Fibronectin isoforms are differentially expressed in normal and adenomatous human anterior pituitaries

The tumour microenvironment of pituitary neuroendocrine tumours

The tumour microenvironment (TME) includes a variety of non-neoplastic cells and non-cellular elements such as cytokines, growth factors and enzymes surrounding tumour cells. The TME emerged as a key modulator of tumour initiation, progression and invasion, with extensive data available in many cancers, but little is known in pituitary tumours. However, the understanding of the TME of pituitary tumours has advanced thanks to active research in this field over the last decade. Different immune and stromal cell subpopulations, and several cytokines, growth factors and matrix remodelling enzymes, have been characterised in pituitary tumours. Studying the TME in pituitary tumours may lead to a better understanding of tumourigenic mechanisms, identification of biomarkers useful to predict aggressive disease, and development of novel therapies. This review summarises the current knowledge on the different TME cellular/non-cellular elements in pituitary tumours and provides an overview of their role in tumourigenesis, biological behaviour and clinical outcomes.

Matrix metalloproteinase 2 (MMP-2) levels are increased in active acromegaly patients

PURPOSE

During follow-up of acromegaly patients, there is a discordance rate of 30% between the measurements of growth hormone and insulin-like growth factor-1 levels. Further tests are required to determine disease activity in patients with discordant results. This study was planned to investigate an association of serum levels of matrix metalloproteinase-2, matrix metalloproteinase-9, and cathepsin B with disease activity in acromegaly patients.

METHODS

In this study, 64 acromegaly patients followed in our clinic were divided into two groups according to the 2010 consensus criteria for cure of acromegaly as patients with active disease (n = 24) and patients with controlled disease (n = 40). Serum matrix metalloproteinase-2, matrix metalloproteinase-9, and cathepsin B levels were measured by the enzyme-linked immunosorbent assay method.

RESULTS

The mean serum matrix metalloproteinase-2 level was significantly higher in the active acromegaly patients than in the controlled acromegaly patients (150.1 ± 54.5 ng/mL vs. 100.2 ± 44.6 ng/mL; p < 0.0001). There was no significant difference between the active and controlled acromegaly patients regarding serum matrix metalloproteinase-9 and cathepsin B levels (p = 0.205 and p = 0.598, respectively). Serum matrix metalloproteinase-2 levels of 118.3 ng/mL and higher had a sensitivity of 75% and a specificity of 77.5% in determining active disease. The risk of active acromegaly was 3.3 fold higher in the patients with a matrix metalloproteinase-2 level of >118.3 ng/mL than in the patients with a matrix metalloproteinase-2 level of <118.3 ng/mL.

CONCLUSIONS

In this study, serum matrix metalloproteinase-2 level is increased in the active acromegaly patients and a threshold value in determining active disease was defined for serum matrix metalloproteinase-2 level. This study is the first to compare acromegaly patients having active or controlled disease in terms of matrix metalloproteinase-2 and matrix metalloproteinase-9 levels. The results need to be confirmed by a study that will be conducted in a larger patient group also including a healthy control group to demonstrate the value of this novel marker in disease activity.

Inhibition of estrogen-induced pituitary tumor growth and angiogenesis in Fischer 344 rats by the matrix metalloproteinase inhibitor batimastat

The development of estrogen-induced pituitary prolactinoma in Fischer 344 (F344) rats is associated with enhanced neovascularization. Based on the significance of matrix metalloproteinases (MMPs) for tumor growth and angiogenesis, we have studied the effect of batimastat (BB-94), a synthetic MMPs inhibitor (MMPI) on the progression of prolactin-secreting pituitary adenoma in rats. Pituitary tumors were induced in male F344 rats by s.c. implantation of Silastic tubes containing diethylstilbestrol (DES). The effects of chronic treatment with BB-94 (30 mg/kg b.w.) on pituitary weight, cell proliferation, apoptosis and vascular density were evaluated. We have stated that chronic treatment with batimastat caused a significant reduction in the pituitary weight. Batimastat has been found to decrease cell proliferation evaluated by a number of PCNA-positive stained cell nuclei. A marked increase in the apoptotic index within the pituitary was observed in the study group. Moreover, the density of microvessels identified by CD31 was reduced in the group treated with BB-94. The results of our study provide evidence for an inhibitory effect of batimastat, a synthetic MMPI, on the growth and angiogenesis in an experimental model of human prolactinoma. The ability of BB-94 to suppress established pituitary tumor growth suggests a possible application of MMPIs in the treatment of pituitary adenomas.

