Butyrate, a non-toxic
short-chain fatty acid (SCFA) and inhibitor of
histone deacetylase (HDAC), has potential as an anti-
tumor agent because it imposes a reversible G1 block in normal cells yet induces apoptosis in
tumor lines. As a potent reactivator of fetal
globin transcription,
butyrate is used clinically in the treatment of
hemoglobinopathies. The anti-proliferative effect of
butyrate and its derivatives on in vivo erythroid cell maturation, however, has limited their utility. The molecular mechanisms underlying the G1 arrest induced by
butyrate and related SCFAs remain unclear. One model, drawing on
tumor cell data, proposes that HDAC inhibition and subsequent transcriptional induction of
cyclin-dependent kinase inhibitor (CKI) p21CIP are required. However, because of potentially confounding genetic mutations present in
tumor models, we examined SCFA effects on CKIs in a non-transformed growth control model. Using murine 3T3 fibroblasts, we find p27KIP1 is also strongly induced. Unlike previously described effects of
butyrate and HDAC inhibition on p21CIP, p27KIP1 induction did not occur at the transcriptional level; instead, the stability of the
p27KIP1 protein increased. Other structurally unrelated
HDAC inhibitors, including
trichostatin A (
TSA), induced p27KIP1 similarly. p27KIP1 was found in
cyclin E/Cdk2 complexes, concomitant with suppression of cdk2 activity. Elevation of p27KIP1 is required for the observed G1 blockade, as p27KIP1-deficient fibroblasts were resistant to HDAC inhibition-induced arrest. These data suggest a novel activity for
HDAC inhibitors and demonstrate a critical role for p27KIP1 in mediating G1 arrest in response to these drugs.