Depth-resolved low-coherence enhanced backscattering

The phenomenon of enhanced backscattering (also known as coherent backscattering), an object of substantial scientific interest, has awaited application to tissue optics for the past two decades. Here we demonstrate, for the first time to our knowledge, depth-resolved spectroscopic elastic light scattering measurements in tissue by use of low-coherence enhanced backscattering (LEBS). We achieve the depth resolution by exploiting the nature of the LEBS peak that contains information about a wide range of tissue depths. We further demonstrate that depth-resolved LEBS spectroscopy has the potential to identify the origin of precancerous transformations in the colon at an early, previously undetectable stage.

The nonsteroidal anti-inflammatory drug, nabumetone, differentially inhibits beta-catenin signaling in the MIN mouse and azoxymethane-treated rat models of colon carcinogenesis

The mechanisms through which beta-catenin signaling is inhibited during colorectal cancer chemoprevention by nonsteroidal anti-inflammatory agents is incompletely understood. We report that nabumetone decreased uninvolved intestinal mucosal beta-catenin levels in the MIN mouse with a concomitant increase in glycogen synthase kinase (GSK)-3beta levels, an enzyme that targets beta-catenin for destruction. However, in the azoxymethane-treated rat, where beta-catenin is frequently rendered GSK-3beta-insensitive, nabumetone failed to alter beta-catenin levels but did decrease beta-catenin nuclear localization and transcriptional activity as gauged by cyclin D1. In conclusion, we demonstrate that the differential mechanisms for beta-catenin suppression may be determined, at least partly, by GSK-3beta.

Low-coherent backscattering spectroscopy for tissue characterization

Although the phenomenon of coherent backscattering (CBS) in nonbiological media has generated substantial research interest, observing CBS in biological tissue has been extremely difficult. Here we show that the combination of low-spatial-coherence, broadband illumination, and low-temporal-coherence, spectrally resolved detection significantly facilitates CBS observation in biological tissue and other random media with long-transport mean-free path lengths, which have been previously beyond the reach of conventional CBS investigations. Furthermore, we demonstrate that depth-selective, speckle-free, low-coherent backscattering spectroscopy has the potential to diagnose the earliest, previously undetectable, precancerous alterations in the colon by means of probing short light paths.

The transcriptional repressor SNAIL is overexpressed in human colon cancer

Overexpression of the transcriptional repressor, SNAIL, has been implicated in the pathogenesis of a number of malignancies; however, there are no previous reports on the role of SNAIL in colorectal cancers (CRCs). We, therefore, evaluated human CRC specimens for the presence of the SNAIL protein. Immunohistochemical studies were performed using samples obtained from archived CRC paraffin blocks and a tissue array. Tissue sections were probed with a polyclonal antibody to human SNAIL and scored by a gastrointestinal pathologist. SNAIL was not detectable in uninvolved mucosa, but immunoreactivity was evident in 78% of tumors. SNAIL protein expression did not correlate with subsite location or gender, however, SNAIL-positive tumors had an older mean age (58.9 +/- 12.7 versus 49.8 +/- 127; P = 0.028). Furthermore, there was a trend that CRCs with metastatic ability more frequently overexpressed SNAIL (100 versus 65%; P = 0.11). In conclusion, we demonstrate, for the first time, that SNAIL is upregulated in human colon cancer, which potentially may have significance in control of metastasis and possibly serve as a target for chemopreventive agents.

Polyethylene glycol inhibits intestinal neoplasia and induces epithelial apoptosis in Apc(min) mice

Efficacy of a safe and clinically utilized polyethylene glycol formulation (PEG-3350) to suppress intestinal tumors was investigated in the Apc(min) mouse-model of experimental carcinogenesis. Furthermore, based on our previous finding on the induction of apoptosis in HT-29 cells by PEG, we evaluated its ability to stimulate epithelial cell apoptosis in both Apc(min) mouse as well as AOM-treated rat as a potential molecular mechanism of chemoprevention. Twenty-two Apc(min) mice were randomized equally to PEG or vehicle (control) supplementation. Tumors were scored and uninvolved intestinal mucosal apoptosis was assayed using a modified terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) assay and by immunohistochemical detection of cleaved caspase-3. Supplementation of Apc(min) mice with 10% PEG 3350 (in drinking water) resulted in a 48% (P<0.05) reduction in intestinal tumor burden and induced 2-3 fold increase in mucosal apoptosis. Dietary supplementation of polyethylene glycol (5%) also stimulated colonic mucosal apoptosis 4-5 fold in AOM-treated rats, the regimen that we previously reported to reduce tumor burden by 76% (P<0.05). In summary, we demonstrate, for the first time, that PEG does protect against Apc(min) mouse tumorigenesis. The correlation between pro-apoptotic actions and chemopreventive efficacy of PEG in these models strongly implicates induction of apoptosis as one of the impending mechanisms of chemoprevention.

