AGRA) blocks the maturation of pre-osteoblastic cells in vitro. Moreover, cytoplasmic lipid droplets are detectable at the end of the culture period, suggesting that GJC inhibition may favor an adipocytic phenotype. We used several human osteoblastic cell lines, as well as bone-derived primary osteoblastic cells, to show that confluent cultures of human osteoblastic cells grown under osteogenic conditions developed an adipocytic phenotype after 3 days of complete inhibition of GJC using AGRA or oleamide, two dissimilar nontoxic reversible inhibitors. Development of an adipogenic phenotype was confirmed by the accumulation of triglyceride droplets and the increase in mRNA expression of the adipocytic markers peroxisome proliferator-activated receptor gamma2 and lipoprotein lipase. Glycyrrhizic acid, a noninhibitory AGRA analog, or alpha-bromopalmitate, a nondegradable fatty acid, had no effect. Modulation of skeletal GJC may represent a new pharmacological target by which inhibition of marrow adipogenesis can take place with the parallel enhancement of osteoblastogenesis, thus providing a novel therapeutic approach to the treatment of human age-related osteopenic diseases and postmenopausal osteoporosis.

Gap-junctional communication is required for the maturation process of osteoblastic cells in culture

Osteoblastic cells in long-term culture undergo a phenotypic maturation process leading to extracellular matrix (ECM) production and bone nodule (BN) formation. Cell-to-cell communication via gap junctions (GJC) can be detected between osteoblastic cells within 24 h of plating. We evaluated, in long-term cultures of osteoblastic cells, the effect of inhibiting GJC on the phenotypic maturation process and the expression of specific genes associated with this process. MC3T3-E1 cells were plated, and, after 24 h (day 0), cells were exposed to 18-alpha-glycyrrhetinic acid (AGA), a nontoxic reversible inhibitor of GJC. GJC, alkaline phosphatase (AP) activity, BN formation, and the relative level of transcripts encoding osteocalcin (OC), bone sialoprotein (bSP), osteopontin (OP), collagen alpha1 type I (alpha1ICol), and elongation factor-1a (EF1a) were evaluated on day 0 and every 4-7 days thereafter through day 30. GJC was assessed by fluorescent dye transfer. Gene expression was analyzed by northern blot and semiquantitative reverse transcription-polymerase chain reaction. GJC was detectable at day 0 and increased with time in culture. AGA (100 micromol/L) strongly inhibited GJC at all timepoints tested. Moreover, AGA-exposed cells showed a dose-dependent decrease in AP activity and a delay in the appearance of BN. This delayed phenotypic expression coincided with an inhibitory effect on the expression of the osteoblast-specific genes OC and bSP. Expression of alpha1ICol mRNA was also affected, but to a lesser extent, whereas OP and EF1a were not affected. Similar results were obtained with oleamide, an additional reversible inhibitor of GJC. In contrast, cells exposed to either vehicle or 100 micromol/L glycyrrhizic acid (a noninhibitory glycoside of 18-beta-glycyrrhetinic acid) were indistinguishable from untreated cells for all parameters evaluated. We conclude that GJC inhibition interferes with the maturation process of osteoblastic cells in culture, possibly by affecting signals regulating the expression of genes involved in the maturation/differentiation of the osteoblastic phenotype.

Cyclosporin A affects extracellular matrix synthesis and degradation by mouse MC3T3-E1 osteoblasts in vitro

BACKGROUND

Immunosuppressant therapy is thought to be a major contributor to post-transplant bone disease. Histological data and serum parameters suggest that Cyclosporin A (CsA) treatment causes osteopenia as a result of an altered bone turnover, but the pathogenic mechanisms of this process remain unclear. We investigate if CsA affects cell turnover and extracellular matrix (ECM) synthesis and degradation in MC3T3-E1 osteoblasts, as a surrogate model for in vivo events.

METHODS

Cells were exposed to increasing doses of CsA (0, 0.5, 1 and 5 microg/ml). Proliferation was evaluated by bromodeoxyuridine (BrdU) incorporation, viability by Trypan Blue exclusion and apoptosis by ELISA. Type I collagen was measured by ELISA and reverse transcription-polymerase chain reaction (RT-PCR), matrix metalloproteinases (MMP) by zymography and RT-PCR, and tissue inhibitors of MMP (TIMP) by reverse zymography.

RESULTS

CsA exposure for 48 h decreased osteoblast number in a dose-dependent manner in the absence of apoptosis or cytotoxicity. CsA at a dose of 5 microg/ml for 72 h caused decreased collagen type I mRNA expression and protein accumulation. While MMP-2 remained unaffected, MMP-9 activity increased. TIMP-1 activity was unaffected, while a dose-dependent increase of TIMP-2 was observed.

CONCLUSIONS

These data suggest that CsA alters ECM synthesis and degradation in MC3T3-E1 osteoblasts by decreasing type I collagen production and increasing MMP-9 activity. The combination of increased MMP-9 with unchanged TIMP-1 activity could reduce the osteoid matrix available for mineralization. In addition, decreased proliferation could further reduce the number of cells synthesizing new osteoid matrix and thus contribute to the process of bone loss.

Overall and disease-specific survival after radical prostatectomy: geographic uniformity

OBJECTIVES

To examine whether the survival (both overall and disease-specific) of patients who underwent radical prostatectomy varies from region to region in the United States. Previous reports have documented a geographic variation in the use of radical prostatectomy.

METHODS

This study was based on the data from nine geographic regions of the Surveillance, Epidemiology, and End Results Program (SEER) for 1983 through 1992. Patients with localized prostate cancer who underwent radical prostatectomy were included in the analysis. A proportional hazards model was used to investigate whether geographic variation is associated with both overall and disease-specific survival.

RESULTS

From 1983 through 1992, the SEER Program collected information from nine geographic regions on 66,293 patients with localized prostate cancer (mean age 71.8 +/- 8.4 years), who had SEER grade codes of 1, 2, or 3. Of these patients, 11,429 (mean age 65.3 +/- 6.5 years) underwent radical prostatectomy and lymph node dissection. Cox's proportional hazards analyses revealed that the impact of geographic location on both overall and disease-specific survival in patients who underwent radical prostatectomy was not statistically significant.

CONCLUSIONS

The results of this study indicate that the survival (both overall and disease-specific) of patients with localized prostate cancer who underwent radical prostatectomy is not influenced by geographic location, suggesting that their survival is relatively uniform across the geographic regions in the United States.

Gap-junctional communication mediates parathyroid hormone stimulation of mineralization in osteoblastic cultures

Previously we showed that physiological levels of parathyroid hormone (PTH) can increase the mineralization of extracellular matrix (ECM) by osteoblast-like cells in vitro. In this study, we assess the role of gap-junctional intercellular communication (GJC) in the PTH-enhanced mineralization of ECM in MC3T3-E1 cells, a murine culture model of osteoblastic differentiation. Messenger RNA and protein for connexin 43 (Cx43), the major component of MC3T3-E1 gap junctions, and GJC increased as the cells progressed toward a mature phenotype. Immunocytochemistry showed accumulation of Cx43 at the area of close contact between cells. The timing of the PTH treatment that increased matrix mineralization in these cells coincided with the highest expression of Cx43 and GJC. Administration of 18-alpha-glycyrrhetinic acid (AGA) promptly blocked GJC in cultures of MC3T3-E1 cells in a dose-dependent and reversible manner at all times tested during the culture period. Treatment with AGA, but not with an inactive analog, reversed the PTH-induced ECM mineralization. These data suggest that GJC mediates anabolic actions of PTH related to osteoblast-mediated mineralization.