Regulation of pituitary hormones and cell proliferation by components of the extracellular matrix

The extracellular matrix is a three-dimensional network of proteins, glycosaminoglycans and other macromolecules. It has a structural support function as well as a role in cell adhesion, migration, proliferation, differentiation, and survival. The extracellular matrix conveys signals through membrane receptors called integrins and plays an important role in pituitary physiology and tumorigenesis. There is a differential expression of extracellular matrix components and integrins during the pituitary development in the embryo and during tumorigenesis in the adult. Different extracellular matrix components regulate adrenocorticotropin at the level of the proopiomelanocortin gene transcription. The extracellular matrix also controls the proliferation of adrenocorticotropin-secreting tumor cells. On the other hand, laminin regulates the production of prolactin. Laminin has a dynamic pattern of expression during prolactinoma development with lower levels in the early pituitary hyperplasia and a strong reduction in fully grown prolactinomas. Therefore, the expression of extracellular matrix components plays a role in pituitary tumorigenesis. On the other hand, the remodeling of the extracellular matrix affects pituitary cell proliferation. Matrix metalloproteinase activity is very high in all types of human pituitary adenomas. Matrix metalloproteinase secreted by pituitary cells can release growth factors from the extracellular matrix that, in turn, control pituitary cell proliferation and hormone secretion. In summary, the differential expression of extracellular matrix components, integrins and matrix metalloproteinase contributes to the control of pituitary hormone production and cell proliferation during tumorigenesis.

Monitoring the Expression Profiles of Integrins and Adhesion/Growth-regulatory Galectins in Adamantinomatous Craniopharyngiomas: Their Ability to Regulate Tumor Adhesiveness to Surrounding Tissue and Their Contribution to Prognosis

OBJECTIVE

The purpose of this study was to identify biological markers that may be involved in the adhesiveness of craniopharyngiomas to optical chiasms and/or pituitary stalks.

METHODS

We determined the complete pattern of integrin expression in three craniopharyngiomas by means of a complementary deoxyribonucleic acid microarray. We quantitatively determined the levels of immunohistochemical expression of the different integrins in a series of 37 cases and the pattern of immunohistochemical expression of 10 extracellular matrix components (acting as integrin ligands) in 7 optical chiasms and 11 pituitary stalks. We also quantitatively (computer-assisted microscopy) determined the levels of immunohistochemical expression of galectin-1, -3, -4, -7, and -8 in 50 adamantinomatous craniopharyngiomas.

RESULTS

The present study shows that at both the ribonucleic acid and protein levels, adamantinomatous craniopharyngiomas express the alpha2, alpha6, alpha(v), beta1, beta5, and beta8 integrin subunits, whereas optical chiasms and pituitary stalks express vitronectin, thrombospondin, and various forms of collagens.

CONCLUSION

Our data suggest that at least part of the adhesiveness of craniopharyngiomas to the surrounding tissue, such as optical chiasms and pituitary stalks, could be explained by the interactions between alpha(2beta1) integrin expressed by craniopharyngiomas and collagens on the one hand, and vitronectin expressed by the surrounding tissue on the other hand. In addition, a Cox regression analysis has revealed that the levels of galectin-4 contribute significant information toward the delay in recurrence independently of surgical status.

Molecular defects in the pathogenesis of pituitary tumours

The majority of pituitary adenomas are trophically stable and change relatively little in size over many years. A comparatively small proportion behave more aggressively and come to clinical attention through inappropriate hormone secretion or adverse effects on surrounding structures. True malignant behaviour with metastatic spread is very atypical. Pituitary adenomas that come to surgery are predominantly monoclonal in origin and roughly half are aneuploid, indicating either ongoing genetic instability or transition through a period of genetic instability at some time during their development. Few are associated with the classical mechanisms of tumour formation but it is generally believed that the majority harbour quantitative if not qualitative differences in molecular composition compared to the normal pituitary. Despite their prevalence and the ready availability of biopsy material, at the present time, the precise molecular pathogenesis of the majority of pituitary adenomas remains unclear. This review summarizes current thinking.

