Colonic retinoblastoma protein and proliferation in cancer and non-cancer patients

Alterations of G1-S checkpoint in chordoma

BACKGROUND

To the authors' knowledge, little is known regarding the alterations of G(1)-S checkpoint and their significance in chordoma, a rare bone tumor. The authors investigated the clinicopathologic relevance of cell cycle abnormalities in chordoma.

METHODS

The expression levels of p53, murine double minute 2 (MDM2), retinoblastoma protein (pRb), cyclin D1, p16(INK4a), and p27(Kip1) were investigated using immunohistochemical techniques; p53 mutations were studied by polymerase chain reaction (PCR)-single-strand conformation polymorphism, and mdm2 amplification was analyzed using real-time quantitative PCR. The results were compared with clinicopathologic parameters in 101 lesions.

RESULTS

Approximately 10-45% of primary tumors presented alterations of p53, MDM2, cyclin D1, and pRb proteins; most tumors lacked expression of p16(INK4a) and p27(Kip1). Alterations of p53, MDM2, cyclin D1, and pRb proteins were found to have cooperative effects on both higher proliferative ability (MIB-1 labeling index [LI]) and increased nuclear pleomorphism, a previously described prognostic indicator for patients with chordoma. Multivariate analyses revealed that, among these alterations, p53 overexpression was the only independent factor for higher MIB-1 LI. At the genetic level, mdm2 gene amplification was detected in 15.4% of the lesions but did not correlate with MDM2 overexpression or other clinicopathologic parameters. No p53 mutations were detected in the current series. Survival analysis revealed that p53 overexpression, but no other cell cycle alterations, was associated with a reduced overall survival.

CONCLUSIONS

Accumulation of cell cycle alterations led to an increased MIB-1 LI and nuclear pleomorphism, a previously described prognostic indicator in chordoma. The authors believe that p53 overexpression in particular is associated with an unfavorable prognosis in patients with chordoma.

Transcriptional down-regulation of the retinoblastoma protein is associated with differentiation and apoptosis in human colorectal epithelial cells

The aim of this study was to investigate the regulation of Rb protein expression in relation to increased differentiation and induction of apoptosis in colonic epithelial cells. In vivo, Rb protein expression was found to be down-regulated towards the top of the normal colonic crypt, coincident with the region of differentiation and apoptosis, but highly expressed in colonic carcinoma tissue. Using in vitro models to study the regulation of Rb expression in pre-malignant colonic epithelial cells, we have been able to show for the first time that Rb protein expression is transcriptionally down-regulated in differentiated pre-malignant cells (in post-confluent cultures) but not in malignant colorectal epithelial cells. Furthermore, suppression of rb protein function by the HPV-E7 viral oncoprotein increased both spontaneous and DNA damage-induced apoptosis. These results suggest that Rb is able to act as a survival factor in colonic epithelial cells by suppressing apoptosis, and that over-expression of pRb in colorectal tumour cells can cause a loss of sensitivity to apoptotic signalling, resulting in aberrant cell survival and resistance to therapy.

Biomarkers of human colonic cell growth are influenced differently by a history of colonic neoplasia and the consumption of acarbose

The nutritional effects of butyrate on the colonic mucosa and studies of transformed cells suggest that butyrate has anti-colon cancer effects. If butyrate has antineoplastic effects, mucosal growth contrasts between normal subjects and those with a history of colonic neoplasia would parallel changes in growth characteristics caused by butyrate in a colon neoplasia population. To test this hypothesis, rectal biopsies from a survey of colonoscopy patients (n = 50) with and without a history of colonic neoplasia (controls) were compared. Similarly, rectal biopsies were compared from subjects (n = 44) with a colon neoplasia history in an acarbose-placebo crossover trial. Control subjects in the colonoscopy survey had higher bromodeoxyuridine (BrdU) uptake than subjects with a history of neoplasia (P = 0.05). The control subjects also had a higher correlation of BrdU and Ki-67 labeling (P = 0.003). Both findings were paralleled by acarbose use. Acarbose augmented BrdU uptake (P = 0.0001) and improved the correlation of BrdU and Ki-67 labeling (P = 0.013). Acarbose also augmented fecal butyrate (P = 0.0001), which was positively correlated with Ki-67 labeling (P = 0.003). p52 antigen had an earlier pattern of crypt distribution in subjects with a history of colon neoplasia but was not affected by acarbose use. Lewis-Y antigen was expressed earlier in the crypt with acarbose but had similar expression in the colonoscopy survey groups. The use of acarbose to enhance fecal butyrate concentration produced mucosal changes paralleling the findings in control subjects as opposed to those with neoplasia, supporting the concept of an antineoplastic role for butyrate.