A role for GATA transcription factors in the androgen regulation of the prostate-specific antigen gene enhancer

The transgenic mouse line Ggamma/T-15 containing the fetal globin promoter linked to SV40 T antigen unexpectedly results in androgen-independent prostate carcinomas. Given the key role of GATA-1 transcription factor in fetal globin gene promoter activity, we investigated whether specific GATA family members are expressed in the prostate and whether they can regulate prostate-specific genes. We found that GATA-2 and -3 are the predominant GATA family members expressed in human and mouse prostate and that GATA mRNA levels are not regulated by androgen. We identified six GATA sites flanking an androgen-response element located in the far-upstream enhancer of the prostate-specific antigen (PSA) gene. These GATA sites are targets for GATA factors and are essential for optimal androgen induction of transfected PSA enhancer/promoter plasmids in LNCaP, a PSA and androgen receptor expressing human prostate cancer cell line. Our results suggest that prostatic GATA-2 and -3 are involved in the androgen regulation of the PSA gene.

Gene therapy of rat medullary thyroid cancer by naked nitric oxide synthase II DNA injection

BACKGROUND

Nitric oxide (NO), produced by NO synthase II (NOS II), is the main mediator of the tumoricidal action of activated macrophages. In the present study we examined the potential of the NOS II gene as a suicide gene for medullary thyroid cancer (MTC) therapy.

METHODS

We orthotopically transplanted rMTC 6-23 cells into the inbred strain of Wag/Rij rats and constructed a plasmid carrying the NOS II gene under the control of the cytomegalovirus (CMV) promoter.

RESULTS

Successive injections of tumor cells (Day 0) and naked DNA (Day 2) caused strong inhibition of tumor growth (50%, p < 0.05). Plasmid injection into established tumors (14-day tumors) resulted in the development of large cavities due to tumor cell destruction, with a significant reduction in tumor tissue volume (35%, p < 0.05). Adjacent quiescent tissues were unaffected. Cell death occurred by apoptosis as demonstrated by specific labeling. Macrophages and CD4+ lymphocytes were recruited in the treated tumors. However, tumor-specific T lymphocytes were undetectable in the spleen of treated rats. In control experiments using Lac Z as a reporter gene, expression of beta-galactosidase was detected in only 1% of the tumor cells.

CONCLUSIONS

Despite a low gene transfer efficiency, NOS II plasmid produced a strong anti-tumor action resulting from its marked 'bystander' effect mainly due to NO production and diffusion. Therefore the NOS II gene appears to be a promising suicide gene therapy of human cancer.

Hepatocyte growth factor and vitamin D cooperatively inhibit androgen-unresponsive prostate cancer cell lines

Expression of MET, the receptor for hepatocyte growth factor (HGF), has been associated with androgen-insensitive prostate cancer. In this study we evaluated MET activation by HGF and HGF action in prostate cancer cell lines. HGF causes phosphorylation (activation) of the MET receptor in three androgen-unresponsive cell lines (DU 145, PC-3, and ALVA-31) together with morphological change. Although HGF is known to stimulate the growth of normal epithelial cells, including those from prostate, we found that HGF inhibited ALVA-31 and DU 145 (hormone-refractory) cell lines. Moreover, HGF and vitamin D additively inhibited growth in each androgen-unresponsive cell line, with the greatest growth inhibition in ALVA-31 cells. Further studies in ALVA-31 cells revealed distinct cooperative actions of HGF and vitamin D. In contrast to the accumulation of cells in G1 seen during vitamin D inhibition of androgen-responsive cells (LNCaP), growth inhibition of the androgen-unresponsive ALVA-31 cell line with the HGF and vitamin D combination decreased, rather than increased, the fraction of cells in G1, with a corresponding increase in the later cell cycle phases. This cell cycle redistribution suggests that in androgen-unresponsive prostate cancer cells, HGF and vitamin D act together to slow cell cycle progression via control at sites beyond the G1/S checkpoint, the major regulatory locus of growth control in androgen-sensitive prostate cells.

Radical prostatectomy: geographic and demographic variation

OBJECTIVES

Previous reports have documented a geographic variation in the use of radical prostatectomy. We examined whether this phenomenon can be explained by factors other than geography alone.

METHODS

This study was based on the data from nine geographic regions of the Surveillance, Epidemiology, and End Results (SEER) program for the years 1983 through 1994. Patients with localized or regional prostate cancer were included in the analysis. Logistic regression analysis was used to investigate the influence of geographic and demographic factors on the use of radical prostatectomy. The squared multiple correlation coefficient R(2) was used to measure the proportion of variation in the selection of radical prostatectomy explained by each factor of interest.

RESULTS

As previously reported, the use of radical prostatectomy was significantly associated with geographic location; the degree of geographic variation varied as a function of age and was most dramatic in the youngest (younger than 45 years) and the oldest (75 years or older) groups. Overall, however, geography explained less than 2% of the total variation in the use of radical prostatectomy. Age was the most important factor that influenced the use of radical prostatectomy.

CONCLUSIONS

Geography explains only a small proportion of the variation in the use of radical prostatectomy. In fact, of the factors examined, only age appeared to meaningfully explain the variation in the use of radical prostatectomy. Overall, our ability to explain the variation in the use of radical prostatectomy remains meager, and new factors must be identified if we are to better understand how patients and physicians make clinical decisions.

Cancer screening in the elderly population

This article reviews the current state of knowledge regarding cancer screening in the geriatric population. Care of the elderly requires knowledge of underlying physiologic changes, comorbidities, quality-of-life factors, and life expectancies. There is always the danger that ageism may prevent elderly cancer patients from receiving the proper treatment. On the other hand, overzealous treatment can lead to adverse results if elderly patients are not properly targeted based on current evidence of the benefits and risks of specific screening practices.

Anabolic or catabolic responses of MC3T3-E1 osteoblastic cells to parathyroid hormone depend on time and duration of treatment

We have investigated signaling (cAMP) and anabolic responses (mineralization of extracellular matrix [ECM]) to parathyroid hormone (PTH) in long-term (30 days) cultures of MC3T3-E1 cells, a murine model of osteoblast differentiation. Expression of PTH/PTH-related peptide receptor (PTH1R) mRNA is detected early and remains relatively constant for 2 weeks with somewhat higher levels observed during the second half of the culture period. In contrast to the relatively stable PTH1R mRNA expression, the cAMP response to PTH varies markedly with no response at day 5 and a marked response (80-fold versus control) by day 10. Responsiveness to PTH remains elevated with fluctuations of 30- to 80-fold stimulation throughout the remainder of the culture period. The timing and duration of PTH treatment to achieve in vitro mineralization of ECM was evaluated. When continuous PTH treatment was initiated before day 20, mineralization decreased. If continuous PTH treatment began on or after day 20, mineralization was unaffected. However, if treatment began on day 20 and then stopped on day 25, mineralization on day 30 was increased 5-fold. This mineralization response to intermittent PTH was confirmed in primary cultures of murine and human osteoblastic cells. These data provide a potential basis for understanding the differential responses to PTH (anabolic versus catabolic) and indicate the developmental temporal variance of anabolic and catabolic responses. Since cAMP signaling was relatively unchanged during this interval (day 10-30) and stimulation of adenylate cyclase only partially mimicked the PTH effect on increased mineralization, other signaling pathways are likely to be involved in order to determine the specific anabolic response to short-term PTH treatment during the differentiation process.