Down-regulation of SNAIL suppresses MIN mouse tumorigenesis: Modulation of apoptosis, proliferation, and fractal dimension

Objectives: Emerging evidence implicates the SNAIL family of transcriptional repressors in cancer development; however, the role of SNAIL in colorectal cancer has not been established. To investigate the importance of SNAIL in colorectal carcinogenesis, we examined the phenotypic and cellular consequences of SNAIL down-regulation in the MIN mouse. Methods: Twenty-eight male MIN mice were randomized to treatment with an antisense phosphorodiamidate morpholino oligomer (AS-PMO) to SNAIL, saline, or a scrambled sequence control for 6 weeks. Tumors were scored and the molecular/cellular effects of anti-SNAIL treatment were evaluated through immunohistochemical analysis of the uninvolved intestinal mucosa for SNAIL and E-cadherin levels along with rates of apoptosis and proliferation. Furthermore, microarchitectural alterations were determined through measurement of fractal dimension. Results: In the uninvolved mucosa, SNAIL AS-PMO treatment moderately decreased SNAIL protein when compared with saline-treated animals (immunohistochemistry scores 3.0 ± 0.8 versus 2.1 ± 0.6, respectively; P = 0.01) with a concomitant increase in E-cadherin expression (1.8 ± 0.6 versus 2.4 ± 0.5; P &lt; 0.05). Anti-SNAIL PMO, but not scramble control, resulted in a significant decrease in both total tumor number and incidence of tumors &gt;2 mm (22% and 54%, respectively; P &lt; 0.05). Furthermore, this was accompanied by an increased apoptosis rate (2-fold), decreased proliferation (3-fold), and normalization of the fractal dimension in the uninvolved intestinal mucosa. Conclusions: We show, for the first time, that SNAIL overexpression is important in intestinal tumorigenesis. While this PMO regimen afforded modest SNAIL suppression and hence tumor reduction, this provides compelling evidence for the role of SNAIL overexpression in colonic neoplasia.

Down-regulation of SNAIL suppresses MIN mouse tumorigenesis: modulation of apoptosis, proliferation, and fractal dimension

OBJECTIVES

Emerging evidence implicates the SNAIL family of transcriptional repressors in cancer development; however, the role of SNAIL in colorectal cancer has not been established. To investigate the importance of SNAIL in colorectal carcinogenesis, we examined the phenotypic and cellular consequences of SNAIL down-regulation in the MIN mouse.

METHODS

Twenty-eight male MIN mice were randomized to treatment with an antisense phosphorodiamidate morpholino oligomer (AS-PMO) to SNAIL, saline, or a scrambled sequence control for 6 weeks. Tumors were scored and the molecular/cellular effects of anti-SNAIL treatment were evaluated through immunohistochemical analysis of the uninvolved intestinal mucosa for SNAIL and E-cadherin levels along with rates of apoptosis and proliferation. Furthermore, microarchitectural alterations were determined through measurement of fractal dimension.

RESULTS

In the uninvolved mucosa, SNAIL AS-PMO treatment moderately decreased SNAIL protein when compared with saline-treated animals (immunohistochemistry scores 3.0 +/- 0.8 versus 2.1 +/- 0.6, respectively; P=0.01) with a concomitant increase in E-cadherin expression (1.8 +/- 0.6 versus 2.4 +/- 0.5; P < 0.05). Anti-SNAIL PMO, but not scramble control, resulted in a significant decrease in both total tumor number and incidence of tumors >2 mm (22% and 54%, respectively; P < 0.05). Furthermore, this was accompanied by an increased apoptosis rate (2-fold), decreased proliferation (3-fold), and normalization of the fractal dimension in the uninvolved intestinal mucosa.

CONCLUSIONS

We show, for the first time, that SNAIL overexpression is important in intestinal tumorigenesis. While this PMO regimen afforded modest SNAIL suppression and hence tumor reduction, this provides compelling evidence for the role of SNAIL overexpression in colonic neoplasia.

