PARENT SESSION
PLATFORM SESSION 14. GENE REGULATION AND FUNCTION I

Monday, August 2, 2004
2:00 PM–4:00 PM
Buchanan A102
Chair: Colin Clay Co-Chair: Ted Chauvin

(329) INDUCTION OF CELL CYCLE ARREST BY ACTIVIN A THROUGH SMAD ACTIVATION IN BREAST CANCER CELLS.

Burdette, Joanna¹, Jeruss, Jaqueline¹, Kurley, Sarah¹, Lee, Eun Jig², Sturgis, Charles³, Woodruff, Teresa^{1, 4, 5}, ¹ Northwestern University, Evanston, IL² Northwestern University Medical School, Chicago, IL³ Northwestern Evanston Healthcare, Evanston, IL⁴ Northwestern University Medical School, Chicago, IL⁵ Robert H. Lurie Comprehensive Cancer Center of Northwestern University, Chicago, IL

ABSTRACT- The TGF superfamily of growth factors is responsible for a variety of physiological actions including cell cycle regulation. Activin is a member of the TGF superfamily known to inhibit the proliferation of breast cancer cells. Activin functions by interacting with its type I and type II receptors to induce phosphorylation of intracellular signaling molecules known as Smads. Smads regulate transcriptional control of many genes in a cell and tissue specific manner. In this study, we investigated the role of activin A on growth inhibition in T47D breast cancer cells. Activin inhibited cellular proliferation of T47D and MCF7 breast cancer cells, an effect that could be abrogated by incubation with the activin binding protein, follistatin. T47D cells were found to be more responsive to activin A than MCF7 cells. In response to activin, T47D cells were growth arrested in the G0/G1 phase as revealed by flow cytometry. Chemical inhibitors of the p38 map kinase pathway could not mitigate activin mediated cell cycle arrest. Infection of T47D cells with adenoviral Smad proteins resulted in growth arrest, while the dominant negative adenoviral Smad 2/3 blocked cell cycle arrest. Nuclear accumulation of Smad 3 was demonstrated by immunofluorescence in activin treated T47D cells. Activin stimulated transcription 2-fold over control using the p3TP-luciferase reporter system. The stimulation of p3TP luciferase was shown to be smad-dependent using a dominant negative adenoviral smad 2/3 construct. Activin altered the cell cycle by increasing cyclin D2 protein and by downregulating cyclin A protein. T47D cells treated with activin also displayed hypophosphorylation of the retinoblastoma protein suggesting that activin prevents proliferation by blocking cells from entering into S-phase. These data indicate that activin A is involved in the growth arrest of cancerous breast cells and suggests that disregulation of activin signaling could be involved in cancerous progression.

KEY WORDS: breast, activin