Extracellular matrix components regulate ACTH production and proliferation in corticotroph tumor cells

The extracellular matrix (ECM) conveys signals through membrane receptors called integrins producing changes in cell morphology, proliferation, differentiation and apoptosis. Previous studies suggest that the ECM plays an important role in pituitary physiology and tumorigenesis. In the present work we studied for the first time the effects of fibronectin, laminin, collagen I and collagen IV on hormone secretion and cell proliferation in the corticotroph tumor cell line AtT-20 and in normal pituitary cells, examining the signal transduction mechanisms that mediate these effects. ACTH production in AtT-20 cells was inhibited by fibronectin, laminin and collagen I. A reporter construct with the POMC promoter showed similar results, indicating that the effects of the ECM take place at the level of POMC gene transcription. In contrast, ACTH production was not significantly altered in normal pituitary cells. AtT-20 cell proliferation was stimulated by collagen IV and fibronectin, but inhibited by collagen I and laminin. In parallel, the cell morphology was modified by the ECM. We found that the production of reactive oxygen species mediate the effects of laminin and collagen IV. On the other hand, the effect of fibronectin was mimicked by beta1-integrin and Rho activation. These results show for the first time that the ECM controls ACTH biosynthesis and proliferation in corticotroph tumor cells and suggest a role for the ECM in corticotroph adenoma development.

High levels of matrix metalloproteinases regulate proliferation and hormone secretion in pituitary cells

Beside the digestion of the extracellular matrix during tumor invasion and metastasis, more recently, new functions for matrix metalloproteinases (MMPs) have been proposed. We studied the expression and function of these enzymes in pituitary cells. We observed the activities of MMP-2 and MMP-9 together with expression of membrane-type MMP and tissue inhibitor of metalloproteinase-1 in all types of human pituitary adenomas. We found surprisingly high levels of MMP activity and low levels of tissue inhibitor of metalloproteinases, indicating a high level of extracellular matrix-degrading activity in pituitary adenomas. To examine the function of metalloproteinase activity in pituitary cells we used the synthetic MMP inhibitor batimastat. These studies demonstrate that MMPs secreted by pituitary cells can release growth factors anchored to the extracellular matrix that, in turn, control pituitary cell proliferation and hormone secretion. These results define a new additional mechanism for the control of pituitary hormone secretion and indicate new potential therapeutic targets for pituitary adenomas.

Serum-free media for culturing and serial-passaging of adult human retinal pigment epithelium

The ability of a chemically-defined serum-free culture medium to support the attachment, growth and serial passaging of primary adult human retinal pigment epithelial (RPE) cells was studied. Primary cultures of adult human RPE were established in a chemically-defined serum-free culture medium on both bare or bovine corneal endothelial extracellular matrix-coated tissue-culture plastic. Confluent cells were serially passaged in chemically-defined serum-free culture medium three times by trypsinization, and trypsin activity was quenched with aprotinin. First passage RPE cells were plated onto tissue-culture plastic precoated with bovine corneal endothelial extracellular matrix or uncoated tissue-culture plastic in 24 well plates at a density of 50 viable cells mm-2. Cells were maintained either in chemically-defined serum-free culture medium, DMEM without serum, or DMEM with 15% fetal bovine serum. For each medium plating, efficiencies were determined 24 hours after plating, and growth rates were determined on the first, third and seventh days after plating. Morphometric image analysis was performed on cells cultured for up to 6 weeks and three serial passages. Seeding efficiency on bovine corneal endothelial extracellular matrix-coated tissue-culture plastic and treated tissue-culture plastic were higher for chemically-defined serum-free culture medium (88.9+/-2.7% and 47.1+/-4.1%, respectively) and DMEM with serum (87.2+/-5.6% and 52.9+/-10.5%, respectively) than DMEM without serum (59.2+/-5.6% and 33.1+/-6.9%, respectively; P<0.01). The RPE proliferation rate in chemically-defined serum-free culture medium was comparable to DMEM with serum on both substrates within the first 3 days, although cells in DMEM with serum had a higher proliferation rate on day 7. Cells cultured in DMEM without serum, eventually decreased in number. RPE maintained in chemically-defined serum-free culture medium maintained a consistent proliferation rate, reached confluence, and retained an epitheloid morphology on either extracellular matrix or tissue-culture plastic for up to 6 weeks and three serial passages. Primary RPE reached confluence at 12+/-3 days on bovine corneal endothelial extracellular matrix-coated tissue-culture plastic and 21+/-5 days on treated tissue-culture plastic. Confluent cultures were composed of small hexagonal cells with epitheloid morphology on both substrates. We concluded that primary adult human RPE can be cultured in this chemically-defined serum-free culture medium. RPE will proliferate, reach confluence, retain their epitheloid morphology and can be serially passaged in the absence of serum.

