It would be intriguing to see how IGFBP exert their actions in cell growth and apop tosis via an IGF independent fashion. Despite this website the fact that the effect of HDAC inhibitors such as SB on the expression of cell cycle regulatory genes, such as cyclins and cyclin related kinase, were docu mented and a few attempts were made to use high throughput approaches, such as microarrays, differen tial display and SAGE, to study the effects of HDAC inhibitors on cell cycle control, the extent of the effect of these inhibitors on cell proliferation and cell cycle has not been fully realized in part due to limited gene representa tion on these microarrays. Due to signifi cant differences in gene representation, species, microarray platforms, and data analysis tools used in these studies, a direct comparison between our results and those published is seemingly difficult.

In general, our results are in good agreement with published reports. For example, we detected 8% of all genes were significantly regulated by butyrate in bovine MDBK cells, which is con sistent with a previous report in which the authors used cDNA microarray consisting of 8000 sequences to demonstrate that approximately 7% of sequences assayed exhibited alteration by butyrate in human colon carci noma cells. Down regulation of cyclins, PCNA, CDKs, and upregulation of IGF2, MMPs, and TIMP2 were also confirmed by previous reports. However, many genes, such as Aurora kinases, BUB1 and BUB1B, centro mere proteins, kinesins, Max interacting protein 1, minichromosomal maintenance deficient pro teins, and spindle pole body components were not previously recognized to be regulated by SB.

Our efforts in this study are among the first to systematically categorize the butyrate regulated genes related with cell cycle control with a genome wide approach in farm ani mals. While the vast majority of these genes are down reg ulated, MXI1 is up regulated. As a key component of the mitotic checkpoint, MXI1 binds with MAX to form a sequence specific DNA binding protein complex and acts as a transcriptional repressor. Up regulation of MXI1 by SB could result in down regulation of cyclins, which in turn negatively regulates centromere proteins. Accumulation of cells with 2C and 4C DNA contents sug gests inhibition by butyrate of cell cycle at G1 and M G2 phases and suggests that a common responding element in genes responsive to the treatment of butyrate is required for progression of both phases G1 and M G2.

This observation is also consistent with the previous report that the inhibition of G1 progression by butyrate is not restricted to a specific mitogenic signaling pathway, but may also include the inhibitory effect on initia tion Brefeldin_A of DNA replication. In this report, multiple genes such as minichromosome maintenance proteins 2, 3, 4, 5, and 6, as well as Orc1 are significantly down regulated.