Wilhelm bernhard workshop on the cell nucleus

NUCLEAR LOCATION AND DISTRIBUTION OF PHOSPHORYLATED c-Myc IN PACLITAXEL-TREATED CELLS

Bottone M.G.¹, Soldani C.¹, Tognon G.², Gorrini C.², Biggiogera M.^1,2, Pellicciari C.^1,2 and Scovassi A.I.²

¹Dipartimento di Biologia Animale, University of Pavia and ²Istituto di Genetica Molecolare del CNR, Pavia, Italy.
The proto-oncogene c-myc encodes a phospho-protein, which plays a crucial role both in driving cell proliferation and in promoting apoptosis. In this work, using immunocytochemical techniques at light and electron microscopy, we analysed the distribution of phosphorylated c-Myc in actively proliferating human HeLa cells. The distribution pattern of c-Myc was compared with that of other ribonucleoprotein (RNP)-containing components (PANA, hnRNP-core proteins, fibrillarin) or RNP-associated nuclear proteins (SC-35 splicing factor). Our results provide the first evidence that phosphorylated c-Myc accumulates in the nucleus of tumor cells, where it colocalizes with fibrillarin, both in the nucleolus and in extranucleolar structures (Soldani et al., 2002). To address the behavior of phosphorylated c-Myc in cells undergoing drug-induced nuclear restructuring, we treated HeLa cells and colon carcinoma cell lines with paclitaxel. This drug affects microtubule stability by binding -tubulin, thus leading to cell accumulation in the G₂/M phase, polyploidization and apoptosis. We demonstrated that after the treatment with paclitaxel, phosphorylated c-Myc undergoes redistribution, becoming diffused in the nucleoplasm. Remarkably, we found that a high c-myc amplification level potentiates paclitaxel cytotoxicity, confers a multinucleated phenotype and promotes apoptosis to a high extent, thus suggesting that c-myc expression level is relevant in modulating the cell responses to paclitaxel (Bottone et al. 2003).

This work was partially supported by Fondo di Ateneo per la Ricerca (FAR 2002, University of Pavia), PRIN 2002 (n. 2002055584) and FIRB Project RBNE0132MY

References :

Soldani C, Bottone MG, Biggiogera M, Alpini C, Scovassi AI, Martin T, Pellicciari C : Nuclear localization of phosphorylated c-Myc protein in human tumor cells. Eur. J. Histochem., 46: 377-380, 2002

Bottone M.G., Soldani C., Tognon G., Gorrini C., Lazzè M.C., Brison O., Ciomei M., Pellicciari C. and Scovassi A.I : Multiple effects of paclitaxel are modulated by a high c-myc amplification level. Exp. Cell Res. (in press)