Hybridocytochemical and immuno-ultrastructural study of calcitonin gene expression in cultured medullary carcinoma cells

Protein kinase C: a putative new target for the control of human medullary thyroid carcinoma cell proliferation in vitro

We investigate the role of protein kinase C (PKC) in the control of medullary thyroid carcinoma (MTC) cell proliferation by a PKC inhibitor, Enzastaurin, in human MTC primary cultures and in the TT cell line. We found that PKC inhibition reduces cell proliferation by inducing caspase-mediated apoptosis and blocks the stimulatory effect of IGF-I on calcitonin secretion. Enzastaurin reduces PKCβII (Thr500) phosphorylation, indicating a direct involvement of this isoform as well as the phosphorylated levels of Akt (Ser 473) and glycogen synthase kinase (Ser9), PKC pathway downstream targets and pharmacodynamic markers for PKC inhibition. PKCβII and PKCδ enzyme isoforms expression and localization were investigated. These data indicate that in vitro PKC is involved in the control of human MTC proliferation and survival by modulating apoptosis, with a mechanism that implicates PKCβII inhibition and translocation in different subcellular compartments. Targeting PKC may represent a useful therapeutic approach for controlling MTC proliferation.

Snapshot peptidomics of the regulated secretory pathway

Neurons and endocrine cells have the regulated secretory pathway (RSP) in which precursor proteins undergo proteolytic processing by prohormone convertase (PC) 1/3 or 2 to generate bioactive peptides. Although motifs for PC-mediated processing have been described ((R/K)X(n)(R/K) where n = 0, 2, 4, or 6), actual processing sites cannot be predicted from amino acid sequences alone. We hypothesized that discovery of bioactive peptides would be facilitated by experimentally identifying signal peptide cleavage sites and processing sites. However, in vivo and in vitro peptide degradation, which is widely recognized in peptidomics, often hampers processing site determination. To obtain sequence information about peptides generated in the RSP on a large scale, we applied a brief exocytotic stimulus (2 min) to cultured endocrine cells and analyzed peptides released into supernatant using LC-MSMS. Of note, 387 of the 400 identified peptides arose from 19 precursor proteins known to be processed in the RSP, including nine peptide hormone and neuropeptide precursors, seven granin-like proteins, and three processing enzymes (PC1/3, PC2, and peptidyl-glycine alpha-amidating monooxygenase). In total, 373 peptides were informative enough to predict processing sites in that they have signal sequence cleavage sites, PC consensus sites, or monobasic cleavage sites. Several monobasic cleavage sites identified here were previously proved to be generated by PCs. Thus, our approach helps to predict processing sites of RSP precursor proteins and will expedite the identification of unknown bioactive peptides hidden in precursor sequences.

Cell lines and primary cell cultures in the study of bone cell biology

Bone is a metabolically active and highly organized tissue consisting of a mineral phase of hydroxyapatite and amorphous calcium phosphate crystals deposited in an organic matrix. Bone has two main functions. It forms a rigid skeleton and has a central role in calcium and phosphate homeostasis. The major cell types of bone are osteoblasts, osteoclasts and chondrocytes. In the laboratory, primary cultures or cell lines established from each of these different cell types provide valuable information about the processes of skeletal development, bone formation and bone resorption, leading ultimately, to the formulation of new forms of treatment for common bone diseases such as osteoporosis.

Effect of follicular cells on calcitonin gene expression in thyroid parafollicular cells in cell culture

Expression of calcitonin (CT) gene in thyroid parafollicular cells involves alternate formation of CT mRNA or CGRP mRNA. High amounts of CT mRNA are formed only in thyroid gland and formation of CGRP mRNA dominates in the remaining organs. Apart from paracrine and endocrine factors, mRNA formation on the CT gene seems to be affected also by direct contacts with other cells present in the thyroid gland, in which parafollicular cells are located next to follicular cells. The present study aimed at examining whether thyroid follicular cells affect formation of mRNAs for CT and CGRP in parafollicular cells. The studies were performed in cell cultures. A parafollicular cell line (TT cells) and a follicular cell line (F6BTY cells) served as the experimental model. For comparison, co-cultures with fibroblasts, 3T3 cells, and malignant melanoma, MM cells, were also examined. CT gene expression was examined at the level of mRNAs (in situ hybridization and morphometric studies) and at the level of hormones (immunocytochemistry, morphometric studies and radioimmunological estimation of hormone levels in the medium). The immunocytochemical and hybridocytochemical studies, in line with morphometry studies, demonstrated that F6BTY and 3T3 cells were capable of affecting mRNA production for CT and CGRP and that they changed the ratio of CGRP/CT secretion by TT cells, as a sequel of contact between the two cell types and due to mediation of secreted substances. On the other hand, the malignant melanoma MM cells showed no effect on the secretion ratio. Our study seems to indicate that control of mRNA formation from CT gene may involve not only humoral factors but also direct contacts with other cells, which may explain differences in expression of the gene between cells localized in different organs.