Endoplasmic Reticulum Calcium Pumps and Tumor Cell Differentiation

Endoplasmic reticulum (ER) calcium homeostasis plays an essential role in cellular calcium signaling, intra-ER protein chaperoning and maturation, as well as in the interaction of the ER with other organelles. Calcium is accumulated in the ER by sarco/endoplasmic reticulum calcium ATPases (SERCA enzymes) that generate by active, ATP-dependent transport, a several thousand-fold calcium ion concentration gradient between the cytosol (low nanomolar) and the ER lumen (high micromolar). SERCA enzymes are coded by three genes that by alternative splicing give rise to several isoforms, which can display isoform-specific calcium transport characteristics. SERCA expression levels and isoenzyme composition vary according to cell type, and this constitutes a mechanism whereby ER calcium homeostasis is adapted to the signaling and metabolic needs of the cell, depending on its phenotype, its state of activation and differentiation. As reviewed here, in several normal epithelial cell types including bronchial, mammary, gastric, colonic and choroid plexus epithelium, as well as in mature cells of hematopoietic origin such as pumps are simultaneously expressed, whereas in corresponding tumors and leukemias SERCA3 expression is selectively down-regulated. SERCA3 expression is restored during the pharmacologically induced differentiation of various cancer and leukemia cell types. SERCA3 is a useful marker for the study of cell differentiation, and the loss of SERCA3 expression constitutes a previously unrecognized example of the remodeling of calcium homeostasis in tumors.

Expression of proline-directed protein kinase, (p34cdc2/p58cyclin A), a novel cell proliferation marker in childhood brain tumors

The presence of two proteins of the proline-directed protein kinase (PDPK), the catalytic subunit p34cdc2 and the regulatory subunit p58cyclin A was determined in seven primitive neuroectodermal tumors (PNETs), three choroid plexus neoplasms and eleven astroglial tumors. The highest expression was registered in the cellularly undifferentiated PNETs and glioblastoma multiforme from the astroglial malignant group. Rabbit immunoantiserum against the two subunits of PDPK, a cell proliferation marker, was employed to detect proliferation activity in childhood brain tumors. The PDPK activity was present from Gl- to M-phases in 21 childhood brain tumors with different central nervous system (CNS) localization and cellular atypia. Immunocytochemical analysis employed an indirect, alkaline phosphatase conjugated biotin-streptavidin antigen detection technique on frozen and routine, formalin-fixed and paraffin-wax-embedded tissue sections of brain tumors. We compared the proliferation activity in the cells of normal, morphologically changed and neoplastically transformed choroid plexus. The average proliferation activity was low in comparison with other tissues. The results in normal and neoplastically transformed choroid plexus were very similar. The lowest proliferation activity in the astroglial group belonged to pilocytic ASTRs. The use of cell differentiation as a prognostic factor in primary brain tumors has already been established and is strongly suggested by our research group. Further systematic neoplasm studies and regular employment of these two polyclonal antibodies for immunocytochemical screening experiments are necessary to determine their true diagnostic and prognostic significance.

Prostaglandin D synthase (beta-trace) in meningeal hemangiopericytoma

The level of prostaglandin D synthase (PGDS), a major protein constituent of cerebrospinal fluid (CSF), is altered in various brain diseases, including meningitis. However, its role in the brain remains unclear. PGDS is mainly synthesized in the arachnoid cells, the choroid plexus and oligodendrocytes in the central nervous system. Among brain tumors, meningiomas showed intense immunoreactivity to PGDS in the perinuclear region. Thus, PGDS has been considered a specific cell marker of meningioma. In this study, we examined 25 meningeal hemangiopericytomas (HPCs) and found that 16 of the tumors (64%) showed immunoreactivity for PGDS in the perinuclear region. For comparison, 15 meningiomas, 14 soft-tissue HPCs, 1 mesenchymal chondrosarcoma, 3 choroid plexus papillomas, and 7 oligodendrogliomas were also examined. Meningiomas showed positive immunoreactivity for PGDS in 13 cases (80%). Except for one case located at the sacrum, none of the other soft-tissue HPCs showed immunostaining for PGDS. Mesenchymal chondrosarcoma arises in the bones of the skull, and its histological pattern resembles that of HPC; however, it showed no immunoreactivity for PGDS. Neither choroid plexus papillomas nor oligodendrogliomas were immunopositive for PGDS. These findings suggest that meningeal HPCs may have a unique molecular phenotype that is distinct from that of the soft-tissue HPCs. The origin of meningeal HPCs may be more closely related to the arachnoid cells.

The expression of Gal beta 1,4GlcNAc alpha 2,6 sialyltransferase and alpha 2,6-linked sialoglycoconjugates in human brain tumors

CMP-NeuAc: Gal beta 1,4GlcNAc alpha 2,6 sialyltransferase (alpha 2,6-ST) [EC 2.4.99.1] is developmentally regulated, shows a high degree of tissue specificity, and appears to play a role in oncogenic transformation and metastasis. In the present study, we have performed the first detailed analysis of the expression of alpha 2,6-ST and alpha 2,6-linked sialoglycoconjugates in human brain tumors. We used a polyclonal, monospecific anti-rat alpha 2,6-ST antibody and the alpha 2,6-linked sialic acid-specific lectin, Sambucus nigra agglutinin (SNA) for histochemical studies, and a human alpha 2,6-ST-specific cDNA probe for Northern analysis. Meningiomas, chordomas and craniopharyngiomas frequently expressed alpha 2,6-ST and alpha 2,6-linked sialoglycoconjugates. Among the different meningioma subtypes, meningothelial meningiomas stained more strongly with both anti-alpha 2,6-ST antibody and SNA than the fibroblastic and anaplastic meningiomas. On the other hand, all tumors of glial origin and medulloblastomas were virtually devoid of either alpha 2,6-ST or alpha 2,6-linked sialoglycoconjugate expression. Moreover, very weak to negligible expression of both alpha 2,6-ST and alpha 2,6-linked sialoglycoconjugates was observed in brain metastases. In conclusion, alpha 2,6-ST and alpha 2,6-linked sialoglycoconjugate expression is associated with non-neuroectodermal epithelial-like tumors.

The choroid plexus carcinomas of childhood: histopathology, immunocytochemistry and clinicopathological correlations

Anaplastic choroid plexus carcinoma is a tumour with a predilection for the posterior fossa of infants and can be difficult to distinguish histologically from medulloblastoma without the aid of immunocytochemistry using a panel of antibodies. Of a series of 17 choroid plexus carcinomas (five of which were classed as moderately differentiated and 12 as anaplastic) 17 expressed antigens to transthyretin, transferrin and cathepsin and 16 expressed carbonic anhydrase II. Eleven expressed at least one epithelial marker (cytokeratin or epithelial membrane antigen). In contrast, none of six medulloblastomas expressed epithelial markers, transrythetin, carbonic anhydrase II or transferrin, though three were positive with antibodies to cathepsin.