Age-related osteogenic potential of mesenchymal stromal stem cells from human vertebral bone marrow

Mesenchymal stem cells (MSCs) residing in bone marrow (BM) are the progenitors for osteoblasts and for several other cell types. In humans, the age-related decrease in bone mass could reflect decreased osteoblasts secondary to an age-related loss of osteoprogenitors. To test this hypothesis, BM cells were isolated from vertebral bodies of thoracic and lumbar spine (T1-L5) from 41 donors (16 women and 25 men) of various ages (3-70 years old) after death from traumatic injury. Primary cultures were grown in alpha modified essential medium with fetal bovine serum for 13 days until adherent cells formed colonies (CFU-Fs). Colonies that stained positive for alkaline phosphatase activity (CFU-F/ALP+) were considered to have osteogenic potential. BM nucleated cells were plated (0.5, 1, 2.5, 5, or 10 x 106 cells/10-cm dish) and grown in dexamethasone (Dex), which promotes osteoblastic differentiation. The optimal plating efficiency using BM-derived cells from donors of various ages was 5 x 106 cells/10-cm dish. BM-derived cells were also grown in the absence of Dex at this plating density. At the optimal plating density, in the presence of Dex, the number of CFU-F/ALP+ present in the BM of the younger donors (3-36 years old) was 66.2 +/- 9.6 per 106 cells (mean +/- SEM), but only 14.7 +/- 2.6 per 106 cells in the older donors (41-70 years old). With longer-term culture (4-5 weeks) of these BM cells in medium containing 10 mM beta-glycerophosphate and 100 microg/ml ascorbic acid, the extracellular matrix mineralized, a result consistent with mature osteoblastic function. These results demonstrate that the number of MSCs with osteogenic potential (CFU-F/ALP+) decreases early during aging in humans and may be responsible for the age-related reduction in osteoblast number. Our results are particularly important in that the vertebrae are a site of high turnover osteoporosis and, possibly, the earliest site of bone loss in age-related osteoporosis.

Suppression of human prostate cancer cell growth by forced expression of connexin genes

The cell-to-cell channels in gap junctions, formed of proteins called connexins (Cxs), provide a direct intercellular pathway for the passage of small signaling molecules (< or = 1 kD) between the cytoplasmic interiors of adjoining cells. It has been proposed that alteration in the expression and function of Cxs may be one of the genetic changes involved in the initiation of neoplasia. To elucidate the role of Cxs in the pathogenesis of human prostate cancer (PCA), the pattern of expression of Cx alpha 1 (Cx43) and Cx beta 1 (Cx32) was studied by immunocytochemical analysis in normal prostate and in prostate tumors of different histological grades. While normal prostate epithelial cells expressed only Cx beta 1, both Cx alpha 1 and Cx beta 1 were detected in PCA cells. The Cxs were localized at the cell-cell contact areas in normal prostate and well-differentiated prostate tumors; however, as prostate tumors progressed to more undifferentiated stages, the Cxs were localized in the cytoplasm, followed by an eventual loss in advanced stages. Thus, epithelial cells from prostate tumors showed subtle and gross alterations with regard to expression of Cx alpha 1 and Cx beta 1 and their assembly into gap junctions during the progression of PCA. Retroviral-mediated transfer of Cx alpha 1 and Cx beta 1 into a Cx-deficient human PCA cell line, LNCaP, inhibited growth, retarded tumorigenicity, and induced differentiation, and these effects were contingent upon the formation of gap junctions. In addition, the capacity to form gap junctions in most Cx-transduced LNCaP cells was lost upon serial passage. Taken together, these findings indicate that the control of proliferation and differentiation of epithelial cells in prostate tumors may depend on the appropriate assembly of Cx beta 1 and Cx alpha 1 into gap junctions and that the development of PCA may involve the positive selection of cells with an impaired ability to form gap junctions.

Suppression of human prostate cancer cell growth by forced expression of connexin genes

The cell-to-cell channels in gap junctions, formed of proteins called connexins (Cxs), provide a direct intercellular pathway for the passage of small signaling molecules (< or = 1 kD) between the cytoplasmic interiors of adjoining cells. It has been proposed that alteration in the expression and function of Cxs may be one of the genetic changes involved in the initiation of neoplasia. To elucidate the role of Cxs in the pathogenesis of human prostate cancer (PCA), the pattern of expression of Cx alpha 1 (Cx43) and Cx beta 1 (Cx32) was studied by immunocytochemical analysis in normal prostate and in prostate tumors of different histological grades. While normal prostate epithelial cells expressed only Cx beta 1, both Cx alpha 1 and Cx beta 1 were detected in PCA cells. The Cxs were localized at the cell-cell contact areas in normal prostate and well-differentiated prostate tumors; however, as prostate tumors progressed to more undifferentiated stages, the Cxs were localized in the cytoplasm, followed by an eventual loss in advanced stages. Thus, epithelial cells from prostate tumors showed subtle and gross alterations with regard to expression of Cx alpha 1 and Cx beta 1 and their assembly into gap junctions during the progression of PCA. Retroviral-mediated transfer of Cx alpha 1 and Cx beta 1 into a Cx-deficient human PCA cell line, LNCaP, inhibited growth, retarded tumorigenicity, and induced differentiation, and these effects were contingent upon the formation of gap junctions. In addition, the capacity to form gap junctions in most Cx-transduced LNCaP cells was lost upon serial passage. Taken together, these findings indicate that the control of proliferation and differentiation of epithelial cells in prostate tumors may depend on the appropriate assembly of Cx beta 1 and Cx alpha 1 into gap junctions and that the development of PCA may involve the positive selection of cells with an impaired ability to form gap junctions.

Testes exhibit elevated expression of calcitonin gene-related peptide receptor component protein

Calcitonin gene-related peptide (CGRP) receptor component protein (RCP) is a novel protein that modulates CGRP responsiveness in a variety of cell types. Using probes based on the isolation of CGRP-RCP complementary DNA (cDNA) from a guinea pig organ of Corti cDNA library, we cloned human (h) and mouse (m) CGRP-RCP cDNAs, both of which encode 148-residue proteins that at the amino acid levels are approximately 88% identical to each other and to the 146-residue guinea pig CGRP-RCP. Northern blot analysis confirmed the presence of CGRP-RCP messenger RNA in all of the human and mouse tissues tested. In these human tissues, hCGRP-RCP messenger RNA (major band at approximately 3.1 kb, minor band at approximately 7.5 kb) was most prevalent in the testis. In the mouse, the highest abundance of CGRP-RCP RNA was clearly in the testis (major band at approximately 1.6 kb, minor band at approximately 1.1 kb). Based on this tissue distribution of RNA, we sought to identify the cells in the murine testis that contained CGRP-RCP protein. Numerous antisera generated against hCGRP-RCP, including one to recombinant hCGRP-RCP, exhibited strong immunoreactivity localized to the head region of spermatozoa. No CGRP-RCP immunoreactivity was observed in other cells at less mature stages of sperm maturation, in Sertoli or interstitial (Leydig) cells, or in human spermatozoa. Murine epididymal (mature) spermatozoa exhibited CGRP-RCP immunoreactivity identical to that of testicular spermatozoa. Spermatozoa that underwent an experimentally induced acrosome reaction (acrosomal discharge) lost their CGRP-RCP immunoreactivity. Therefore, it appears that CGRP-RCP is associated with the acrosome, suggesting that it may play an important role in reproduction.