Coherent backscattering spectroscopy

Coherent backscattering (CBS) of light in random media has been previously investigated by use of coherent light sources. Here we report a novel method of CBS measurement that combines low spatial coherence, broadband illumination, and spectrally resolved detection. We show that low spatial coherence illumination leads to an anomalously broad CBS peak and a dramatic speckle reduction; the latter is further facilitated by low temporal coherence detection. Thus CBS can be observed in biological tissue and other media that previously were beyond the reach of conventional CBS measurements. We also demonstrate, for the first time to our knowledge, spectroscopic analysis of CBS. CBS spectroscopy may find important applications in probing random media such as biological tissue in which depth-selective measurements are crucial.

Four-dimensional elastic light-scattering fingerprints as preneoplastic markers in the rat model of colon carcinogenesis

BACKGROUND & AIMS

Identification of preneoplastic changes in histologically normal epithelium (the "field effect") could provide a powerful screening tool for colorectal cancer. However, to date, reliable detection has not been possible. We have recently developed a new generation of optical technology, 4-dimensional elastic light-scattering fingerprinting (4D-ELF), which enables us to probe the nanoscale/microscale architecture of living cells. We therefore investigated whether 4D-ELF would be able to identify preneoplastic changes in the colonocytes of the azoxymethane (AOM)-treated rat model of colon carcinogenesis.

METHODS

Forty-eight Fisher 344 rats were randomized to either 2 weekly injections of AOM or saline. Animals were killed 2-20 weeks after the second injection of AOM. Colons were removed and subjected to 4D-ELF analysis, with a subset undergoing assessment of aberrant crypt foci (ACF). All AOM-treated animals were compared with age-matched saline-treated controls.

RESULTS

AOM-induced ACF became apparent at approximately 4-6 weeks and continued to increase over time. ACF were predominantly located in the distal colon. At 2 weeks (before development of ACF), there were marked changes in a number of 4D-ELF signatures. The relevance to carcinogenesis of these 4D-ELF-detected microarchitectural abnormalities is supported by their spatial and temporal correlation with subsequent development of ACF. All changes reported were highly statistically significant.

CONCLUSIONS

We show that probing the nanoscale cellular architecture with 4D-ELF provided an unprecedented tool for detecting the earliest stages of colon carcinogenesis. Future studies are necessary to explore the clinical applicability of this technology and elucidate the biological determinants of these microarchitectural changes.

Ursodeoxycholic acid inhibits Ras mutations, wild-type Ras activation, and cyclooxygenase-2 expression in colon cancer

K-ras mutations occur frequently in colon cancer and contribute to autonomous growth. In the azoxymethane (AOM) model of colon cancer, in addition to K-ras mutations, we have shown that wild-type (WT) Ras can be activated by upstream pathways, including, e.g., signaling by ErbB receptors. Tumors with mutant or activated WT Ras had increased cyclooxygenase-2 (Cox-2) expression. We have also shown that ursodeoxycholic acid (UDCA) prevented AOM-induced colon cancer and suppressed Cox-2 induction. In this study, we examined the role of Ras in Cox-2 inhibition by UDCA. Rats were fed AIN-76A chow alone, or supplemented with 0.4% UDCA, and received 20 mg/kg AOM i.p. weekly x 2 weeks. At 40 weeks, rats were sacrificed, and tumors were harvested. K-ras mutations were assessed by primer-mediated RFLP, allele-specific oligonucleotide hybridization, and direct DNA sequencing. Ras was immunoprecipitated and defined as activated if [Ras - GTP/(Ras - GTP + Ras - GDP)] was >3 SD above normal colonocytes. Cox-2 mRNA was determined by reverse transcription-PCR, and protein expression was assessed by Western blotting and immunostaining. In the AOM alone group, Ras was activated by mutations in 8 of 30 (27%) tumors, and WT Ras was activated in 7 of 30 (23%) tumors. UDCA significantly suppressed the incidence of tumors with mutant Ras (1 of 31, 3.2%; P < 0.05) and totally abolished the development of tumors with activated WT Ras (0 of 10; P < 0.05). In the AOM alone group, Cox-2 was up-regulated >50-fold in tumors with normal Ras activity and further enhanced in tumors with mutant or signaling-activated Ras. UDCA significantly inhibited Cox-2 protein and mRNA levels in tumors with normal Ras activity. In summary, we have shown for the first time that UDCA suppressed the development of tumors with Ras mutations and blocked activation of WT Ras. Furthermore, UDCA inhibited Cox-2 induction by Ras-dependent and -independent mechanisms.