RT-PCR investigation of fibronectin mRNA isoforms in malignant, normal and reactive oral mucosa

This study aimed to establish patterns of cellular fibronectin mRNA splice variants in normal oral mucosa, oral squamous cell carcinoma, oral leukoplakias with and without atypia, and focal reactive overgrowths of oral mucosa. Particular emphasis was placed on evaluation of either the EDA or EDB domains as markers of malignancy. Total RNA was extracted from normal oral mucosa, oral squamous cell carcinoma, oral leukoplakias with and without atypia, reactive epulides, fibroepithelial polyps and denture-related hyperplasia. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to identify different fibronectin transcripts at three splice sites (EDA, EDB and IIICS). All the tissues investigated produced EDA+, EDA-, EDB+ and EDB- splice variants, and this study did not support RT-PCR-based detection of either EDA or EDB domains as markers of malignancy in oral tissues. Variations in IIICS splice patterns were observed, although these were not specific to any lesion group. In particular, there were differences in either the inclusion or omission of the domain coding for the CS-5 binding site for alpha 4 beta 1 integrin, whereas the CS-1 binding site for alpha 4 beta 1 integrin was typically present when additional domains were included at the IIICS splice site. In conclusion, complex patterns of fibronectin splice variant transcripts exist in normal and pathological oral mucosa. This may reflect the multiple biological functions identified for fibronectin proteins, although the significance of different specific fibronectin splice variants has yet to be fully elucidated.

Cellular fibronectin concentration in the plasma of patients with malignant and benign diseases: a comparison with CA 19-9 and CEA

EDAcFN enzyme immunoassay (EIA) is a new tumour marker assay measuring the extra domain A-containing isoform of cellular fibronectin (cFN), a component mainly found in extracellular matrices. The concentration cFN was measured in plasma and serum from 468 patients with malignant and benign diseases. The concentrations of cFN were higher in plasma than in serum. Using receiver operating characteristic (ROC) curve analysis, determination from plasma was superior to serum at specificity levels higher than 78% and was chosen for further analysis. The highest frequencies of elevated cFN values were seen in patients with hepato-pancreato-biliary malignancies (50-67%). In pancreatic and bile duct cancers, cFN provided little further information to that obtained by CA 19-9. The greatest advantage over CA 19-9 and CEA was seen in patients with local colorectal cancer and in hepatocellular carcinomas. Four out of nine patients with Dukes' stage B colorectal cancer had an elevated cFn level, but only one had an abnormal CEA level. In hepatocellular carcinomas, cFN was also compared with alpha-fetoprotein. The sensitivity of cFN (72%) was superior to that of AFP (61%), and concomitant use of cFN and AFP raised the sensitivity to 83%. The highest frequencies of elevated values in patients with benign diseases were observed in those with severe liver disease (32%) and biliary (17%) and pancreatic (24%) diseases. A combination of cFN and CA 19-9 showed the highest overall sensitivity of 47%, compared with 31% for cFN and 33% for CA 19-9. The corresponding specificities were 76% for cFN +/- CA 19-9, 85% for cFN and 83% for CA 19-9. The accuracy of a combination of cFN and CA 19-9 or CEA (60% respectively) was higher than that of cFN (55%), CA 19-9 (55%) or CEA (45%) alone. In conclusion, the results of the new cFN test are encouraging and further studies on larger patient materials have been started.