HDAC Up-Regulation in Early Colon Field Carcinogenesis Is Involved in Cell Tumorigenicity through Regulation of Chromatin Structure

Abstract

Normal cell function is dependent on the proper maintenance of chromatin structure. Regulation of chromatin structure is controlled by histone modifications that directly influence chromatin architecture and genome function. Specifically, the histone deacetylase (HDAC) family of proteins modulate chromatin compaction and are commonly dysregulated in many tumors, including colorectal cancer (CRC). However, the role of HDAC proteins in early colorectal carcinogenesis has not been previously reported. We found HDAC1, HDAC2, HDAC3, HDAC5, and HDAC7 all to be up-regulated in the field of human CRC. Furthermore, we observed that HDAC2 up-regulation is one of the earliest events in CRC carcinogenesis and observed this in human field carcinogenesis, the azoxymethane-treated rat model, and in more aggressive colon cancer cell lines. The universality of HDAC2 up-regulation suggests that HDAC2 up-regulation is a novel and important early event in CRC, which may serve as a biomarker. HDAC inhibitors (HDACIs) interfere with tumorigenic HDAC activity; however, the precise mechanisms involved in this process remain to be elucidated. We confirmed that HDAC inhibition by valproic acid (VPA) targeted the more aggressive cell line. Using nuclease digestion assays and transmission electron microscopy imaging, we observed that VPA treatment induced greater changes in chromatin structure in the more aggressive cell line. Furthermore, we used the novel imaging technique partial wave spectroscopy (PWS) to quantify nanoscale alterations in chromatin. We noted that the PWS results are consistent with the biological assays, indicating a greater effect of VPA treatment in the more aggressive cell type. Together, these results demonstrate the importance of HDAC activity in early carcinogenic events and the unique role of higher-order chromatin structure in determining cell tumorigenicity.

Ultrastructural alterations in field carcinogenesis measured by enhanced backscattering spectroscopy

“…Mechanistically, this provides a general road map of which morphological structures to investigate. Ongoing research to implicate specific mucosal components suggests that the alterations occur due to a combination of intracellular (e.g., condensation of chromatin in the nucleus [2][3][4] or abnormalities in the cytoskeleton 5 ) and extracelluar components (e.g., collagen cross-linking 4,6 ). Interestingly, these changes appear to be attenuated versions of other classical markers of neoplasia.…”

“…Although the concept of field carcinogenesis has been under study since 1953, the ultrastructural changes that compose the field are still being uncovered. Several changes whose role in field carcinogenesis has been implicated include chromatin condensation, [2][3][4] cytoskeleton disruption, 5 and collagen crosslinking in the extracellular matrix. 6 Still, the exact origin and carcinogenic advantage these transformations confer are not fully understood.…”

Label-free imaging of the native, living cellular nanoarchitecture using partial-wave spectroscopic microscopy

“…This relation is derived from the properties of fractal media with conserved mass and volume-as compaction increases locally, the variations in mass density (heterogeneity) must also increase. Previous molecular dynamics simulations have further confirmed that increases in δn*L c correspond to an increase in macromolecular compaction, and experimental results have shown that this increase within the nucleus quantitatively describes an increase in chromatin heterogeneity (21,25,26).…”

Valproic acid, an anti-epileptic drug and a histone deacetylase inhibitor, in combination with proteasome inhibitors exerts antiproliferative, pro-apoptotic and chemosensitizing effects in human colorectal cancer cells: Underlying molecular mechanisms

“…Specifically, the HDAC families of proteins modulate chromatin compaction and are commonly deregulated in many tumors, including colorectal cancer (23). HDACIs interfere with tumorigenic HDAC activity; however, the precise mechanisms involved in this process remain to be elucidated (23).…”

“…HDACIs interfere with tumorigenic HDAC activity; however, the precise mechanisms involved in this process remain to be elucidated (23). The anti-proliferative effects of VPA on human colorectal cancer cells may be based on the direct inhibition of HDACs by a direct influence on enzymes that are responsible for acetyla- tion and deacetylation of nucleosomal histones.…”