Ursodeoxycholic acid inhibits Ras mutations, wild-type Ras activation, and cyclooxygenase-2 expression in colon cancer

K-ras mutations occur frequently in colon cancer and contribute to autonomous growth. In the azoxymethane (AOM) model of colon cancer, in addition to K-ras mutations, we have shown that wild-type (WT) Ras can be activated by upstream pathways, including, e.g., signaling by ErbB receptors. Tumors with mutant or activated WT Ras had increased cyclooxygenase-2 (Cox-2) expression. We have also shown that ursodeoxycholic acid (UDCA) prevented AOM-induced colon cancer and suppressed Cox-2 induction. In this study, we examined the role of Ras in Cox-2 inhibition by UDCA. Rats were fed AIN-76A chow alone, or supplemented with 0.4% UDCA, and received 20 mg/kg AOM i.p. weekly x 2 weeks. At 40 weeks, rats were sacrificed, and tumors were harvested. K-ras mutations were assessed by primer-mediated RFLP, allele-specific oligonucleotide hybridization, and direct DNA sequencing. Ras was immunoprecipitated and defined as activated if [Ras - GTP/(Ras - GTP + Ras - GDP)] was >3 SD above normal colonocytes. Cox-2 mRNA was determined by reverse transcription-PCR, and protein expression was assessed by Western blotting and immunostaining. In the AOM alone group, Ras was activated by mutations in 8 of 30 (27%) tumors, and WT Ras was activated in 7 of 30 (23%) tumors. UDCA significantly suppressed the incidence of tumors with mutant Ras (1 of 31, 3.2%; P < 0.05) and totally abolished the development of tumors with activated WT Ras (0 of 10; P < 0.05). In the AOM alone group, Cox-2 was up-regulated >50-fold in tumors with normal Ras activity and further enhanced in tumors with mutant or signaling-activated Ras. UDCA significantly inhibited Cox-2 protein and mRNA levels in tumors with normal Ras activity. In summary, we have shown for the first time that UDCA suppressed the development of tumors with Ras mutations and blocked activation of WT Ras. Furthermore, UDCA inhibited Cox-2 induction by Ras-dependent and -independent mechanisms.

Vitamin D receptor is not required for the rapid actions of 1,25-dihydroxyvitamin D3 to increase intracellular calcium and activate protein kinase C in mouse osteoblasts

The rapid, non-genomic actions of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] have been well described, however, the role of the nuclear vitamin D receptor (VDR) in this pathway remains unclear. To address this question, we used VDR(+/+) and VDR(-/-) osteoblasts isolated from wild-type and VDR null mice to study the increase in intracellular calcium ([Ca(2+)](i)) and activation of protein kinase C (PKC) induced by 1,25(OH)(2)D(3). Within 1 min of 1,25(OH)(2)D(3) (100 nM) treatment, an increase of 58 and 53 nM in [Ca(2+)](i) (n = 3) was detected in VDR(+/+) and VDR(-/-) cells, respectively. By 5 min, 1,25(OH)(2)D(3) caused a 2.1- and 1.9-fold increase (n = 6) in the phosphorylation of PKC substrate peptide acetylated-MBP(4-14) in VDR(+/+) and VDR(-/-) osteoblasts. The 1,25(OH)(2)D(3)-induced phosphorylation was abolished by GF109203X, a general PKC inhibitor, in both cell types, confirming that the secosteroid induced PKC activity. Moreover, 1,25(OH)(2)D(3) treatment resulted in the same degree of translocation of PKC-alpha and PKC-delta, but not of PKC-zeta, from cytosol to plasma membrane in both VDR(+/+) and VDR(-/-) cells. These experiments demonstrate that the 1,25(OH)(2)D(3)-induced rapid increases in [Ca(2+)](i) and PKC activity are neither mediated by, nor dependent upon, a functional nuclear VDR in mouse osteoblasts. Thus, VDR is not essential for these rapid actions of 1,25(OH)(2)D(3) in osteoblasts.

Ursodeoxycholic acid and F(6)-D(3) inhibit aberrant crypt proliferation in the rat azoxymethane model of colon cancer: roles of cyclin D1 and E-cadherin