Suppression of human prostate cancer cell growth by forced expression of connexin genes

The cell-to-cell channels in gap junctions, formed of proteins called connexins (Cxs), provide a direct intercellular pathway for the passage of small signaling molecules (< or = 1 kD) between the cytoplasmic interiors of adjoining cells. It has been proposed that alteration in the expression and function of Cxs may be one of the genetic changes involved in the initiation of neoplasia. To elucidate the role of Cxs in the pathogenesis of human prostate cancer (PCA), the pattern of expression of Cx alpha 1 (Cx43) and Cx beta 1 (Cx32) was studied by immunocytochemical analysis in normal prostate and in prostate tumors of different histological grades. While normal prostate epithelial cells expressed only Cx beta 1, both Cx alpha 1 and Cx beta 1 were detected in PCA cells. The Cxs were localized at the cell-cell contact areas in normal prostate and well-differentiated prostate tumors; however, as prostate tumors progressed to more undifferentiated stages, the Cxs were localized in the cytoplasm, followed by an eventual loss in advanced stages. Thus, epithelial cells from prostate tumors showed subtle and gross alterations with regard to expression of Cx alpha 1 and Cx beta 1 and their assembly into gap junctions during the progression of PCA. Retroviral-mediated transfer of Cx alpha 1 and Cx beta 1 into a Cx-deficient human PCA cell line, LNCaP, inhibited growth, retarded tumorigenicity, and induced differentiation, and these effects were contingent upon the formation of gap junctions. In addition, the capacity to form gap junctions in most Cx-transduced LNCaP cells was lost upon serial passage. Taken together, these findings indicate that the control of proliferation and differentiation of epithelial cells in prostate tumors may depend on the appropriate assembly of Cx beta 1 and Cx alpha 1 into gap junctions and that the development of PCA may involve the positive selection of cells with an impaired ability to form gap junctions.

Diabetes mellitus in older persons

The relative importance and mechanisms of deficient insulin secretion versus deficient action during aging are still debated. Whatever mechanisms eventually explain the emergence of impaired glucose tolerance during aging, the clinically important extrinsic modifiers of glycemic levels include diet, medications, activity, and chronic illness and stress. Although prospective studies are not available in the elderly, retrospective studies suggest that good blood glucose control reduces the likelihood and severity of stroke, cardiovascular disease, visual impairment, nephropathy, infections, and even cognitive dysfunction. Good control also seems to reduce nocturia, polyuria, and hypovolemia. Therapy of older persons begins with diet, exercise, and oral agents, failing which, insulin is employed. Since many of the newer oral agents carry less risk of hypoglycemia, achieving tighter control in the elderly has become more feasible.

Expression of rat thyrotropin-releasing hormone (TRH) gene in TRH-producing tissues of transgenic mice requires sequences located in exon 1

TRH, an amidated tripeptide secreted by certain hypothalamic neurons, is a principal regulator of TSH secretion and thyroid hormone release. TRH is also produced by other neurons in the central nervous system, where it appears to function as a neuromodulator or neurotransmitter, and by certain endocrine cells, where it may act as an autocrine or paracrine factor. The genomic organization of the rat TRH (rTRH) gene is well understood; however, the domains of the rTRH gene that regulate expression are less well characterized. We observed that the region between -47 and +6 of the rTRH gene (relative to the transcription start site at +1) was active in CA-77 cells, a medullary thyroid carcinoma cell line model of TRH production, but was not active in transgenic mice. Inclusion of most of exon 1 (84 out of 103 bp; -47 to +84) increased promoter activity in CA-77 cells and was active in transgenic mice, principally in tissues that normally express the TRH gene. Further lengthening of the 5' end to -243, -547, or -776 retained this expression in TRH-producing tissues in transgenic mice, while further increasing activity in CA-77 cells. These results suggest that cis element(s) located within exon 1 are necessary for the expression of the rTRH gene in vivo.

Parathyroid hormone up-regulation of connexin 43 gene expression in osteoblasts depends on cell phenotype

Accumulating evidence indicates that gap junctions, primarily composed of connexin 43 (Cx43), are distributed extensively throughout bone. We have previously reported that in osteoblastic cells parathyroid hormone (PTH) increases both the steady-state levels of transcripts for Cx43 and gap-junctional intercellular communication in a process involving cyclic adenosine monophosphate (cAMP). We now present data showing that the mechanism of stimulation of Cx43 gene expression by PTH involves an increased rate of Cx43 gene transcription without affecting Cx43 transcript stability in UMR 106 osteoblastic cells. Activation of the protein kinase C pathway is not involved in this process. Inhibiting translation consistently decreases the PTH-mediated stimulation of Cx43 gene expression at all the times we tested (1-3 h). However, this effect is only partial, demonstrating that de novo protein synthesis is required for full stimulation. PTH increases the steady-state levels of Cx43 mRNA in several osteoblastic cell lines, albeit to different levels. We were unable to detect PTH stimulation in ROS 17/2.8 osteoblastic cells, suggesting that the effect of PTH on Cx43 gene expression may depend on the developmental state of the cell along the osteoblastic differentiation pathway. In the MC3T3-E1 preosteoblastic cell line, we find that PTH increases Cx43 gene expression in proliferating and maturing osteoblastic cells, but not in nondividing, differentiated osteoblasts, where the basal level of Cx43 gene expression is elevated. Unlike PTH, the osteotropic hormones 1,25-dihydroxyvitamin D3 and 17beta-estradiol do not appear to affect Cx43 gene expression in UMR 106 osteoblastic cells.

Absence of androgen-mediated transcriptional effects in osteoblastic cells despite presence of androgen receptors

Androgen excess and deficiency affect skeletal maturation and bone cell function. Understanding the molecular basis for these androgen effects could improve therapy/prevention of short stature and osteoporosis. Androgens act through binding to androgen receptors (ARs), which modulate gene transcription via interactions with DNA response elements on target genes. Because osteoblasts contain ARs at levels just below certain androgen-sensitive tissues, we sought to define the function of AR in a number of commonly used osteoblastic cell lines. Presence and quantification of AR protein and mRNA were evaluated by ligand binding assay, western blotting, and RNAse protection assay. AR-containing osteoblastic cell lines were exposed to nonaromatizable androgens and effects on gene expression were assessed. We found no evidence for direct effects of androgen on endogenous genes nor was androgen involved in modulation of parathyroid hormone effects on early gene activation. Androgen-sensitive reporter gene constructs were stimulated by androgen only when AR cDNA expression vectors were introduced into cells by cotransfection. We conclude that, in commonly used osteoblastic cell lines, the presence of AR at the levels described here does not guarantee androgen transcriptional activity. The effects of androgen on bone in vivo may involve direct stimulation of osteoblastic cells in a different setting or stage of differentiation. Alternatively, androgen may act on bone cells other than osteoblasts, or through metabolic conversion to estrogens.

