Sodium butyrate (NaBt) and the pro-apoptotic IGFBP-3 protein, expressed at the top of the normal colonic crypt, have both been implicated in the regulation of apoptosis in colonic epithelial cells. Recent studies in human breast and hepatic cell lines have shown that NaBt can transcriptionally upregulate IGFBP-3 expression. However, the role of butyrate in the regulation of IGFBP-3 expression in the colon is less clear, with reports of both up- and downregulation of the IGFBP-3 protein in colorectal cancer cell lines. In this study we have shown that the level of IGFBP-3 protein expression in colonic epithelial cells correlates with the p53 status of the cells; wildtype p53 cells secrete higher levels of IGFBP3 protein than mutant p53 cell lines. Data presented shows that, when treated with a dose of NaBt that induced significant apoptosis (4 mM for 48 h), there was an upregulation of IGFBP-3 protein in both wildtype and mutant p53 expressing cell lines. The NaBt-induced increase in secreted IGFBP-3 protein was associated with transcriptional upregulation of the IGFBP-3 gene. Using a transfected derivative of the S/RG/C2 adenoma-derived cell line, which stably expressed exogenous IGFBP-3 protein at levels equivalent to that secreted by the 4 mM NaBt-treated parental line (1-3 ng/10(6) cells), we have shown a >2-fold increase in the sensitivity of the cells to NaBt-induced apoptosis when compared with the vector control and parental cell lines. Furthermore, inhibition of the secreted IGFBP-3 protein, by addition of neutralizing antibodies, resulted in a significant decrease in NaBt-induced apoptosis. These data suggest that IGFBP-3 may act as a positive regulator of NaBt-induced apoptosis in colonic epithelial cells, and represents a potentially important mechanism whereby the sensitivity of colonic epithelial cells to NaBt-induced apoptosis can be increased.

The objective of these experiments was to determine the pattern of mRNA expression for cytochrome P450 side-chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase/delta 5,delta 4 isomerase (3 beta-HSD) during luteinization of the follicle and in ovine luteal tissue on Days 3, 6, 9, 12, and 15 of the estrous cycle. Mean concentration of mRNA for P450scc was not different in follicles collected 4 or 24 h after the onset of estrus but increased (p < 0.05) 3-fold by 48 h (corpus hemorrhagicum). With the methods used, mRNA for 3 beta-HSD was not detected until after ovulation and formation of the corpus hemorrhagicum (48 h after onset of estrus). In luteal tissue, mean concentration of mRNA for P450scc increased from Days 3 to 9 (p < 0.05) and had decreased (p < 0.05) by Day 15. Mean concentration of mRNA for P450scc was higher (p < 0.05) in small luteal cells on Day 9 than on Day 15, with values on Days 6 and 12 being intermediate. In large luteal cells, mean concentrations of P450scc mRNA increased (p < 0.05) between Days 6 and 12 and then decreased (p < 0.05) on Day 15. Mean concentration of mRNA for 3 beta-HSD was not different (p = 0.33) in luteal tissue on any day examined. In small luteal cells, mean concentrations of mRNA for 3 beta-HSD decreased between Days 6 and 15 (p < 0.05) while in large luteal cells, mean concentrations decreased (p < 0.05) between Days 12 and 15.(ABSTRACT TRUNCATED AT 250 WORDS)

A partial cDNA was used to measure steady-state concentrations of mRNA encoding the receptor for luteinizing hormone (LH) in ovine corpora lutea. In experiment 1, luteal tissue and purified preparations of small and large steroidogenic luteal cells (n=4 per day) were obtained on days 3 (tissue only), 6, 9, 12 and 15 of the estrous cycle (estrus=day 0). Steady-state concentrations (fmoles receptor mRNA/μg poly(A)(+) RNA) and total quantities of mRNA (fmoles/corpus luteum) encoding the receptor for LH in luteal tissue increased (P<0.05) from day 3 to days 9 and 12 of the cycle; values on days 6 and 15 were intermediate. Small luteal cells contained at least four-fold greater (P<0.001) concentrations of mRNA encoding the receptor for LH than large luteal cells on days 6, 9, 12 and 15 of the cycle. In experiment 2, ewes on days 11 or 12 of the cycle received an infusion of either 1 μmol prostaglandin F(2α) (PGF(2α)) or saline into the ovarian artery. Luteal tissue was collected 1 (n=6), 4 (n=5), 12 (n=5) or 24 (n=5) h following PGF(2α) infusion, and 0 (no infusion;n=3), 12 (n=3) or 24 (n=4) h following saline administration. Concentrations of progesterone in sera decreased (P<0.05) within 12 h and remained low, whereas luteal weight and concentrations of progesterone in luteal tissue did not decrease (P<0.05) until 24 h after PGF(2α) treatment. Steady-state concentrations of mRNA encoding the receptor for LH were reduced (P<0.05) within 4 h of PGF(2α) infusion, and continued to decrease at 12 and 24 h post treatment. Calculated amounts of mRNA encoding the receptor for LH per corpus luteum were reduced (P<0.05) at 12 h after the PGF(2α) treatment and were 10% (P<0.05) of the values in saline-treated ewes at 24 h post-treatment. The increase during the estrous cycle in steady-state concentrations of mRNA encoding the receptor for LH appears to occur prior to the previously observed increase in number of receptors for LH. Following PGF(2α)-induced luteal regression, concentrations of mRNA encoding LH receptor decreased prior to the previously reported decrease in LH binding. Thus, changes in the number of receptors for LH in ovine luteal tissue during luteal development and luteolysis appears to be preceded by corresponding changes in mRNA encoding this receptor.

SummaryThe 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. targeted inactivation of the RB-1 gene in mouse embryonic fibroblasts induces apoptosis. Therefore, pRb appears to suppress apoptosis in some cell systems, perhaps through the sequestration of the E2F-1 protein, which can induce apoptosis if over-expressed (Qin et al, 1994;Field et al, 1996). In this case, pRb needs to be removed or inactivated before apoptosis can occur. To support this, a 30 kD protein has been detected in apoptotic cells harvested from colon tumour cell lines, CMSV40 fibroblasts and BJA-B lymphocyte cells, suggesting that the Rb protein is cleaved during the apoptotic process (Browne et al, 1994;An and Dou, 1996). Furthermore, cleavage at the C-terminus of pRb results in a p100 and ~5 kDa polypeptide (Chen et al, 1997). The p100 Rb protein can still bind to E2F-1 and inhibit E2F-mediated transcriptional activity, but its anti-apoptotic function is reduced, perhaps through its inability to bind to the oncogene MDM2. Thus the growthsuppressive and anti-apoptotic functions of pRb appear to be distinct from one another. The notion that pRb functions can be separated from one another has been explored previously, and experimental evidence indicates that the multiple functions of pRb can be genetically uncoupled, providing distinct functions in cellcycle control or in tissue-specific gene expression during differentiation (reviewed in Yee et al, 1998). Mice with mutations of the N-terminal region of Rb protein exhibit defects in muscle differentiation, whilst retaining the ability to bind to E2F (Riley et al, 1997). Conversely, cells with pRb mutations in the pocket domain are able to differentiate normally even when E2F binding is abrogated (Sellers et al, 1998).The functional loss of the Rb protein, by deletion or mutation, has been implicated not only in retinoblastoma, but in many types of tumour, including bladder, breast, lung and ovarian ca...

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