We have previously demonstrated that ursodeoxycholic acid(UDCA) and a fluorinated analogue of vitamin D(3), F(6)-D(3),inhibited colonic carcinogenesis in the azoxymethane (AOM) model. Generalized colonic mucosal hyperproliferation and aberrant crypt foci (ACF) are intermediate biomarkers of colon cancer. Using these biomarkers, in this study we examined the anticarcinogenic mechanisms of these chemopreventive agents. Rats were maintained on AIN-76A chow or supplemented with 0.4% UDCA or F(6)-D(3) (2.5 nmol/kg chow) and treated weekly with AOM 20 mg i.p./kg wt or saline x 2 weeks. F(6)-D(3) was continued for an additional 2 weeks and UDCA for the duration of the study. At 40 weeks, animals received bromodeoxyuridine (BrdUrd) i.p. 2 h before sacrifice. A portion of each tumor was fixed in formalin and the remainder flash frozen. Colons were divided longitudinally and half-fixed in formalin and half in ethanol. The size and location of methylene blue-stained ACF were recorded. Cell proliferation (BrdUrd labeling) and apoptosis (terminal deoxynucleotidyl transferase-mediated nick end labeling assay) were measured in colonic crypts and tumors. Protein expression levels of several regulators of cell proliferation were analyzed by immunostaining and Western blotting. Colonic crypt cyclin D1 and E-cadherin mRNA levels were measured by real-time PCR. In saline injected controls, neither UDCA nor F(6)-D(3) alone had any effect on cytokinetic parameters or on the expression of mitogenic regulators. AOM significantly increased the proliferation (percentage of BrdUrd-positive cells) of both ACF (23.1 +/- 1.7%) and non-ACF crypts (17.6 +/- 1.6%), compared with normal colonic crypts (4.5 +/- 0.8%; P < 0.05). This hyperproliferation was accompanied by a 5-fold increase in cyclin D1 and >50% decrease in E-cadherin protein (P < 0.05) in ACF, both of which are predicted to be growth-enhancing alterations. UDCA and F(6)-D(3) significantly (P < 0.05) inhibited AOM-induced crypt cell hyperproliferation, ACF development, and tumor burden. These chemopreventive agents also significantly blocked AOM-induced alterations in cyclin D1 and E-cadherin protein in ACF and tumors. In ACF, changes in mRNA levels of cyclin D1, but not E-cadherin, paralleled alterations in protein expression. Cyclooxygenase-2 and inducible nitric oxide synthase were increased in AOM tumors but not in ACF, and these changes were blocked by UDCA and F(6)-D(3). UDCA and F(6)-D(3) significantly inhibited ACF development and hyperproliferation, in part, by preventing carcinogen-induced alterations in cyclin D1 and E-cadherin. In established tumors, UDCA and F(6)-D(3) also limited inductions of cyclooxygenase-2 and inducible nitric oxide synthase, which together with their effects on cyclin D1 and E-cadherin, contribute to their chemopreventive actions.

Ursodeoxycholic acid inhibits the initiation and postinitiation phases of azoxymethane-induced colonic tumor development

Colonic tumorigenesis involves the processes of initiation and promotion/progression from normal epithelial cells to tumors. Studies in both humans and experimental models of colon cancer indicate that secondary bile acids promote tumor development. In contrast, we have demonstrated previously that another bile acid, ursodeoxycholic acid (UDCA), inhibits the development of azoxymethane (AOM)-induced colon cancer in rats. More recently, we have shown that UDCA inhibits AOM-induced hyperproliferation, and aberrant crypt formation and growth. In our previous studies, we supplemented UDCA throughout the experiment. The efficacy of a chemopreventive agent may depend on the timing of administration, which has important clinical implications. In the present investigation, we examined the ability of UDCA, when administered only in the initiation or the promotion/progression phase, to block tumor development. Male Fisher 344 rats were divided in a 2 x 3 factorial design, with animals receiving AOM or vehicle, and fed an unsupplemented diet or diet supplemented with 0.4% UDCA in the initiation or promotion/progression phase. Thirty-two weeks later, rats were sacrificed and tumor histology determined, and colons were examined for aberrant crypt foci (ACF). In the carcinogen-treated dietary control group, tumor incidence was 72.3%, and tumor multiplicity was 1.9 tumors per tumor-bearing rat. UDCA, in the initiation or promotion/progression phase, significantly decreased tumor incidence to 46.2% and 38.4% (P < 0.05), respectively; and tumor multiplicity to 1.4 and 1.3 tumors per tumor-bearing rat (P < 0.05), respectively. UDCA did not alter tumor size, histology, or location, although there were trends for smaller tumors and less advanced histological grades in the group given UDCA during the promotion phase. UDCA, in the initiation but not the promotion phase, inhibited ACF formation and growth. In summary, UDCA significantly inhibited AOM-induced colonic carcinogenesis during either tumor initiation or in the promotion/progression phase. In contrast, UDCA inhibited ACF formation only when administered in the initiation phase, suggesting that the mechanisms of chemoprevention by this bile acid differ in these two phases.