Prostate cancer progression, metastasis, and gene expression in transgenic mice

We previously reported that a transgenic mouse line containing the fetal globin promoter linked to the SV40 T antigen (T Ag) viral oncogene (Ggamma/T-15) resulted in prostate tumors. In this study, we further explored tumor origin, frequency, invasiveness, androgen sensitivity, and gene expression pattern. T Ag was detected in adult but not fetal and neonatal prostates, suggesting a role for androgens in tumor progression. However, castration shortly after prostate morphogenesis did not prevent tumor development, suggesting an androgen-independent phenotype. Tumors originated within ventral or dorsal prostate lobes and involved intraepithelial neoplasia, rapid growth in the pelvic region, and metastasis to lymph nodes and distant sites. In addition, the primary cancers could be propagated in nude mice or nontransgenic mice. Seventy-five percent of hemizygous and 100% of homozygous transgenic males developed prostate tumors, suggesting a T Ag dosage effect. Biochemical characterization of advanced tumors revealed markers of both neuroendocrine and epithelial phenotypes; markers of terminal differentiation are lost early in tumorigenesis. Tumor suppressor genes (p53 and Rb), normally bound to T Ag, were up-regulated; bcl-2 proto-oncogene, which prevents apoptosis, was slightly up-regulated. Myc, a stimulus to cell cycle progression, was unchanged. We propose the Ggamma/T-15 transgenic line as a model of highly aggressive androgen-independent metastatic prostate carcinoma with features similar to end-stage prostate cancer in humans.

Endopeptidase 24.11 activity in the human prostate cancer cell lines LNCaP and PPC-1

Human endopeptidase 24.11 (EP) occurs in greatest abundance on terminally differentiated prostate cells; thus, loss of EP could mark dedifferentiation of prostate epithelium. To identify laboratory models that would permit continuous work on the biochemistry and hormonal regulation of EP, we examined the well-differentiated LNCaP and poorly differentiated PPC-1 human prostate cancer cell lines. Ultrastructural analysis revealed that LNCaP secretes electron-dense material that resembles the particulate matter of seminal plasma, which is associated with endopeptidase activity. LNCaP medium contained EP activity while PPC-1 medium did not. Whether the apparent deletion of EP from the PPC-1 cell line is characteristic of poorly differentiated prostate adenocarcinoma is not yet clear. However, it may be relevant to the carcinogenic process that EP can limit growth of lung small carcinomas by inactivating cell growth-promoting bombesin-like peptides. Because bombesin has been identified in aggressive human prostate cancers, loss of EP in PPC-1 could represent a necessary step in transformation to aggressive phenotype. The combination of LNCaP and PPC-1, which offers well-differentiated and poorly differentiated cancer phenotypes, appears well suited to studying the relevance of EP in prostate cancer biology.

Hepatocyte growth factor and its actions in growth plate chondrocytes

Hepatocyte growth factor (HGF) has been implicated as a paracrine regulator of organogenesis and repair in many tissues. Here we have studied the expression and actions of HGF in intact rachitic rat growth plate and derived cultures of proliferative zone chondrocytes. In vivo and in vitro chondrocytes express HGF mRNA; 1,25(OH)2 has a three-fold maximal stimulatory effect, which can be blocked by H-7, an inhibitor of protein kinase C. Although HGF elaboration and action generally follow a paracrine model, chondrocytes appear capable of both expressing and responding to HGF. mRNA encoding the HGF receptor (c-met) was detected in both growth cartilage and derived chondrocyte cultures. HGF addition to chondrocyte cultures increased collagen II mRNA and alkaline phosphatase enzymatic activity to degrees comparable to that observed for active vitamin D metabolites. Combining HGF and 1,25-D evoked a synergistic response (ninefold) of alkaline phosphatase activity. To assess whether a similar stimulatory effect might be seen with bioactive peptides and HGF, we investigated the effect of HGF pretreatment on acute responses of chondrocytes to synthetic human calcitonin, an anabolic chondrocyte regulator whose skeletal action are mediated principally by cAMP elevation and subsequent protein kinase A activation. CT's maximal activation of protein kinase A was increased by prior HGF treatment from 56% to 78%. In concert, our findings indicate that in addition to HGF's classical paracrine role during skeletal growth, this growth factor may modulate hormonal sensitivity of the chondrocyte during proliferation, differentiation, and/or apoptosis.

Identification of a protein that confers calcitonin gene-related peptide responsiveness to oocytes by using a cystic fibrosis transmembrane conductance regulator assay

An expression-cloning strategy was used to isolate a cDNA that encodes a protein that confers calcitonin gene-related peptide (CGRP) responsiveness to Xenopus laevis oocytes. A guinea pig organ of Corti (the mammalian hearing organ) cDNA library was screened by using an assay based on the cystic fibrosis transmembrane conductance regulator (CFTR). The CFTR is a chloride channel that is activated upon phosphorylation; this channel activity was used as a sensor for CGRP-induced activation of intracellular kinases. A cDNA library from guinea pig organ of Corti was screened by using this oocyte-CFTR assay. A cDNA was identified that contained an open reading frame coding for a small hydrophilic protein that is presumed to be either a CGRP receptor or a component of a CGRP receptor complex. This CGRP receptor component protein confers CGRP-specific activation to the CFTR assay, as no activation was detected upon application of calcitonin, amylin, neuropeptide Y, vasoactive intestinal peptide, or beta-endorphin. In situ hybridization demonstrated that the CGRP receptor component protein is expressed in outer hair cells of the organ of Corti and is colocalized with CGRP-containing efferent nerve terminals.

Calcitonin gene-related peptide rapidly inhibits calcium uptake in osteoblastic cell lines via activation of adenosine triphosphate-sensitive potassium channels

In certain neurons, alternative RNA processing generates calcitonin gene-related peptide (CGRP) from the same gene that encodes the hormone calcitonin. As CGRP-containing nerve fibers are prominent in skeleton, we evaluated the effects of CGRP on osteoblasts. Because the vasodilatory effect of neural CGRP in smooth muscle probably involves inhibition of unstimulated Ca2+ uptake, we examined the acute effects of CGRP on this parameter in rat osteoblastic cells. CGRP inhibits 45Ca2+ uptake in both UMR 106 osteosarcoma and RCOB-3 osteoblastic cells. This inhibition is rapid (0.5 min), occurs with an EC50 of 1 nM, and cannot be demonstrated in the presence of 0.1 mM diltiazem, a blocker of voltage-dependent Ca2+ channels. Depolarization of bone cells with high extracellular potassium (K+) also blocks the effect of CGRP on 45Ca2+ uptake, suggesting a central role for K+ channels in mediating this action. In agreement with this hypothesis, the effect of CGRP is blocked by 1 microM glybenclamide, a specific inhibitor of ATP-sensitive potassium (K(ATP)) channels, or by pretreatment of cells with 1 mM iodoacetic acid to deplete intracellular ATP. Blocking Ca2+-activated potassium channels with 1 mM tetraethylammonium does not prevent CGRP's effect. Pinacidil, a specific activator of K(ATP) channels, mimics CGRP's effect. Both CGRP and pinacidil also produce a small significant stimulation of cellular Ca2+ efflux in UMR 106 cells. These data suggest that inhibition of diltiazem-sensitive Ca2+ channels occurs secondary to the hyperpolarization engendered by CGRP activation of K(ATP) channels in osteoblastic cells, an effect similar to that of CGRP on smooth muscle cells.

