phorbol and Thyroid-Neoplasms

Phorbol 12-myristate 13-acetate (PMA) is known to affect a variety of cellular processes, including cell proliferation, differentiation, and migration. PMA has been shown to promote antiproliferative and antimigratory effects in many types of cancer cells. Our findings show that PMA induced a strong antiproliferative effect in two anaplastic (FRO and ARO) and one follicular (ML-1) thyroid cancer cell lines, and increased the fraction of FRO cells in G1 phase of the cell cycle. The fractions in the S and G2 phases were decreased. Moreover, PMA evoked a significant increase in the levels of the cell cycle regulators p21Waf1/Cip1 and p27Kip1. The levels of cyclin D3 and the cyclin-dependent kinases cdk4 and cdk6 decreased, as did the phosphorylation of the Rb-protein. PMA did not induce apoptosis. PMA stimulated the translocation of protein kinase C (PKC) alpha, betaI and delta isoforms to the cell membrane. PKCdelta small interfering RNA attenuated the PMA-induced antiproliferative effect and prevented the upregulation of p21Waf1/Cip1 and p27Kip1. Prolonged stimulation with PMA decreased the phosphorylation of mitogen-activated protein (MAP) kinase. PMA also decreased the phosphorylation of Akt and evoked a biphasic change in the phosphorylation of the forkhead box class-O protein (FOXO): an increase in phosphorylation, followed by a dephosphorylation. In addition, PMA inhibited FRO, ARO and ML-1 cell migration toward serum. The inactive phorbol ester analog 4alpha-phorbol and the diacylglycerol analog 1,2-dioctanoyl-sn-glycerol were without an effect on proliferation and migration. The results indicate that PMA is an effective inhibitor of thyroid cancer cell proliferation and migration by a mechanism involving PKC-MAP kinase/Akt and FOXO signaling.

Topics: Carcinoma; Cell Line, Tumor; Cell Movement; Cell Proliferation; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinase Inhibitor p27; Forkhead Box Protein O1; Forkhead Transcription Factors; G1 Phase; Humans; Isoenzymes; Mitogen-Activated Protein Kinases; Phorbols; Phosphorylation; Protein Kinase C-delta; Protein Transport; Proto-Oncogene Proteins c-akt; RNA, Small Interfering; S Phase; Tetradecanoylphorbol Acetate; Thyroid Neoplasms; Transfection

We have undertaken studies of the regulation of the secretion and cytoplasmic mRNA of chromogranin-A (CgA) and calcitonin (CT) in cells that secrete both substances in order to determine if they are regulated through the same mechanisms. Studies were conducted in cell lines derived from a human medullary thyroid carcinoma (MTC) and a human lung cancer (M103). Treatment with phorbol-12-myristate-13-acetate (PMA) resulted in a dose-dependent increase in the secretion of both CT and CgA by the two cell lines. Phorbol at 1000 nM resulted in 4- and 10-fold increases in CgA secretion and 3- and 5-fold increases in CT secretion by the MTC and M103 cells, respectively. The secretory patterns were similar for CgA and CT. In the M103 cells the same treatment resulted in a 100% increase in CgA-specific cytoplasmic RNA and a 70% increase in CT-specific cytoplasmic RNA. The secretion of CgA and CT was coordinately regulated by phorbol in both MTC and M103 cells, and related mRNA changes could be detected in the M103 cells. These observations support the hypothesis that CT and CgA secretion and gene expression are under similar regulatory controls.

Topics: Calcitonin; Cell Line; Chromogranin A; Chromogranins; Dose-Response Relationship, Drug; Humans; Lung Neoplasms; Nerve Tissue Proteins; Nucleic Acid Hybridization; Phorbol Esters; Phorbols; RNA; Tetradecanoylphorbol Acetate; Thyroid Neoplasms; Tumor Cells, Cultured