Mutational and nonmutational activation of p21ras in rat colonic azoxymethane-induced tumors: effects on mitogen-activated protein kinase, cyclooxygenase-2, and cyclin D1

Azoxymethane (AOM)-induced colonic carcinogenesis involves a number of mutations, including those in the K-ras gene and CTNNB1, that codes for beta-catenin. Prior in vitro studies have also demonstrated that wild type p21(K-ras) can be activated by epigenetic events. We identified 15 K-ras mutations in 14 of 84 AOM-induced colonic tumors by three independent methods. By single strand conformational polymorphism, we also observed mutations in 22 of 68 tumors in exon 3 of CTNNB1. A highly sensitive method was then used to measure p21ras activation levels. All tumors assayed possessing K-ras mutations had significantly higher p21ras activation levels (8.8 +/- 1.5%; n = 13) compared with that of control colon (3.7 +/- 0.4; n = 6; P < 0.05) or tumors without such mutations (4.2 +/- 0.4%; n = 70; P < 0.05). Among tumors with wild-type K-ras, there was a subset of tumors (18 of 70) that had significantly higher p21ras activation levels (8.0 +/- 0.9%; n = 18) compared with control colons. In three of four tumors examined with activated wild-type p21ras, we observed increased c-erbB-2 receptor expression and decreased Ras-GAP expression. In contrast, only one of eight tumors examined with wild-type ras and nonactivated p21ras demonstrated these alterations. Mitogen-activated protein kinase (MAPK) activation and cyclooxygenase-2 (COX-2) expression were increased in tumors with mutated or activated wild-type p21ras, compared with their nonactivated counterparts. Although beta-catenin mutations did not alter COX-2 expression or MAPK activity, mutations in either K-ras or beta-catenin significantly increased cyclin D1 expression. In contrast, in tumors with wild-type but activated p21-ras, cyclin D1 expression was not enhanced. Thus, the spectrum of changes in MAPK, COX-2, and cyclin D1 is distinct among tumors with ras or beta-catenin mutations or nonmutational activation of p21ras.

Inhibition of O(6)-methylguanine-DNA methyltransferase increases azoxymethane-induced colonic tumors in rats

Azoxymethane (AOM) causes O(6)-methylguanine adduct formation which leads to G-->A transitions. Their repair is carried out by O(6)-methylguanine-DNA methyltransferase (MGMT). To evaluate the importance of this repair event in AOM-induced carcinogenesis, we examined the effect of O(6)-benzylguanine (BG), a potent inhibitor of MGMT, on colonic tumor development. Rats were treated weekly for 2 weeks at 0 and 24 h with BG (60 mg/kg body wt i.p.) or vehicle (40% polyethylene glycol, PEG-400), followed 2 h after the first dose of BG with AOM (15 mg/kg body wt) or vehicle (saline) i.p. Rats were killed 35 weeks later and tumors harvested and DNA extracted. In the AOM-treated groups, BG caused a significant increase in tumor incidence with tumors in 65.9%, versus 30.8% in the AOM/PEG-treated group (P < 0.05). In the BG/AOM group there was also a significant increase in tumor multiplicity, with 2.3 tumors/tumor-bearing rat, versus 1.6 tumors/tumor- bearing rat in the AOM/PEG group (P < 0.05). Since O(6)-methylguanine adducts can cause activating mutations in the K-ras and beta-catenin genes, we examined the effects of BG on these mutations. In the BG group there were seven mutations in codon 12 or 13 of exon 1 of the K-ras gene in 51 tumors examined, compared with no K-ras mutations in 17 tumors analyzed in the AOM/PEG group (P = 0.12). In the BG/AOM group there were 10 mutations in exon 3 of the beta-catenin gene among 48 tumors evaluated, compared with six mutations in 16 tumors analyzed in the PEG/AOM group (P = 0.16). In summary, MGMT inhibition increases AOM-induced colonic tumor incidence and multiplicity in rats.

Hypertensive cardiovascular disease in African Americans

Hypertension is the most common public health challenge in the United States because of its prevalence and associated increase in comorbid cardiovascular diseases. Yearly expenses related directly or indirectly to the treatment and detection of hypertension in the United States are approximately $10 billion, excluding the enormous yearly financial burden of $259 billion and the social burden from heart disease and stroke, which remain the first and third leading causes of death, respectively, in the United States. Despite the importance of these observations, blood pressure is poorly controlled in the United States.