Prostate, adrenocortical, and brown adipose tumors in fetal globin/T antigen transgenic mice

Targeted oncogenesis in transgenic mice has unexpectedly produced predictable tissue-specific tumors. We previously showed that hybrid gene constructs of the human fetal G gamma- or mouse embryonic beta h1-globin promoter linked to the viral simian virus 40 T antigen (G gamma/T and beta h1/T) expressed appropriately in embryonic erythroid tissue, with some unexpected expression elsewhere. Tumors arising in the G gamma/T and beta h1/T transgenic mice were identified by histology, electron microscopy, cell culture, and RNase protection analyses. In one G gamma/T transgenic line, males developed prostate tumors that showed mixed neuroendocrine and epithelial cell features, whereas females developed adrenocortical tumors. In several other G gamma/T lines, brown adipose tumors, or hibernomas, developed in the subcutaneous interscapular neck and shoulder area, as well as internally in the periadrenal and pericardial areas. Little or no expression of T antigen was detected in adult animals before visible tumor formation. In contrast, beta h1/T transgenic mice developed only choroid plexus tumors. Transient transfection assays in prostate and adrenocortical tumor-derived cell lines showed that the G gamma-globin promoter is 7-to 10-fold more active than the beta h1-globin promoter. Activity of 5' G gamma-globin promoter-deletion DNA plasmids was analyzed by transient transfection in a variety of human prostate cancer cell lines. The G gamma-globin promoter region between -140 and -201 also showed high activity in the androgen-independent human prostate cancer cell lines DU-145 and PPC-1, but low activity in the androgen-responsive human prostate cell line LNCaP. We conclude that tumor formation in the G gamma/T transgenic lines apparently results from cryptic positive DNA cis elements active in prostate and adrenocortical cells. Because G gamma-globin promoter activity is highest in embryonic tissue, tumors in adult transgenic mice may result from expression of T antigen in embryonic prostate, adrenal glands, and brown adipose tissue.

Gap-junctional communication in normal and neoplastic prostate epithelial cells and its regulation by cAMP

Gap-junctional communication and expression of gap junction-forming proteins were investigated in normal human prostate epithelial cells and in several malignant prostate cell lines. In comparison with normal cells, gap-junctional communication in malignant cells, as assayed by the transfer of 443-Da fluorescent tracer Lucifer yellow, was either reduced or not detected. Malignant cells expressed mRNA transcripts for connexin (Cx) 43, whereas normal cells expressed mRNA transcripts for Cx32 and Cx40. In both normal and malignant cells, gap-junctional communication was enhanced twofold to fivefold by treatment with forskolin, an agent known to increase intracellular levels of cAMP. Immunocytochemical staining with a Cx43-specific antibody revealed that in malignant cells this enhancement correlated with the number of gap junctions and occurred without any qualitative or quantitative alteration in Cx43 mRNA or protein. Moreover, western blot analyses showed that both control and forskolin-treated malignant cells expressed only one form of Cx43. Our data suggest that gap-junctional communication in both normal and malignant prostate cells may be regulated by hormones that work via a cAMP-dependent signal transduction pathway. Thus, both normal and malignant cells offer a new experimental model system in which interactions between a hormonal form of cellular communication and intercellular communication mediated via gap junctions can be studied.

Calcitonin gene-related peptide (CGRP) in the developing mouse limb

The mitogenic effects of neuropeptides and their localization to developing tissues suggest an important role for these peptides during gestation. We examined the expression and action of the neuropeptide calcitonin gene-related peptide (CGRP) in the developing mouse limb bud, an excellent model system for studying musculoskeletal development. CGRP immunoreactivity (CGRP-ir) was detected in the developing limb at day 16.5 of gestation (E 16.5) and was limited to nerve fibers surrounding blood vessels, within the developing muscle or in close proximity to the developing cartilaginous skeleton. Although CGRP-ir was not observed until E 16.5, limb buds were responsive to CGRP as early as E 11.5. Within 5 min of exposure to CGRP (10(-8) to 10(-7) M) a 2--3-fold increase in cyclic AMP (cAMP) levels was observed. This CGRP-induced increase in cAMP was abolished by the addition of human CGRP8-37, a CGRP receptor antagonist. This result suggests that the effect on cAMP was mediated by the interaction of CGRP with CGRP receptors. Our findings indicate that mouse limbs are responsive to CGRP when they are composed of primarily undifferentiated mesenchyme and that CGRP-ir appears at a later stage of development in association with cartilage and muscle differentiation.

Review of the literature: severe hyperphosphatemia

A patient with a markedly elevated serum phosphorus level (23.9 mg/dL) is described, followed by a brief review of severe hyperphosphatemia. Elevated serum phosphorus levels may be artifactual or true. True hyperphosphatemia is usefully subdivided according to (a) whether phosphorus is added to the extracellular fluid from a variety of exogenous or endogenous sources, or (b) whether the urinary excretion of phosphorus is reduced from either decreased glomerular filtration or increased tubular reabsorption. Severe hyperphosphatemia, defined herein as levels of 14 mg/dL or higher, is almost invariably multifactorial--usually resulting from addition of phosphorus to the extracellular fluid together with decreased phosphorus excretion. The hyperphosphatemia of the patient described herein appeared to result from a combination of dietary phosphorus supplementation, acute renal failure, acute pancreatitis, and ischemic bowel disease, complicated by lactic acidosis.

Neuroendocrine peptides stimulate adenyl cyclase in normal and malignant prostate cells

Elevations of intracellular cAMP in human prostate cancer cells have been shown to increase invasiveness and to promote neuronal differentiation. Since neuroendocrine peptides capable of activating adenyl cyclase are present in prostatic nerves and epithelial neuroendocrine cells, we investigated normal and malignant human prostate cells for changes in intracellular cAMP in response to the prostatic peptides vasoactive intestinal peptide (VIP), calcitonin (CT), and calcitonin gene-related peptide (CGRP). Normal prostate epithelial cells and LNCaP prostate cancer cells exhibited, respectively, 6- and 30-fold increases in intracellular cAMP in response to VIP. ALVA-31 and PPC-1 prostate cancer cells demonstrated 20- to 200-fold increases in cAMP in response to CGRP, while normal epithelial cells and LNCaP cells exhibited smaller (2- to 6-fold) responses. Only DU-145 cells increased cAMP substantially in response to CT. VIP receptor mRNA was identified by Northern blot analysis only in those cells that responded to VIP. CT receptor mRNA was identified only in DU-145 cells by polymerase chain reaction and Southern blot analysis. These results suggest that VIP and possibly CGRP receptors are likely to be present in both normal and malignant prostate cells. VIP or CGRP may regulate secretion of proteases by normal or prostate cancer cells and may influence epithelial cell differentiation.

