An immunohistochemical analysis of human colorectal
adenocarcinomas showed that
cancer cells express widely varying levels of HDAC3. The SW480
colon cancer cell line was found to express high levels of HDAC3 compared to other
colon cancer cell lines. p21 was poorly induced in SW480 cells relative to the lower HDAC3-expressing HT-29 cells. RNAi-induced reduction of HDAC3 in SW480 cells increased their constitutive,
butyrate-,
TSA-, and
TNF-alpha-induced expression of p21, but did not cause all the gene expression changes induced upon general
histone deacetylase (HDAC) inhibition. SW480 cells with lower HDAC3 expression appeared to be poised for gene expression responses with increased
histone H4-K12 acetylation, but not K5, K8, or K16 acetylation. Even though p21 was readily activated in HT29 cells, HDAC3
siRNA nonetheless stimulated p21 expression in these cells to a greater degree than HDAC1 and HDAC2
siRNA. SW480 cells with lower HDAC3 levels displayed an enhanced cell cycle arrest and growth inhibition by
butyrate, but without changes in apoptosis or sensitivity to chemotherapeutic agents. As reported for other
colon cancer cell lines,
butyrate induced the rapid downregulation of the secretory cell differentiation markers
mucin 2 and
intestinal trefoil factor in SW480 cells. Interestingly, selective HDAC3 inhibition was sufficient to downregulate these genes. Our data support a central role for HDAC3 in regulating the cell proliferation and differentiation of
colon cancer cells and suggest a potential mechanism by which
colon cancers may become resistant to
luminal butyrate.