1,25-dihydroxyvitamin D3 and TPA activate phospholipase D in Caco-2 cells: role of PKC-alpha

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] and 12-O-tetradecanoylphorbol 13-acetate (TPA) both activated phospholipase D (PLD) in Caco-2 cells. GF-109203x, an inhibitor of protein kinase C (PKC) isoforms, inhibited this activation by both of these agonists. 1,25(OH)2D3 activated PKC-alpha, but not PKC-beta1, -betaII, -delta, or -zeta, whereas TPA activated PKC-alpha, -beta1, and -delta. Chronic treatment with TPA (1 microM, 24 h) significantly reduced the expression of PKC-alpha, -betaI, and -delta and markedly reduced the ability of 1,25(OH)2D3 or TPA to acutely stimulate PLD. Removal of Ca2+ from the medium, as well as preincubation of cells with Gö-6976, an inhibitor of Ca2+-dependent PKC isoforms, significantly reduced the stimulation of PLD by 1,25(OH)2D3 or TPA. Treatment with 12-deoxyphorbol-13-phenylacetate-20-acetate, which specifically activates PKC-betaI and -betaII, however, failed to stimulate PLD. In addition, the activation of PLD by 1,25(OH)2D3 or TPA was markedly reduced or accentuated in stably transfected cells with inhibited or amplified PKC-alpha expression, respectively. Taken together, these observations indicate that PKC-alpha is intimately involved in the stimulation of PLD in Caco-2 cells by 1,25(OH)2D3 or TPA.

Expression of G protein alpha subunits in normal rat colon and in azoxymethane-induced colonic neoplasms

BACKGROUND & AIMS

Heterotrimeric G proteins are important in growth-regulating signal transduction. The aim of this study was to characterize the relative expression of G protein alpha subunits in rat colonocytes, colonocyte antipodal plasma membranes, and colonic neoplasms.

METHODS

Antipodal plasma membranes were prepared from isolated colonocytes. Azoxymethane was administered to rats to induce colonic neoplasms. K-ras mutations in the neoplasms were determined by oligonucleotide hybridization and confirmed by primer mediated-restriction fragment length polymorphism. Colonocyte and tumor homogenates or membranes were probed for Galpha subunits by Western blotting with isoform-specific antibodies.

RESULTS

The expressions of Galphai2, alphai3, and alphaq/11 were significantly enriched in the basolateral compared with brush border fraction of colonic antipodal plasma membranes. In neoplasms without K-ras mutations, the expression of Galphai2 increased 4-fold, Galphas(long) increased 2.5-fold, and Galphai3 increased 1.5-2-fold. Expression did not differ among tumor grades. K-ras mutations were associated with lowered expression of G proteins, especially Galphao.

CONCLUSIONS

In colonocytes, Galpha subunits are localized primarily in basolateral plasma membranes. The increased expressions of Galphai2 and, to a lesser degree, Galphai3 and Galphas(long) in tumors was independent of tumor grade but was modulated by the presence of K-ras mutations.

1,25-Dihydroxyvitamin D3 targets PKC-betaII but not PKC-alpha to the basolateral plasma membranes of rat colonocytes

Prior studies by our laboratory have shown that 1, 25-dihydroxyvitamin D3 activated PKC-alpha, but not PKC-delta, -epsilon, or -zeta, in normal rat colonocytes. In the present studies we demonstrate for the first time that this secosteroid also activated PKC-betaII, another DAG- and Ca2+-dependent PKC isoform recently shown to be present in these cells. Moreover, this activation of PKC-betaII by 1,25-dihydroxyvitamin D3 treatment of isolated colonocytes was shown to be lost in cells from vitamin D-deficient rats and, at least partially, restored by repleting these animals with this secosteroid for 7 days. Under basal conditions, the expression of PKC-alpha and -betaII in brush-border membranes was comparable to their respective expression in basolateral plasma membranes of rat colonocytes. In contrast, the expression of PKC-delta was significantly greater in brush-border membranes, whereas PKC-epsilon and -zeta were enriched in the basolateral plasma membranes. Furthermore, 1,25-dihydroxyvitamin D3 specifically induced the translocation of PKC-betaII, but not PKC-alpha, to the basolateral, but not brush-border plasma membranes of rat colonocytes, via a pp60(c-src)-dependent mechanism.