Neuroendocrine peptides in the prostate

Circulating androgens are required for normal growth and maintenance of function of the prostate. However, the prostate also contains neuroendocrine peptides, found either in nerve terminals or in prostatic neuroendocrine cells, which are likely to regulate prostate growth or function. The neuronal peptides are likely to participate in the regulation of the synthesis and secretion of prostatic secretory products. While the function of the neuroendocrine cells is undefined, there is evidence for growth-regulating effects of several neuroendocrine cell peptides. Since neuroendocrine differentiation has been correlated with tumor grade and poor prognosis in prostate cancer, the peptide products of the neuroendocrine cells may influence cancer cell replication as well. Recent evidence in other tissues suggests that peptide hormone receptor second-messenger systems may interact with steroid receptors to modulate their actions. These findings raise the possibility that prostatic neuroendocrine peptides may modulate the response of prostate to androgens.

Diverse actions of calcitonin gene-related peptide on intracellular free Ca2+ concentrations in UMR 106 osteoblastic cells

Calcitonin gene-related peptide (CGRP) was examined for its effects on intracellular free Ca2+ concentration ([Ca2+]i) in UMR 106 osteoblast-like cells. Cells loaded with the Ca2+ dye FURA-2 dose-dependently responded to CGRP (1-100 nM) with transient two-fold increases in [Ca2+]i. An intracellular source for this Ca2+ transient was suggested by the failure of membrane depolarization with high extracellular K+ or acute depletion of extracellular Ca2+ ([Ca2+]e) with EGTA to attenuate this response. After cells were incubated for 45 min with 0.1 mM extracellular Ca2+ to deplete intracellular Ca2+ stores, CGRP produced a 25-30% decrease in [Ca2+]i rather than a transient increase. This calcium decrease was mimicked by membrane depolarization or by pinacidil, a specific activator of adenosine triphosphate (ATP)-sensitive potassium (KATP) channels, and blocked by glybenclamide, a specific blocker of KATP channels. Our data suggest that CGRP has diverse Ca2+ regulatory effects in UMR 106 cells, mobilizing Ca2+ from intracellular stores via classical signaling while possibly promoting cellular Ca2+ efflux or inhibiting uptake through voltage-dependent Ca2+ channels via KATP-mediated hyperpolarization.

Cartilage metalloproteases in disuse atrophy

A canine knee model of disuse atrophy produced by nonrigid fixation (sling) was characterized in respect to variables of proteoglycan size distribution, as well as biomechanical properties versus controls. Using this model, we found, in addition to the accepted dogma attributing changes to reduced protein synthesis by chondrocytes, that there is elevation of proteases and depression of tissue inhibitor of metalloproteases (TIMP) in atrophic knee cartilage. The findings are suggestive of cartilage remodelling reminiscent of bone remodelling in disuse atrophy reported by others. Whether the abnormal changes of protease-TIMP balance in knee cartilage can be retarded prophylactically by concurrent treatment with pentosan polysulfate and insulin like growth factor 1 remains uncertain.

Identification of the human seminal TRH-like peptide pGlu-Phe-Pro-NH2 in normal human prostate

Human and rat prostate contain thyrotropin-releasing hormone immunoreactivity (iTRH) including TRH and an uncharged TRH-like peptide. Recently the uncharged TRH-like peptide pGlu-Phe-Pro-NH2 was purified from human semen. To determine whether this peptide was of prostatic origin, human and rat prostate extracts were analyzed by ion-exchange chromatography and reversed-phase HPLC. The predominant uncharged iTRH comigrated exactly with synthetic pGlu-Phe-Pro-NH2 on HPLC and had identical affinity to pGlu-Phe-Pro-NH2 in a TRH radioimmunoassay. We conclude that prostate is a source of this peptide in humans and rats. This amidated TRH-like peptide may play a role in human reproductive physiology.

Expression of prostatic TRH-like peptides differs between species and between malignant and nonmalignant tissues

Thyrotropin-releasing hormone-immunoreactive peptides (iTRH) were analyzed in normal rat and rabbit prostates and in human benign prostatic hyperplasia (BPH) and prostate cancer. Peptides were extracted from tissues, fractionated by anion and cation exchange chromatography, and analyzed by TRH radioimmunoassay. pGlu-Glu-Pro-NH2 predominated in rabbit, but accounted for only 10-15% of iTRH in rat and human BPH. Uncharged peptides predominated in rat and human prostate. Authentic TRH (pGlu-His-Pro-NH2) is not present in rabbit prostate, but may account for up to 25% of iTRH in rat and human prostate. iTRH was virtually absent in prostate cancer. These results demonstrate considerable heterogeneity in the expression of TRH-like peptides in the prostates of various animal species, and suggest decreased expression of these peptides in prostate cancer.

Hormonal regulation of intercellular communication: parathyroid hormone increases connexin 43 gene expression and gap-junctional communication in osteoblastic cells

The presence of gap junctions between osteoblastic cells has been previously reported. For this study we used the rat osteosarcoma cell line UMR 106, which expresses the osteoblastic phenotype, as a model to characterize further the nature, physiology, and regulation of gap junctions. Northern blot analysis identified a 3.0-kilobase RNA species corresponding to the gap junction protein connexin 43. The presence of two other connexin RNA species (26 and 32) could not be detected by this method in these cells. The identified connexin RNA was amplified by reverse transcription coupled to polymerase chain reaction; the sequence of the amplified product appears identical to the sequence of a cloned rat heart connexin 43 gene. After treatment with PTH, forskolin, and 8-Br-cAMP (a cAMP analog), the levels of connexin 43 RNA in UMR 106 cells increased. Further evidence for the role of PTH and cAMP in the physiology of gap junctions in these cells was obtained with Lucifer yellow dye transfer experiments. Gap-junctional intercellular communication increased in response to PTH and forskolin (an inducer of adenylate cyclase activity). Expression of connexin 43 RNA increased severalfold in response to PTH in a concentration- and time-dependent fashion. Connexin 43 RNA and its PTH-mediated stimulation were also observed in several other osteoblastic cell lines. The roles of PTH and forskolin in regulating the physiological state of gap junctions were confirmed in primary cultures of rat calvaria osteoblasts.

Pituitary corticotroph hyperplasia in rats implanted with a medullary thyroid carcinoma cell line transfected with a corticotropin-releasing hormone complementary deoxyribonucleic acid expression vector

CRH stimulates both the synthesis and release of ACTH and other derivatives of POMC by the adenohypophysis. It is uncertain, however, whether it also causes proliferation of corticotrophs. Patients with CRH-producing tumors develop Cushing's syndrome, and some have been reported to have pituitary corticotroph hyperplasia. We now report an animal model that accurately reproduces the human disorder of ectopic production of CRH by a neoplasm. Prolonged CRH secretion by a transplanted medullary thyroid carcinoma cell line stably transfected with a CRH cDNA under transcriptional control of a cytomegalovirus promoter resulted in corticotroph hyperplasia and hypertrophy; the percentage of ACTH-containing cells in animals bearing W2CRH tumors was increased at 9.8 +/- 0.5% (controls, 6.2 +/- 0.3%; W2 implanted tumors, 7.7 +/- 0.4%). Occasional mitotic figures were identified, and the cells were larger, with abundant cytoplasm but generally less intense immunohistochemical staining for ACTH due to relative degranulation compared to controls. Melanotrophs of the intermediate lobe were also increased in number and were larger, with abundant cytoplasm. No corticotroph adenomas were found. Our experiment accurately reproduces the gradually increasing CRH levels in the general circulation produced by a growing tumor, as found in the human ectopic CRH syndrome, and confirms that long term exposure to CRH excess, as produced by a tumor, results in an increased number of corticotrophs in the adenohypophysis.

