NERVE GROWTH FACTOR-INDUCED ACCUMULATION OF PC12 CELLS EXPRESSING CYCLIN D1 - EVIDENCE FOR A G1 PHASE BLOCK

The anti-proliferative effect of nerve growth factor (NGF) on the rat pheochromocytoma cell line PC12 has been previously shown to be accomp anied by the accumulation of cells in either the G1 phase with a 2c DN A content, or with a 4c DNA content characteristic for G2/M, as eviden ced by flow cytometric analysis of DNA distribution using propidium io dide. Herein, these apparently conflicting results are clarified. The present studies indicate that a simple DNA distribution profile obtain ed by this technique can confound interpretation of the biological eff ects of NGF on cell-cycle distribution due to the presence of tetraplo id cells. Using cyclin D1 and incorporation of bromodeoxyuridine as ma rkers of respectively, G1 and S phase, we show that PC12 cultures can have a considerable amount of tetraploid cells which, when in the G1 p hase, have a 49 DNA content and express cyclin D1. During exposure to NGF, this population increases, reflecting the accumulation of cells i n the G1 phase of the cell cycle. The data presented, support the poss ibility that events affecting the expression or action of G1 regulator y proteins may be involved in the molecular mechanism of the antimitog enic effect of NGF.