Decreased PKC-alpha expression increases cellular proliferation, decreases differentiation, and enhances the transformed phenotype of CaCo-2 cells

Previous studies have shown that PKC-alpha protein expression is decreased in sporadic human colon cancers, as well as in colonic tumors of rats induced by chemical carcinogens. To elucidate the potential role of PKC-alpha on several phenotypic characteristics of colon cancer cells, we have transfected cDNAs for PKC-alpha in sense or antisense orientations into CaCo-2 cells, a human colonic adenocarcinoma cell line. Transfected clones were isolated that demonstrated approximately 3-fold increases (sense transfectants) and approximately 95% decreases (antisense transfectants) in PKC-alpha expression with no significant alterations in other PKC isoforms. Transfection of CaCo-2 cells with PKC-alpha in the antisense orientation resulted in enhanced proliferation and decreased differentiation, as well as in a more aggressive transformed phenotype compared with empty vector-transfected control cells. In contrast, cells transfected with PKC-alpha cDNA in the sense orientation demonstrated decreased proliferation, enhanced differentiation, and an attenuated tumor phenotype compared with these control cells. These data show that alterations in the expression of PKC-alpha induce changes in the proliferation, differentiation, and tumorigenicity of CaCo-2 cells. Furthermore, these findings indicate that loss of PKC-alpha expression in sporadic human and chemically induced colonic cancers may confer a relative growth advantage during colonic malignant transformation.

1,25 dihydroxyvitamin D3 stimulates phospholipase C-gamma in rat colonocytes: role of c-Src in PLC-gamma activation

Our laboratory has previously demonstrated that 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) rapidly stimulated polyphosphoinositide (PI) hydrolysis, raised intracellular Ca2+, and activated two Ca2+-dependent protein kinase C (PKC) isoforms, PKC-alpha and -betaII in the rat large intestine. We also showed that the direct addition of 1,25(OH)2D3 to isolated colonic membranes failed to stimulate PI hydrolysis, but required secosteroid treatment of intact colonocytes, suggesting the involvement of a soluble factor. Furthermore, this PI hydrolysis was restricted to the basal lateral plasma membrane of these cells. In the present studies, therefore, we examined whether polyphosphoinositide-phospholipase C-gamma (PI-PLC-gamma), a predominantly cytosolic isoform of PI-PLC, was involved in the hydrolysis of colonic membrane PI by 1,25(OH)2D3. This isoform has been shown to be activated and membrane-associated by tyrosine phosphorylation. We found that 1,25(OH)2D3 caused a significant increase in the biochemical activity, particulate association, and the tyrosine phosphorylation of PLC-gamma, specifically in the basal lateral membranes. This secosteroid also induced a twofold increase in the activity of Src, a proximate activator of PLC-gamma in other cells, with peaks at 1 and 9 min in association with Src tyrosine dephosphorylation. 1,25(OH)2D3 also increased the physical association of activated c-Src with PLC-gamma. In addition, Src isolated from colonocytes treated with 1,25(OH)2D3, demonstrated an increased ability to phosphorylate exogenous PLC-gamma in vitro. Inhibition of 1,25(OH)2D3-induced Src activation by PP1, a specific Src family protein tyrosine kinase inhibitor, blocked the ability of this secosteroid to stimulate the translocation and tyrosine phosphorylation of PLC-gamma in the basolateral membrane (BLM). Src activation was lost in D deficiency, and was reversibly restored with the in vivo repletion of 1,25(OH)2D3. These studies demonstrate for the first time that 1,25(OH)2D3 stimulates PLC-gamma as well as c-Src in rat colonocytes, and indicate that PLC-gamma is a direct substrate of secosteroid-activated c-Src in these cells.

Protein kinase C isoforms in the chemopreventive effects of a novel vitamin D3 analogue in rat colonic tumorigenesis

BACKGROUND & AIMS

We recently showed that dietary supplementation with an analogue of 1alpha,25-dihydroxy-vitamin D3, 1alpha,25-dihydroxy-16-ene-23-yne-26,27 F6-vitamin D3 (RO24-5531), reduced the incidence of colonic tumors in rats treated with azoxymethane (AOM). The aim of this study was to determine whether alterations in specific isoforms of protein kinase C (PKC) are involved in this phenomenon.

METHODS

Protein abundance and subcellular distribution of several PKC isoforms were examined and compared in AOM-induced tumors of rats fed control and RO24-5531-supplemented diets.

RESULTS

In both AOM-induced colonic adenomas and carcinomas, a significant down-regulation of PKC-alpha, -delta, and -zeta and an up-regulation of PKC-beta11 were found compared with control colonocytes. Dietary RO24-5531 preserved the expression of PKC-zeta and increased the abundance of PKC-epsilon in carcinogen-induced adenomas.

CONCLUSIONS

Because identical changes in specific isoforms of PKC were found in AOM-induced adenomas and carcinomas, these alterations may be involved in the early stage(s) of colonic malignant transformation. Moreover, the ability of RO24-5531 to block the changes in PKC-zeta induced by AOM, as well as to up-regulate PKC-epsilon, may underlie its ability to prevent adenomas from progressing to carcinomas.