Ectopic corticotropin-releasing hormone produced by a transfected cell line chronically activates the pituitary-adrenal axis in transkaryotic rats

Hypothalamic CRH is the primary positive regulatory factor of the pituitary-adrenal axis. The purpose of our study was to analyze the chronic effects of CRH on the production and secretion of POMC peptides from both the anterior lobe (AL) and neurointermediate lobe (NIL) of the pituitary by mimicking the syndrome of ectopic CRH secretion from neuroendocrine tumors. We first generated stably transfected W2 medullary thyroid carcinoma cell lines with a rat CRH expression vector under the transcriptional control of a cytomegalovirus gene promoter. These cell lines constitutively expressed the foreign gene, accurately processed the encoded prepro-CRH, and secreted biologically active CRH with an estimated potency equivalent to that of synthetic CRH-(1-41)NH2. The cell line designated W2CRH-7 was implanted sc in the syngeneic rat strain WAG/Rij and produced tumors that abundantly secreted CRH into the peripheral circulation. Four weeks postimplantation, W2CRH-7, but not wild-type W2, cells caused significant increases in the AL content of beta-endorphin-like immunoreactivity comparable to that caused by adrenalectomy (ADX). Plasma ACTH and serum beta-endorphin-like immunoreactivity were increased to a greater extent by ADX than by W2CRH-7 cell implantation. The NIL of both male and female rats showed either no change or a tendency to decreased beta-endorphin concentrations with no change in the acetylation or carboxy-shortening profiles judged by cation exchange chromatography in response to the ectopic CRH treatment. Rats of both sexes maintained a profound activation of the pituitary adrenal axis up to 16 weeks postimplantation, with normalized adrenal gland weights 5 times that of controls. The chronic secretion of CRH by W2CRH-7 cells resulted in a complete cessation of body growth in all rats up to the maximum time tested of 16 weeks. The lack of growth was partly ameliorated by concomitant ADX, suggesting an important role for adrenal glucocorticoids in these effects. We conclude that 1) the transplantable W2CRH-7 cell line provides a highly effective and reproducible means of sustained CRH treatment that mimics the syndrome of ectopic CRH expression by neuroendocrine tumors; 2) AL corticotrophs respond to chronic CRH by a sustained production and secretion of POMC peptides, leading to a marked adrenal cortical hyperplasia, with no evidence of biologically significant desensitization; 3) chronic CRH tends to decrease the NIL content of beta-endorphin,with remarkably little effect on posttranslational processing; and 4) the syndrome of chronic ectopic CRH in WAG/Rij rats includes a cessation of body growth at least partly due to products of the adrenal glands.

The thyrotrophin-releasing hormone (TRH)-like peptides in rat prostate are not formed by expression of the TRH gene but are suppressed by thyroid hormone

Thyrotrophin-releasing hormone (TRH)-immunoreactive peptides were extracted from rat prostate and divided into two groups by mini-column cation exchange chromatography. The amounts of the peptides in each group were determined by radioimmunoassay with a TRH antiserum. The unretained peptides which lacked a basic group and the retained peptides which possessed a basic group were further purified by high-performance liquid chromatography. The unretained fraction was found to contain a series of TRH-immunoreactive peptides, one of which corresponded chromatographically to synthetic pGlu-Glu-Pro amide and another to pGlu-Phe-Pro amide. None of the TRH-immunoreactive peptides in either fraction exhibited the chromatographic behaviour of TRH. Additional evidence for the absence of TRH gene expression in the prostate was obtained by Northern blot analysis and by application of polymerase chain reaction amplification, which failed to reveal TRH mRNA. Furthermore the preproTRH-derived peptide, preproTRH(53-74), could not be detected by radioimmunoassay. The influence of thyroid status was investigated on the levels of the TRH-like peptides in the prostate. Adult rats were treated chronically with thyroxine (T4) or propylthiouracil (PTU) and the concentrations of the TRH-immunoreactive peptides were determined by chromatography and radioimmunoassay. Treatment with T4 caused the levels of the neutral and acidic TRH-like peptides to fall to approximately one-third of the levels in the controls. No significant difference from the controls was seen in the concentrations of the peptides in the prostates of rats rendered hypothyroid by administration of PTU. The results demonstrate that rat prostate contains TRH-immunoreactive peptides which are not derived from the TRH gene.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Phenyl-3-butenoic acid, an in vivo inhibitor of peptidylglycine hydroxylase (peptide amidating enzyme)

The ability of a series of non-peptide carboxylic acids to act as substrates or inhibitors of the peptide-amidating enzyme (peptidyl-glycine hydroxylase) was assessed by determining their ability to reduce the rate of enzymic conversion of D-tyrosyl-valyl-glycine or D-tyrosyl-phenylalanyl-glycine to the corresponding dipeptide amide. The inclusion of a phenyl substituent in a position distal to the carboxyl group promoted the inhibitory action. The inhibition was found to be irreversible when an olefinic double bond, alpha or beta to the carboxyl group, was present in the molecule; the inhibition appeared to be associated with a covalent interaction between the amidating enzyme and the inhibitor. With 4-phenyl-3-butenoic acid the inhibitory properties were manifest only in the presence of cofactors of the enzyme. When 4-phenyl-3-[2-14C]butenoic acid was used, the radioactivity was shown to be incorporated into protein that co-chromatographed with active enzyme. Incubation of rat thyroid carcinoma CA77 cells in the presence of 4-phenyl-3-butenoic acid led to a decrease in the levels of intracellular amidating activity and of thyrotropin-releasing hormone, an amidated peptide produced by these cells. The inhibitory effects reached a maximum at approximately 15 h after which the enzyme levels returned to the control values even though the concentration of 4-phenyl-3-butenoic acid in the cells remained unchanged. The results indicate that a mechanism exists in these cells for regulation of amidating activity.

Changes in calcitonin gene RNA processing during growth of a human medullary thyroid carcinoma cell line

The ratios of calcitonin (CT) to calcitonin gene-related peptide (CGRP) mRNA, both generated by alternative RNA processing from the same primary RNA transcript, are shown by Northern blotting of cytoplasmic RNA to vary as a function of growth in a human medullary thyroid carcinoma cell line (TT). Upon initial seeding, CT mRNA levels are relatively high, and CGRP mRNA levels are relatively low. During the early logarithmic growth phase, CGRP mRNA levels rise severalfold, while CT mRNA levels change only slightly. As the cells approach confluence, both CT and CGRP mRNA levels rise. Subsequently, CGRP mRNA levels fall substantially in postconfluent cells, while CT mRNA levels remain high. By actinomycin D blocking of nascent transcription, we have shown that these growth-related, reversible changes in the ratio of CT to CGRP mRNA are not due to changes in mRNA stability. Our data rather suggest that TT cells reversibly alter alternative RNA-processing patterns dependent upon growth conditions in vitro, such that CT mRNA is lowest and CGRP mRNA is highest during rapid growth. The mechanisms underlying this RNA-processing alteration may play a role in certain patients with aggressive forms of medullary thyroid carcinoma, in whom a decrease or loss of CT levels heralds a poor prognosis.