cyclin-d1 and Pheochromocytoma

Pheochromocytoma (PCC) is a rare catecholamine-producing tumor that arises from the adrenal medulla and is often familial. The genetic basis for familial PCC involves mutations of RET, VHL, SHDx or NF-1 in more than 20% of cases. Additional genes may be important in pathogenesis of both familial and sporadic PCC. ErbB-2/Her2/Neu is a growth factor receptor tyrosine kinase that is frequently overexpressed in tumors and there is clinical evidence suggesting that enhanced ErbB-2 growth factor receptor signaling may play a role in PCC. In the present study, ectopic expression of an activated ErbB-2 transgene resulted in bilateral adrenal PCC. Analyses of tumor samples and normal adrenal tissue revealed that levels of the Pten tumor suppressor protein were greatly reduced in PCCs, while levels of the cell cycle regulatory protein cyclin D1 were usually increased. In addition, levels of phospo-AKT were increased in PCCs versus normal adrenal tissue. Biochemical analyses established that PCC's were functionally active, producing abundant levels of the catecholamines, epinephrine and norepinephrine. These data establish that increased ErbB-2 growth factor receptor signaling in the adrenal medulla can lead to PCC through combined influences on Pten, AKT andcyclin D1.

Topics: Adrenal Gland Neoplasms; Animals; Cell Transformation, Neoplastic; Cyclin D1; Gene Expression Regulation, Neoplastic; Immunohistochemistry; Mice; Pheochromocytoma; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; PTEN Phosphohydrolase; Receptor, ErbB-2; Signal Transduction

The function of cell cycle regulator molecules during apoptosis induced by serum withdrawal was examined in rat pheochromocytoma PC12 cells. When human cDNAs encoding cyclins, cyclin-dependent kinase 2 (CDK2), CDK4, and cell-division cycle 2 (CDC2), were introduced, only CDK4-overexpressing cells were more prone to apoptosis compared with parental cells. In the parental cells, serum withdrawal resulted in the upregulation of CDK4 protein expression 6.6-fold for the first 12 h after serum withdrawal. In contrast, CDK4 protein levels in CDK4-overexpressing cells remained constant for the first 12 h followed by a gradual decline. Expression of cyclin D1 was upregulated in both cell lines. The change in CDK4 kinase activity almost paralleled that of CDK4 protein expression. These results suggest that CDK4 kinase activity is one of the critical regulators in the apoptotic cascade in PC12 cells.

Topics: Animals; Apoptosis; CDC2 Protein Kinase; CDC2-CDC28 Kinases; Cell Survival; Culture Media, Serum-Free; Cyclin D1; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinases; DNA Fragmentation; Nerve Tissue; Nucleosomes; PC12 Cells; Pheochromocytoma; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Rats; Recombinant Proteins

The anti-proliferative effect of nerve growth factor (NGF) on the rat pheochromocytoma cell line PC12 has been previously shown to be accompanied by the accumulation of cells in either the G1 phase with a 2c DNA content, or with a 4c DNA content characteristic for G2/M, as evidenced by flow cytometric analysis of DNA distribution using propidium iodide. Herein, these apparently conflicting results are clarified. The present studies indicate that a simple DNA distribution profile obtained by this technique can confound interpretation of the biological effects of NGF on cell-cycle distribution due to the presence of tetraploid cells. Using cyclin D1 and incorporation of bromodeoxyuridine as markers of respectively, G1 and S phase, we show that PC12 cultures can have a considerable amount of tetraploid cells which, when in the G1 phase, have a 4c DNA content and express cyclin D1. During exposure to NGF, this population increases, reflecting the accumulation of cells in the G1 phase of the cell cycle. The data presented, support the possibility that events affecting the expression or action of G1 regulatory proteins may be involved in the molecular mechanism of the anti-mitogenic effect of NGF.

Topics: Adrenal Gland Neoplasms; Animals; Bromodeoxyuridine; Cell Cycle; Cell Division; Cyclin D1; Cyclins; DNA, Neoplasm; Flow Cytometry; G1 Phase; Gene Expression; Kinetics; Nerve Growth Factors; Oncogene Proteins; PC12 Cells; Pheochromocytoma; Rats; S Phase