High levels of CUG-initiated FGF-2 expression cause chromatin compaction, decreased cardiomyocyte mitosis, and cell death.

Fibroblast growth factor 2 (FGF-2) is a multifunctional mitogen present in CUG-and AUG-initiated forms, referred to as 'hi' and 'lo' FGF-2, respectively. We have used an adenoviral vector to express the predominantly nuclear human 'hi' FGF-2 and examined the relationship between expression levels, mitotic entry, cell number and chromatin compaction of cardiac myocytes, over 1-3 days in culture. At a multiplicity of infection (m.o.i.) of 50, levels of 'hi' FGF-2 (assessed by Western blotting) and mitotic index (fraction of myocyte nuclei staining positive for phosphorylated histone H3) paralleled each other, becoming maximal at 2 days. At 200 m.o.i., maximal expression of 'hi' FGF-2 (approximately double that at 50 m.o.i) was achieved at 2 days and coincided with decreased mitotic index and increased chromatin compaction. At 3 days compaction was maximal, mitotic index was minimal, and cell numbers decreased, accompanied by the appearance of DNA laddering, an indicator of apoptosis. Overall, the lower dose of 'hi' FGF-2 and early time points favored a proliferative phenotype while the higher dose, and later time points, promoted chromatin compaction, inhibition of proliferation and cell death.